Solid-state alternating-current under-voltage protection circuit and device

Abstract

The invention relates to the field of alternating-current input electric devices, in particular to a solid-state alternating-current under-voltage protection circuit and device.According to the circuit, input voltage is monitored in real time, the circuit is cut off when the voltage is too low, a load can be effectively protected against the influence of insufficient voltage, the stability and reliability of the circuit are improved, under-voltage protection of an alternating-current circuit is achieved, and the service life of the circuit is prolonged. The voltage protection circuit is simple in structure, low in cost, easy to implement and high in reliability, and can be widely applied to alternating-current circuits needing voltage protection.

Description

Technical Field

[0001] The invention relates to the field of AC input electrical devices, in particular to a solid-state AC undervoltage protection circuit and device. Background Art

[0002] For electrical devices with single-phase AC input, such as motors and power converters, the applicable input voltage has a limited range. When the input voltage is lower than its rated range, the electrical devices may be damaged or fail to achieve the expected functions, such as the motor output power drops, the motor cannot rotate normally or even burns out, the power converter restarts frequently, the output voltage is wrong or even damaged. Since the external input voltage may be uncontrollable, in order to protect the electrical devices, it is necessary to cut off the connection between the electrical devices and the input after the external input voltage is reduced.

[0003] Reference Figure 1 At present, relays are usually used to disconnect the input line when the input voltage is too low. That is, a relay (or AC contactor) is connected in series at the input end of the line to monitor the input voltage. When the input voltage is lower than the set value, the relay disconnects the electrical device from the input to achieve the purpose of protecting the electrical device. However, this solution has problems such as complex circuits, large volume, low reliability, and arcing of relay contacts. In addition, the relay needs to be continuously powered to maintain the closed state during operation, and an additional power supply circuit needs to be added, which has problems such as complex circuits and high losses. Summary of the invention

[0004] Aiming at the problems of complex circuit, large volume, low reliability and arcing of relay contacts when performing undervoltage protection in the prior art, the present invention provides a solid-state AC undervoltage protection circuit and device.

