OVERVOLTAGE PROTECTION FOR HID LAMP BALLAST

摘要

The present invention relates to a device for operating a high-pressure discharge lamp, comprising a switched mode power supply circuit (SMPS) for supplying power to the high pressure discharge lamp from a supply voltage, the power supply circuit comprising a half bridge commutating forward (HBCF) circuit including an inductance (Lhbcf), a capacitor circuit of a first capacitor (Cs1) and a second capacitor (Cs2) in series, the lamp (LA) being connectable between the inductance (Lhbcf) and a point (M) between the first and second capacitor(Cs1,Cs2); wherein overvoltage protection means are connected parallel to the lamp, which switch from an off-state with a high resistance operation to an on-state with a low resistance operation when the voltage difference across the protection means exceeds a breakover voltage (Vbo), the breakover voltage (Vbo) being selected to correspond to a predetermined maximum voltage across the first or the second capacitor (Cs1,Cs2).