An electronic ballast with piezoelectric transformer for cold cathode fluorescent lamps

To miniaturize 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 in the load resonant circuit as a stage of voltage amplifier to increase the lamp voltage and hence to reduce the sizes of the reactive components. The lamp power is regulated by duty-ratio control with asymmetrical pulse-width-modulation (APWM). The circuit analyses are performed by fundamental approximation based on the equivalent circuit of the PT and the power-dependent resistance model of the CCFL. The circuit parameters are designed to operate the inverter at a switching-frequency to have the highest boost-ratio of the PT, and with zero-voltage-switching (ZVS) for the active power switches to achieve high circuit efficiency. An electronic ballast designed for a CCFL of 2.2-W is built and tested to verify the simulated results.