[0005] The present invention is achieved through the following technical solutions: A solid-state AC undervoltage protection circuit comprises a first MOSFET tube T1, a second MOSFET tube T2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a reference voltage source IC1, a first resistor R1, a second resistor R2, a seventh resistor R7, a first voltage regulator tube Dz1 and an optocoupler circuit, wherein the drain of the first MOSFET tube T1 is connected to a first AC voltage input terminal 1P, the drain of the second MOSFET tube T2 is connected to a first AC output voltage 3P, the source of the first MOSFET tube T1 is connected to the source of the second MOSFET tube T2, the gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the cathode of the first voltage regulator tube Dz1 and the optocoupler circuit; The anode of the first diode D1 is connected to the first AC voltage input terminal 1P, the cathode is connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the second AC voltage input terminal 2P and the second AC output terminal 4P; The anode of the second diode D2 is connected to the cathode of the first diode D1, the cathode is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the anode of the first voltage regulator tube Dz1; the third capacitor C3 is connected in parallel with the first voltage regulator tube Dz1; The gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to the cathode of the reference voltage source IC1, the anode of the reference voltage source IC1 is connected to the anode of the first voltage regulator tube Dz1, and the reference pin of the reference voltage source IC1 is connected to the optocoupler circuit; The optocoupler circuit includes a first optocoupler circuit, a second optocoupler circuit and an optocoupler diode circuit. The first optocoupler circuit includes a first optocoupler IC2A, a fifth resistor R5, a fifth diode D5, a seventh resistor R7, a fourth capacitor C4 and a sixth capacitor C6. One end of the fifth resistor R5 is connected to the second resistor R2, an anode of the fifth diode D5 is connected to the collector of the first optocoupler IC2A, and an emitter of the first optocoupler IC2A is connected to the anode of the reference voltage source IC1; a cathode of the fifth diode D5 is connected to the anode of the reference voltage source IC1 through R7, the sixth capacitor C6 is connected to the seventh resistor R7 in parallel, and the fourth capacitor C4 is connected to the first optocoupler IC2A in parallel; The second optocoupler circuit includes a second optocoupler IC3A, a sixth resistor R6, a sixth diode D6, and a fifth capacitor C5. One end of the sixth resistor R6 is connected to the second resistor R2, and the other end is connected to the reference pin of the reference voltage source IC1 through the sixth diode D6. The fifth capacitor C5 is connected in parallel with the second optocoupler IC3A. The collector of the second optocoupler IC3A is connected to the anode of the second diode D6, and the emitter of the second optocoupler IC3A is connected to the anode of the reference voltage source IC1. The optocoupler diode circuit includes a third resistor R3, a fourth resistor R4, a second voltage regulator tube DZ2, a first optocoupler diode IC2B, a third diode D3, a fourth diode D4, a second optocoupler diode IC3B, and a third voltage regulator tube Dz3, one end of the third resistor is connected to the anode of the first diode D1, and the other end is connected to the cathode of the second voltage regulator tube Dz2, the anode of the second voltage regulator tube Dz2 is connected to the anode of the first optocoupler diode IC2B, the cathode of the first optocoupler diode IC2B is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the anode of the second voltage regulator tube Dz2; The anode of the fourth diode D4 is connected to the anode of the third diode D3, the cathode of the fourth diode D4 is connected to the anode of the second optocoupler diode IC3B, the cathode of the second optocoupler diode IC3B is connected to the anode of the fourth diode D4, the anode of the third voltage regulator tube Dz3 is connected to the anode of the second optocoupler diode IC3B, the cathode of the third voltage regulator tube Dz3 is connected to one end of the fourth resistor R4, and the other end of the fourth resistor R4 is connected to the fourth AC output terminal 4P.

[0006] Preferably, both the first MOSFET tube T1 and the second MOSFET tube T2 are N-channel MOSFET tubes.

[0007] Preferably, the rated withstand voltage V of the first MOSFET tube T1 and the second MOSFET tube T2 is DS The amplitude is greater than the maximum input voltage, and the rated current is greater than twice the maximum input current.

[0008] Preferably, the model of each component in the second optocoupler circuit is consistent with the model of each component in the first optocoupler circuit.

[0009] Preferably, the third diode D3 and the fourth diode D4 are both low-voltage and low-current diodes.

[0010] Preferably, the voltage regulation value range of the first voltage regulator tube DZ1 is 8-15V.

[0011] Preferably, the undervoltage protection setting value of the circuit is the sum of the voltage value of the second voltage regulator tube DZ2, the forward voltage drop of the internal diode of the optocoupler, the forward voltage drop of the third diode D3, and the forward voltage drop of the third voltage regulator tube DZ3.

[0012] Preferably, the resistance of the fifth resistor R5 is between 1 kΩ and 10 kΩ.

[0013] Preferably, the voltage on the third capacitor C3 ranges from 2.6V to 3V.

[0014] A device comprising the solid-state AC undervoltage protection circuit.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The solid-state AC undervoltage protection circuit of the present invention can effectively protect the load from the influence of insufficient voltage by monitoring the input voltage in real time and cutting off the circuit when the voltage is too low, thereby improving the stability and reliability of the circuit and realizing undervoltage protection of the AC circuit. The circuit has a simple structure, low cost, easy implementation and high reliability, and can be widely used in AC circuits requiring voltage protection.

[0016] Furthermore, the rated withstand voltage and rated current of the MOSFET switch tube are limited in order to ensure the safe and stable operation of the choke circuit.

