Overvoltage protection circuit

1. An overvoltage protection circuit, comprising:

an output transistor connected between a power supply terminal and an output terminal, the output terminal being a terminal for being connected to a load;

a dynamic clamping circuit to control a voltage difference between the power supply terminal and the output terminal according to a voltage of the output terminal; and

a clamp selection switch electrically connected between the dynamic clamping circuit and the output terminal, the clamp selection switch including an N-channel type MOS transistor including:

a gate terminal applied to a ground terminal;

a substrate terminal electrically connected to the output terminal;

a drain terminal connected to the dynamic clamping circuit; and

a source terminal connected to a gate terminal of the output transistor.

2. The overvoltage protection circuit according to claim 1 , further comprising:

a gate resistance; and

a gate charge discharging circuit connected between the gate terminal of the output transistor and the output terminal,

wherein the gate charge discharging circuit is conductive to discharge a charge in the . gate terminal of the output transistor.

3. The overvoltage protection circuit according to claim 2 , wherein the gate charge discharging circuit is controlled by a second control signal which is an inverted signal of a first signal for controlling the output transistor.

4. The overvoltage protection circuit according to claim 1 , wherein the dynamic clamping circuit comprises a diode,

wherein a cathode of the diode is connected to the first power supply, and

wherein an anode of the diode is connected to the clamp selection switch.

5. The overvoltage protection circuit according to claim 1 , wherein the output transistor is controlled by a first control signal inputted via a gate resistance.

6. The overvoltage protection circuit according to claim 1 , wherein the output transistor and the dynamic clamping circuit are in the same chip.

7. A power control apparatus, comprising:

a dynamic clamping circuit that controls a voltage difference between a power supply terminal and an output terminal according to a voltage of the output terminal;

an output transistor connected between the power supply terminal and the output terminal, the output transistor comprising an N-channel type MOS transistor, said N-channel type MOS transistor including:

a gate terminal receiving a control signal;

a drain terminal connected to the power supply terminal; and

a source terminal connected to the output terminal; and

a clamp selection switch connected in series with the dynamic clamping circuit and the output terminal, the clamp selection switch including an N-channel type MOS transistor, said N-channel type MOS transistor comprising:

a gate terminal applied to a ground terminal;

a substrate terminal connected to the output terminal;

a drain terminal connected to the dynamic clamping circuit; and

a source terminal connected to the gate terminal of the output transistor.

8. The power control apparatus of claim 7 , wherein the output terminal comprises a terminal for being connected to a load.

9. The power control apparatus of claim 8 , wherein the control signal is defined as a first control signal, and

wherein the power control apparatus further comprises:

a gate resistance element including a first node connected to the gate terminal of the N-channel type MOS transistor of the output transistor and a second node; and

a gate charge discharging circuit connected between the second node of the gate resistance element and the output terminal, the gate charge discharging circuit comprising an N-channel type MOS transistor, said N-channel type MOS transistor comprising:

a gate terminal receiving a second control signal opposite to the first control signal;

a drain terminal connected to the second node of the gate resistance element; and

a source terminal connected in common with the substrate terminal of the N-channel type MOS transistor of the clamp selection switch and the output terminal, and

wherein the source terminal of the N-channel type MOS transistor of the clamp selection switch is further connected to the first node of the gate resistance element.