An undervoltage release

Abstract

The present invention discloses an under-voltage release. The under-voltage release of the present invention includes a dual-coil electromagnet having a holding suction coil and a starting suction coil, a first switching circuit and a second switching circuit respectively used to control the on / off of the holding suction coil and the starting suction coil, and a control circuit used to control the first switching circuit and the second switching circuit according to the grid voltage; when the grid voltage value is greater than or equal to the set value, the control circuit controls the first switching circuit to conduct while controlling the second switching circuit to conduct first for a preset time and then turn off; when the grid voltage value is less than the set value, the control circuit controls both the first switching circuit and the second switching circuit to turn off. Compared with the prior art, the present invention has the advantages of no high-frequency noise, no high-frequency radiation, simple control circuit, strong anti-interference ability, and low circuit power consumption.

Description

Technical Field

[0001] The present invention relates to an under-voltage release. Background Art

[0002] For the miniaturization of the circuit breaker, the volume of the internal accessories is also made smaller, and the under-voltage release is also miniaturized. Due to the miniaturization of the electromagnet coil used in the under-voltage release, in the traditional single-coil method, the full voltage is usually adopted during suction, and the PWM method is used to control the current during holding to achieve the purpose of low power consumption. Since the coil current is a PWM pulse current, relatively large radiation interference will inevitably be generated. When the input voltage is not conducive to electromagnetic compatibility, and the electromagnet will inevitably generate high-frequency noise, which affects the user experience. And when the power supply voltage drops for a short time, the under-voltage release will be accidentally released, causing the circuit breaker to trip and affecting the power supply. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an under-voltage release, which has no high-frequency noise, no high-frequency radiation, a simple control circuit, and can prevent the under-voltage release from being accidentally released and causing the circuit breaker to trip when the voltage drops for a short time and the voltage drop is not deep enough to affect the power supply.

[0004] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0005] An undervoltage release includes a dual-coil electromagnet having a holding coil and a starting coil, a first switch circuit and a second switch circuit respectively used to control the on / off of the holding coil and the starting coil, and a control circuit used to control the first switch circuit and the second switch circuit according to the grid voltage; the control circuit includes: a rectifying circuit, a power supply circuit, a voltage sampling circuit, a first comparison circuit, a second comparison circuit, and a differentiating circuit; the rectifying circuit converts the grid voltage into a DC voltage U1 and uses it as the working power supply voltage of the holding coil and the starting coil; the DC voltage U1 is stepped down and filtered by the power supply circuit to become a low-voltage DC voltage U2 and used as the working power supply of the first comparison circuit, the second comparison circuit, the first switch circuit, and the second switch circuit; the DC voltage U1 is divided by the voltage sampling circuit to obtain comparison voltages U3, U4, U5, and U3>U4>U5; both the first comparison circuit and the second comparison circuit are hysteresis comparators with two-way comparison voltage inputs, the input of the first comparison circuit is the comparison voltages U3, U4, and the input of the second comparison circuit is the comparison voltages U3, U5; when the comparison voltage U3 is greater than the closing reference voltage, the first comparison circuit outputs a conduction control signal to the first switch circuit, and the second comparison circuit outputs a conduction control signal to the second switch circuit through the differentiating circuit and converts the conduction control signal into a cut-off control signal after a preset time under the action of the differentiating circuit; when the comparison voltage U4 is less than the release reference voltage, the first comparison circuit outputs a cut-off control signal to the first switch circuit; when the comparison voltage U5 is less than the restart reference voltage, the second comparison circuit outputs a cut-off control signal to the second switch circuit through the differentiating circuit.

[0006] Further preferably, the power supply circuit includes a first resistor, a second resistor, a first MOS transistor, a first capacitor, a second capacitor, and a first voltage regulator diode; the output terminal of the rectifying circuit is connected to one end of the first resistor, one end of the second resistor, the input terminal of the voltage sampling circuit, and the connection terminal of the holding circuit and the starting circuit; the other end of the first resistor is connected to the gate of the first MOS transistor, one end of the first capacitor, and the negative electrode of the first voltage regulator diode; the other end of the second resistor is connected to the drain of the first MOS transistor; the source of the first MOS transistor is used as the output terminal of the power supply circuit and connected to the first comparison circuit and the second comparison circuit; the other end of the first capacitor and the positive electrode of the first voltage regulator diode are connected to the ground of the rectifier bridge; one end of the second capacitor is connected to the source of the first MOS transistor, and the other end of the second capacitor is connected to the ground.