[0017] The invention discloses a solid-state AC undervoltage protection device, which is designed with power semiconductor devices as the core, has a simple structure, a small size, and high reliability, and can cut off the connection between the electrical device and the input terminal when the input voltage is lower than a set value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the undervoltage protection using a relay in the prior art; Figure 2 It is a circuit diagram of a solid-state AC undervoltage protection circuit of the present invention; Figure 3 The invention discloses an application manual wiring schematic diagram of a solid-state AC undervoltage protection device. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0020] The present invention discloses a solid-state AC undervoltage protection circuit. Figure 2 , including a first MOSFET tube T1, a second MOSFET tube T2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a reference voltage source IC1, a first resistor R1, a second resistor R2, a seventh resistor R7, a first voltage regulator tube Dz1 and an optocoupler circuit, the drain of the first MOSFET tube T1 is connected to the first AC voltage input terminal 1P, the drain of the second MOSFET tube T2 is connected to the first AC output voltage 3P, the source of the first MOSFET tube T1 is connected to the source of the second MOSFET tube T2, the gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the cathode of the first voltage regulator tube Dz1 and the optocoupler circuit.

[0021] The anode of the first diode D1 is connected to the first AC voltage input terminal 1P, the cathode is connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the second AC voltage input terminal 2P and the second AC output terminal 4P.

[0022] The anode of the second diode D2 is connected to the cathode of the first diode D1, the cathode is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the anode of the first voltage regulator Dz1; the third capacitor C3 is connected in parallel with the first voltage regulator Dz1. The voltage range of the first voltage regulator DZ1 is 8 to 15V.

[0023] The gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to the cathode of the reference voltage source IC1, the anode of the reference voltage source IC1 is connected to the anode of the first voltage regulator tube Dz1, and the reference pin of the reference voltage source IC1 is connected to the optocoupler circuit.

[0024] The optocoupler circuit includes a first optocoupler circuit, a second optocoupler circuit and an optocoupler diode circuit, and the models of the components in the second optocoupler circuit are consistent with the models of the components in the first optocoupler circuit. The first optocoupler circuit includes a first optocoupler IC2A, a fifth resistor R5, a fifth diode D5, a seventh resistor R7, a fourth capacitor C4, and a sixth capacitor C6. One end of the fifth resistor R5 is connected to the second resistor R2, the anode of the fifth diode D5 is connected to the collector of the first optocoupler IC2A, and the emitter of the first optocoupler IC2A is connected to the anode of the reference voltage source IC1; the cathode of the fifth diode D5 is connected to the anode of the reference voltage source IC1 through R7, the sixth capacitor C6 is connected in parallel with the seventh resistor R7, and the fourth capacitor C4 is connected in parallel with the first optocoupler IC2A.

[0025] The second optocoupler circuit includes a second optocoupler IC3A, a sixth resistor R6, a sixth diode D6, and a fifth capacitor C5. One end of the sixth resistor R6 is connected to the second resistor R2, and the other end is connected to the reference pin of the reference voltage source IC1 through the sixth diode D6. The fifth capacitor C5 is connected to the second optocoupler IC3A in parallel; the collector of the second optocoupler IC3A is connected to the anode of the second diode D6, and the emitter of the second optocoupler IC3A is connected to the anode of the reference voltage source IC1.

[0026] The optocoupler diode circuit includes a third resistor R3, a fourth resistor R4, a second voltage regulator DZ2, a first optocoupler diode IC2B, a third diode D3, a fourth diode D4, a second optocoupler diode IC3B, and a third voltage regulator Dz3. One end of the third resistor is connected to the anode of the first diode D1, and the other end is connected to the cathode of the second voltage regulator Dz2. The anode of the second voltage regulator Dz2 is connected to the anode of the first optocoupler diode IC2B, the cathode of the first optocoupler diode IC2B is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the anode of the second voltage regulator Dz2.

