POWER SUPPLY CIRCUIT FOR VEHICLE, AND DC-DC CONVERTER CIRCUIT USED FOR THE VEHICLE

摘要

PROBLEM TO BE SOLVED: To supply power from a low-voltage battery to a starter at emergency, such as battery shortage in a high voltage specification of vehicle, where both a high-voltage battery and a low-voltage battery are mounted. SOLUTION: A converter circuit 21 of a DC-DC converter 7 is equipped with a step-down circuit 23 for lowering high voltage V1 to low voltage V2 and a step-up circuit 24 for boosting low voltage V2 to high voltage V1. For the circuit 21, that the converter circuit 21 uses, either the step-down circuit 23 or the step-up circuit 24 is switched selectively, and normally, it is switched to the step-down circuit 23. A control circuit 22 switches the circuit that the converter circuit 21 uses over to the step-up circuit 24, when an operation switch 27 is on, and switches it over to the step-down circuit 23 when the operation switch 27 is off.