[0007] Further preferably, the voltage sampling circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor and a third capacitor; after the third resistor, the fourth resistor, the fifth resistor and the sixth resistor are connected in series in sequence, one end is connected to the DC voltage U1 and the other end is grounded; one end of the third capacitor is connected to the common connection end of the third resistor and the fourth resistor, and the other end of the third capacitor is grounded; the comparison voltage U3 is output from the common connection end of the third resistor and the fourth resistor; the comparison voltage U4 is output from the common connection end of the fourth resistor and the fifth resistor; the comparison voltage U5 is output from the common connection end of the fifth resistor and the sixth resistor.

[0008] Further preferably, the first comparison circuit includes a seventh resistor, an eighth resistor, a fourth capacitor, a second MOS transistor and a first timer circuit 7555; the low-voltage DC voltage U2 is connected to the 4th and 8th pins of the first timer circuit 7555; the comparison voltage U3 is connected to the 6th pin of the first timer circuit 7555; the comparison voltage U4 is connected to the 2nd pin of the first timer circuit 7555; one end of the seventh resistor is connected to the low-voltage DC voltage U2 and the other end is connected to the drain of the second MOS transistor; one end of the eighth resistor is connected to the 3rd pin of the first timer circuit 7555 and the gate of the second MOS transistor; one end of the fourth capacitor is connected to the 5th pin of the first timer circuit 7555; the other end of the eighth resistor, the other end of the fourth capacitor, the source of the second MOS transistor and the 1st pin of the first timer circuit 7555 are commonly connected to the ground; the second comparison circuit includes a ninth resistor, a tenth resistor, a fifth capacitor, a third MOS transistor and a second timer circuit 7555; the low-voltage DC voltage U2 is connected to the 4th and 8th pins of the second timer circuit 7555; the comparison voltage U3 is connected to the 6th pin of the second timer circuit 7555; the comparison voltage U5 is connected to the 2nd pin of the second timer circuit 7555; one end of the ninth resistor is connected to the low-voltage DC voltage U2 and the other end is connected to the drain of the third MOS transistor; one end of the tenth resistor is connected to the 3rd pin of the first timer circuit 7555 and the gate of the third MOS transistor; one end of the fifth capacitor is connected to the 5th pin of the first timer circuit 7555; the other end of the tenth resistor, the other end of the fifth capacitor, the source of the third MOS transistor and the 1st pin of the second timer circuit 7555 are commonly connected to the ground.

[0009] Further preferably, the first switch circuit includes a fifth MOS transistor and a fifth diode. The fifth diode is connected in parallel with the maintenance suction coil. The negative electrode of the fifth diode is connected to the DC voltage U1, the positive electrode of the fifth diode is connected to the drain of the fifth MOS transistor, the gate of the fifth MOS transistor is connected to the output end of the first comparison circuit, and the source of the fifth MOS transistor is grounded.

[0010] Further preferably, the second switch circuit includes a fourth MOS transistor and a sixth diode. The sixth diode is connected in parallel with the start suction coil. The negative electrode of the sixth diode is connected to the DC voltage U1, the positive electrode of the sixth diode is connected to the drain of the fourth MOS transistor, the gate of the fourth MOS transistor is connected to the output end of the differentiating circuit, and the source of the fourth MOS transistor is grounded.

