Abstract: A power supply circuit includes a comparator, first to third electronic switches, a D-trigger, a power supply unit (PSU), and a complex programmable logic device (CPLD). When a voltage from the PSU is greater than a reference voltage, the first electronic switch is turned on. An electronic device connected to the first electronic does not receive power from the PSU. The second electronic switch is turned on. The third electronic switch is turned off. The D-trigger outputs a low level signal to make the CPLD control the PSU stop supplying power.