Patent ID: 7924540

Claim:
An over-voltage protection circuit comprising: an input terminal that receives a power supply voltage from the external; an output terminal that outputs the power supply voltage to the external; a reference voltage terminal that receives a reference voltage; a reverse current prevention transistor and a main transistor provided in series between the input terminal and the output terminal; an input diode provided between a connection point of the reverse current prevention transistor and the main transistor and the reference voltage terminal in such a direction that the anode becomes the reference voltage terminal side; and a control unit that controls the voltage applied to a control terminal of the main transistor according to the power supply voltage, wherein the reverse current prevention transistor is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) arranged in such a direction that the anode of a body diode of the reverse current prevention transistor becomes the input terminal, and a fixed voltage is applied to a control terminal of the reverse current prevention transistor such that the reverse current prevention transistor is biased to be turned on in a normal state that the input terminal becomes high potential and the reference voltage terminal becomes low potential and to be turned off in a reverse polarity state that the input terminal becomes low potential and the reference voltage terminal becomes high potential.