[0011] Further preferably, the differentiating circuit includes a sixth capacitor and an eleventh resistor connected in series. The other end of the sixth capacitor is connected to the output end of the second comparison circuit, the other end of the eleventh resistor is grounded, and the common connection end of the sixth capacitor and the eleventh resistor is the output end of the differentiating circuit.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention adopts a dual-coil structure to achieve the functions and performances specified by the standard, and respectively controls the on and off of the holding suction coil and the starting suction coil according to the grid voltage condition. Compared with the prior art of current coil high-frequency PWM pulse current control, the present invention has the advantages of no high-frequency noise, no high-frequency radiation, simple control circuit, strong anti-interference ability, and low circuit power consumption. It can prevent the accidental release of the under-voltage release from causing the circuit breaker to trip and affecting the power supply in the case of short-time voltage drop. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic structural principle diagram of the present invention;

[0015] Figure 2 is a circuit diagram of a preferred embodiment of the present invention;

[0016] Figure 3 is a schematic diagram of the voltage state change at each point. DETAILED DESCRIPTION OF THE INVENTION

[0017] Aiming at the deficiencies of the prior art, the solution idea of the present invention is to adopt a dual-coil structure to achieve the functions and performances of the under-voltage release specified by the standard, and respectively control the on and off of the holding suction coil and the starting suction coil according to the grid voltage condition.

[0018] The present invention specifically adopts the following technical solutions:

[0019] An under-voltage release includes a dual-coil electromagnet having a holding coil and a starting coil, a first switch circuit and a second switch circuit respectively used to control the on / off of the holding coil and the starting coil, and a control circuit used to control the first switch circuit and the second switch circuit according to the grid voltage; the control circuit includes: a rectifying circuit, a power supply circuit, a voltage sampling circuit, a first comparison circuit, a second comparison circuit, and a differentiating circuit; the rectifying circuit converts the grid voltage into a DC voltage U1 and uses it as the working power supply voltage of the holding coil and the starting coil; the DC voltage U1 is stepped down and filtered by the power supply circuit to become a low-voltage DC voltage U2 and used as the working power supply of the first comparison circuit, the second comparison circuit, the first switch circuit, and the second switch circuit; the DC voltage U1 is divided by the voltage sampling circuit to obtain comparison voltages U3, U4, U5, and U3>U4>U5; both the first comparison circuit and the second comparison circuit are hysteresis comparators with two-way comparison voltage inputs, the input of the first comparison circuit is the comparison voltages U3, U4, and the input of the second comparison circuit is the comparison voltages U3, U5; when the comparison voltage U3 is greater than the closing reference voltage, the first comparison circuit outputs a conduction control signal to the first switch circuit, and the second comparison circuit outputs a conduction control signal to the second switch circuit through the differentiating circuit and converts the conduction control signal into a cut-off control signal after a preset time under the action of the differentiating circuit; when the comparison voltage U4 is less than the release reference voltage, the first comparison circuit outputs a cut-off control signal to the first switch circuit; when the comparison voltage U5 is less than the restart reference voltage, the second comparison circuit outputs a cut-off control signal to the second switch circuit through the differentiating circuit.

[0020] The above technical solution can be flexibly built using various existing circuit modules and components according to actual situations and needs. For the convenience of public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment in conjunction with the drawings:

[0021] Figure 1 Shows the basic circuit structure and principle of the under-voltage release in this embodiment. The under-voltage release includes a rectifying circuit, a power supply circuit, a voltage sampling circuit, comparison circuit 1, comparison circuit 2, switch circuit 1, differentiating circuit, switch circuit 2, a holding coil, and a starting coil.

