Switching power supply with overcurrent protection

摘要

A switching power supply with overcurrent protection is provided that comprises a current detection resistor (8) for detecting electric current through an FET (5); a capacitor (11) for accumulating electric charge in response to overcurrent through the current detection resistor (8) due to late OFF switching of the FET (5); and a transistor (12) for reducing source voltage applied to a feed terminal of a control circuit (7) below an operation voltage. When accumulated electric charge in the capacitor (11) exceeds a predetermined level, the transistor (12) is operated to reduce source voltage for the control circuit (7) below operative voltage to stop operation of the control circuit (7) and to thereby restrain overcurrent during delayed time until OFF switching of the FET (5).