Control circuit of double-coil electromagnet and under-voltage release

Abstract

The utility model discloses a control circuit of a double-coil electromagnet. The special timing circuit is arranged in the control circuit of the double-coil electromagnet, the control signal with the fixed time length can be output under the excitation of the control signal so as to control the conduction time length of the electronic switch of the starting coil, and due to the fact that the rising edge and the falling edge of the control signal are steep, the control signal can be switched on. The time of the electronic switch from conduction to cut-off is greatly shortened, so that the core temperature of the electronic switch from conduction to cut-off is greatly reduced, the working reliability of the MOS tube and the bipolar transistor is improved, the time length of high level output by the special timing circuit is relatively stable, and the reliability of the electronic switch is improved. And the power-on time of the starting coil can be accurately controlled. The utility model also discloses an under-voltage release. Compared with the prior art, the power-on time of the starting coil can be accurately controlled, the unnecessary coil starting power consumption is reduced, the power supply burden is reduced, and the circuit reliability is improved.

Description

Technical Field

[0001] The utility model relates to a control circuit of a double-coil electromagnet. Background Art

[0002] Most of the electric controls of existing switchgear use electromagnet devices to perform actions, such as electric closing and opening, various trippers, remote reset, etc.; in order to obtain greater starting suction force and smaller holding power consumption, current electromagnets generally adopt a double-coil structure, which is divided into a starting coil and a holding coil. When the electromagnet is attracted, the starting coil is energized to make the electromagnet attracted. After attraction, the holding coil is energized, and the current of the starting coil is turned off, so that the holding coil is energized alone, and the electromagnet is in a maintained attracted state. Generally, the attracting coil is coarse and small, and the holding coil is thin and large, so as to achieve the function of large current attraction and small current holding.

[0003] The on and off of the start coil is usually controlled by an electronic switch circuit, and a differential circuit can be set at the control end of the electronic switch. The differential circuit has the function of converting a high-level square wave signal into a gradual signal that decreases exponentially, and can realize the function of the electronic switch turning off automatically after being turned on for a period of time. In order to ensure that the electromagnet is reliably attracted, generally, the conduction time of the electronic switch circuit that controls the start coil is greater than 50ms, resulting in a relatively slow decrease in the gradual signal output by the differential circuit, so that the start coil has sufficient power-on time.

[0004] The most commonly used electronic switches are MOS tubes and bipolar transistors. In the process of changing from the on state to the off state, these two electronic switches must first pass through the amplification state. When the MOS tube and the bipolar transistor work in the amplification state, under the control of the gradual signal, their on-resistance gradually increases from the on-resistance value to the off-resistance value. The slowly decreasing control signal will make the MOS tube and the bipolar transistor work in the amplification state for a longer time, and the on-resistance value of the MOS tube and the bipolar transistor will change from small to large. Under the action of the coil current, the MOS tube and the bipolar transistor will generate greater power consumption, causing the core temperature of the MOS tube and the bipolar transistor to rise sharply, especially for the coil that controls low voltage and high current. Under the action of large current, the core temperature of the MOS tube and the bipolar transistor will exceed the maximum operating temperature, and the MOS tube and the bipolar transistor will be overheated and damaged. In addition, the on-time of the MOS tube and the bipolar transistor is determined by comparing the gradient signal with the threshold voltage or threshold current of the MOS tube and the bipolar transistor. The discreteness of the threshold voltage or threshold current of different models of MOS tubes and bipolar transistors or different batches of the same model is relatively large, resulting in a large discreteness of the on-time of the MOS tube and the bipolar transistor. It is necessary to lengthen the on-time of the MOS tube and the bipolar transistor to ensure the minimum power-on time of the starting coil, thereby further lengthening the time for the MOS tube and the bipolar transistor to change from on to off, aggravating the heating of the core of the MOS tube and the bipolar transistor, and reducing the working reliability of the MOS tube and the bipolar transistor. This phenomenon is particularly common under high-temperature working conditions. Utility Model Content

[0005] The purpose of the utility model is to overcome the technical problems of high power consumption and poor reliability caused by the use of electronic switches to control the starting coil in the prior art, and to provide a control circuit for a double-coil electromagnet that can accurately control the power-on time of the starting coil, reduce unnecessary coil starting power consumption, reduce the power supply burden, and improve circuit reliability.

