US Patent 7170330 Hysteresis comparator circuit

An input voltage is applied to an inverting input terminal of a comparator having no hysteresis. A first constant voltage is divided by resistors to create a reference voltage. The reference voltage is applied to a non-inverting input terminal of the comparator through a resistor. Only while an output voltage of the comparator is a low level, a predetermined constant current is supplied to a supply point of the reference voltage and a constant current of the same magnitude is absorbed from the non-inverting input terminal of the comparator.