Patent ID: 8134349

Claim:
A power supply circuit that outputs a voltage stepped down from a power supply voltage, comprising: a constant voltage circuit that outputs a constant voltage; a first MOS transistor having one end connected to ground and a gate fed with a fixed voltage; a second MOS transistor having one end connected to an other end of the first MOS transistor; a third MOS transistor which is connected between an other end of the second MOS transistor and the power supply and has a gate connected to an output of the constant voltage circuit; an output terminal connected between the second MOS transistor and the third MOS transistor to output the output voltage stepped down from the power supply voltage; a first voltage dividing circuit that outputs a first divided voltage obtained by dividing the voltage of the output terminal by a first voltage dividing ratio; and a first differential amplifier circuit which is fed with a reference voltage and the first divided voltage and has an output connected to a gate of the second MOS transistor, wherein the first differential amplifier circuit outputs a signal to turn on the second MOS transistor when the first divided voltage is higher than the reference voltage, and the first differential amplifier circuit outputs a signal to turn off the second MOS transistor when the first divided voltage is lower than the reference voltage.