[0027] The anode of the fourth diode D4 is connected to the anode of the third diode D3, the cathode of the fourth diode D4 is connected to the anode of the second optocoupler diode IC3B, the cathode of the second optocoupler diode IC3B is connected to the anode of the fourth diode D4, the anode of the third voltage regulator tube Dz3 is connected to the anode of the second optocoupler diode IC3B, the cathode of the third voltage regulator tube Dz3 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is connected to the fourth AC output terminal 4P, the third diode D3 and the fourth diode D4 are both low-voltage and low-current diodes, and the second voltage regulator tube DZ2 and the third voltage regulator tube DZ3 are of the same model.

[0028] In a solid-state AC undervoltage protection circuit of the present invention, the drain of the first MOSFET tube T1 is connected to the first AC voltage input terminal 1P, the drain of the second MOSFET tube T2 is connected to the first AC output voltage 3P, the sources of the two are connected, and the gates are connected to the cathode of the first voltage regulator tube Dz1 and the optocoupler circuit through the second resistor R2. The first diode D1 to the second diode D2, the capacitors C1 to C3 and other components constitute the input voltage filtering and voltage stabilization network. The reference voltage source IC1 cooperates with the first voltage regulator tube Dz1 and the optocoupler circuit to realize voltage monitoring and protection logic. The optocoupler circuit includes a first optocoupler circuit (including the first optocoupler IC2A, the fifth resistor R5 and other components, the resistance of R5 is 1kΩ to 10kΩ), a second optocoupler circuit (the component model is consistent with the first optocoupler circuit) and an optocoupler diode circuit (including the third diode D3, the fourth diode D4, etc.), and realizes voltage isolation and transmission through photoelectric conversion, and at the same time controls the gate voltage of the MOSFET tube according to the input voltage condition, thereby realizing undervoltage protection of the AC circuit.

[0029] When the input voltage is normal, the first voltage regulator Dz1 stabilizes the gate voltage, the first MOSFET tubes T1 and T2 are in the on state, and the circuit works normally. When the input voltage is lower than the set value, the output voltage of the reference voltage source IC1 decreases, causing the optocoupler diode in the optocoupler circuit to emit less light or go out, and then the optocoupler transistor is turned off. At this time, the gate voltage of the MOSFET tube drops below the threshold, the MOSFET tube is turned off, and the circuit is cut off, thereby protecting the load.

[0030] The first MOSFET tube T1 and the second MOSFET tube T2 are both N-channel MOSFET tubes, and the rated withstand voltage V DS The amplitude is greater than the maximum input voltage, and the rated current is greater than twice the maximum input current.

[0031] The AC voltage input by 1P and 2P passes through the voltage doubling rectification circuit composed of the first diode D1, the second diode D2, the first capacitor C1 and the second capacitor C2 to generate a DC voltage at both ends of the second capacitor C2; the voltage stabilizing circuit composed of the first resistor R1, the first voltage regulator DZ1 and the third capacitor C3 forms a stable DC voltage.

[0032] When the first optocoupler IC2 and the second optocoupler IC3 are not conducting, the voltage at the reference voltage terminal of the reference voltage source IC1 is: , wherein VDZ1 is the voltage stabilization value of the first voltage regulator DZ1, the resistance value of the fifth resistor R5 is in the range of 1kΩ to 10kΩ, and the voltage value range of the third capacitor C3 is in the range of 2.6 to 3V, which can be adjusted according to specific needs.

[0033] When the first optocoupler IC2 and the second optocoupler IC3 are turned on, the voltage at the reference voltage terminal of the reference voltage source IC1 drops to 0V.

[0034] The undervoltage protection setting value of the circuit is the sum of the voltage value of the second voltage regulator tube DZ2, the forward voltage drop of the internal diode of the optocoupler, the forward voltage drop of the third diode D3, and the forward voltage drop of the third voltage regulator tube DZ3.

