Patent ID: 7385378

Claim:
A constant-voltage circuit having an input terminal pulled up to an input voltage and an output terminal outputting an output voltage, the constant-voltage circuit comprising: a first transistor configured to control an output current flowing from the input terminal to the output terminal in accordance with a first control signal; and a control circuit configured to cause the first transistor to increase the output current when the output voltage varies to an extent greater than a predetermined output voltage variation value to provide an output at the terminal substantially equal to a predetermined voltage, wherein the control circuit comprises: a second transistor configured to control an operation of the first transistor in accordance with a second control signal; and a differential amplifier circuit, and wherein the differential amplifier circuit comprises: a non-inverting input terminal connected to a bias voltage; an inverting input terminal connected to the non-inverting input terminal via a resistor and to the output terminal via a capacitor; and a differential pair of third and fourth transistors.