Power supply control circuit

1. A power supply control circuit, comprising:

a first and second power supply lines, a power supply voltage being applied between the first and second power supply lines;

an output transistor coupled between the first power supply line and an output terminal;

a first switch coupling the first power supply line with a control terminal of the output transistor when a counter electromotive voltage from a load, which is connected to the output terminal, is applied to the output terminal;

a switching element coupling the second power supply line with the control terminal of the output transistor when the power supply voltage is applied in a reverse direction between the first and second power supply lines; and

a reference voltage control circuit applying a potential corresponding to a potential of the second power supply line to a reference voltage node coupled to a control terminal of the first switch when the power supply voltage is applied in a forward direction between the first and second power supply lines, and that applies a potential corresponding to a potential of the first power supply line to the reference voltage node when the power supply voltage is applied in the reverse direction between the first and second power supply lines.

2. The power supply control circuit according to claim 1 , wherein the first switch comprises first and second transistors connected in series with each other, a substrate terminal of the first transistor being connected in common with a substrate terminal of the second transistor.

3. The power supply control circuit according to claim 1 , further comprising:

a resistor provided between the switching element and the second power supply line;

a second switch comprising a transistor coupled between a node electrically connected to the switching element and the resistor, and the output terminal; and

a substrate terminal control circuit applying one of a voltage at the reference voltage node and a voltage at the output terminal to the substrate terminal of the transistor included in the second switch.

4. The power supply control circuit according to claim 1 , wherein the reference voltage control circuit comprises:

a diode coupled between the first power supply line and the reference voltage node; and

a resistor coupled between the reference voltage node and the second power supply line.

5. The power supply control circuit according to claim 1 , wherein the reference voltage control circuit comprises:

third and fourth transistors connected in series with each other between the first power supply line and the reference voltage node, a gate of the third transistor and a gate of the fourth transistor being connected to the second power supply line; and

fifth and sixth transistors connected in series with each other between the reference voltage node and the second power supply line, a gate of the fifth transistor and a gate of the sixth transistor being connected to the first power supply line.

6. The power supply control circuit according to claim 3 , wherein the substrate terminal control circuit comprises:

seventh and eighth transistors connected in series with each other between the substrate terminal of the transistor included in the second switch and the output terminal, a gate of the seventh transistor and a gate of the eighth transistor being connected to the reference voltage node; and

ninth and tenth transistors connected in series with each other between a substrate terminal of the transistor included in the second switch and the reference voltage node, a gate of the ninth transistor and a gate of the tenth transistor being connected to the output terminal.

7. A power supply control circuit, comprising:

an output transistor coupled between a first power supply line and an output terminal;

a load coupled to the output terminal;

a gate charge discharging switch coupled between a control terminal of the output transistor and the output terminal;

a power supply reverse connection protection circuit supplying an electric charge from a second power supply line to the control terminal of the output transistor when a power supply is reversely connected; and

an overvoltage protection circuit, the overvoltage protection circuit comprises:

a dynamic clamp circuit limiting a voltage difference between the first power supply line and the output terminal to a predetermined voltage value; and

a first switch coupled in series between the dynamic clamp circuit and the control terminal of the output transistor, and to be conductive or non-conductive state based on a result of comparison between a reference voltage and a voltage at the control terminal of the output transistor, the reference voltage being set to a voltage corresponding to a voltage of the second power supply line when a power supply is normally connected and being set to a voltage corresponding to a voltage of the first power supply line when the power supply is reversely connected.

8. The power supply control circuit according to claim 7 , wherein the first switch comprises first and second transistors connected in series with each other, control terminals of the first transistor and the second transistor being connected in common with each other and substrate terminals of the first transistor and the second transistor being connected in common with each other.

9. The power supply control circuit according to claim 8 , wherein the first and second transistors are formed in a second conductivity type semiconductor region formed in a first conductivity type semiconductor region.

10. The power supply control circuit according to claim 7 , further comprising:

a second switch including a transistor with one end coupled to the output terminal and another end coupled to the second power supply through a first resistor, the second switch being rendered conductive when a negative voltage is generated at the output terminal; and

a substrate terminal control circuit switching a voltage at a substrate terminal of the transistor included in the second switch, between a voltage at the output terminal and the reference voltage, depending on a connection state of the power supply and a state of the output terminal.

11. The power supply control circuit according to claim 10 , further comprising:

a diode coupled between the transistor included in the second switch and the output terminal.

12. A power supply control circuit, comprising:

first and second power supply lines, a power supply voltage being applied between the first power supply line and the second power supply line;

an output transistor connected between the first power supply line and an output terminal;

a first switch that electrically connects the first power supply line with a control terminal of the output transistor when a counter electromotive voltage from a load, which is connected to the output terminal, is applied to the output terminal;

a switching element that electrically connects the second power supply line and the control terminal of the output transistor to each other when the power supply voltage is applied in a reverse direction between the first and second power supply lines; and

a control circuit that applies a potential corresponding to a potential of the second power supply line to a control terminal of the first switch when the power supply voltage is applied in a forward direction between the first and second power supply lines, and that applies a potential corresponding to a potential of the first power supply line to the control terminal of the first switch when the power supply voltage is applied in the reverse direction between the first and second power supply lines.

13. The power supply control circuit according to claim 12 , wherein the first switch comprises first and second transistors connected in series, a substrate terminal of the first transistor being connected in common with a substrate terminal of the second transistor.

14. The power supply control circuit according to claim 12 , further comprising:

a resistor provided between the switching element and the second power supply line;

a second switch comprising a transistor provided between a node between the switching element and the resistor, and the output terminal; and

a substrate terminal control circuit that applies one of a potential applied from the control circuit and a potential applied at the output terminal to a substrate terminal of the transistor included in the second switch.

15. The power supply control circuit according to claim 12 , wherein the control circuit comprises:

a diode coupled between the first power supply line and the control terminal of the first switch; and

a resistor coupled between the control terminal of the first switch and the second power supply line.

16. The power supply control circuit according to claim 12 , wherein the control circuit comprises:

third and fourth transistors connected in series with each other between the first power supply line and the control terminal of the first switch, a gate of the third transistor and a gate of the fourth transistor being connected to the second power supply line; and

fifth and sixth transistors connected in series with each other between the control terminal of the first switch and the second power supply line, a gate of the fifth transistor and a gate of the sixth transistor being connected to the first power supply line.