Patent ID: 7274113

Claim:
A power supply circuit for supplying power to a circuit unit, comprising: a first power supply system for supplying a first voltage to said circuit unit at a normal operation; and a second power supply system for supplying said first voltage to said circuit unit when said first voltage cannot be supplied by said first power supply system, said second power supply system including a first power supply for outputting a second voltage, a regulator supplied with power from the first power supply, a reverse flow preventing diode arranged between an output portion of the regulator and said circuit unit, and a feedback circuit for detecting a voltage to be applied to said circuit unit between both ends of said reverse flow preventing diode and feeding back the detected voltage to said regulator, and said regulator adjusting an output voltage thereof, so that a voltage to be applied to said circuit unit for a predetermined time after said first power supply system becomes unable to supply said first voltage, said voltage to be applied to said circuit unit becomes lower with respect to said first voltage.