A single-phase AC input voltage overvoltage protection circuit

Abstract

The present invention discloses a single-phase AC input voltage overvoltage protection circuit, the circuit comprising: a step-down module, an AC-DC conversion module, and a relay switch module connected in sequence; the step-down module is used to receive an externally input AC voltage and step down the AC voltage; the AC-DC conversion module is used to convert the stepped-down AC voltage into a DC voltage; the relay switch module comprises: a first switch circuit, a second switch circuit, and a relay switch, the first switch circuit, the second switch circuit, and the relay switch are all connected to the output end of the AC-DC conversion module, and the second switch circuit is also connected to the relay switch and the first switch circuit. The circuit of the present invention is relatively simple, and can quickly close the output relay by relying on the functions of its own components without the need for external signal control, thereby cutting off the output circuit.

Description

Technical Field

[0001] The present invention relates to the field of protection circuits, and in particular to a single-phase AC input voltage overvoltage protection circuit. Background Art

[0002] When the load instrument equipment needs to use a three-phase AC input voltage, a three-phase 4-wire input is used. During operation, if the staff or other people mistakenly connect the phase line and the neutral line in reverse, so that the input neutral line and the phase line have a 380VAC voltage or other reasons cause the input voltage to be too high, this will cause damage to the machine and cause great economic losses. In order to prevent the above situation from happening, the commonly used input protection method is to use fuses and varistors, but fuses and varistors cannot be used repeatedly for overvoltage, and the reaction time of protection is too long. The fuse needs to be completely blown before it can play a protective role. Once damaged, it needs to be repaired and processed by people to recover. In addition, the output relay is controlled by the signal of the single-chip microcomputer. There will be a time difference in the process from the single-chip microcomputer sampling the input voltage to the control signal output. The circuit is also more complicated, and the stability of the product is also low. Summary of the invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide a single-phase AC input voltage overvoltage protection circuit, which is relatively simple and can quickly close the output relay by relying on the functions of its own components without the need for external signal control, thereby cutting off the output circuit.

[0004] Based on this, the present invention provides a single-phase AC input voltage overvoltage protection circuit, the circuit comprising:

[0005] A step-down module, an AC-DC conversion module, and a relay switch module connected in sequence;

[0006] The step-down module is used to receive an externally input AC voltage and step down the AC voltage;

[0007] The AC-DC conversion module is used to convert the stepped-down AC voltage into a DC voltage;

[0008] The relay switch module includes: a first switch circuit, a second switch circuit and a relay switch. The first switch circuit, the second switch circuit and the relay switch are all connected to the output end of the AC-DC conversion module, and the second switch circuit is also connected to the relay switch and the first switch circuit.

[0009] The step-down module includes: a transformer, a first capacitor, and a fifth capacitor; the first capacitor and the fifth capacitor are connected in series and then connected in parallel at both input ends of the transformer, and a fifth resistor is also connected in parallel at both output ends of the transformer.

[0010] The AC-DC conversion module includes: a bridge rectifier circuit, a second capacitor and a third capacitor, the first end and the third end of the bridge rectifier circuit are connected to the output ends of the step-down module, the fourth end of the bridge rectifier circuit is grounded, one end of the second capacitor and one end of the third capacitor are both connected to the second end of the bridge rectifier circuit, the other end of the second capacitor and the other end of the third capacitor are both grounded, and the second capacitor is an electrolytic capacitor.

[0011] Among them, the first switching circuit includes: a first resistor, a second resistor, a voltage regulator and a first transistor; one end of the first resistor is connected to the output end of the AC-DC conversion module, the other end of the first resistor is connected to the negative electrode of the voltage regulator, the positive electrode of the voltage regulator is respectively connected to one end of the second resistor and the base of the first transistor, the other end of the second resistor is grounded, the emitter of the first transistor is grounded, and the collector of the first transistor is connected to the second switching circuit.

