Patent ID: 7719242

Claim:
A voltage regulator converting a voltage input to an input terminal into a predetermined constant voltage and outputting the constant voltage from an output terminal, the voltage regulator comprising: an output transistor formed of a MOS transistor, the output transistor being configured to output a current according to an input control signal from the input terminal to the output terminal; a control circuit part configured to control an operation of the output transistor so that a voltage proportional to the voltage output from the output terminal is a predetermined reference voltage; a switching circuit part configured to connect a substrate gate of the output transistor to one of the input terminal and the output terminal and to connect a gate of the output transistor to one of an output of the control circuit part and the output terminal in accordance with a relationship in magnitude between a voltage at the input terminal and a voltage at the output terminal; a first rectifier element connected between the input terminal and a power supply end, from which power is supplied to the control circuit part and the switching circuit part, so as to allow current to flow from the input terminal to the control circuit part and the switching circuit part; and a second rectifier element connected between the output terminal and the power supply end so as to allow current to flow from the output terminal to the control circuit part and the switching circuit part.