Patent ID: 7215145

Claim:
A power supply circuit comprising: a comparator circuit comprising: a differential pair which includes: a first metal oxide semiconductor (MOS) transistor of enhancement mode n-type having a gate electrode at which an input signal is supplied; and a second MOS transistor of depletion mode n-type, a source of the second MOS transistor being connected with a source of the first MOS transistor, and a threshold voltage of the second MOS transistor being lower than a threshold voltage of the first MOS transistor; a first current source inserted between a first power supply line and the differential pair, a first power supply voltage being supplied to the first power supply line; and a current mirror circuit which is inserted between a second power supply line and the differential pair and generates a drain current of the second MOS transistor corresponding to a drain current of the first MOS transistor, a second power supply voltage being supplied to the second power supply line, wherein the pate electrode of the first MOS transistor is formed by polycrystalline silicon which contains a p-type impurity, wherein a gate electrode of the second MOS transistor is formed by polycrystalline silicon containing an n-type impurity and is connected with the first power supply line, and wherein an output signal is output based on a drain voltage of the second MOS transistor; a logic circuit which is connected with the first and second power supply lines and generates a discharge signal based on an output from the comparator circuit; and a booster circuit which is connected with the first and second power supply lines and boosts a voltage difference between the first and second power supply voltages by a charge-pump operation using a capacitor which stores an electric charge, wherein the booster circuit includes a discharge switch element for discharging the electric charge in the capacitor into the first power supply line at a time of discharging, and wherein the discharging switch element is switch-controlled based on the discharge signal.