Class d LC/sub s/C/sub p/ series-parallel resonant inverter with inherent maximum output power suitable for driving HPS lamps

This paper proposes a design method for a class D series-parallel (LC/sub s/C/sub p/) resonant inverter suitable to drive high-intensity discharge lamps. The high voltage needed to achieve the ignition of the lamp is reached by using the gain voltage of the resonant LC/sub s/C/sub p/ network with no auxiliary circuits for this purpose. By means of a soft start-up sequence the maximum voltage and current stress are maintained below prefixed values. In steady state, the operation point is calculated to limit the maximum power that the inverter delivers to the lamp. In this way, the variation of the lamp power caused by the lamp aging is limited in order to fulfil the standard. This design results in cost-effective circuits, simplifying the DC/AC power stage of an electronic ballast. The experimental results are given for two similar 100 W high-pressure sodium lamps with different aging.