[0022] As Figure 1As shown in the figure, the power supply voltage Ui is rectified by the rectifier circuit to become the DC voltage U1. The DC voltage U1 is the working power supply voltage for maintaining the holding coil and starting the holding coil. The DC voltage U1 is processed by the power supply circuit for step-down and filtering to become the low-voltage DC voltage U2, which serves as the working power supply for the comparison circuit 1, comparison circuit 2, switch circuit 1, and switch circuit 2. U2 is also used as the reference voltage. The DC voltage U1 is divided by the sampling circuit to obtain the comparison voltages U3, U4, and U5, and U3 > U4 > U5. The comparison circuit 1 is a hysteresis comparator with two-way comparison voltage inputs, which is used to make corresponding output actions according to the levels of the comparison voltages U3 and U4. The output terminal of the comparison circuit 1 controls the switch circuit 1 to make the holding coil energized or de-energized. When the grid voltage value is greater than the set value (the comparison voltage U3 is greater than the holding reference voltage), the output terminal of the comparison circuit 1 outputs a high level, and the holding coil is controlled to conduct through the switch circuit 1. When the grid voltage value is less than the set value (the comparison voltage U4 is less than the release reference voltage), the output terminal of the comparison circuit 1 outputs a low level, and the holding coil is controlled to be de-energized through the switch circuit 1. The comparison circuit 2 is a hysteresis comparator with two-way comparison voltage inputs, which is used to make corresponding output actions according to the levels of the comparison voltages U3 and U5. The output terminal of the comparison circuit 2 is connected to the differentiating circuit. The differentiating circuit converts the high-level square wave signal into a gradually changing signal that decays according to an exponential law. When the grid voltage value is greater than the set value (the comparison voltage U3 is greater than the holding reference voltage), the output terminal of the comparison circuit 1 outputs a high level, and the switch circuit 2 is turned on. When the gradually changing signal output by the differentiating circuit is lower than the minimum turn-on voltage of the switch circuit 2, the switch circuit 2 is turned off, disconnecting the power supply of the starting holding coil. When the grid voltage value is less than the set value (the comparison voltage U5 is less than the restart reference voltage), the output terminal of the comparison circuit 2 outputs a low level, and the starting holding coil is de-energized.

[0023] Figure 2 A specific implementation circuit is shown, which uses two low-power time-base circuits 7555 to control the holding coil and the starting holding coil respectively, and has the advantages of simple circuit structure and low power consumption.

[0024] As Figure 2 shown, the rectifier circuit includes diodes D1~D4, whose function is to convert the power input voltage Ui into the DC voltage U1.

[0025] The power supply circuit includes resistor R1, resistor R2, capacitor C1, capacitor C2, zener diode DW1, and MOS transistor VT1. One end of resistor R1 and resistor R2 is connected to U1. The other end of resistor R1 is connected to the gate of MOS transistor VT1, one end of capacitor C1, and the cathode of zener diode DW1. The other end of resistor R2 is connected to the drain of MOS transistor VT1. The source of the MOS transistor is U2. One end of capacitor C2 is connected to U2. The other end of capacitor C1, the other end of capacitor C2, and the anode of zener diode DW1 are connected to ground. The function of the power supply circuit is to reduce the DC voltage U1 to the low-voltage working power supply U2.

[0026] The voltage sampling circuit includes resistor R3, resistor R4, resistor R5, resistor R6, and capacitor C3. Resistors R3 to R6 are connected in series in turn. The other end of resistor R3 is connected to U1. One end of capacitor C3 is connected to the common connection end of resistor R3 and R4. The other end of capacitor C3 and the other end of resistor R6 are connected to ground. The voltage sampling circuit obtains three voltages U3, U4, and U5 through resistor voltage division. The common connection end of resistor R3 and R4 is voltage U3. The common connection end of resistor R4 and R5 is voltage U4. The common connection end of resistor R5 and R6 is voltage U5.

[0027] Comparator circuit 1 includes resistor R7, resistor R8, capacitor C4, MOS transistor VT2, and integrated circuit IC1. Integrated circuit IC1 is a timer circuit 7555. U2 is connected to pins 4 and 8 of integrated circuit IC1. U3 is connected to pin 6 of integrated circuit IC1. U4 is connected to pin 2 of integrated circuit IC1. One end of resistor R7 is connected to U2, and the other end is connected to the drain of MOS transistor VT2. One end of resistor R8 is connected to pin 3 of integrated circuit IC1 and the gate of MOS transistor VT2. One end of capacitor C4 is connected to pin 5 of integrated circuit IC1. The other end of resistor R8, the other end of capacitor C4, the source of MOS transistor VT2, and pin 1 of integrated circuit IC1 are all connected to ground.

