Patent ID: 7609099

Claim:
A circuit for detecting a power-on voltage of a power supply, comprising: a voltage divider connected between a first power supply and a second power supply, the potential of the second power supply is lower than the potential of the first power supply, the voltage divider including a series circuit which includes: a diode; a first dividing resistor connected to the diode; and a second dividing resistor connected between the first dividing resistor and the second power supply; and a detecting circuit connected between the first power supply and the second power supply, the detecting circuit including: a pMOS transistor whose gate electrode is connected to a connection node between the first dividing resistor and the second dividing resistor; a source resistor connected between the first power supply and the source electrode of the pMOS transistor; and a drain resistor connected to the drain electrode of the pMOS transistor and the second power supply, wherein a resistance value R 1 of the first dividing resistor, a resistance value R 2 of the second dividing resistor, a resistance value R 3 of the source resistor R 3 and a resistance value R 4 of the drain resistor satisfy: R 2 /( R 1 +R 2 )=( dV th /dT×R 4 /( R 3 +R 4 ))/( dV dio /dT ), where dV th /dT is a temperature dependence of a threshold voltage of the pMOS transistor, and dV dio /dT is a temperature dependence of an on-state voltage of the diode.