Piezoelectric transformer driving circuit
First Claim
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1. A piezoelectric transformer driving circuit comprising:
- a piezoelectric transformer having a pair of primary electrodes and a pair of secondary electrodes so that when an AC voltage is applied between said pair of primary electrodes, a stepped-up AC voltage is generated between said pair of secondary electrodes;
a first coil and a first transistor each connected at its one end to a first primary electrode of said pair of primary electrodes;
a second coil and a second transistor each connected at its one end to a second primary electrode of said pair of primary electrodes;
a boosting circuit having a frequency dividing circuit for alternately driving said first transistor and said second transistor;
a third transistor having one end connected to receive an input DC voltage and the other end connected to the other end of each of said first coil and said second coil;
a current maintaining means connected to the other end of each of said first coil and said second coil;
a drive voltage control means for turning off said third transistor in accordance with a variable duty ratio signal during an on-period of each of said first and second transistors, thereby to control a drive voltage applied to said primary electrodes of said piezoelectric transformer at a predetermined voltage; and
a frequency control means for changing a driving frequency supplied to said first and second transistors, to control a step-up ratio of said piezoelectric transformer so that an output voltage of a predetermined magnitude can be obtained from said pair of secondary electrodes of said piezoelectric transformer.
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Abstract
A piezoelectric transformer driving circuit includes a boosting circuit receiving an input DC voltage to generate an AC voltage for driving a piezoelectric transformer, a frequency control circuit for controlling the frequency of the AC voltage applied to the piezoelectric transformer to control a step-up ratio of the piezoelectric transformer, and a drive voltage control circuit for controlling the voltage of the AC voltage applied to the piezoelectric transformer at a predetermined level, regardless of variation of the input DC voltage.
135 Citations
20 Claims
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1. A piezoelectric transformer driving circuit comprising:
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a piezoelectric transformer having a pair of primary electrodes and a pair of secondary electrodes so that when an AC voltage is applied between said pair of primary electrodes, a stepped-up AC voltage is generated between said pair of secondary electrodes; a first coil and a first transistor each connected at its one end to a first primary electrode of said pair of primary electrodes; a second coil and a second transistor each connected at its one end to a second primary electrode of said pair of primary electrodes; a boosting circuit having a frequency dividing circuit for alternately driving said first transistor and said second transistor; a third transistor having one end connected to receive an input DC voltage and the other end connected to the other end of each of said first coil and said second coil; a current maintaining means connected to the other end of each of said first coil and said second coil; a drive voltage control means for turning off said third transistor in accordance with a variable duty ratio signal during an on-period of each of said first and second transistors, thereby to control a drive voltage applied to said primary electrodes of said piezoelectric transformer at a predetermined voltage; and a frequency control means for changing a driving frequency supplied to said first and second transistors, to control a step-up ratio of said piezoelectric transformer so that an output voltage of a predetermined magnitude can be obtained from said pair of secondary electrodes of said piezoelectric transformer. - View Dependent Claims (2, 3, 4, 5)
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6. A piezoelectric transformer driving circuit comprising:
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a piezoelectric transformer having a pair of primary electrodes and a pair of secondary electrodes so that when an AC voltage is applied between said pair of primary electrodes, a stepped-up AC voltage is generated between said pair of secondary electrodes; a first autotransformer having a secondary terminal connected to a first primary electrode of said pair of primary electrodes and an intermediate tap connected to one end of a first transistor; a second autotransformer having a secondary terminal connected to a second primary electrode of said pair of primary electrodes and an intermediate tap connected to one end of a second transistor; a boosting circuit having a frequency dividing circuit for alternately driving said first transistor and said second transistor; a third transistor having one end connected to receive an input DC voltage and the other end connected to a primary terminal of each of said first autotransformer and said second autotransformer; a current maintaining means connected to said primary terminal of each of said first autotransformer and said second autotransformer; a drive voltage control means for turning off said third transistor in accordance with a variable duty ratio signal during an on-period of each of said first and second transistors, thereby to control a drive voltage applied to said primary electrodes of said piezoelectric transformer at a predetermined voltage; and a frequency control means for changing a driving frequency supplied to said first and second transistors, to control a step-up ratio of said piezoelectric transformer so that an output voltage of a predetermined magnitude can be obtained from said pair of secondary electrodes of said piezoelectric transformer. - View Dependent Claims (7, 8, 9, 10)
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11. A piezoelectric transformer driving circuit comprising:
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a piezoelectric transformer having a primary electrode side and a secondary electrode side so that when an AC voltage is applied to said primary electrode side, a stepped-up AC voltage is generated at said secondary electrode side; a boosting means having a coil connected to receive at its one end a DC voltage and a first transistor connected to the other end of said coil, said boosting means selectively turning on said first transistor within each one driving period for said piezoelectric transformer so that a current energy is supplied to said coil from said input DC voltage, and then, selectively turning off said first transistor so that an electric energy accumulated in said coil is supplied as a voltage energy to said secondary electrode side of said piezoelectric transformer; drive voltage control means including a second transistor and a current maintaining means for maintaining a current flowing through said coil, each of said second transistor and said current maintaining means being connected to said one end of said coil, said drive voltage control means turning on and off said second transistor within said each one driving period for said piezoelectric transformer and within a period in which said first transistor is on, thereby to change a duty ratio of an operation of said current maintaining means, for controlling a drive voltage applied to said piezoelectric transformer at a predetermined level; and a frequency control means for changing a driving frequency supplied to said boosting means, to control a step-up ratio of said piezoelectric transformer so that an output voltage of a predetermined magnitude can be obtained from said secondary electrode side of said piezoelectric transformer. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification