Digitally controlled low-frequency square-wave electronic ballast with resonant ignition and power loop

Abstract — The paper proposes the use of a dsPIC30F2010 for implementing the ignition sequence, a double loop control and selecting the operation modes of a low frequency square wave (LFSW) electronic ballast for two-stage HID lamps. The first stage is the power factor correction (PFC) stage, and the second is a single full-bridge (FB) inverter with LC filter. The latter stage performs function of a resonant circuit for lamp ignition and a current controlled low frequency square wave inverter for normal operation. Ignition is achieved at the resonant frequency of the LC filter when the FB converter is working as a resonant inverter. After ignition the converter operates as a LFSW inverter by controlling the FB to act alternately as a Buck converter supplying positive or negative current. While ignition occurs at the LC filter resonance (fo=25kHz), the Buck converter switching frequency (fsw=200kHz) is selected significantly higher to attenuate high frequency harmonics and avoid exciting acoustic resonance. Lamp stability is achieved by controlling the inductor current of the LC filter, and power mode control is achieved adjusting average current supplied by the PFC stage. The microcontroller selects the different operation modes of the FB converter according to the lamp requirements. I