[0012] Among them, the second switch circuit includes: a third resistor, a fourth resistor, a fourth capacitor, a third diode and a second triode, one end of the third resistor is connected to the output end of the AC-DC conversion module, the other end of the third resistor is respectively connected to the positive electrode of the third diode, one end of the fourth resistor, one end of the fourth capacitor and the first switch circuit, the other end of the fourth capacitor and the other end of the fourth resistor are both grounded, the cathode of the third diode is connected to the base of the second triode, the emitter of the second triode is grounded, and the collector of the second triode is connected to the relay switch module.

[0013] Wherein, the relay switch module includes: a relay and a second diode, the cathode of the second diode and the first end of the relay are connected to the output end of the AC-DC conversion module, and the anode of the second diode and the second end of the relay are connected to the second switch circuit.

[0014] The first transistor is an NPN transistor, and the model is 2SC5171.

[0015] The bridge rectifier circuit is used to convert the low-voltage AC full-wave voltage into a half-wave DC voltage, and the second capacitor and the third capacitor are both filter capacitors used to filter the half-wave DC voltage into a smooth DC power supply.

[0016] The first resistor is a current limiting resistor of the voltage regulator tube, and the second resistor is a base pull-down resistor of the first transistor, which is used to prevent the first transistor from being mistakenly turned on when the voltage regulator tube is not turned on.

[0017] The fourth capacitor is used to stabilize the turn-on voltage of the third diode and the working state of the second transistor.

[0018] In the present invention, it includes: a step-down module, an AC-DC conversion module, and a relay switch module connected in sequence; the step-down module is used to receive an external input AC voltage and step down the AC voltage; the AC-DC conversion module is used to convert the stepped-down AC voltage into a DC voltage; the relay switch module includes: a first switch circuit, a second switch circuit, and a relay switch, the first switch circuit, the second switch circuit, and the relay switch are all connected to the output end of the AC-DC conversion module, and the second switch circuit is also connected to the relay switch module and the first switch circuit. In the present invention, when the input AC voltage is too high, the input AC voltage is first stepped down by a transformer, and the stepped-down AC voltage is converted into a DC voltage, the first switch circuit is turned on, so that the second switch circuit is disconnected, so that the relay disconnects the output circuit, and the phenomenon of damage to the load instrument and equipment caused by the input AC voltage being too high is avoided. The circuit structure of the present invention is relatively simple, and accurate protection can be achieved using fewer peripheral devices. The protection time of the present invention is faster than the fuse time of the fuse, and the protection action time is less than 5ms. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 is a schematic diagram of a single-phase AC input voltage overvoltage protection circuit provided by an embodiment of the present invention;

[0021] Figure 2 It is a circuit diagram of a single-phase AC input voltage overvoltage protection circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Figure 1: is a schematic diagram of a single-phase AC input voltage overvoltage protection circuit provided by an embodiment of the present invention, the circuit comprising:

[0024] A step-down module 101, an AC-DC conversion module 102, and a relay switch module 103 connected in sequence;

[0025] The step-down module 101 is used to receive an externally input AC voltage and step down the AC voltage;

[0026] The AC-DC conversion module 102 is used to convert the stepped-down AC voltage into a DC voltage;

[0027] The relay switch module 103 includes: a first switch circuit 1031, a second switch circuit 1032 and a relay 1033. The first switch circuit 1031, the second switch circuit 1032 and the relay switch 1033 are all connected to the output end of the AC-DC conversion module 102, and the second switch circuit 1032 is also connected to the relay 1033 and the first switch circuit 1031.

[0028] Figure 2 It is a circuit diagram of a single-phase AC input voltage overvoltage protection circuit provided by an embodiment of the present invention, and the step-down module includes: a transformer T1, a first capacitor C1, and a fifth capacitor C5; the first capacitor C1 and the fifth capacitor C5 are connected in series and then connected in parallel at both ends of the input of the transformer, and a fifth resistor R5 is also connected in parallel at both ends of the output of the transformer.

