Patent ID: 8508200

Claim:
A power supply circuit comprising: a power transistor which is placed between an input power supply and an output terminal; a differential amplifier which outputs, as a current difference, a difference between a feedback voltage obtained by dividing an output voltage which is a voltage on the output terminal and a reference voltage; an I/V converter circuit which converts the current difference into a voltage difference; and an amplifier which amplifies the voltage difference and which supplies the amplified voltage difference to a control terminal of the power transistor as a signal for controlling an ON resistance of the power transistor, wherein the differential amplifier comprises: a first current path in which a first current mirror transistor and a first control transistor are connected in series, wherein the first current mirror transistor is connected to the input power supply, a predetermined current mirror current flows in the first current mirror transistor via a first resistor element, and the reference voltage is input to the first control transistor; a second current path in which a second current mirror transistor and a second control transistor are connected in series, wherein the second current mirror transistor is connected to the input power supply, a predetermined current mirror current flows in the second current mirror transistor via a second resistor element, and the feedback voltage is input to the second control transistor; and a constant current source section which sets a sum of a current flowing in the first current path and a current flowing in the second current path to be a predetermined constant current, and the power supply circuit further comprises: a first capacitor element which is connected in parallel with the amplifier; and a second capacitor element to minimize the difference in AC gain between the first and second current paths which is connected either between ground and a connection point between the first resistor element and the first current mirror transistor, or between the ground and a connection point between the second resistor element and the second current mirror transistor.