Electronic ballast for metal halide lamps using a quasi-resonant inverter with digital control

A digital control electronic ballast for the metal halide lamp is proposed based on the low-frequency square wave, and a comprehensive control strategy is employed for the zero-voltage-switching quasi-square-wave dual buck converter. To achieve the self-adaptive zero-voltage-switching control, the digital control method is used, which greatly reduces the switching losses of the circuit. A single-cycle-peak-current control method is adopted to restrain the overcurrent generated by reversing during the low-frequency transition from the turn-on to the steady state. The complicated process of igniting is analyzed in detail, and a constant-current control method is proposed to diminish the power overshoot and to decrease the current and voltage stress in the transition stage. A power closed-loop duty ratio control method is adopted, and its correctness is proved. An experimental prototype of 70 W is implemented, and the system can achieve reliable operation from the transient state to the steady state, with the highest efficiency of 92% and with no acoustic resonance occurring.