Patent ID: 8108701

Claim:
A power supply circuit arranged in a circuit board to supply a determined voltage to an element, the power supply circuit comprising: a first voltage receiving terminal to receive a first voltage signal, wherein the first voltage receiving terminal is connected to a divider circuit; a second voltage receiving terminal to receive a second voltage signal; a voltage output terminal outputting the determined voltage to the element; a window comparator, wherein a non-inverting terminal of the window comparator is connected to the divider circuit, an inverting terminal of the comparator is connected to the voltage output terminal; and an electrical switch, wherein an output terminal of the comparator is connected to a control terminal of the electrical switch, and connected to the voltage output terminal via a resistor, a first terminal of the electrical switch is connected to the voltage output terminal, a second terminal of the electrical switch is connected to the second voltage receiving terminal; wherein the second voltage signal minus a voltage drop between the first terminal and the second terminal of the electrical switch equals the determined voltage, the divider circuit satisfy the voltage of the non-inverting terminal of the comparator equals to the determined voltage.