Patent ID: 8405429

Claim:
A power supply voltage monitor circuit comprising: a constant voltage circuit receiving a power supply voltage and outputting a first constant voltage; a level shift circuit receiving the first constant voltage and outputting a second constant voltage obtained by subjecting the first constant voltage to level shift; a clamping circuit receiving the first constant voltage and fixing the received first constant voltage at a clamping voltage; a first differential circuit including a differential unit receiving a constant current supplied from a current source and outputting an output voltage in accordance with a potential difference between a first input voltage obtained by subjecting the second constant voltage to resistive division and a second input voltage obtained by subjecting the power supply voltage to resistive division, and an output unit outputting a rectangular signal in accordance with the output voltage of the differential unit; and a second differential circuit which, in a case where the clamping circuit does not fix the first constant voltage, turns off the current source of the differential unit depending on a potential difference between the first constant voltage and the first input voltage to control the output operation of the output unit, whereas in a case where the clamping circuit fixes the first constant voltage, turns on the current source of the differential unit depending on a potential difference between the clamping voltage and the first input voltage.