[0006] The utility model specifically adopts the following technical solutions to solve the above technical problems:

[0007] A control circuit for a double-coil electromagnet, the double-coil electromagnet comprising a holding coil, a starting coil, and a first switch circuit and a second switch circuit based on an electronic switch for respectively controlling the on and off of the holding coil and the starting coil; the control circuit is used to control the first switch circuit and the second switch circuit according to a grid voltage, and comprises:

[0008] A rectifier circuit, used for converting the grid voltage into a DC voltage U1 to serve as a working power supply voltage for the holding coil and the starting coil;

[0009] A power supply circuit, used to convert the DC voltage U1 into a low-voltage DC voltage U2 after voltage reduction and filtering;

[0010] A voltage sampling circuit is used to generate comparison voltages U3 and U4 after dividing the DC voltage U1, and U3>U4;

[0011] A comparison circuit, used to use the DC voltage U2 as a working power supply, to compare the input comparison voltages U3 and U4 to generate a control level Uo1;

[0012] An inverting circuit, used for inverting a control level Uo1 to generate a control signal Uo4 for the first switch circuit;

[0013] Differentiator circuit, used for converting another control level Uo1 into control signal Uo3;

[0014] The timing circuit is used to generate a control signal Uo5 for the second switch circuit under the stimulation of the control signal Uo3. The timing circuit is a monostable circuit that can output a high-level control signal of a fixed time length after being triggered by the stimulation signal.

[0015] Preferably, the voltage sampling circuit includes a resistor R3, a resistor R4, a resistor R5, a resistor R6, a diode D6 and a capacitor C2; the resistors R3 and R4 are connected in series, the resistors R5 and R6 are connected in series, the anode of the diode D6 is connected to the common end of the resistors R3 and R4, the other end of the resistor R3 is connected to the DC voltage U1, and the other end of the resistor R4 is grounded; one end of the capacitor C2 is connected to the cathode of the diode and one end of the resistor R5, and the other end of the capacitor C2 and the other end of the resistor R6 are grounded; the common connection end of the resistor R5 and the cathode of the diode D6 is the output end of the comparison voltage U3, and the common connection end of the resistors R5 and R6 is the output end of the comparison voltage U4.

[0016] Preferably, the comparison circuit includes a capacitor C5 and an integrated circuit IC1, the integrated circuit IC1 is a timing circuit 7555; the DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC1; the comparison voltage U3 is connected to pin 6 of the integrated circuit IC1; the comparison voltage U4 is connected to pin 2 of the integrated circuit IC1; one end of the capacitor C5 is connected to pin 5 of the integrated circuit IC1; the other end of the capacitor C5 and pin 1 of the integrated circuit IC1 are commonly connected to ground.

[0017] Preferably, the inverting circuit includes a resistor R8 and a MOS tube VT5; one end of the resistor R8 is connected to the DC voltage U2, and the other end is connected to the drain of the MOS tube VT5; the control level Uo1 is connected to the gate of the MOS tube VT5; the source of the MOS tube VT5 is grounded; and the drain of the MOS tube VT5 is the output end of the control signal Uo4.

[0018] Preferably, the differential circuit includes a capacitor C6 and a resistor R7, one end of the capacitor C6 is connected to the control level Uo1, the other end of the capacitor C6 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the DC voltage U2; the common connection end of the capacitor C6 and the resistor R7 is the output end of the control signal Uo3.

