A power supply circuit comprises a switching element configured to supply electric power to a load when a driving signal is input, a driving signal generation unit having a resistor and a p-n junction connected in series with a power supply, and a switch connected in parallel to the p-n junction. The p-n junction is connected in a forward direction with regard to the voltage of the power supply, and the generation unit outputs the driving signal to the switching element when the switch is in a close state.
