Switch circuit and power supply system
In a switch circuit for use in a vehicle, conduction between a drain electrode and a gate electrode of each of a first main transistor and a second main transistor is switched on or off depending on a voltage between the gate electrode and a source electrode. A first surge protection device is connected between the drain electrodes of the first main transistor and the second main transistor. The first surge protection device keeps a voltage that is applied to the first surge protection device at a first predetermined voltage or lower. A sub transistor is provided between the gate electrodes and the source electrodes of the first main transistor and the second main transistor. The sub transistor is turned on when the first main transistor and the second main transistor are turned off.
1. A switch circuit for use in a vehicle comprising:
a transistor circuit including a first main transistor and a second main transistor, the first main transistor includes a first electrode, a second electrode, and a control electrode, and in which conduction between the first electrode and the second electrode is switched on or off depending on a voltage between the control electrode and the second electrode, the second main transistor is connected to the first electrode or the second electrode of the first main transistor, and the first main transistor and the second main transistor are turned on or off at the same time;
a first surge protection device that is connected between ends of the transistor circuit, and is configured to keep a voltage that is applied to the first surge protection device at a first predetermined voltage or lower; and
a sub transistor that is provided between the control electrode and the second electrode of the first main transistor, and is turned on when the first main transistor is turned off,
a first wire is connected to one end of the transistor circuit,
a second wire is connected to another end of the transistor circuit,
an electric current flows through the first wire, the transistor circuit, and the second wire while the first main transistor is ON, and
an electric current flows through the first wire, the first surge protection device, and the second wire when the first main transistor is turned off; and
a second surge protection device that is connected between the transistor circuit and the first surge protection device, and is configured to keep a voltage that is applied to the second surge protection device at a second predetermined voltage or lower; and
a protection transistor that is connected between a connection node located between the first main transistor and the second main transistor, and a connection node located between the first surge protection device and the second surge protection device.
2. The switch circuit according to claim 1 , further comprising:
an interrupting switch that is connected between the transistor circuit and the first surge protection device.
3. The switch circuit according to claim 2 , further comprising:
a switch control unit that is configured to turn on the interrupting switch prior to turning on the first main transistor, and turn off the interrupting switch when a predetermined period has elapsed since the first main transistor was turned off.
4. The switch circuit according to claim 1 , further comprising:
a switch control unit that is configured to turn on the protection transistor prior to turning on the first main transistor and the second main transistor, and turn off the protection transistor when a predetermined period has elapsed since the first main transistor and the second main transistor were turned off.
5. The switch circuit according to claim 1 , wherein an energy is accumulated in the first wire and the second wire, due to an electric current flowing through the first wire, the transistor circuit, and the second wire while the first main transistor is ON, and the energy accumulated in the first wire and the second wire is consumed, due to an electric current flowing through the first wire, the first surge protection device, and the second wire when the first main transistor is turned off.
6. The switch circuit according to claim 1 , further including a first electric storage unit having a positive electrode, the positive electrode of the first electric storage unit is connected to the one end of the transistor circuit via the first wire, and a positive electrode of a second electric storage unit is connected to the other end of the transistor circuit via the second wire.
7. The switch circuit according to 1 , wherein the sub transistor includes:
a third electrode that is connected to the second electrode of the first main transistor; a fourth electrode that is connected to the control electrode of the first main transistor; and a second control electrode,
the sub transistor is turned on if a voltage at the second control electrode that takes a potential at the third electrode as a reference is equal to or greater than a predetermined voltage, and
the switch circuit further includes:
a resistor that is connected between the third electrode and the second control electrode of the sub transistor; and
a diode whose cathode is connected to the second control electrode of the sub transistor, and whose anode is grounded.
8. A power supply system comprising:
the switch circuit according to claim 1 ; and
a first electric storage unit whose positive electrode is connected to the one end of the transistor circuit via the first wire; and
a second electric storage unit whose positive electrode is connected to the other end of the transistor circuit via the second wire.