Patent ID: 8253404

Claim:
A constant voltage circuit configured to become active or inactive according to an applied signal and to convert an input voltage applied to an input terminal into a predetermined constant voltage for output from an output terminal, the constant voltage circuit comprising: an output transistor configured to supply, from the input terminal to the output terminal, an output current responsive to an applied control signal; an error amplifier circuit unit configured to control operations of the output transistor to make a first proportional voltage equal to a predetermined reference voltage, the first proportional voltage being proportional to the output voltage from the output terminal; a ramp voltage generating circuit unit configured to generate and output a ramp voltage whose voltage level increases at a predetermined speed from start-up; and an amplifier circuit unit configured to amplify a voltage difference between the ramp voltage and a second proportional voltage and output the amplified voltage difference to a control electrode of the output transistor, the second proportional voltage being proportional to the output voltage from the output terminal; wherein the amplifier circuit unit controls the operations of the output transistor to make the second proportional voltage equal to or lower than the ramp voltage.