1. Technical Field
The present disclosure relates to an overvoltage protection circuit.
2. Description of Related Art
Some electronic equipment is powered by an alternating current (AC) power source. The electronic equipment may be damaged by overvoltage from the AC power source, and more seriously, fire or electric shock may occur. Therefore, there is room for improvement in the art.
Many aspects of the embodiments can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments.
The FIGURE is a circuit diagram of an embodiment of an overvoltage protection circuit.
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 connector 10 connected to an alternating current (AC) power source, a second connector 50 connected to electronic device, such as a computer, an alternating current to direct current (AC/DC) rectifying circuit 20, two resistors R2 and R3, a voltage regulating diode D6, a diode D5, a relay RL1, and two bipolar junction transistors (BJTs) Q1 and Q2. In the embodiment, the BJTs Q1 and Q2 are npn type BJTs. The second connector 50 is 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 circuit 20 is connected to the first connector 10, and utilized to convert the AC power from the first connector 10 into DC power. The first connector 10 includes 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 connector 10 is grounded.
The AC/DC rectifying circuit 20 includes capacitors C1 and C2, diodes D1-D4 connected end to end, and a resistor R1. A node E between an anode of the diode D1 and a cathode of the diode D4 is connected to the live terminal of the first connector 10 through the capacitor C1. A node F between a cathode of the diode D1 and a cathode of the diode D2 is grounded through the resistor R1 and the capacitor C2 connected in parallel. A node G between an anode of the diode D2 and a cathode of the diode D3 is connected to the neutral terminal of the first connector 10. A node H between an anode of the diode D3 and an anode of the diode D4 is connected to the ground terminal of the first connector 10. The node F functions as an output terminal of the AC/DC rectifying circuit 20.
The node F is connected to a cathode of the voltage regulating diode D6 through the resistor R2. An anode of the voltage regulating diode D6 is connected to a base of the BJT Q1. A collector of the BJT Q1 is connected to the node F through the resistor R3. An emitter of the BJT Q1 is grounded.
The collector of the BJT Q1 is further connected to a base of the BJT Q2. A collector of the BJT Q2 is connected to an anode of the diode D5. A cathode of the diode D5 is connected to the node F. An emitter of the BJT Q2 is grounded.
The relay RL1 includes 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 connector 10. A second terminal of the switch K is connected to the second connector 50.
The second connector 50 includes 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 connector 10. The ground pin C is grounded.
The AC/DC rectifying circuit 20 converts the AC power received by the first connector 10 to the DC power. The AC/DC rectifying circuit 20 outputs the DC power through the node F. In the embodiment, a breakdown voltage U of the voltage regulating diode D6 is 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 D6 is turned off. The base of the BJT Q1 receives no signal and is turned off. The base of the BJT Q2 receives 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 D6 is turned on. The base of the BJT Q1 receives a high level signal and is turned on. The base of the BJT Q2 receives 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-D4 forms a rectification circuit, where the nodes E and G function as two inputs of the AC/DC rectifying circuit 20.
In other embodiments, the BJTs Q1 and Q2 can be replaced by other electronic switches, such as metallic oxide semiconductor field effect transistors.
Even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Date | Country | Kind |
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2013101305591 | Apr 2013 | CN | national |