[0029] Specifically, the first capacitor C1 and the fifth capacitor C5 are both safety X capacitors, which play the role of filtering the power supply voltage, with a rated voltage of 275V and a capacitance of 0.22F. The transformer T1 is a 380VAC:15VAC isolation step-down transformer, which provides an isolated low voltage, and the model is PE2820S-1. The fifth resistor R5 is the load resistor of the transformer, which is used to stabilize the transformer output, and the resistance value of the fifth resistor R5 is 5.1KΩ.

[0030] Wherein, the AC-DC conversion module includes: a bridge rectifier circuit DB1, a second capacitor C2 and a third capacitor C3, the first end and the third end of the bridge rectifier circuit DB1 are connected to the output ends of the step-down module, the fourth end of the bridge rectifier circuit DB1 is grounded, one end of the second capacitor C2 and one end of the third capacitor C3 are both connected to the second end of the bridge rectifier circuit DB1, the other end of the second capacitor C2 and the other end of the third capacitor C3 are both grounded, wherein the second capacitor C2 is an electrolytic capacitor.

[0031] Specifically, the bridge rectifier circuit DB1 converts the low-voltage AC full-wave voltage output by the transformer into a half-wave DC voltage, and the model of the bridge rectifier circuit DB1 is DB155S. The second capacitor C2 and the third capacitor C3 are both filter capacitors, which play a filtering role and are used to filter the half-wave DC voltage output by the bridge rectifier circuit DB1 into a smooth DC power supply. The second capacitor C2 is an electrolytic capacitor with a rated voltage of 35V and a capacitance value of 220 սF, and the capacitance value of the third capacitor C3 is 100 nF.

[0032] Among them, the first switch circuit includes: a first resistor R1, a second resistor R2, a voltage regulator D1 and a first transistor Q1; one end of the first resistor R1 is connected to the output end of the AC-DC conversion module, the other end of the first resistor R1 is connected to the negative electrode of the voltage regulator D1, the positive electrode of the voltage regulator D1 is respectively connected to one end of the second resistor R2 and the base of the first transistor Q1, the other end of the second resistor R2 is grounded, the emitter of the first transistor Q1 is grounded, and the collector of the first transistor Q1 is connected to the second switch circuit.

[0033] Specifically, the first resistor R1 is the current limiting resistor of the voltage regulator tube, and the second resistor R2 is the base pull-down resistor of the first transistor Q1, which is used to prevent the first transistor Q1 from being turned on by mistake when the voltage regulator tube D1 is not turned on. The function of the voltage regulator tube D1 is: when the negative voltage of the voltage regulator tube D1 is greater than 15V, the voltage regulator tube D1 is turned on to provide the base conduction current for the first transistor Q1. The first transistor Q1 is an NPN transistor, and the model is 2SC5171. The function of the first transistor Q1 is: when there is input current at the base, the first transistor Q1 is turned on and grounded through the emitter, and the collector voltage (and the voltage of the fourth capacitor C4) is pulled down to about 0.6V. (The saturation voltage drop Uce after the first transistor Q1 is turned on is approximately equal to 0.6V).

[0034] The resistance of the first resistor R1 is 4.7 kΩ, the resistance of the second resistor R2 is 2 kΩ, the voltage regulator tube model is ZMM15, and the first transistor Q1 model is a 2SC5171 NPN transistor.

[0035] Among them, the second switch circuit includes: a third resistor R3, a fourth resistor R4, a fourth capacitor C4, a third diode D3 and a second triode Q2, one end of the third resistor R3 is connected to the output end of the AC-DC conversion module, the other end of the third resistor R3 is respectively connected to the positive electrode of the third diode D3, one end of the fourth resistor R4, one end of the fourth capacitor C4 and the first switch circuit, the other end of the fourth capacitor C4 and the other end of the fourth resistor R4 are both grounded, the cathode of the third diode D3 is connected to the base of the second triode Q2, the emitter of the second triode Q2 is grounded, and the collector of the second triode Q2 is connected to the relay switch module.

