Frequency control and phase surveillance in resonant electronic ballast

Soft-saturation magnetic cores, traditionally used in low current ripple application, are employed to build the inductor in HF resonant inverters to drive HPS lamps because no oversize is required to accept the over current and voltage during the resonant ignition transient. Soft-saturation core behavior and lamp ignition states are modeled. A frequency control under phase surveillance (FCPS) is proposed during the ignition and steady state operation to assure zero-voltage-switch in the MOSFETs turn-on transients in resonant circuits and high output impedance to stabilize the lighting arc. The result is a reduction in the inductor size along with a reliable converter operation, paving the way for the resonant ballast to increase the switching frequency in high power applications.