[0019] Preferably, the timing circuit includes a resistor R12, a capacitor C3, a capacitor C4, and an integrated circuit IC2, wherein the integrated circuit IC2 is a timing circuit 7555; a DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC2; one end of the resistor R12, one end of the capacitor C3, and pins 7 and 6 of the integrated circuit IC2 are connected together; the other end of the resistor R12 is connected to the DC voltage U2, and one end of the capacitor C4 is connected to pin 5 of the integrated circuit IC2; the other end of the capacitor C3, the other end of the capacitor C4, and pin 1 of the integrated circuit IC2 are connected to ground; pin 2 of the integrated circuit IC2 is connected to the control signal Uo3; and pin 3 of the integrated circuit IC2 is the output end of the control signal Uo5.

[0020] Preferably, the first switch circuit and the second switch circuit have the same structure, and are both composed of an electronic switch and a diode; the diode is connected in parallel with the controlled coil, the cathode of the diode is connected to the DC voltage U1, the anode of the diode is connected to the input end of the electronic switch, the control end of the electronic switch is connected to the corresponding control signal, and the output end of the electronic switch is grounded.

[0021] Preferably, the electronic switch is a MOS tube or a bipolar transistor.

[0022] Based on the same inventive concept, the following technical solutions can also be obtained:

[0023] An undervoltage release includes a double-coil electromagnet and a control circuit for the double-coil electromagnet, wherein the double-coil electromagnet includes a holding coil, a starting coil, and a first switch circuit and a second switch circuit for respectively controlling the on and off of the holding coil and the starting coil; the control circuit is the control circuit described in any of the above technical solutions.

[0024] Compared with the prior art, the technical solution of the utility model has the following beneficial effects:

[0025] In order to reduce the core temperature of the MOS tube and the bipolar transistor during the process of changing from conduction to cutoff, and to ensure the power-on time of the start coil, the utility model sets a special timing circuit for the above situation. The timing circuit can output a control signal of a fixed time length under the stimulation of the control signal to control the conduction time length of the electronic switch of the start coil. Since the rising edge and the falling edge of the control signal are both relatively steep, the time for the MOS tube and the bipolar transistor to change from conduction to cutoff is greatly shortened, thereby greatly reducing the core temperature of the MOS tube and the bipolar transistor during the process of changing from conduction to cutoff, improving the working reliability of the MOS tube and the bipolar transistor, and the high level time length output by the special timing circuit is relatively stable, which can accurately control the power-on time of the start coil, reduce unnecessary coil startup power consumption, and reduce the power supply burden. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the structural principle block diagram of the utility model;

[0027] Figure 2 It is a specific implementation circuit of the utility model;

[0028] Figure 3 This is a schematic diagram of the control process principle of the utility model. DETAILED DESCRIPTION

[0029] In order to overcome the technical problems of high power consumption and poor reliability caused by the use of electronic switches to control the starting coil in the prior art, the solution of the utility model is to set a dedicated timing circuit in the control circuit of the double-coil electromagnet. The timing circuit can output a control signal of a fixed time length under the stimulation of the control signal to control the on-time length of the electronic switch of the starting coil. Since the rising edge and the falling edge of the control signal are relatively steep, the time for the MOS tube and the bipolar transistor to change from on to off is greatly shortened, thereby greatly reducing the core temperature of the MOS tube and the bipolar transistor in the process of changing from on to off, improving the working reliability of the MOS tube and the bipolar transistor, and the high level time length output by the dedicated timing circuit is relatively stable, which can accurately control the power-on time of the starting coil, reduce unnecessary coil startup power consumption, and reduce the power supply burden.

[0030] In order to facilitate public understanding, the technical solution of the utility model is described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

[0031] This embodiment takes the double-coil electromagnet control in the undervoltage release as an example for explanation. Figure 1As shown, the undervoltage release includes a double-coil electromagnet and a control circuit thereof, wherein the double-coil electromagnet includes a holding coil, a starting coil, and a first switch circuit and a second switch circuit based on an electronic switch for respectively controlling the on and off of the holding coil and the starting coil; the control circuit is used to control the first switch circuit and the second switch circuit according to the grid voltage, and includes:

[0032] A rectifier circuit, used for converting the grid voltage Ui into a DC voltage U1 as a working power supply voltage for the holding coil and the starting coil;