[0028] Comparator circuit 2 includes resistor R9, resistor R10, capacitor C5, MOS transistor VT3, and integrated circuit IC2. Integrated circuit IC2 is a timer circuit 7555. U2 is connected to pins 4 and 8 of integrated circuit IC2. U3 is connected to pin 6 of integrated circuit IC2. U5 is connected to pin 2 of integrated circuit IC2. One end of resistor R9 is connected to U2, and the other end is connected to the drain of MOS transistor VT3. One end of resistor R10 is connected to pin 3 of integrated circuit IC2 and the gate of MOS transistor VT3. One end of capacitor C5 is connected to pin 5 of integrated circuit IC2. The other end of resistor R8, the other end of capacitor C5, the source of MOS transistor VT3, and pin 1 of integrated circuit IC2 are all connected to ground.

[0029] The differentiating circuit includes a capacitor C6 and a resistor R11 connected in series. The other end of the capacitor C6 is connected to the drain of the MOS transistor VT3, and the other end of the resistor R11 is grounded. The function of the differentiating circuit is to convert the input high-level signal into a gradually changing signal that decays according to an exponential law.

[0030] The switching circuit 1 includes a MOS transistor VT5 and a diode D5. The diode D5 is connected in parallel with the maintaining pull-in coil. The negative electrode of the diode D5 is connected to the DC voltage U1, the positive electrode of the diode D5 is connected to the drain of the MOS transistor VT5, the gate of the MOS transistor VT5 is connected to the output terminal of the comparison circuit 1, and the source of the MOS transistor VT5 is grounded. The function of the switching circuit 1 is to control the energization and de-energization of the maintaining pull-in coil.

[0031] The switching circuit 2 includes a MOS transistor VT4 and a diode D6. The diode D6 is connected in parallel with the starting pull-in coil. The negative electrode of the diode D6 is connected to the DC voltage U1, the positive electrode of the diode D6 is connected to the drain of the MOS transistor VT4, the gate of the MOS transistor VT4 is connected to the output terminal of the differentiating circuit, and the source of the MOS transistor VT4 is grounded. The function of the switching circuit 2 is to control the energization and de-energization of the starting pull-in coil.

[0032] Figure 2 The working process and principle of the shown circuit are specifically as follows:

[0033] The power supply voltage Ui is rectified by the rectifying circuit to become the DC voltage U1. The DC voltage U1 is stepped down by the power supply circuit to obtain the low-voltage DC voltage U2, which is used to provide the working power supply for IC1 and IC2 and also serves as the reference voltage reference.

[0034] (1) After the DC voltage U1 is divided by the resistors R3, R4, R5, and R6, the sampling voltages U3, U4, and U5 are obtained, where U3 > U4 > U5. According to the characteristics of the integrated circuit 7555, when the sampling voltage U3 is greater than When U2 is present, the voltage at pin 3 of integrated circuits IC1 and IC2 changes from high level to low voltage. MOS transistors VT2 and VT3 have no control high level and turn off. At this time, the low-voltage DC voltage U2 outputs a control voltage Uo1 through resistor R7 to make the control electrode of MOS transistor VT5 energized. VT5 conducts, maintaining the energization of the suction coil to generate electromagnetic suction. Diode D5 provides freewheeling, keeping the coil continuously energized. At the same time, the low-voltage DC voltage U2 outputs a control voltage Uo2 through resistor R9 to charge capacitor C6 in the differentiating circuit, outputting a control voltage Uo3 to make the control electrode of MOS transistor VT4 energized. VT4 conducts, starting the energization of the suction coil to generate electromagnetic suction. Diode D6 provides freewheeling, keeping the coil continuously energized. The electromagnet attracts under the combined action of the electromagnetic suction generated by the maintaining suction coil and the starting suction coil. After C6 finishes charging, the control electrode of VT4 loses power and VT4 turns off. The starting suction coil loses power and stops working. At this time, the electromagnet only maintains the attracted state under the action of the electromagnetic suction generated by the maintaining suction coil. Since the resistance value of the maintaining suction coil is relatively large, it is in a low-power consumption working state, generates less heat, and can work for a long time without overheating damage.