[0036] Specifically, the third resistor R3 and the fourth resistor R4 are base bias resistors, providing base bias voltage for the second transistor Q2. The fourth capacitor C4 is used to stabilize the turn-on voltage of the third diode D3 and the working state of the second transistor Q2. The third diode D3 can increase the turn-on voltage of the base of the second transistor Q2 through its own 0.6V dead zone voltage difference. Since the first transistor Q1 has a voltage drop of about 0.6V after being turned on, if the 0.6V voltage drop of the third diode D3 is not added, the second transistor Q2 can be turned on, so that the second transistor Q2 is mis-turned on to close the relay. In other words, the second transistor Q2 is a relay control transistor, which controls the relay to be pulled in when there is a signal. The resistance of the third resistor R3 is 3.3kΩ, and the resistance of the fourth resistor R4 is 1 kΩ. The second transistor Q2 is an NPN transistor with a model of 2SC5171.

[0037] Wherein, the relay switch module includes: a relay K1 and a second diode D2, the cathode of the second diode D2 and the first end of the relay K1 are connected to the output end of the AC-DC conversion module, and the anode of the second diode D2 and the second end of the relay K1 are connected to the second switch circuit.

[0038] The relay K1 is used to control the on and off of the output voltage. The second diode D2 is a common diode, which is connected in reverse at both ends of the relay coil, and plays a role in absorbing the reverse electromotive force of the relay coil when the relay is disconnected.

[0039] The working modes of the above circuit are divided into two types, namely the relay closed output circuit mode and the relay disconnected output circuit mode. The working principle is:

[0040] In the relay closed output loop mode, i.e., the normal mode: when the circuit input terminal P1 is connected to the 220V AC voltage, first, an AC voltage of about 8V is obtained through the isolation and step-down output of the transformer T1, and a DC voltage of 12V is obtained through filtering by the bridge rectifier circuit DB1 and the second capacitor C2. The 12V DC voltage passes through the first resistor R1. Since the voltage regulator D1 is a 15V voltage regulator, the 12V DC voltage cannot make it conductive, and the voltages at the base of the first transistor Q1 and the second resistor R2 are close to 0V. At this time, the first transistor Q1 cannot be turned on, and the voltage divided by the third resistor R3 and the fourth resistor R4 cannot be pulled down to less than 0.6V, and the second transistor Q2 cannot be turned off. At the same time, the 12V voltage is divided by the third resistor R3 and the fourth resistor R4 and then connected to the third diode D3, so that the 0.7V voltage at the base of the second transistor Q2 can make it turned on, and the output relay K1 closes the output loop.

[0041] In the relay disconnect output loop mode, i.e., abnormal mode, when the circuit input terminal P1 is connected to 380V AC voltage, an AC voltage of about 15V is obtained through the isolation and step-down output of the transformer T1, and a DC voltage of 21V is obtained through filtering by the bridge rectifier circuit DB1 and the second capacitor C2. The DC voltage of 21V passes through the first resistor R1. Since the voltage regulator D1 is a 15V voltage regulator, the DC voltage of 21V can make it conductive. Then, after voltage division by the second resistor R2, it is added to the base of the first transistor Q1 to turn on the first transistor Q1, and the voltage division of the third resistor R3 and the fourth resistor R4 is pulled down to less than 0.6V (the voltage difference between the collector and the emitter after the transistor is saturated and turned on is 0.6V). The bases of the third diode D3 and the second transistor Q2 both have a dead zone voltage of about 0.7V, and 0.6V cannot turn on the third diode D3 and the second transistor Q2, and the output relay K1 disconnects the output loop.

