Driving circuit and driving method for piezoelectric transformer, backlight apparatus, liquid crystal display apparatus, liquid crystal monitor, and liquid crystal TV
First Claim
1. A driving circuit for a piezoelectric transformer, comprising:
- a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series;
a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series;
a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect;
a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer;
a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series;
a first driving portion generating the first and second driving signals;
a second driving portion generating the third and fourth driving signals;
a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and
a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions,the control portion comprising;
an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value;
a comparator comparing the current detecting data from the A/D converter with reference data; and
a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator,whereinat a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, andafter lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data.
1 Assignment
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Accused Products
Abstract
A driving circuit for a piezoelectric transformer is provided, which is capable of driving a piezoelectric transformer at a high efficiency and with low distortion, and being miniaturized. At the commencement of lighting a cold-cathode fluorescent tube, a digital controller fixes frequencies of first and second control signals VC1 and VC2 at a predetermined frequency and controls the phase difference therebetween so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power. After lighting of the cold-cathode fluorescent tube, the digital controller controls the phase difference between the first and second control signals VC1 and VC2 so that current detecting data CD substantially is matched with reference data RD.
30 Citations
82 Claims
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1. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and after lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor as a current detecting value after rectifying it; a comparator comparing the current detecting value from the feedback portion with a reference voltage value; and a control portion receiving a comparison result from the comparator to output first and second control signals respectively to the first and second driving portions, the control portion comprising a phase controller changing a phase difference between the first and second control signals based on the comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and after lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting value substantially is matched with the reference voltage value.
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16. A method for driving a piezoelectric transformer using:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion receiving a first control signal to generate the first and second driving signals; a second driving portion receiving a second control signal to generate the third and fourth driving signals; and a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it, the method comprising; at a commencement of lighting of the cold-cathode fluorescent tube, fixing frequencies of the first and second control signals at a predetermined frequency; controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power; after lighting of the cold-cathode fluorescent tube, comparing current detecting data corresponding to the voltage signal from the feedback portion with reference data; and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data.
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17. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a first frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and when the current detecting data becomes the first reference data or more, the control portion fixes the frequencies of the first and second control signals at a second frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; a first comparator comparing the current detecting value from the feedback portion with a first reference voltage value; a second comparator comparing the current detecting value from the feedback portion with a second reference voltage value; and a control portion receiving a comparison result from the first or second comparator to output first and second control signals respectively to the first and second driving portions, the control portion comprising a phase controller changing a phase difference between the first and second control signals based on the comparison result from the first or second comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a first frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and when the current detecting value becomes the first reference voltage value or more, the control portion fixes the frequencies of the first and second control signals at a second frequency, and controls the phase difference between the first and second control signals so that the current detecting value substantially is matched with the second reference voltage value.
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37. A method for driving a piezoelectric transformer using:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion receiving a first control signal to generate the first and second driving signals; a second driving portion receiving a second control signal to generate the third and fourth driving signals; and a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it, the method comprising;
at a commencement of lighting of the cold-cathode fluorescent tube,fixing frequencies of the first and second control signals at a first frequency; controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power; comparing current detecting data corresponding to the voltage signal from the feedback portion with first reference data; when the current detecting data becomes the first reference data or more, fixing the frequencies of the first and second control signals at a second frequency; comparing the current detecting data with second reference data; and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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38. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion performs the frequency sweep until the stop frequency is reached, and simultaneously controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data. - View Dependent Claims (39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50)
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51. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor as a current detecting value after rectifying it; a first comparator comparing the current detecting value from the feedback portion with a first reference voltage value; a second comparator comparing the current detecting value from the feedback portion with a second reference voltage value; and a control portion receiving a comparison result from the first or second comparator to output first and second control signals respectively to the first and second driving portions, the control portion comprising a phase controller changing a phase difference between the first and second control signals based on the comparison result from the first or second comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting value becomes the first reference voltage value or more during frequency sweep, the control portion performs the frequency sweep until the stop frequency is reached, and simultaneously controls the phase difference between the first and second control signals so that the current detecting value substantially is matched with the second reference voltage value.
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52. A method for driving a piezoelectric transformer using:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion receiving a first control signal to generate the first and second driving signals; a second driving portion receiving a second control signal to generate the third and fourth driving signals; and a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it, the method comprising; at a commencement of lighting of the cold-cathode fluorescent tube, fixing a phase difference between the first and second control signals; sweeping frequencies of the first and second control signals from a start frequency to a stop frequency; during frequency sweep, comparing current detecting data corresponding to the voltage signal from the feedback portion with first reference data; when the current detecting data becomes the first reference data or more during the frequency sweep, performing the frequency sweep until the stop frequency is reached; comparing the current detecting data with second reference data; and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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53. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion fixes the frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data. - View Dependent Claims (54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64)
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65. A driving circuit for a piezoelectric transformer, comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor as a current detecting value after rectifying it; a first comparator comparing the current detecting value from the feedback portion with a first reference voltage value; a second comparator comparing the current detecting value from the feedback portion with a second reference voltage value; and a control portion receiving a comparison result from the first or second comparator to output first and second control signals respectively to the first and second driving portions, the control portion comprising a phase controller changing a phase difference between the first and second control signals based on the comparison result from the first or second comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting value becomes the first reference voltage value or more during frequency sweep, the control portion fixes the frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that the current detecting value substantially is matched with the second reference voltage value.