[0035] When the input voltage amplitude is lower than the set value of the under-voltage protection, the first optocoupler IC2 and the second optocoupler IC3 are not turned on, so that the voltage at the reference voltage terminal of IC1 exceeds the internal set value of IC1, and the internal cathode and anode of the reference voltage source IC1 are turned on, and the gate voltage of the first MOSFET tube T1 and the second MOSFET tube T2 are pulled down, thereby turning off the first MOSFET tube T1 and the second MOSFET tube T2, disconnecting the circuit, and the output voltage on the first AC voltage output terminal 3P and the second AC voltage output terminal 4P becomes 0, thereby achieving the function of under-voltage protection.

[0036] When the input voltage amplitude is higher than the set value of the undervoltage protection, the first optocoupler IC2 and the first optocoupler IC3 are turned on. When the voltage at the reference voltage terminal of the reference voltage source IC1 is lower than the internal set value of the reference voltage source IC1, the internal cathode and anode of the reference voltage source IC1 are turned off, and the voltage on the third capacitor C3 passes through the second resistor R2, so that the gate voltage of the first MOSFET tube T1 and the second MOSFET tube T2 increases, thereby turning on the first MOSFET tube T1 and the second MOSFET tube T2. The output voltage on the first AC voltage output terminal 3P and the second AC voltage output terminal 4P is basically the same as the input voltage on the first AC voltage input terminal 1P and the second AC voltage input terminal 2P, so the electrical components connected to the first AC voltage output terminal 3P and the second AC voltage output terminal 4P can work normally.

[0037] The setting value of the undervoltage protection can be adjusted by changing the values ​​of the second voltage regulator tube DZ2 and the third voltage regulator tube DZ3. The third resistor R3 and the fourth resistor R4 limit the current flowing through the first optocoupler IC2 and the second optocoupler IC3 to protect the first optocoupler IC2 and the second optocoupler IC3. The third diode D3 and the fourth diode D4 are reversely connected in parallel with the internal diodes IC2B and IC3B of the first optocoupler IC2 and the second optocoupler IC3 to ensure that the reverse current can flow normally.

