Patent ID: 8227997

Claim:
A lamp driving circuit for operating a high-intensity discharge (HID) lamp, the lamp driving circuit comprising: a supply voltage terminal for receiving a supply voltage; an inverter circuit coupled to the supply voltage terminal, the inverter circuit comprising: a commutation circuit for generating a commutation voltage, the commutation circuit comprising at least two switching devices, the switching devices being configured to operate alternately at a commutation frequency, each switching device being configured to operate at a switching frequency, wherein the switching frequency is substantially equal to the commutation frequency during an ignition mode and the switching frequency is higher than the commutation frequency during a steady state mode; an inverter resonant circuit coupled to the commutation circuit for receiving the commutation voltage for generating a supply current at a node; and a clamping circuit coupled to the inverter resonant circuit for limiting a voltage at the node of the inverter resonant circuit to a predetermined maximum voltage level; and an output circuit coupled to the inverter circuit for receiving the supply current, the output circuit comprising: an output resonant circuit for generating an ignition voltage for igniting the lamp in the ignition mode, and for reducing a switching frequency ripple in the supply current in order to generate a commutation frequency output current, when operating the lamp in the steady state mode; and a set of output terminals for supplying the output current to the HID lamp.