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66. A method for driving a piezoelectric transformer using:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion receiving a first control signal to generate the first and second driving signals; a second driving portion receiving a second control signal to generate the third and fourth driving signals; and a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it, the method comprising;
at a commencement of lighting of the cold-cathode fluorescent tube,fixing a phase difference between the first and second control signals; sweeping frequencies of the first and second control signals from a start frequency to a stop frequency; during frequency sweep, comparing current detecting data corresponding to the voltage signal from the feedback portion with first reference data; when the current detecting data becomes the first reference data or more during the frequency sweep, fixing the frequencies of the first and second control signals at a predetermined frequency; comparing the current detecting data with second reference data; and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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67. A backlight apparatus including a driving circuit for a piezoelectric transformer, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing frequencies of the first and second control signals at a predetermined frequency, and controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, after lighting of the cold-cathode fluorescent tube, the control portion controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data, and the cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface.
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68. A backlight apparatus including a driving circuit for a piezoelectric transformer, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing frequencies of the first and second control signals at a first frequency, and controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, when the current detecting data becomes the first reference data or more, the control portion fixing the frequencies of the first and second control signals at a second frequency, and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface.
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69. A backlight apparatus comprising a driving circuit for a piezoelectric transformer, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing the phase difference between the first and second control signals, and sweeping the frequencies of the first and second control signals from a start frequency to a stop frequency, when the current detecting data becomes the first reference data or more during frequency sweep, the control portion performing the frequency sweep until the stop frequency is reached, and simultaneously controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface.
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70. A backlight apparatus comprising a driving circuit for a piezoelectric transformer, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which a cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing the phase difference between the first and second control signals, and sweeping the frequencies of the first and second control signals from a start frequency to a stop frequency, when the current detecting data becomes the first reference data or more during frequency sweep, the control portion fixing the frequencies of the first and second control signals at a predetermined frequency, and controlling the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface.
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71. A liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing the frequencies of the first and second control signals at a predetermined frequency, and controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, after lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data, and the object to be illuminated is a liquid crystal panel.
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72. A liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixing the frequencies of the first and second control signals at a first frequency, and controlling the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, when the current detecting data becomes the first reference data or more, the control portion fixes the frequencies of the first and second control signals at a second frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the object to be illuminated is a liquid crystal panel.
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73. A liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, when the current detecting data becomes the first reference data or more during frequency sweep, the control portion performs the frequency sweep until the stop frequency is reached, and simultaneously controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the object to be illuminated is a liquid crystal panel.
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74. A liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates an object to be illuminated from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, when the current detecting data becomes the first reference data or more during frequency sweep, the control portion fixes the frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data, and the object to be illuminated is a liquid crystal panel.
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75. A liquid crystal monitor with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and after lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data.
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76. A liquid crystal monitor with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a first frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and when the current detecting data becomes the first reference data or more, the control portion fixes the frequencies of the first and second control signals at a second frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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77. A liquid crystal monitor with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion performs the frequency sweep until the stop frequency is reached, and simultaneously controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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78. A liquid crystal monitor with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion fixes the frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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79. A liquid crystal TV with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and after lighting of the cold-cathode fluorescent tube, the control portion controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the reference data.
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80. A liquid crystal TV with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes frequencies of the first and second control signals at a first frequency, and controls the phase difference between the first and second control signals so that an output power of the piezoelectric transformer becomes from substantially zero to a predetermined output power, and when the current detecting data becomes the first reference data or more, the control portion fixes the frequencies of the first and second control signals at a second frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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81. A liquid crystal TV with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion performs the frequency sweep until the stop frequency is reached, and simultaneously controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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82. A liquid crystal TV with a liquid crystal display apparatus mounted thereon, the liquid crystal display apparatus comprising a backlight apparatus including a driving circuit for a piezoelectric transformer and being composed so that a cold-cathode fluorescent tube illuminates a liquid crystal panel from a back surface, the driving circuit comprising:
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a first series connection body connected to both terminals of a DC power source, in which first and second switching members are turned on/off alternately by first and second driving signals and are connected in series; a second series connection body connected in parallel with the first series connection body, in which third and fourth switching members are turned on/off alternately by third and fourth driving signals respectively having the same frequency and duty ratio as those of the first and second driving signals and are connected in series; a piezoelectric transformer outputting a voltage, which is input from a primary side electrode, from a secondary side electrode after stepping-up or down the voltage by using a piezoelectric effect; a third series connection body connected between a connection point of each switching member of the first series connection body and a connection point of each switching member of the second series connection body, including an inductor and a pair of input electrodes of the piezoelectric transformer; a fourth series connection body connected between a pair of output electrodes of the piezoelectric transformer, in which the cold-cathode fluorescent tube and a current detecting resistor are connected in series; a first driving portion generating the first and second driving signals; a second driving portion generating the third and fourth driving signals; a feedback portion returning a voltage signal generated at the current detecting resistor after rectifying it; and a control portion receiving the voltage signal from the feedback portion to output first and second control signals respectively to the first and second driving portions, the control portion comprising; an A/D converter converting the voltage signal from the feedback portion to current detecting data having a digital value; a comparator comparing the current detecting data from the A/D converter with first or second reference data; and a phase controller changing a phase difference between the first and second control signals based on a comparison result from the comparator, wherein at a commencement of lighting of the cold-cathode fluorescent tube, the control portion fixes the phase difference between the first and second control signals, and sweeps the frequencies of the first and second control signals from a start frequency to a stop frequency, and when the current detecting data becomes the first reference data or more during frequency sweep, the control portion fixes the frequencies of the first and second control signals at a predetermined frequency, and controls the phase difference between the first and second control signals so that the current detecting data substantially is matched with the second reference data.
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Specification