[0035] (2) When the power supply voltage Ui drops, the sampling voltages U3, U4, and U5 drop accordingly. When the sampling voltage U5 drops below U2, the output of pin 3 of IC2 changes from low level to high level. MOS transistor VT3 conducts, and the capacitor C6 in the differentiating circuit discharges, preparing for the next charging process. When the sampling voltage U4 is lower than U2, the output of pin 3 of IC1 changes from low level to high level. MOS transistor VT2 conducts, and at the same time outputs a control voltage Uo1 to make the control electrode of MOS transistor VT5 turn to low level. MOS transistor VT5 turns off, and the maintaining suction coil loses power, and the electromagnet releases.

[0036] (3) When the sampling voltage Ui has a short-term drop as shown in Figure 3 and the drop time is short, at this time the electromagnet may not be able to maintain and release. The drop of the power supply voltage Ui causes the sampling voltages U4 and U5 to drop accordingly. Since the sampling voltage U4 > U5, when the sampling voltages U4 and U5 drop to , at this time, as described above, the output level of pin 3 of IC2 flips, and the output level of pin 3 of IC1 does not flip, which has no impact on the states of switch circuit 1 and switch circuit 2. At this time, when the power supply voltage Ui rises and the sampling voltage U3 rises above U2, the voltage at pin 3 of IC2 changes from high level to low level. As described in (1) above, the starting suction coil will be energized to start the attracting process of the electromagnet. In this way, it can be prevented that when there is a short-term voltage drop in the power supply circuit of the under-voltage release, the electromagnet can still re-attract after the voltage recovers during the accidental release process due to power loss and will not be completely released. Since the sampling U5

Claims

1. An under-voltage release, characterized in that, It includes a double-coil electromagnet having a holding suction coil and a starting suction coil, a first switch circuit and a second switch circuit respectively used to control the on / off of the holding suction coil and the starting suction coil, and a control circuit used to control the first switch circuit and the second switch circuit according to the grid voltage; the control circuit includes: a rectifying circuit, a power supply circuit, a voltage sampling circuit, a first comparison circuit, a second comparison circuit, and a differentiating circuit; the rectifying circuit converts the grid voltage into a DC voltage U1 and uses it as the working power supply voltage of the holding suction coil and the starting suction coil; after the DC voltage U1 is step-down filtered by the power supply circuit, it becomes a low-voltage DC voltage U2 and is used as the working power supply of the first comparison circuit, the second comparison circuit, the first switch circuit, and the second switch circuit; the DC voltage U1 is divided by the voltage sampling circuit to obtain comparison voltages U3, U4, and U5, and U3>U4>U5; both the first comparison circuit and the second comparison circuit are hysteresis comparators with two-way comparison voltage inputs, the input of the first comparison circuit is the comparison voltages U3 and U4, and the input of the second comparison circuit is the comparison voltages U3 and U5; when the comparison voltage U3 is greater than the suction reference voltage, the first comparison circuit outputs a conduction control signal to the first switch circuit, and the second comparison circuit outputs a conduction control signal to the second switch circuit through the differentiating circuit and converts the conduction control signal into a turn-off control signal after a preset time under the action of the differentiating circuit; when the comparison voltage U4 is less than the release reference voltage, the first comparison circuit outputs a turn-off control signal to the first switch circuit; when the comparison voltage U5 is less than the restart reference voltage, the second comparison circuit outputs a turn-off control signal to the second switch circuit through the differentiating circuit.

2. The under-voltage release as claimed in claim 1, wherein, The power supply circuit includes a first resistor, a second resistor, a first MOS transistor, a first capacitor, a second capacitor, and a first voltage regulator diode; the output terminal of the rectifying circuit is connected to one end of the first resistor, one end of the second resistor, the input terminal of the voltage sampling circuit, and the connection terminal of the holding suction circuit and the starting suction circuit; the other end of the first resistor is connected to the gate of the first MOS transistor, one end of the first capacitor, and the negative electrode of the first voltage regulator diode; the other end of the second resistor is connected to the drain of the first MOS transistor; the source of the first MOS transistor is used as the output terminal of the power supply circuit and is connected to the first comparison circuit and the second comparison circuit; the other end of the first capacitor and the positive electrode of the first voltage regulator diode are connected to the ground of the rectifier bridge; one end of the second capacitor is connected to the source of the first MOS transistor, and the other end of the second capacitor is connected to the ground.

