Over-voltage and under-voltage protection circuit

Abstract

The utility model discloses an overvoltage and undervoltage protection circuit in the technical field of electrical equipment protection, which comprises a power supply circuit, the power supply circuit is respectively connected with a voltage comparison circuit and a sampling circuit, and the voltage comparison circuit is respectively connected with the sampling circuit and a control circuit. The power supply circuit provides stable direct-current voltage for the voltage comparison circuit, the control circuit and the like; the sampling circuit takes out the numerical value of the power grid voltage in proportion and sends to the voltage comparison circuit; the voltage comparison circuit compares the input sampling voltage with a threshold voltage set by the voltage comparison circuit, obtains a judgment result and outputs the judgment result to the control circuit; and the control circuit performs on-off control on a power supply of the electrical equipment according to a result given by the voltage comparison circuit.

Description

Technical Field

[0001] The utility model relates to an overvoltage and undervoltage protection circuit in the technical field of electrical equipment protection. Background Art

[0002] In power supply, various faults such as line breakage, short circuit, shedding and grounding, and loose contact often occur. The occurrence of these faults will cause serious changes in the grid voltage, making electrical equipment unable to work properly or even damaged. For example, too high voltage is easy to cause equipment burnout, while too low voltage cannot start, resulting in too large current in the equipment and burnout. And the overvoltage and undervoltage protection devices in the prior art are expensive and not easy to be used by small-scale manufacturers. Content of the Utility Model

[0003] The purpose of the utility model is to provide an overvoltage and undervoltage protection circuit, which will automatically cut off the power supply when the grid voltage is too high or too low, play a good protective role for electrical equipment, and the circuit has high cost performance and is easy to manufacture.

[0004] To achieve the above purpose, the utility model provides an overvoltage and undervoltage protection circuit, including a power supply circuit, the power supply circuit is respectively connected with a voltage comparison circuit and a sampling circuit, and the voltage comparison circuit is respectively connected with the sampling circuit and a control circuit.

[0005] Compared with the prior art, the beneficial effect of the utility model lies in that the power supply circuit provides stable DC voltage for the voltage comparison circuit, the control circuit, etc.; the sampling circuit extracts the value of the grid voltage in proportion and sends it to the voltage comparison circuit; the voltage comparison circuit compares the input sampling voltage with the set threshold voltage of itself, and outputs the judgment result to the control circuit; the control circuit conducts on-off control on the power supply of the electrical equipment according to the result given by the voltage comparison circuit.

[0006] As a further improvement of the utility model, the power supply circuit includes a transformer B, the 1st and 2nd pins of the transformer B are connected with the grid voltage, the 3rd and 4th pins of the transformer B are respectively connected with the 1st and 2nd pins of a bridge rectifier, the 3rd pin of the bridge rectifier is connected with the sampling circuit, the 4th pin of the bridge rectifier is respectively connected with one end of a resistor R1 and the 1st pin of a voltage stabilizing chip, a capacitor C2 is connected between the 2nd and 3rd pins of the voltage stabilizing chip, the other end of the resistor R1 is connected with the positive pole of a light-emitting diode D1, and the negative pole of the light-emitting diode D1 is connected with the 3rd pin of the bridge rectifier.

[0007] In this way, after the grid voltage is transformed by the transformer, rectified by the bridge rectifier, and filtered by the capacitor, a direct current proportional to the grid voltage is obtained at the capacitor C1 end for the sampling circuit to use. At the same time, this DC voltage is regulated by the voltage stabilizing chip AN7812 to output a stable +12V voltage for other circuits to use. Among them, the capacitor C2 plays a filtering role, and the light-emitting diode D1 is used as a power supply indicator.

[0008] As a further improvement of the present utility model, the sampling circuit includes a capacitor C1. The positive electrode of the capacitor C1 is connected to the 4th pin of the bridge rectifier. The negative electrode of the capacitor C1 is respectively connected to the 3rd pin of the bridge rectifier and one end of a variable resistor R2. The other end of the variable resistor R2 is connected to the 1st pin of the voltage regulator chip. The variable terminal of the variable resistor R2 is connected to the voltage comparison circuit.

