Regulator circuit and integrated circuit device forming the regulator circuit

A regulator circuit which lowers an external power supply voltage and supplies the lowered voltage to a load circuit, comprising:

• an external power supply voltage terminal;
• a transistor having first, second, and third terminals, a signal received by the third terminal controlling conduction between the first and second terminals;
• a backflow limiter circuit, connected between the external power supply voltage terminal and the first terminal of the transistor, for limiting backflow of current to the external power supply voltage terminal during a momentary drop in the external power supply voltage, the backflow limiter circuit including a diode and a resistor connected in parallel to the diode;
• a first resistor connected to the second terminal of the transistor at a first connection point;
• a second resistor having an end that is connected to the first resistor at a second connection point and having another end that is connected to ground;
• an operational amplifier which controls the regulator circuit;
• a reference voltage circuit connected to a positive input terminal of the operational amplifier, and
• an output terminal for connection to the load,
• wherein a negative input terminal of the operational amplifier is connected to the second connection point of the first resistor and second resistor, an output terminal of the operational amplifier is connected to the third terminal of the transistor, and the output terminal is connected to the first connection point of the transistor and first resistor.