Feed-Forward Control Circuit for CFL Ballast Compatible with TRIAC Based Dimmer

Abstract

Conventional triac based dimmer for light dimming of compact fluorescent lamps (CFLs) results in poor power factor (PF) and light flickering. In this paper a feed-forward control circuit based on phase-cut dimmer capable of regulating lamp power from 10% to full power with high PF and without flickering is proposed. The control circuit detects the firing angle (α) of the triac based dimmer and determines the duty cycle of the switch of CFL ballast circuit. The control circuit is located inside the CFL as part of its electronic ballast and then the relevant lighting circuit of the CFL does not need any additional wiring to the triac based dimmer. The lamp power is regulated by both the duty cycle of the ballast single switch and the input voltage cut. The proposed control circuit offers simplicity, high PF, low crest factor (CF) and zero voltage switching over the whole dimming range. To verify proper operation of the proposed control circuit, a laboratory prototype of the proposed control circuit compatible with an electronic ballast topology is implemented for a 42 W CFL lamp tube. Experimental results confirm the analysis and design of the proposed control circuit.