Digitally group-asymmetrical PWM controlled dimmable ballast for fluorescent lamp

Digitally group-asymmetrical PWM (DGAPWM) ballast for a dimmable fluorescent lamp is explored. The proposed DGAPWM can adaptively provide suitable duty-ratio in group pulse train for generating proper odd as well as even harmonics over whole spectrum of the lamp current so as to eliminate striation and thermostat effect. The DGAPWM activates during low luminance under 3,000 Cd/m² and operates the ballast working in continuous conduction mode (CCM), which achieves zero-voltage-switching (ZVS) to gain high efficiency over 90%. The proposed DGAPWM for the fluorescent lamp can increase lighting efficiency better over 20% than traditional one and provide wide dimmable range between 100% and 0%.