Single-switch high power factor inverter for driving piezoelectric ceramic transducer

A novel cost-effective and high-efficiency single-switch resonant inverter with power-factor-correction (PFC) scheme is proposed to drive a piezoelectric ceramic transducer (PCT) for an ultrasonic cleaner. The circuit topology is derived by integrating a flyback converter served as PFC stage with a class-E resonant inverter for driving a thin PCT at its resonance frequency. A unity power factor is achieved by operating the flyback converter in discontinuous conduction mode (DCM). With tactfully designed circuit parameters, the class-E resonant inverter is operated at the suboptimum mode to minimize switching losses of the active switch, leading to high circuit efficiency. The active switch is controlled by pulse-width modulation at a fixed switching frequency and constant duty ratio to adjusting the output power of the PCT. The operation modes, design equations and steps for the circuit parameters are proposed. A prototype circuit designed for a 42-W ultrasonic cleaner was built and tested to verify the analytical predictions. Satisfactory performances are obtained from the experimental results.