[0038] The present invention discloses a solid-state AC undervoltage protection device, referring to Figure 3 When in use, the solid-state AC undervoltage protection device is inserted between the electrical device and the AC input terminal, with pins 3 and 4 connected to the electrical device, and pins 1 and 2 directly connected to the power input terminal, regardless of polarity. The implementation principle is to accurately control the on and off of the internal first MOSFET tube T1 and the second MOSFET tube T2 by detecting the amplitude of the AC voltage at the input terminal. When the amplitude of the AC voltage at the input terminal is lower than the set value, the first MOSFET tube T1 and the second MOSFET tube T2 are turned off, and the input of the electrical device is closed. When the amplitude of the AC voltage at the input terminal is higher than the set value, the first MOSFET tube T1 and the second MOSFET tube T2 are turned on, and the input voltage of the electrical device is normal, thereby achieving undervoltage protection for the electrical device.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A solid-state AC undervoltage protection circuit, characterized in that: It includes a first MOSFET tube T1, a second MOSFET tube T2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a reference voltage source IC1, a first resistor R1, a second resistor R2, a seventh resistor R7, a first voltage regulator tube Dz1 and an optocoupler circuit, wherein the drain of the first MOSFET tube T1 is connected to the first AC voltage input terminal 1P, the drain of the second MOSFET tube T2 is connected to the first AC output voltage 3P, the source of the first MOSFET tube T1 is connected to the source of the second MOSFET tube T2, the gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the cathode of the first voltage regulator tube Dz1 and the optocoupler circuit; The anode of the first diode D1 is connected to the first AC voltage input terminal 1P, the cathode is connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the second AC voltage input terminal 2P and the second AC output terminal 4P; The anode of the second diode D2 is connected to the cathode of the first diode D1, the cathode is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the anode of the first voltage regulator tube Dz1; the third capacitor C3 is connected in parallel with the first voltage regulator tube Dz1; The gate of the first MOSFET tube T1 and the gate of the second MOSFET tube T2 are both connected to the cathode of the reference voltage source IC1, the anode of the reference voltage source IC1 is connected to the anode of the first voltage regulator tube Dz1, and the reference pin of the reference voltage source IC1 is connected to the optocoupler circuit; The optocoupler circuit includes a first optocoupler circuit, a second optocoupler circuit and an optocoupler diode circuit. The first optocoupler circuit includes a first optocoupler IC2A, a fifth resistor R5, a fifth diode D5, a seventh resistor R7, a fourth capacitor C4 and a sixth capacitor C6. One end of the fifth resistor R5 is connected to the second resistor R2, an anode of the fifth diode D5 is connected to the collector of the first optocoupler IC2A, and an emitter of the first optocoupler IC2A is connected to the anode of the reference voltage source IC1; a cathode of the fifth diode D5 is connected to the anode of the reference voltage source IC1 through R7, the sixth capacitor C6 is connected to the seventh resistor R7 in parallel, and the fourth capacitor C4 is connected to the first optocoupler IC2A in parallel; The second optocoupler circuit includes a second optocoupler IC3A, a sixth resistor R6, a sixth diode D6, and a fifth capacitor C5, one end of the sixth resistor R6 is connected to the second resistor R2, and the other end is connected to the reference pin of the reference voltage source IC1 through the sixth diode D6, and the fifth capacitor C5 is connected in parallel with the second optocoupler IC3A; The collector of the second optical coupler IC3A is connected to the anode of the second diode D6, and the emitter of the second optical coupler IC3A is connected to the anode of the reference voltage source IC1; The optocoupler diode circuit includes a third resistor R3, a fourth resistor R4, a second voltage regulator tube DZ2, a first optocoupler diode IC2B, a third diode D3, a fourth diode D4, a second optocoupler diode IC3B, and a third voltage regulator tube Dz3, one end of the third resistor is connected to the anode of the first diode D1, and the other end is connected to the cathode of the second voltage regulator tube Dz2, the anode of the second voltage regulator tube Dz2 is connected to the anode of the first optocoupler diode IC2B, the cathode of the first optocoupler diode IC2B is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the anode of the second voltage regulator tube Dz2; The anode of the fourth diode D4 is connected to the anode of the third diode D3, the cathode of the fourth diode D4 is connected to the anode of the second optocoupler diode IC3B, the cathode of the second optocoupler diode IC3B is connected to the anode of the fourth diode D4, the anode of the third voltage regulator tube Dz3 is connected to the anode of the second optocoupler diode IC3B, the cathode of the third voltage regulator tube Dz3 is connected to one end of the fourth resistor R4, and the other end of the fourth resistor R4 is connected to the fourth AC output terminal 4P.

2. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The first MOSFET tube T1 and the second MOSFET tube T2 are both N-channel MOSFET tubes.

3. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The rated withstand voltage V of the first MOSFET tube T1 and the second MOSFET tube T2 DS The amplitude is greater than the maximum input voltage, and the rated current is greater than twice the maximum input current.

4. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The types of components in the second optocoupler circuit are consistent with the types of components in the first optocoupler circuit.

5. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The third diode D3 and the fourth diode D4 are both low-voltage and low-current diodes.

6. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The voltage regulation value range of the first voltage regulator tube DZ1 is 8 to 15V.

7. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The undervoltage protection setting value of the circuit is the sum of the voltage value of the second voltage regulator tube DZ2, the forward voltage drop of the internal diode of the optocoupler, the forward voltage drop of the third diode D3, and the forward voltage drop of the third voltage regulator tube DZ3.

8. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The resistance of the fifth resistor R5 is between 1 kΩ and 10 kΩ.

9. The solid-state AC undervoltage protection circuit according to claim 1, characterized in that: The voltage on the third capacitor C3 ranges from 2.6V to 3V.

10. A device comprising the solid-state AC undervoltage protection circuit according to any one of claims 1.

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