Patent ID: 7723971

Claim:
A power supply apparatus, comprising: a switching regulator which includes a switching transistor therein and which converts an input voltage to a desired output voltage by a switching operation of the switching transistor and outputs the voltage through an output terminal thereof; a control unit which controls the switching operation of the switching transistor, and receives a power supply voltage at a power supply terminal; a voltage generation circuit which supplies a supply voltage to the power supply terminal of said control unit, to drive said control unit; a switch which is provided between the output terminal of the switching regulator and the power supply terminal of the control unit; and a timer circuit which measures time elapsed from a start of operation of the switching transistor and which turns on the switch by varying an output thereof when a predetermined period of time has elapsed, wherein said control unit is driven by the supply voltage supplied from said voltage generation circuit during a period before the output of said timer circuit changes, whereas said control unit is driven by the output voltage of said switching regulator during a period after the output of said timer circuit has changed, the voltage generation circuit is provided with an enable terminal operative to receive an enable signal determined by the output of the timer circuit, and the voltage generation circuit is placed in an enable state before the output of the timer circuit varies, and is placed in a disabled state after the output of the timer circuit varies.