Arc Stabilization in Metal Halide Lamps using a Post-Regulator Working at the Zero-Duty-Cycle Boundary

The most commonly used power topology to drive metal halide lamps is based in three cascaded stages. The first stage is used for power factor correction, the second stage is used to stabilize the discharge and the last stage is used to turn the DC output of the previous stage to a low frequency AC square waveform suitable to supply the lamp. The dynamic impedance of the lamp does not allow using the power factor correction stage to stabilize the discharge. This is due to the fact that voltage in the bulk capacitor can not be changed fast enough to stabilize the lamp current. In this paper, a boost-type post-regulator working at the zero-duty-cycle limit is proposed to stabilize the discharge. This way, a non-linear post-regulator with very high efficiency is obtained. A simplified procedure to design the regulator is also presented in this paper. A laboratory prototype has been built to verify the proposed procedure.