A first protection circuit includes a first diode and a first transistor. The anode of the first diode is connected to a terminal to be protected. The first transistor is configured as an N-channel MOSFET, and arranged such that the first terminal of the conduction channel thereof is connected to the cathode of the first diode, and the second terminal of the conduction channel thereof, and the gate and the back gate thereof are connected to a fixed voltage terminal. The first transistor is configured as a floating MOSFET formed within an N-type well formed in a P-type semiconductor substrate. The first diode is formed in the shared N-type well in which the first transistor is formed. The cathode of the first diode and the first terminal of the conduction channel of the first transistor are connected to the N-type well.