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To miniaturise the ballast circuit, a half-bridge series-resonant inverter with a cascading Rosen-type piezoelectric transformer (PT) is designed for cold cathode fluorescent lamps (CCFLs). The PT is interposed between the resonant circuit and the lamp as a stage of the voltage amplifier to increase the lamp voltage and hence to reduce the sizes of the reactive components. The circuit parameters are designed to operate the inverter at a switching frequency that will have the highest boost ratio of PT, and with zero voltage switching (ZVS) for the active power switches to achieve high circuit efficiency. The lamp power is regulated by duty-ratio control with asymmetrical pulsewidth modulation (APWM). An electronic ballast designed for a 2.2 W CCFL is built and tested to verify the; simulated results.
Date of Publication: May 2003