Patent ID: 8278991

Claim:
A power supply circuit comprising: a charge pump circuit configured to raise a voltage inputted from an input terminal and supply the raised voltage from an output terminal to a given load; and a control circuit unit, wherein the charge pump circuit includes: a fly-back capacitor configured to store a charge he voltage inputted from the input terminal; and an output transistor connected between one terminal of the fly-back capacitor and the output terminal of the charge pump circuit, wherein the control circuit unit receives a reference voltage and the voltage outputted from the charge pump circuit and is configured to generate a proportional voltage proportional to the voltage outputted from the charge pump circuit and output a voltage to control the output transistor depending on a difference between the proportional voltage and the reference voltage so that the proportional voltage has the same voltage level as the reference voltage, wherein the control circuit unit includes a proportional voltage generating circuit unit configured to divide the voltage outputted from the output terminal of the charge pump circuit at a predetermined dividing ratio to generate the proportional voltage, and an error amplifier circuit configured to amplify a voltage corresponding to a difference between the proportional voltage and the reference voltage to output the amplified voltage to a control electrode of the output transistor, wherein the error amplifier circuit further comprises: an operational amplifier circuit which includes an input terminal to receive the proportional voltage, another input terminal to receive the reference voltage, and an output terminal configured to output an output signal; and an output circuit including a constant current source capable of generating and outputting a predetermined constant current and a first transistor having a control electrode to which the output signal outputted by the operational amplifier circuit is inputted, the constant current source and the first transistor being connected in series between the input voltage and a ground potential, wherein a connection between the constant current source and the first transistor serves as an output terminal which is connected to the control electrode of the output transistor, and wherein the power supply circuit further comprises a second transistor connected between the output terminal of the operational amplifier circuit and the ground potential, wherein the second transistor is controlled to be turned on only during a cycle in which the fly-back capacitor is discharged.