Abstract: A discharge lamp lighting control device comprises an H-bridge circuit connected between the secondary coil of a transformer and a discharge lamp and provided with a first pair of transistors and a second pair of transistors, capable of converting a DC voltage produced from an AC voltage that appears at the secondary coil of the transformer into an AC voltage whose polarity is changed at predetermined intervals so as to apply the AC voltage to the discharge lamp. The first pair of transistors have withstand voltage characteristic superior to that of the second pair of transistors. The on-state resistances of the four transistors of the first and second pairs can be equal to each other so that the difference between the on-state resistances may be ignored. A control unit turns on only the first pair of transistors when applying a high voltage to the discharge lamp to cause a discharge to pass through the gas contained in the discharge lamp.

Abstract: A discharge lamp lighting controller that detects the voltage applied to a discharge lamp used by a vehicle, for example, and stops power supply to the discharge lamp if the voltage goes out of an estimated rated voltage range in a design stage. Circuit components are protected from possible impairment due to excessive current that may flow depending on the state of the discharge lamp under the constant power control of the discharge lamp.