Voltage-fed push LLC resonant LCD backlighting inverter circuit
AssigneeKoninklijke Philips Electronics N.V.
InventorChin Chang
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Abstract
An improved electronic LCD backlighting inverter circuit for high frequency operation under low frequency pulse width modulation (PWM) for dimming control. The improved electronic LCD backlighting inverter is based on a voltage-fed push-pull LLC resonant inverter circuit configuration including a resonant inductor (L), magnetizing inductance of an output transformer (L), and resonant capacitor (C). For large values of magnetizing inductance the LLC circuit effectively becomes an LC resonant circuit. By synchronizing the high frequency switching signal and the low frequency modulation frequency using logic control circuitry, a wide dimming range and higher efficiency are achieved under PWM control.
Claims22
An improved electronic LCD backlighting inverter circuit for performing high frequency dimming with a low frequency modulation, said improved electronic LCD backlighting inverter circuit comprising:
- switching means for operating said LCD backlighting inverter circuit at a high frequency modulated by a low frequency signal;
- low frequency signal generator means for generating said low frequency signal, said low frequency signal having positive and negative portions;
- and
- logic means for controlling said switching means and being driven from said low frequency signal, said logic means extinguishing the operation of said switching means during said negative portion of said low frequency signal thereby causing said electronic LCD backlighting inverter circuit to be frequency modulated by said low frequency signal.
An LCD backlighting inverter circuit comprising:
- a high frequency generator;
- a low frequency generator;
- a switching stage having an output;
- a logic means coupled to the high frequency generator and the low frequency generator for controlling said switching stage;
- and
- a circuit having a resonant frequency and coupled to the output of the switching stage;
- wherein the resonant frequency is formed from a resonant inductor, a load, a magnetizing inductance of a transformer and a resonant capacitor, said resonant inductor having a low inductance value such that it is a part of an LLC resonant circuit with said magnetizing inductance and the resonant capacitor.
An inverter circuit for operating a discharge lamp, comprising;
- first and second switching transistors, an inductance, a capacitor and a resonant inductor coupled together in a push-pull resonant converter circuit configuration wherein said resonant inductor has an inductance value such that the circuit effectively operates as a voltage-fed push-pull LLC resonant inverter circuit;
- a control circuit including logic circuit means for supplying switching signals to control the operation of said first and second switching transistors;
- a high frequency signal generator;
- a low frequency signal generator, and
- means for coupling the high frequency signal generator and the low frequency signal generator to the logic circuit means which in turn drives the first and second switching means transistor to operate the inverter circuit at a high frequency modulated by a low frequency modulation signal of the low frequency signal generator.
Dependencies are inferred from the claim text.