[0042] In the present invention, when the input AC voltage is too high, the input AC voltage is firstly stepped down by a transformer, and the stepped-down AC voltage is converted into a DC voltage, the first switch circuit is turned on, so that the second switch circuit is disconnected, and the relay disconnects the output circuit, thereby avoiding the phenomenon that the input AC voltage is too high and the load equipment is damaged. The circuit structure of the present invention is relatively simple, and accurate protection can be achieved with fewer peripheral devices. The protection time of the present invention is faster than the fuse time of the fuse, and the protection action time is less than 5ms.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A single-phase AC input voltage overvoltage protection circuit, characterized in that: include: A step-down module, an AC-DC conversion module, and a relay switch module connected in sequence; The step-down module is used to receive an externally input AC voltage and step down the AC voltage; The AC-DC conversion module is used to convert the stepped-down AC voltage into a DC voltage; The relay switch module includes: a first switch circuit, a second switch circuit and a relay switch, the first switch circuit, the second switch circuit and the relay switch are all connected to the output end of the AC-DC conversion module, the second switch circuit is also connected to the relay switch and the first switch circuit, the first switch circuit includes: a first resistor, a second resistor, a voltage regulator and a first transistor; one end of the first resistor is connected to the output end of the AC-DC conversion module, the other end of the first resistor is connected to the negative electrode of the voltage regulator, the positive electrode of the voltage regulator is respectively connected to one end of the second resistor and the base of the first transistor, the other end of the second resistor is grounded, the emitter of the first transistor is grounded, and the collector of the first transistor is connected to the second switch circuit; The relay switch comprises: a relay and a second diode, wherein the cathode of the second diode and the first end of the relay are connected to the output end of the AC-DC conversion module, and the anode of the second diode and the second end of the relay are connected to the second switch circuit; When the input AC voltage is too high, the first switch circuit of the relay switch module is turned on and the second switch circuit is turned off, so that the relay disconnects the output loop.

2. The single-phase AC input voltage overvoltage protection circuit according to claim 1, characterized in that: The step-down module includes: a transformer, a first capacitor, and a fifth capacitor; the first capacitor and the fifth capacitor are connected in series and then connected in parallel at both input ends of the transformer, and a fifth resistor is also connected in parallel at both output ends of the transformer.

3. The single-phase AC input voltage overvoltage protection circuit according to claim 1, characterized in that: The AC-DC conversion module includes: a bridge rectifier circuit, a second capacitor and a third capacitor, the first end and the third end of the bridge rectifier circuit are connected to the output ends of the step-down module, the fourth end of the bridge rectifier circuit is grounded, one end of the second capacitor and one end of the third capacitor are both connected to the second end of the bridge rectifier circuit, the other end of the second capacitor and the other end of the third capacitor are both grounded, wherein the second capacitor is an electrolytic capacitor.

4. The single-phase AC input voltage overvoltage protection circuit according to claim 1, characterized in that: The second switch circuit includes: a third resistor, a fourth resistor, a fourth capacitor, a third diode and a second triode, one end of the third resistor is connected to the output end of the AC-DC conversion module, the other end of the third resistor is respectively connected to the positive electrode of the third diode, one end of the fourth resistor, one end of the fourth capacitor and the first switch circuit, the other end of the fourth capacitor and the other end of the fourth resistor are both grounded, the cathode of the third diode is connected to the base of the second triode, the emitter of the second triode is grounded, and the collector of the second triode is connected to the relay switch module.

5. The single-phase AC input voltage overvoltage protection circuit according to claim 1, characterized in that: The first transistor is an NPN transistor, and its model is 2SC5171.

6. The single-phase AC input voltage overvoltage protection circuit according to claim 3, characterized in that: The bridge rectifier circuit is used to convert a low-voltage AC full-wave voltage into a half-wave DC voltage. The second capacitor and the third capacitor are both filter capacitors used to filter the half-wave DC voltage into a smooth DC power supply.

7. The single-phase AC input voltage overvoltage protection circuit according to claim 1, characterized in that: The first resistor is a current limiting resistor of the voltage regulator tube, and the second resistor is a base pull-down resistor of the first transistor, which is used to prevent the first transistor from being mistakenly turned on when the voltage regulator tube is not turned on.

8. The single-phase AC input voltage overvoltage protection circuit according to claim 4, characterized in that: The fourth capacitor is used to stabilize the turn-on voltage of the third diode and the working state of the second transistor.

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