Power supply protection device

1. Field of the Invention

Embodiments of the present disclosure relate to overvoltage protectors, and particularly to a power supply protection device having an overvoltage protection function.

2. Description of Related Art

Electric appliances powered by the mains power (also known as household power, grid power, etc.) have corresponding rated input voltages. However, parameters, such as voltage and frequency, for different mains power systems vary among regions. The voltages supplied by the mains power systems are generally in the range 100-240 volts (expressed as root-mean-square voltage). When an electric appliance is connected to a mains power system supplying a voltage higher than the rated input voltage of the electric appliance, the electric appliance may be damaged. In another case, even if the electric appliance is connected to a mains power system supplying a voltage conforming to the rated input voltage of the electric appliance, the electric appliance may also be damaged by high voltage surges.

Therefore, a power supply protection device having an overvoltage protection function for an electric appliance is needed to address the limitations described.

FIG. 1 is a block diagram of a power supply protection device in accordance with an embodiment of the present disclosure.

FIG. 2 is a circuit diagram of the power supply protection device of FIG. 1 .

Reference will now be made to the drawings to describe certain inventive embodiments of the present disclosure.

Referring to FIG. 1 , a power supply protection device 100 is capable of supplying power received from an external power supply 200 , such as a mains power system, to an electric appliance 300 when an external voltage (root-mean-square voltage) of the external power supply 200 is normal, and inhibiting the power when the external voltage becomes an overvoltage. The power supply protection device 100 may include an input interface 101 , a sampling circuit 103 , a rectifying and filtering circuit 105 , a detecting circuit 107 , an alert circuit 109 , a switching circuit 111 , and an output interface 113 .

The input interface 101 is used for receiving the external voltage. The output interface 113 is connected to the input interface 101 via the switching circuit 111 . The output interface 113 is used for outputting the external voltage to the electric appliance 300 when the switching circuit 111 establishes an electrical connection between the input and output interfaces 101 , 113 . The input interface 101 and the output interface may be power plugs or jacks.

The sampling circuit 103 is connected between the input interface 101 and the rectifying and filtering circuit 105 , for generating a first sample voltage proportional to the external voltage. The rectifying and filtering circuit 105 is used for rectifying the first sample voltage into a direct current (DC) voltage, and then filtering the DC voltage. Understandably, the DC voltage is proportional to the external voltage. For example, when the external voltage is 220 volts, the DC voltage may be about 20 volts. If the sampling circuit 103 is omitted, the DC voltage may be about 140 volts, and a power consumption of the power supply protection device 100 is much higher than that when the DC voltage is about 20 volts.

The detecting circuit 107 is configured for receiving the DC voltage, and determining whether the external voltage is at the overvoltage level, that is, the external voltage is equal to or higher than a predetermined value. Because the DC voltage is proportional to the external voltage, when the external voltage is equal to or higher than the predetermined value, the DC voltage is equal to or higher than a critical voltage. In this embodiment, the detecting circuit 107 generates a switch-off signal when the DC voltage is equal to or higher than the critical voltage, and generates a switch-on signal when the DC voltage is lower than the critical voltage.

The alert circuit 109 is used for generating an audible or visual alert signal to signal that the external voltage becomes the overvoltage when receiving the switch-off signal from the detecting circuit 107 .

As described above, the switching circuit 111 is used for establishing the electrical connection between the input interface 101 and the output interface 113 , such that the external voltage is transmitted from the input interface 101 to the output interface 113 and then outputted to the electric appliance 300 . In this embodiment, the switching circuit 111 establishes/closes the electrical connection when receiving the switch-on signal from the detecting circuit 107 , and breaks/opens the electrical connection when receiving the switch-off signal, such that the power supply protection device 100 stops supplying the power to the electric appliance 300 .

Referring also to FIG. 2 , the input interface 101 includes a plug J 1 having two terminals 101 a , 101 b , which are capable of connecting to the external power supply 200 to receive the external voltage. The output interface 113 includes a jack (may also be a plug) J 2 having two terminals 113 a , 113 b , which are capable of connecting to the electric appliance 300 . The terminal 101 a of the plug J 1 is connected to the terminal 113 a of the jack J 2 via the switching circuit 111 . The terminal 101 b is directly connected to the terminal 113 b.

The sampling circuit 103 includes a first resistor R 1 , a second resistor R 2 , a first zener diode D 1 , and a second zener diode D 2 connected together in series between the two terminals 101 a , 101 b for receiving the external voltage from the input interface 101 . The sampling circuit 103 further includes a capacitor C 1 connected in parallel to the first resistor R 1 . Anodes of the first and second zener diodes D 1 , D 2 are connected together. The first sample voltage equals to a sum of voltages of the second resistor R 2 , the first zener diode D 1 , and the second zener diode D 2 .

