Design of low voltage control IC improving CF of electronic ballast with passive PFC circuit

Abstract

This thesis focuses low cost solution for high performance electronic ballast. First part introduces a gate-driven mixed mode excitation that is applicable to dimmable electronic ballasts. The proposed approach combines the characteristics of self-oscillating mode and external excitation. In the mixed mode excitation, the MOSFETs in an electronic ballast are turned on by the resonant current and turned off by the gate driver, which is triggered by a low voltage control IC, which is fabricated in a 3.3V standard CMOS process. It can substitute for expensive high voltage IC. Second part introduces variable current control scheme and control IC that improves crest factor of electronic ballast with cheap passive PFC circuit instead of expensive active PFC circuit. Lamp current is fed back to control IC and its envelope is controlled to maintain acceptable crest factor without degrading performance of passive PFC circuit. Using this scheme, crest factor is 1.46 and power factor is 0.99. Harmonic distortions meet international standard. Third part introduces a digital control IC for closed loop power control of electronic ballast. Digital integration method which extends the resolution of digital control IC is proposed. To verify this idea digital control IC having 4bit ADC is designed using 0.35um CMOS process. Simulation result shows 4 times resolution extension effect and experiment result shows 3 times resolution extension effect. This idea can be applied to the resonant inverter such as electronic ballast whose output current is sinusoidal. Using this idea the complexity and area of digital control IC for electronic ballasts can be reduced and implementation of low cost digital control IC is possible.