Patent ID: 7301315

Claim:
A power supply circuit, comprising: an output driver transistor configured to output a current in accordance with a first control signal input thereto; a reference voltage generator circuit configured to generate and output a predetermined reference voltage; an output voltage detector circuit configured to detect an output voltage and to output a divided voltage generated based on the output voltage; an amplifier circuit having at least one transistor of a first polarity and at least one transistor of a second polarity opposite to the first polarity and configured to compare the predetermined reference voltage and the divided voltage and to output a second control signal; and a buffer circuit configured to receive the second control signal output by the amplifier circuit and to control the operation of the output driver transistor in accordance with the second control signal, to make the divided voltage substantially equal to the reference voltage, the buffer circuit comprising: a first transistor having an output terminal which is grounded; and a second transistor being a load of the first transistor, the first and second transistors having a polarity same as the second polarity of the amplifier circuit, wherein the amplifier circuit includes a first current mirror circuit and a constant current source configured to supply a current to drive the first current mirror circuit, and wherein the second transistor of the buffer circuit forms a second current mirror circuit with the first current mirror circuit of the amplifying circuit.