Schmitt trigger circuit and power supply monitoring apparatus

The present invention relates to a Schmitt trigger circuit and a power supply monitoring apparatus using the Schmitt trigger circuit. The Schmitt trigger circuit that can improve the accuracy of voltage measurement while extending the life of an LED included in a photocoupler. The Schmitt trigger circuit according to an embodiment includes a voltage dividing circuit that divides an input voltage and outputs a divided voltage, and a basic Schmitt trigger circuit that includes a transistor as a current controlling element and controls current flowing through the LED included in the external photocoupler on the basis of the output voltage of the voltage dividing circuit proportional to the input voltage. The voltage dividing circuit has a positive temperature coefficient.