[0009] Changing the resistance value of R2 in this way can change the sampling ratio. It is used during the circuit debugging of R2. The sampling voltage u is output from the variable terminal of R2 to the ground to the voltage comparison circuit.

[0010] As a further improvement of the present utility model, the voltage comparison circuit includes operational amplifiers A1 and A2. The 2nd pin of the operational amplifier A1 is connected to the variable terminal of a variable resistor R3. The 5th pin of the operational amplifier A2 is connected to the variable terminal of a variable resistor R4. One end of the variable resistor R3 and one end of the variable resistor R4 are connected. The other end of the variable resistor R3 is connected to the 3rd pin of the voltage regulator chip. The other end of the variable resistor R4 is connected to one end of the variable resistor R2. The 3rd pin of the operational amplifier A1 and the 6th pin of the operational amplifier A2 are connected and connected to the variable terminal of the variable resistor R2; the 1st pin of the operational amplifier A1 is connected to the positive electrode of a diode D2. The 4th pin of the operational amplifier A2 is connected to the positive electrode of a diode D3. The negative electrode of the diode D3 and the negative electrode of the diode D2 are connected and connected to one end of a resistor R6. The resistor R6 is connected in parallel with a capacitor C3. The other end of the resistor R6 is connected to the control circuit. One end of the resistor R6 is also connected to one end of a resistor R5. The other end of the resistor R5 is respectively connected to the other end of the variable resistor R4 and the control circuit.

[0011] In this way, the threshold voltage is set by R3 and R4. Among them, R3 sets the upper threshold voltage UH, and R4 sets the lower threshold voltage UL, where UL < UH. The two threshold voltages are preset. The grid voltage samples the DC voltage u according to a certain ratio and inputs it to the operational amplifier. Among them, UL corresponds to the minimum value of u; UH corresponds to the maximum value of u.

[0012] As a further improvement of the present utility model, the control circuit includes a triode T. The base of the triode T is connected to the other end of the resistor R6. The emitter of the triode T is connected to the 3rd pin of the voltage regulator chip. The collector of the triode T is connected to one end of the coil of a relay K. The other end of the coil of the relay K is connected to the other end of the resistor R5. The normally open contact of the relay K is connected to the 1st pin of the transformer. The normally open contact of the relay K is also connected in parallel with a reset switch J.

[0013] When the grid voltage is within the normal range, the output voltage of the voltage comparison circuit is 0V, the transistor T is saturated and conducting, the normally open contact of the relay K is closed, and the grid supplies power normally; when the grid voltage is too high or too low, the output voltage of the voltage comparator is 12V, the transistor T is cut off, the relay K loses power, the normally open contact is disconnected, and the grid voltage stops supplying power, so that the electrical equipment is protected. After the grid voltage returns to normal, the reset switch J needs to be pressed for the circuit to enter the working state. Brief Description of the Drawings

[0014] Figure 1 It is a circuit diagram of the present utility model. Detailed Embodiment

[0015] The present utility model will be further described below in conjunction with the drawings:

[0016] As Figure 1 shown, an overvoltage and undervoltage protection circuit includes a power supply circuit, the power supply circuit is respectively connected to a voltage comparison circuit and a sampling circuit, and the voltage comparison circuit is respectively connected to the sampling circuit and a control circuit.

[0017] The power supply circuit includes a transformer B. The 1st and 2nd pins of the transformer B are connected to the grid voltage. The 3rd and 4th pins of the transformer B are respectively connected to the 1st and 2nd pins of a bridge rectifier. The 3rd pin of the bridge rectifier is connected to the sampling circuit. The 4th pin of the bridge rectifier is respectively connected to one end of a resistor R1 and the 1st pin of a voltage regulator chip. A capacitor C2 is connected between the 2nd and 3rd pins of the voltage regulator chip. The other end of the resistor R1 is connected to the positive pole of a light-emitting diode D1. The negative pole of the light-emitting diode D1 is connected to the 3rd pin of the bridge rectifier.