The rectifying and filtering circuit 105 includes a full bridge rectifier D 3 and a filter capacitor C 2 . The rectifier D 3 includes two input terminals 201 , 205 for receiving the first sample voltage, and two output terminals 203 , 207 for outputting the DC voltage. The terminal 207 is a higher potential output terminal, and the terminal 203 is a lower potential output terminal. The filter capacitor C 2 is connected in parallel to the two output terminals 203 , 207 .

The detecting circuit 107 includes a third resistor R 3 , a fourth resistor R 4 , a fifth resistor R 5 , a third zener diode D 4 , and a comparator U 1 A. The third and fourth resistors R 3 , R 4 are connected in series between the two output terminals 203 , 207 for receiving the DC voltage. A connecting node of the third and fourth resistors R 3 , R 4 is connected to an inverting input terminal of the comparator U 1 A. A second sample voltage is generated on the fourth resistor R 4 , and supplied to the inverting input terminal of the comparator U 1 A. The second sample voltage is proportional to the DC voltage. The fifth resistor R 5 and the third zener diode D 4 are connected in series between the two output terminals 203 , 207 , and the third zener diode D 4 is reverse biased. A connecting node of the fifth resistor R 5 and the third zener diode D 4 is connected to a non-inverting input terminal of the comparator U 1 A, for providing a reference voltage to the comparator U 1 A. An output terminal of the comparator U 1 A is connected to the alert circuit 109 and the switching circuit 111 .

In this embodiment, the third zener diode D 4 is normal and off when the external voltage is within a normal range, and the reference voltage equals to the external voltage and higher than the second sample voltage on the fourth resistor R 4 . Thus, the comparator U 1 A outputs a high level voltage, that is, the switch-on signal is the high level voltage. When the external voltage increases, the second sample voltage on the fourth resistor R 4 increases, too. When the external voltage becomes equal to or higher than the predetermined value, the DC voltage becomes equal to or higher than the critical voltage, and the second sample voltage becomes higher than a zener voltage of the third zener diode D 4 . The third zener diode D 4 is breakdown and on, and the reference voltage equals to the zener voltage of the third zener diode D 4 and is lower than the second sample voltage. Thus, the comparator U 1 A outputs a low level voltage, that is, the switch-off signal is the low level voltage.

The alert circuit 109 includes a sixth resistor R 6 and a light emitting diode D 5 connected in series between the terminal 207 of the rectifying and filtering circuit 105 and the output terminal of the comparator U 1 A. When the comparator U 1 A outputs the high level voltage (switch-on signal), the light emitting diode D 5 does not emit light. When the comparator U 1 A outputs the low level voltage (switch-off signal), the light emitting diode D 5 emits light to signal that the external voltage is an overvoltage.

The switching circuit 111 includes a seventh resistor R 7 , an eighth resistor R 8 , a bipolar junction transistor Q 1 , and a relay 300 . The relay 300 is a solid state relay. The relay 300 includes two input terminals 301 , 303 , and two output terminals 305 , 307 . The terminal 301 is connected to the terminal 207 of the rectifying and filtering circuit 105 . The terminal 303 is connected to a collector of the bipolar junction transistor Q 1 . The terminal 305 is connected to the terminal 101 a of the input interface 101 . The terminal 307 is connected to the terminal 113 a of the output interface 113 . When a voltage at the terminal 301 is higher than a voltage at the terminal 303 , the terminal 305 is connected to the terminal 307 .

A gate of the bipolar junction transistor Q 1 is connected to the output terminal of the comparator U 1 A via the eighth resistor R 8 . The collector of the bipolar junction transistor Q 1 is connected to the terminal 207 of the rectifying and filtering circuit 105 via the seventh resistor R 7 . An emitter of the bipolar junction transistor Q 1 is connected to the terminal 203 of the rectifying and filtering circuit 105 .

When receiving the high level voltage (switch-on signal), the bipolar junction transistor Q 1 turns on, the voltage at the terminal 303 is equal to a voltage at the terminal 203 of the rectifying and filtering circuit 105 . Thus the voltage at the terminal 301 is higher than that at the terminal 303 , and the terminal 305 is connected to the terminal 307 of the relay 300 . As a result, the external voltage is outputted from the output interface 113 .

When receiving the low level voltage (switch-off signal), the bipolar junction transistor Q 1 turns off, the voltage at the terminal 303 is equal to the voltage at the terminal 301 , and the terminal 305 is disconnected from the terminal 307 of the relay 300 . As a result, the electrical connection between the input interface 101 and the output interface 113 is broken.

To sum up, the power supply protection device 100 establishes the electrical connection between the external power supply 200 and the electric appliance 300 for transmitting power when the external voltage supplied by the external power supply 200 is normal, and breaks the electrical connection when the external voltage becomes an overvoltage. As a result, the electric appliance 300 is protected from damage by high voltage surges or overvoltages.

In other embodiments, when the external voltage is a DC voltage, the sampling circuit 103 and the rectifying and filtering circuit 105 can be omitted.

It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the present disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.