Mixed mode control for dimming electronic ballast

A novel control technique has been developed for high frequency dimming ballast of fluorescent lamps. By using the integration of duty-ratio modulating and frequency modulating the lamp power was regulated smoothly and a wide dimming range was achieved. Based on the power-dependent lamp model, the control equations were derived by fundamental approximation, and then the dimming characteristics of the fluorescent lamp can be calculated. An electronic ballast with the half bridge series-resonant parallel-load inverter for the fluorescent lamps was used as an example for illustrating the design procedure. A laboratory circuit was built and tested. The experimental results were presented to verify the theoretical discussions.