Patent ID: 7492137

Claim:
A series regulator for supplying a stable output voltage to a load, the series regulator comprising: an output control transistor that supplies the output voltage in accordance with a control signal; a voltage divider circuit that divides the output voltage and outputs the divided voltage; and a differential amplifier circuit that outputs the control signal to the output control transistor in accordance with a differential voltage of difference between a preset reference voltage and the divided voltage output from the voltage divider circuit, wherein the differential amplifier circuit includes: a differential input stage for detecting the differential voltage between the reference voltage and the divided voltage output from the voltage divider circuit; and an amplification stage having a first MOS transistor and a resistor having a predetermined resistance connected to the gate and the drain of the first MOS transistor, and a constant-current circuit connected in series with the first MOS transistor, wherein the differential input stage includes a differential pair of second and third MOS transistors, with the drain of one of the second or third MOS transistor directly connected to the gate of the first MOS transistor, wherein a connecting part between the first MOS transistor and the constant-current circuit serves as an output terminal of the amplification stage, wherein the amplification stage converts current output from the differential input stage to a voltage to generate the control signal, which is output to the output control transistor, wherein if the preset reference voltage is larger than the divided voltage, the amplification stage generates the control signal for increasing the output voltage to be output by the output control transistor, wherein if the divided voltage is larger than the preset reference voltage, the amplification stage generates the control signal for decreasing the output voltage to be output by the output control transistor, and wherein only the amplification stage exclusively outputs the control signal to the output control transistor when a differential voltage exists between the preset reference voltage and the divided voltage.