[0018] The sampling circuit includes a capacitor C1. The positive pole of the capacitor C1 is connected to the 4th pin of the bridge rectifier. The negative pole of the capacitor C1 is respectively connected to the 3rd pin of the bridge rectifier and one end of a variable resistor R2. The other end of the variable resistor R2 is connected to the 1st pin of the voltage regulator chip. The variable end of the variable resistor R2 is connected to the voltage comparison circuit.

[0019] The voltage comparison circuit includes operational amplifiers A1 and A2. The 2nd pin of the operational amplifier A1 is connected to the variable end of a variable resistor R3. The 5th pin of the operational amplifier A2 is connected to the variable end of a variable resistor R4. One end of the variable resistor R3 and one end of the variable resistor R4 are connected. The other end of the variable resistor R3 is connected to the 3rd pin of the voltage regulator chip. The other end of the variable resistor R4 is connected to one end of the variable resistor R2. The 3rd pin of the operational amplifier A1 and the 6th pin of the operational amplifier A2 are connected and connected to the variable end of the variable resistor R2.

[0020] Pin 1 of operational amplifier A1 is connected to the positive electrode of diode D2. Pin 4 of operational amplifier A2 is connected to the positive electrode of diode D3. The negative electrode of diode D3 and the negative electrode of diode D2 are connected and then connected to one end of resistor R6. Resistor R6 is in parallel with capacitor C3. The other end of resistor R6 is connected to the control circuit. One end of resistor R6 is also connected to one end of resistor R5. The other end of resistor R5 is respectively connected to the other end of rheostat R4 and the control circuit.

[0021] The control circuit includes triode T. The base of triode T is connected to the other end of resistor R6. The emitter of triode T is connected to pin 3 of the voltage regulator chip. The collector of triode T is connected to one end of the coil of relay K. The other end of the coil of relay K is connected to the other end of resistor R5. The normally open contact of relay K is connected to pin 1 of the transformer. The normally open contact of relay K is also in parallel with reset switch J.

[0022] In the present utility model, taking the 220V grid voltage as an example, it is specifically described as follows:

[0023] After the grid voltage passes through the transformer, rectification and filtering circuits, a DC voltage proportional to the grid voltage is obtained across C1 (when the grid voltage is 220V, this DC voltage is about 25V), which is used by the sampling circuit. At the same time, this DC voltage is regulated by voltage regulator chip AN7812 to output a stable +12V voltage for other circuits to use, where capacitor C2 plays a filtering role.

[0024] Changing the resistance value of R2 can change the sampling ratio. R2 is used during circuit debugging. The sampling voltage u is output from the sliding end of R2 to the ground and given to the voltage comparison circuit. After the grid voltage passes through the transformer, rectification and filtering circuits, a DC sampling voltage proportional to the grid voltage is obtained across C1. This voltage is then divided by R2 to obtain the final sampling voltage and sent to the input ends of operational amplifiers A1 and A2.

[0025] When the input sampling voltage u is less than UL, it is also necessarily less than UH. Therefore, A1 outputs a low level of 0V, and A2 outputs a high level of 12V. Thus, D3 conducts and D2 cuts off, and the voltage comparison circuit outputs a voltage of 12V.

[0026] When UL < u < UH, A1 outputs a low level of 0V, and A2 outputs a low level of 0V. So D3 cuts off and D2 cuts off, and the voltage comparison circuit outputs a voltage of 0V.

[0027] When the input sampling voltage u is greater than UH, it is also necessarily greater than UL. Therefore, A1 outputs a low level of 12V, and A2 outputs a high level of 0V. Thus, D2 conducts and D3 cuts off, and the voltage comparison circuit outputs a voltage of 12V.

[0028] According to the normal range of the 220V grid voltage (160V - 250V), after being stepped down by an 18V transformer, it is approximately alternating current (13V - 20V). After rectification and filtering, a DC voltage is obtained (the output voltage of full-wave rectification and capacitor filtering is about 1.2 times the input AC voltage), which is approximately (16V - 24V). If the sampling resistor R2 samples at a one-third ratio, the sampled DC voltage input to the voltage comparison circuit is approximately (5V - 8V). Therefore, the threshold voltages of this circuit are set as: UL = 5V, UH = 8V. The setting of the threshold voltages is adjusted by the variable resistors R3 and R4.