[0033] A power supply circuit, used to convert the DC voltage U1 into a low-voltage DC voltage U2 after voltage reduction and filtering;

[0034] A voltage sampling circuit is used to generate comparison voltages U3 and U4 after dividing the DC voltage U1, and U3>U4;

[0035] A comparison circuit, used to use the DC voltage U2 as a working power supply, to compare the input comparison voltages U3 and U4 to generate a control level Uo1;

[0036] An inverting circuit, used for inverting a control level Uo1 to generate a control signal Uo4 for the first switch circuit;

[0037] Differentiator circuit, used for converting another control level Uo1 into control signal Uo3;

[0038] The timing circuit is used to generate a control signal Uo5 for the second switch circuit under the stimulation of the control signal Uo3. The timing circuit is a monostable circuit that can output a high-level control signal of a fixed time length after being triggered by the stimulation signal.

[0039] like Figure 1As shown, the power supply voltage Ui is rectified by the rectifier circuit to become a DC voltage U1. The DC voltage U1 is the working power supply voltage for the holding coil and the starting coil. The DC voltage U1 is processed by the power supply circuit to become a low-voltage DC voltage U2 as the working power supply for the comparison circuit, the inverter circuit and the timing circuit. U2 is also used as a reference voltage. The DC voltage U1 is divided by the sampling circuit to obtain comparison voltages U3 and U4, and U3>U4. The comparison circuit is a hysteresis comparator, which is used to make corresponding output actions according to the high and low comparison voltages U3 and U4. The control signal Uo1 output from the output end of the comparison circuit is inverted by the inverter circuit and then output as a control signal Uo4 to control the opening and closing of the first switch circuit, thereby controlling the power on or off of the holding coil; the other path of the control signal Uo1 output by the comparison circuit is connected to the differential circuit, and is converted by the differential circuit into a short-time low-level pulse control signal Uo3. If the grid voltage value is greater than the set value (the comparison voltage U3 is greater than the pull-in reference value), the control signal Uo1 output from the output end of the comparison circuit is output as a control signal Uo4 to control the opening and closing of the first switch circuit, thereby controlling the power on or off of the holding coil; the control signal Uo1 output by the comparison circuit is connected to the differential circuit, and is converted by the differential circuit into a short-time low-level pulse control signal Uo3. If the grid voltage value is greater than the set value (the comparison voltage U3 is greater than the pull-in reference value), the control signal Uo1 output from the comparison circuit is output as a control signal Uo4 to control the opening and closing of the first switch circuit, thereby controlling the power on or off of the holding coil. Voltage), the control signal Uo1 outputted from the output end of the comparison circuit is low level, and after the inverting circuit, the high level control signal Uo4 is outputted to control the first switch circuit to be turned on, and the control coil is energized to work. At the same time, the control signal Uo1 outputs the control signal Uo3 through the differential circuit to excite the timing circuit to output the high level control signal Uo5, and the starting coil is energized. The undervoltage release is attracted when the starting coil and the maintaining coil are energized at the same time. The timing circuit is a monostable circuit. After maintaining the fixed time length t1, the control signal Uo5 becomes low level, and the second switch circuit is controlled to be closed, thereby disconnecting the power supply of the starting coil. At this time, the maintaining coil is energized alone, and the undervoltage release remains in the attracted state; if the grid voltage value is less than the set value (the comparison voltage U4 is less than the release reference voltage), the control signal Uo1 outputted from the output end of the comparison circuit is high level, and the control signal Uo3 becomes low level after the inverting circuit to control the first switch circuit to be turned off, and the control coil is de-energized, and the undervoltage release is released.

[0040] Each functional circuit in the above control circuit can be implemented by using a variety of different existing technologies and can be designed according to actual needs. Figure 2 A specific implementation circuit is shown, which uses two low-power time base circuits 7555 to form a comparison circuit and a timing circuit respectively, and has the advantages of simple circuit structure, low power consumption, and stable electromagnet attraction.

[0041] like Figure 2 As shown, the rectifier circuit in this embodiment includes diodes D1-D4, which are used to rectify the power input voltage Ui into a DC voltage U1.