3. The under-voltage release as claimed in claim 1, wherein, The voltage sampling circuit includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a third capacitor; after the third resistor, the fourth resistor, the fifth resistor, and the sixth resistor are connected in series in sequence, one end is connected to the DC voltage U1 and the other end is grounded; one end of the third capacitor is connected to the common connection terminal of the third resistor and the fourth resistor, and the other end of the third capacitor is grounded; the common connection terminal of the third resistor and the fourth resistor outputs the comparison voltage U3; the common connection terminal of the fourth resistor and the fifth resistor outputs the comparison voltage U4; the common connection terminal of the fifth resistor and the sixth resistor outputs the comparison voltage U5.

4. The under-voltage release as claimed in claim 1, wherein The first comparison circuit includes a seventh resistor, an eighth resistor, a fourth capacitor, a second MOS transistor, and a first 555 timer circuit; the low-voltage DC voltage U2 is connected to pins 4 and 8 of the first 555 timer circuit; the comparison voltage U3 is connected to pin 6 of the first 555 timer circuit; the comparison voltage U4 is connected to pin 2 of the first 555 timer circuit; one end of the seventh resistor is connected to the low-voltage DC voltage U2, and the other end is connected to the drain of the second MOS transistor; one end of the eighth resistor is connected to pin 3 of the first 555 timer circuit and the gate of the second MOS transistor; one end of the fourth capacitor is connected to pin 5 of the first 555 timer circuit; the other end of the eighth resistor, the other end of the fourth capacitor, the source of the second MOS transistor, and pin 1 of the first 555 timer circuit are all connected to the ground; The second comparison circuit includes a ninth resistor, a tenth resistor, a fifth capacitor, a third MOS transistor, and a second 555 timer circuit; the low-voltage DC voltage U2 is connected to pins 4 and 8 of the second 555 timer circuit; the comparison voltage U3 is connected to pin 6 of the second 555 timer circuit; the comparison voltage U5 is connected to pin 2 of the second 555 timer circuit; one end of the ninth resistor is connected to the low-voltage DC voltage U2, and the other end is connected to the drain of the third MOS transistor; one end of the tenth resistor is connected to pin 3 of the first 555 timer circuit and the gate of the third MOS transistor; one end of the fifth capacitor is connected to pin 5 of the first 555 timer circuit; the other end of the tenth resistor, the other end of the fifth capacitor, the source of the third MOS transistor, and pin 1 of the second 555 timer circuit are all connected to the ground.

5. The under-voltage release according to claim 1, characterized in that, The first switch circuit includes a fifth MOS transistor and a fifth diode. The fifth diode is connected in parallel with the maintenance pull-in coil. The negative electrode of the fifth diode is connected to the DC voltage U1, the positive electrode of the fifth diode is connected to the drain of the fifth MOS transistor, the gate of the fifth MOS transistor is connected to the output end of the first comparison circuit, and the source of the fifth MOS transistor is grounded.

6. The under-voltage release according to claim 1, characterized in that, The second switch circuit includes a fourth MOS transistor and a sixth diode. The sixth diode is connected in parallel with the start pull-in coil. The negative electrode of the sixth diode is connected to the DC voltage U1, the positive electrode of the sixth diode is connected to the drain of the fourth MOS transistor, the gate of the fourth MOS transistor is connected to the output end of the differentiating circuit, and the source of the fourth MOS transistor is grounded.

7. The under-voltage release according to claim 1, wherein The differentiating circuit includes a sixth capacitor and an eleventh resistor connected in series. The other end of the sixth capacitor is connected to the output end of the second comparison circuit, the other end of the eleventh resistor is grounded, and the common connection end of the sixth capacitor and the eleventh resistor is the output end of the differentiating circuit.

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