Patent ID: 8536819

Claim:
A power supply device, comprising: an electronic switch provided on a wiring which connects a DC power supply to a motor load; a driving portion that controls the electronic switch with PWM to drive the motor load; a semiconductor element that has a parasitic diode and is disposed in parallel to the motor load so that a forward direction of the parasitic diode is in opposite to a flowing direction of a current flowing through the motor load; and a control portion that controls the semiconductor element so as to be turned on during a part of a period during which the electronic switch is placed in an off state under a control with the PWM, wherein in a case where electromagnetic energy accumulated in an inductance of the motor load disappears until the electronic switch is turned on again after the electronic switch is turned off, the part of the period is set to a period from a time point where a voltage at a first connection point for connecting between the electronic switch and the motor load reduces to a level equal to or lower than a grounding level after the electronic switch is turned off to a time point before the voltage at the first connection point starts increasing due to disappearance of the electromagnetic energy.