OVERVOLTAGE PROTECTION CIRCUIT

An overvoltage protection circuit includes a first connector connected to an alternating current (AC) power source, a second connector connected to an electronic device, an alternating current to direct current (AC/DC) rectifying circuit, a voltage regulating diode, a relay, a first electronic switch, and a second electronic switch. The first connector is connected to the AC/DC rectifying circuit. The AC/DC rectifying circuit is connected to the first electronic switch through the voltage regulating diode. The first electronic switch is connected to the second electronic switch. The second electronic switch is connected to the relay. The first connector is connected to the second connector through the relay.

DETAILED DESCRIPTION

The disclosure, including the accompanying drawing, is illustrated by way of example and not by way of limitation. References to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.

The FIGURE is an embodiment of an overvoltage protection circuit. The overvoltage protection circuit includes a first connector10connected to an alternating current (AC) power source, a second connector50connected to electronic device, such as a computer, an alternating current to direct current (AC/DC) rectifying circuit20, two resistors R2and R3, a voltage regulating diode D6, a diode D5, a relay RL1, and two bipolar junction transistors (BJTs) Q1and Q2. In the embodiment, the BJTs Q1and Q2are npn type BJTs. The second connector50is a three-hole power outlet JP1. The electronic device can be powered through a power plug connected to the power outlet JP1.

The AC/DC rectifying circuit20is connected to the first connector10, and utilized to convert the AC power from the first connector10into DC power. The first connector10includes a ground terminal connected to the ground wire of the AC power source, a live terminal connected to the live wire of the AC power source, and a neutral terminal connected to the neutral wire of the AC power source. The ground terminal of the first connector10is grounded.

The AC/DC rectifying circuit20includes capacitors C1and C2, diodes D1-D4connected end to end, and a resistor R1. A node E between an anode of the diode D1and a cathode of the diode D4is connected to the live terminal of the first connector10through the capacitor C1. A node F between a cathode of the diode D1and a cathode of the diode D2is grounded through the resistor R1and the capacitor C2connected in parallel. A node G between an anode of the diode D2and a cathode of the diode D3is connected to the neutral terminal of the first connector10. A node H between an anode of the diode D3and an anode of the diode D4is connected to the ground terminal of the first connector10. The node F functions as an output terminal of the AC/DC rectifying circuit20.

The node F is connected to a cathode of the voltage regulating diode D6through the resistor R2. An anode of the voltage regulating diode D6is connected to a base of the BJT Q1. A collector of the BJT Q1is connected to the node F through the resistor R3. An emitter of the BJT Q1is grounded.

The collector of the BJT Q1is further connected to a base of the BJT Q2. A collector of the BJT Q2is connected to an anode of the diode D5. A cathode of the diode D5is connected to the node F. An emitter of the BJT Q2is grounded.

The relay RL1includes a coil J and a switch K. The switch K is turned on when there is current flowing through the coil J. The switch K is turned off when there is no current flowing through the coil J. A first terminal of the coil J is connected to the node F. A second terminal of the coil J is connected to the collector of the BJT Q2. A first terminal of the switch K is connected to the live terminal of the first connector10. A second terminal of the switch K is connected to the second connector50.

The second connector50includes a live pin A, a neutral pin B, and a ground pin C. The live pin A is connected to the second terminal of the switch K. The neutral pin B is connected to the neutral terminal of the first connector10. The ground pin C is grounded.

The AC/DC rectifying circuit20converts the AC power received by the first connector10to the DC power. The AC/DC rectifying circuit20outputs the DC power through the node F. In the embodiment, a breakdown voltage U of the voltage regulating diode D6is a preset voltage. When the voltage of node F is less than the preset voltage, the AC power source provides power to the electronic device. When the voltage of the node F is greater than or equal to the preset voltage, the electronic device is powered off.

In detail, when the voltage of the node F is less than the preset voltage, the voltage regulating diode D6is turned off. The base of the BJT Q1receives no signal and is turned off. The base of the BJT Q2receives a high level signal, such as logic 1, and is turned on. There is current flowing through the coil J, and the switch K is turned on, such that the AC power source provides power to the electronic device.

When the voltage of the node F is greater than or equal to the preset voltage, the voltage regulating diode D6is turned on. The base of the BJT Q1receives a high level signal and is turned on. The base of the BJT Q2receives a low level signal, such as logic 0, and is turned off. There is no current flowing through the coil J, and the switch K is turned off, such that the electronic device is powered off for overvoltage protection.

The diodes D1-D4forms a rectification circuit, where the nodes E and G function as two inputs of the AC/DC rectifying circuit20.

In other embodiments, the BJTs Q1and Q2can be replaced by other electronic switches, such as metallic oxide semiconductor field effect transistors.