A disclosed overvoltage protection circuit includes a power source input terminal of an electronic device, the power source input terminal being configured to receive a power source voltage; an internal power source terminal configured to supply power to internal circuits of the electronic device; a voltage blocking circuit connected between the power source input terminal and the internal power source terminal, the voltage blocking circuit being configured to prevent the power source voltage received at the power source input terminal from being provided; and a constant voltage output unit connected in parallel with the voltage blocking circuit, the constant voltage output unit being configured to output a constant voltage. In the event that the power source voltage received at the power source input terminal is higher than or equal to a predetermined voltage, the voltage blocking circuit blocks the power source voltage received at the power source input terminal.