Method and apparatus for controlling a discharge lamp in a backlighted display
DCFirst Claim
1. An apparatus for efficiently converting a direct current (DC) signal into an alternating current (AC) signal for driving a load, comprising:
- (a) a H-bridge network of a plurality of switches for generating an AC signal from a DC signal coupled to the network of the plurality of switches, the AC signal being generated by a first portion of the network of the plurality of switches periodically opening and closing opposite to the periodic opening and closing of a second portion of the network of the plurality of switches, said first portion of the network being diagonally opposed to said second portion of the network;
(b) a tank circuit being coupled between the network of the plurality of switches and the load, the tank circuit filtering the AC signal delivered to the load; and
(c) a controller for periodically opening and closing portions of the network of the plurality of switches based on a resonant frequency of the tank circuit, so that the optimal amount of electrical power is provided for driving the load under a range of voltages provided by the DC signal.
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Abstract
The described DC to AC inverter efficiently controls the amount of electrical power used to drive a cold cathode fluorescent lamp (CCFL). The output is a fairly pure sine wave which is proportional to an input control voltage. The output waveform purity is ensured by driving a symmetrical rectangular waveform into a second-order, low pass filter at the resonant frequency of the filter for all conditions of line voltage and delivered power. Operating stress on the step-up transformer is minimized by placing the load (lamp) directly across the secondary side of the transformer. When configured to regulate delivered power, the secondary side may be fully floated which practically eliminates a thermometer effect on the operation of the lamp. All of the active elements, including the power switches, may be integrated into a monolithic silicon circuit.
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Citations
26 Claims
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1. An apparatus for efficiently converting a direct current (DC) signal into an alternating current (AC) signal for driving a load, comprising:
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(a) a H-bridge network of a plurality of switches for generating an AC signal from a DC signal coupled to the network of the plurality of switches, the AC signal being generated by a first portion of the network of the plurality of switches periodically opening and closing opposite to the periodic opening and closing of a second portion of the network of the plurality of switches, said first portion of the network being diagonally opposed to said second portion of the network;
(b) a tank circuit being coupled between the network of the plurality of switches and the load, the tank circuit filtering the AC signal delivered to the load; and
(c) a controller for periodically opening and closing portions of the network of the plurality of switches based on a resonant frequency of the tank circuit, so that the optimal amount of electrical power is provided for driving the load under a range of voltages provided by the DC signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
(a) determining if a current to the load has exceeded a predetermined maximum current; and
if true(b) causing the AC signal to not drive the load.
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19. The apparatus of claim 1, wherein the controller implements logical instructions, comprising:
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(a) determining if an on mode is selected; and
if so(b) enabling the AC signal to drive the load.
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20. The apparatus of claim 17, further comprising a gate driver for each MOSFET in the H-bridge network, each gate driver providing amplification of logic signals that control the operation of the associated MOSFET.
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21. The apparatus of claim 1, wherein the DC signal provides a range of voltages.
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22. The apparatus of claim 1, wherein the controller periodically opens and closes portions of the network of the plurality of switches based on a trailing edge of a current waveform of the AC signal, so that a reduced amount of power is delivered to the load.
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23. The apparatus of claim 1, wherein the controller periodically opens and closes portions of the network of the plurality of switches based on a leading edge of a current waveform of the AC signal, so that a reduced amount of power is delivered to the load.
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24. The apparatus of claim 1, wherein the controller periodically opens and closes portions of the network of the plurality of switches based on a duty cycle to phase modulate the AC signal.
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25. The apparatus of claim 1, wherein the duty cycle is varied so that the AC signal delivers a reduced amount of power to the load.
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26. The apparatus of claim 1, wherein the controller periodically opens and closes portions of the network of the plurality of switches based on a double sided phase modulation of the AC signal.
Specification