Patent ID: 7719810

Claim:
An overvoltage protection circuit comprising: 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 provide an un-interrupted power supply and output a constant voltage; wherein 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, the voltage blocking circuit unblocks the power source voltage received at the power source input terminal once the power source voltage received at the power source input terminal is lower than the predetermined voltage, and wherein the predetermined voltage and the constant voltage are lower than or substantially equal to a lowest withstand voltage among withstand voltages of transistors employed in the internal circuits, and wherein the voltage blocking circuit includes a switching transistor and the constant voltage output unit includes an output transistor, the switching transistor and the output transistor are connected in parallel with each other.