[0029] When the grid voltage is within the normal range (160V - 250V), the sampling voltage u is within the range of 5V < u < 8V. The output voltage of the voltage comparison circuit is 0V, the transistor T is saturated and conducting, and the coil of the relay K is energized and its normally open contact closes, and the grid powers the electrical equipment RL; when the grid voltage is lower than 160V or higher than 250V, the sampled voltage u of the circuit is less than 5V or greater than 8V, then the output voltage of the voltage comparison circuit is 12V, the transistor T is cut off, the coil of the relay K loses power and its normally open contact opens, and the grid voltage no longer powers the electrical equipment, so that the electrical equipment is protected against over- and under-voltage. When the grid voltage returns to normal, after pressing the reset switch J, the circuit re-enters the working state.

[0030] The utility model has a simple structure, is easy to manufacture, has a low cost, effectively reduces the operation and maintenance costs of enterprise equipment, works stably and reliably after startup, has a sensitive protection function, and can play a very good protective role for electrical equipment.

[0031] The utility model is not limited to the above embodiments. Based on the disclosed technical solutions, those skilled in the art can make some substitutions and deformations to some of the technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the utility model.

Claims

1. An overvoltage and undervoltage protection circuit, characterized in that: It includes a power supply circuit, which is respectively connected to a voltage comparison circuit and a sampling circuit, and the voltage comparison circuit is respectively connected to the sampling circuit and a control circuit; The power supply circuit includes a transformer B. Pin 1 and pin 2 of the transformer B are connected to the grid voltage. Pin 3 and pin 4 of the transformer B are respectively connected to pin 1 and pin 2 of a bridge rectifier. Pin 3 of the bridge rectifier is connected to the sampling circuit. Pin 4 of the bridge rectifier is respectively connected to one end of a resistor R1 and pin 1 of a voltage regulator chip. A capacitor C2 is connected between pin 2 and pin 3 of the voltage regulator chip. The other end of the resistor R1 is connected to the positive electrode of a light-emitting diode D1, and the negative electrode of the light-emitting diode D1 is connected to pin 3 of the bridge rectifier; The sampling circuit includes a capacitor C1. The positive electrode of the capacitor C1 is connected to pin 4 of the bridge rectifier. The negative electrode of the capacitor C1 is respectively connected to pin 3 of the bridge rectifier and one end of a variable resistor R2. The other end of the variable resistor R2 is connected to pin 1 of the voltage regulator chip. The variable terminal of the variable resistor R2 is connected to the voltage comparison circuit; The voltage comparison circuit includes operational amplifiers A1 and A2. Pin 2 of the operational amplifier A1 is connected to the variable terminal of a variable resistor R3. Pin 5 of the operational amplifier A2 is connected to the variable terminal of a variable resistor R4. One end of the variable resistor R3 and one end of the variable resistor R4 are connected. The other end of the variable resistor R3 is connected to pin 3 of the voltage regulator chip. The other end of the variable resistor R4 is connected to one end of the variable resistor R2. Pin 3 of the operational amplifier A1 and pin 6 of the operational amplifier A2 are connected and connected to the variable terminal of the variable resistor R2; Pin 1 of the operational amplifier A1 is connected to the positive electrode of a diode D2. Pin 4 of the operational amplifier A2 is connected to the positive electrode of a diode D3. The negative electrode of the diode D3 and the negative electrode of the diode D2 are connected and connected to one end of a resistor R6. The resistor R6 is connected in parallel with a capacitor C3. The other end of the resistor R6 is connected to the control circuit. One end of the resistor R6 is also connected to one end of a resistor R5. The other end of the resistor R5 is respectively connected to the other end of the variable resistor R4 and the control circuit.

2. The overvoltage and undervoltage protection circuit according to claim 1, characterized in that: The control circuit includes a triode T. The base of the triode T is connected to the other end of the resistor R6. The emitter of the triode T is connected to pin 3 of the voltage regulator chip. The collector of the triode T is connected to one end of the coil of a relay K. The other end of the coil of the relay K is connected to the other end of the resistor R5. The normally open contact of the relay K is connected to pin 1 of the transformer. A reset switch J is also connected in parallel with the normally open contact of the relay K.

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