Patent ID: 7642760

Claim:
A power supply circuit comprising: a voltage converter receiving an external voltage from an external voltage source and outputting an internal voltage which is different from the external voltage; a first switching element and a second switching element connected between an output of the voltage converter and a constant voltage source; a resistor provided between the first switching element and the second switching element, and dividing the internal voltage; a comparator including a first input unit, a second input unit, and an output unit which is connected to the voltage converter; a reference voltage source supplying a reference voltage to the first input unit; a feedback unit feeding back a voltage divided by the resistor to the second input unit from a node between the first switching element and the second switching element; a setting voltage source supplying a voltage which is arbitrarily set, to the second input unit; a third switching element connected between the setting voltage source and the second input unit; and a control signal generator controlling the first switching element, the second switching element, and the third switching element, wherein when the voltage converter is controlled by the comparator, the control signal generator controls the first switching element and the second switching element to be in an ON state and controls the third switching element to be in an OFF state, and when the voltage converter is controlled by the external voltage source, the control signal generator controls the first switching element and the second switching element to be in the OFF state and controls the third switching element to be in the ON state.