SYNCHRONOUS RECTIFICATION DC-DC CONVERTER AND SWITCHING POWER SUPPLY DEVICE

A DC-DC converter includes a synchronous rectification converter that converts electric power, a voltage detection circuit that detects a voltage proportional to an output voltage of the converter, a converter controller that compares a detection voltage detected by the voltage detection circuit with a reference voltage and controls an operation of the converter to provide a constant or substantially constant voltage of the detection voltage, and a command processor that sets, in a case where a target voltage command value input from an ECU is lower than a voltage value of the output voltage of the converter, a voltage value of the reference voltage to be equal or substantially equal to a voltage value of the detection voltage.