[0042] The voltage sampling circuit in this embodiment includes a resistor R3, a resistor R4, a resistor R5, a resistor R6, a diode D6 and a capacitor C2; the resistors R3 and R4 are connected in series, the resistors R5 and R6 are connected in series, the anode of the diode D6 is connected to the common end of the resistors R3 and R4, the other end of the resistor R3 is connected to the DC voltage U1, and the other end of the resistor R4 is grounded; one end of the capacitor C2 is connected to the cathode of the diode and one end of the resistor R5, and the other end of the capacitor C2 and the other end of the resistor R6 are grounded; the common connection end of the resistor R5 and the cathode of the diode D6 is the output end of the comparison voltage U3, and the common connection end of the resistors R5 and R6 is the output end of the comparison voltage U4.

[0043] The comparison circuit in this embodiment includes a capacitor C5 and an integrated circuit IC1, wherein the integrated circuit IC1 is a time base circuit 7555; a DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC1; a comparison voltage U3 is connected to pin 6 of the integrated circuit IC1; a comparison voltage U4 is connected to pin 2 of the integrated circuit IC1; one end of the capacitor C5 is connected to pin 5 of the integrated circuit IC1; the other end of the capacitor C5 and pin 1 of the integrated circuit IC1 are commonly connected to ground.

[0044] The inverting circuit in this embodiment includes a resistor R8 and a MOS tube VT5; one end of the resistor R8 is connected to the DC voltage U2, and the other end is connected to the drain of the MOS tube VT5; the control level Uo1 is connected to the gate of the MOS tube VT5; the source of the MOS tube VT5 is grounded; and the drain of the MOS tube VT5 is the output end of the control signal Uo4.

[0045] The differential circuit in this embodiment includes a capacitor C6 and a resistor R7, one end of the capacitor C6 is connected to the control level Uo1, the other end of the capacitor C6 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the DC voltage U2; the common connection end of the capacitor C6 and the resistor R7 is the output end of the control signal Uo3.

[0046] The timing circuit in this embodiment includes a resistor R12, a capacitor C3, a capacitor C4, and an integrated circuit IC2, wherein the integrated circuit IC2 is a timing circuit 7555; a DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC2; one end of the resistor R12, one end of the capacitor C3, and pins 7 and 6 of the integrated circuit IC2 are commonly connected; the other end of the resistor R12 is connected to the DC voltage U2, and one end of the capacitor C4 is connected to pin 5 of the integrated circuit IC2; the other end of the capacitor C3, the other end of the capacitor C4, and pin 1 of the integrated circuit IC2 are commonly connected to ground; pin 2 of the integrated circuit IC2 is connected to the control signal Uo3; and pin 3 of the integrated circuit IC2 is the output end of the control signal Uo5.

[0047] The first switch circuit in this embodiment includes a MOS tube VT3 and a diode D9. The diode D9 is connected in parallel with the maintenance coil L1. The cathode of the diode D9 is connected to the DC voltage U1, the anode of the diode D9 is connected to the drain of the MOS tube VT3, the gate of the MOS tube VT3 is connected to the control signal Uo4 output by the inverter circuit, and the source of the MOS tube VT3 is grounded. The function of the first switch circuit is to control the power on and off of the maintenance coil L1.

[0048] The second switch circuit in this embodiment includes a MOS tube VT4 and a diode D11. The diode D11 is connected in parallel with the starting coil L2. The cathode of the diode D11 is connected to the DC voltage U1, the anode of the diode D11 is connected to the drain of the MOS tube VT4, the gate of the MOS tube VT4 is connected to the control signal Uo5 output by the timing circuit, and the source of the MOS tube VT4 is grounded. The function of the second switch circuit is to control the power on and off of the starting coil L2.

[0049] Figure 2 The working process and principle of the circuit shown are as follows Figure 3 As shown, the details are as follows:

[0050] The power supply voltage Ui is rectified by the rectifier circuit and becomes a DC voltage U1. The DC voltage U1 is stepped down by the power supply circuit to obtain a low-voltage DC voltage U2, which is used to provide the working power supply for IC1 and IC2 and is also used as a reference voltage.

