Patent ID: 7705573

Claim:
A constant voltage circuit converting an input voltage input from an input terminal into a predetermined constant voltage and outputting the same from an output terminal, comprising: an output transistor outputting an electric current according to an input control signal from the input terminal, to the output terminal; a control circuit part having a first error amplifying circuit carrying out operation control of the output transistor in such a manner that the a first proportional voltage proportional to the output voltage output from the output terminal may be a predetermined first reference voltage; a voltage change detecting circuit part detecting a change of the output voltage output from the output terminal, and amplifying an output signal of a differential amplifying circuit included in the first error amplifying circuit, converting the amplified signal into a binary signal and outputting the binary signal; and a discharging circuit part amplifying a discharge electric current for discharging a capacitance parasitic on a control electrode of the output transistor, according to an output voltage from the voltage change detecting circuit part, wherein: said voltage change detecting circuit part amplifies the output signal of the differential amplifying circuit so that a slew rate thereof may be larger than that of the control signal output from the first error amplifying circuit to the output transistor, responds to a change of the output voltage output from the output terminal quicker than the control signal output from the first error amplifying circuit to the output transistor, to cause the discharging circuit part to carry out discharging operation.