[0051] (1) After the DC voltage U1 is divided by resistors R3 and R4, it is smoothed and filtered by diode D5 and capacitor C2 to obtain the sampling voltage U3. The sampling voltage U3 is further divided by resistors R5 and R6 to obtain the sampling voltage U4, where U3>U4. According to the characteristics of the integrated circuit 7555, when the sampling voltage U3 is greater than , the control signal Uo1 output from the 3rd pin of the integrated circuit IC1 changes from a high level to a low level, and one path of the control signal Uo1 makes the MOS tube VT5 of the inverting circuit cut off without a control high level. At this time, the low-voltage DC voltage U2 outputs the control signal Uo4 through the resistor R8 to control the opening of the first switch circuit, thereby controlling the power supply of the maintaining coil to generate electromagnetic attraction; the other path of the control signal Uo1 is connected to the differential circuit, and the control signal Uo1 changes from a high level to a low level, so that the capacitor C6 in the differential circuit is charged under the action of the voltage U2 and the resistor R7. Since the voltage across the capacitor C6 cannot suddenly change, a short-term low-level and gradually rising control signal Uo3 is output. The control signal Uo3 controls the voltage of the 2nd pin of the integrated circuit IC2 of the timing circuit to be less than According to the characteristics of the integrated circuit 7555, the control signal Uo4 output from the 3rd pin of the integrated circuit IC2 changes from a low level to a high level, so that the control pole of the MOS tube VT4 is energized, VT4 is turned on, the starting coil is energized, and the electromagnet is attracted under the combined action of the electromagnetic attraction generated by the holding coil and the starting coil. At this time, according to the characteristics of the integrated circuit 7555, the 7th pin and the 1st pin of the integrated circuit IC2 change from the on state to the off state, and the capacitor C3 is charged under the action of the voltage U2 and the resistor R12. When the voltage of the capacitor C3 is charged to a value greater than When the control signal Uo4 outputted from the 3rd pin of the integrated circuit IC2 changes from high level to low level, the VT4 control pole loses power, VT4 is cut off, the starting coil loses power and stops working, and the electromagnet remains in the attracted state only under the action of the electromagnetic attraction generated by the maintaining coil. At this time, according to the characteristics of the integrated circuit 7555, the 7th pin and the 1st pin of the integrated circuit IC2 change from cut-off to conduction state, and the capacitor C3 discharges through the 7th pin of the integrated circuit IC2, and restores the original voltage-free state.

[0052] (2) The power supply voltage Ui decreases, causing the sampling voltages U3 and U4 to decrease accordingly. When the sampling voltage U4 drops below When the MOS tube VT5 of the inverting circuit is turned on, the output control signal Uo4 turns to a low level, the capacitor C6 of the differential circuit is discharged, and the next charging process is prepared. The output control signal Uo4 turns the gate of the MOS tube VT3 to a low level, the MOS tube VT3 is turned off, the maintenance coil is de-energized, and the electromagnet is released.

Claims

1. A control circuit for a double-coil electromagnet, the double-coil electromagnet comprising a holding coil, a starting coil, and a first switch circuit and a second switch circuit based on an electronic switch for respectively controlling the on and off of the holding coil and the starting coil; characterized in that: The control circuit is used to control the first switch circuit and the second switch circuit according to the grid voltage, and includes: A rectifier circuit, used for converting the grid voltage into a DC voltage U1 to serve as a working power supply voltage for the holding coil and the starting coil; A power supply circuit, used to convert the DC voltage U1 into a low-voltage DC voltage U2 after voltage reduction and filtering; A voltage sampling circuit is used to generate comparison voltages U3 and U4 after dividing the DC voltage U1, and U3>U4; A comparison circuit, used to use the DC voltage U2 as a working power supply, to compare the input comparison voltages U3 and U4 to generate a control level Uo1; An inverting circuit, used for inverting a control level Uo1 to generate a control signal Uo4 for the first switch circuit; Differentiator circuit, used for converting another control level Uo1 into control signal Uo3; The timing circuit is used to generate a control signal Uo5 for the second switch circuit under the stimulation of the control signal Uo3. The timing circuit is a monostable circuit that can output a high-level control signal of a fixed time length after being triggered by the stimulation signal.

2. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The voltage sampling circuit includes a resistor R3, a resistor R4, a resistor R5, a resistor R6, a diode D6 and a capacitor C2; the resistors R3 and R4 are connected in series, the resistors R5 and R6 are connected in series, the anode of the diode D6 is connected to the common end of the resistors R3 and R4, the other end of the resistor R3 is connected to the DC voltage U1, and the other end of the resistor R4 is grounded; one end of the capacitor C2 is connected to the cathode of the diode and one end of the resistor R5, and the other end of the capacitor C2 and the other end of the resistor R6 are grounded; the common connection end of the resistor R5 and the cathode of the diode D6 is the output end of the comparison voltage U3, and the common connection end of the resistors R5 and R6 is the output end of the comparison voltage U4.

3. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The comparison circuit includes a capacitor C5 and an integrated circuit IC1, wherein the integrated circuit IC1 is a time base circuit 7555; a DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC1; a comparison voltage U3 is connected to pin 6 of the integrated circuit IC1; and a comparison voltage U4 is connected to pin 2 of the integrated circuit IC1; One end of the capacitor C5 is connected to the 5th pin of the integrated circuit IC1; the other end of the capacitor C5 and the 1st pin of the integrated circuit IC1 are connected to the ground.

4. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The inverting circuit includes a resistor R8 and a MOS tube VT5; one end of the resistor R8 is connected to the DC voltage U2, and the other end is connected to the drain of the MOS tube VT5; the control level Uo1 is connected to the gate of the MOS tube VT5; the source of the MOS tube VT5 is grounded; and the drain of the MOS tube VT5 is the output end of the control signal Uo4.

5. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The differential circuit includes a capacitor C6 and a resistor R7, one end of the capacitor C6 is connected to the control level Uo1, the other end of the capacitor C6 is connected to one end of the resistor R7, and the other end of the resistor R7 is connected to the DC voltage U2; the common connection end of the capacitor C6 and the resistor R7 is the output end of the control signal Uo3.

6. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The timing circuit includes a resistor R12, a capacitor C3, a capacitor C4, and an integrated circuit IC2, wherein the integrated circuit IC2 is a time base circuit 7555; a DC voltage U2 is connected to pins 4 and 8 of the integrated circuit IC2; one end of the resistor R12, one end of the capacitor C3, and pins 7 and 6 of the integrated circuit IC2 are commonly connected; the other end of the resistor R12 is connected to the DC voltage U2, and one end of the capacitor C4 is connected to pin 5 of the integrated circuit IC2; the other end of the capacitor C3, the other end of the capacitor C4, and pin 1 of the integrated circuit IC2 are commonly connected to ground; pin 2 of the integrated circuit IC2 is connected to the control signal Uo3; and pin 3 of the integrated circuit IC2 is the output end of the control signal Uo5.

7. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The first switch circuit has the same structure as the second switch circuit, and both are composed of an electronic switch and a diode; the diode is connected in parallel with the controlled coil, the cathode of the diode is connected to the DC voltage U1, the anode of the diode is connected to the input end of the electronic switch, the control end of the electronic switch is connected to the corresponding control signal, and the output end of the electronic switch is grounded.

8. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The electronic switch is a MOS tube.

9. The control circuit of the double-coil electromagnet as claimed in claim 1, characterized in that: The electronic switch is a bipolar transistor.

10. An undervoltage release, comprising a double-coil electromagnet and a control circuit for the double-coil electromagnet, wherein the double-coil electromagnet comprises a holding coil, a starting coil, and a first switch circuit and a second switch circuit for respectively controlling the on and off of the holding coil and the starting coil; characterized in that: The control circuit is the control circuit according to any one of claims 1 to 9.

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