Double-coil electromagnet control circuit and under-voltage release

Abstract

The utility model discloses a double-coil electromagnet control circuit. The double-coil electromagnet control circuit comprises a first switching circuit, a second switching circuit, a one-way circuit, a rectifying circuit, a power supply circuit, a voltage sampling circuit, an oscillating circuit, a comparison circuit, a differentiating circuit and a third switching circuit. The utility model also discloses an under-voltage release. When the electromagnet needs to be attracted, the control circuit controls the starting coil and the maintaining coil to be in a full-voltage applying state, the starting attraction force of the electromagnet is increased, the starting reliability is improved, when the electromagnet needs to be kept attracted, the current of the starting coil is closed, and the maintaining coil works in a PWM (Pulse-Width Modulation) current state; compared with the prior art, according to the utility model, the attraction reliability of the electromagnet can be effectively improved, the burden of the starting coil is reduced, the circuit is simple and reliable, and the implementation cost is low.

Description

Technical Field

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

[0002] At present, most of the electric control of circuit breakers uses electromagnet devices to perform actions, such as electric closing and opening, various releases, remote reset, etc. In order to obtain greater starting suction and smaller holding power consumption, the existing electromagnets generally adopt a double-coil structure. Generally, the double-coil structure is divided into a series double-coil structure and a parallel double-coil structure. The parallel double-coil structure is more widely used.

[0003] The parallel type double coil is divided into a starting coil and a holding coil. When the electromagnet is attracted, the starting coil is energized to attract the electromagnet. After attraction, the holding coil is energized. At this time, the current of the starting coil is turned off, so that the holding coil is energized alone and the electromagnet is in a state of maintaining attraction. Generally, the attraction coil is thick and few, and the holding coil is thin and many, so as to achieve the function of large current attracting small current and maintaining.

[0004] Generally, the starting coil and the maintaining coil are both applied with full voltage, which brings a contradiction. Since the maintaining coil works in the full voltage application state, when the power supply voltage changes, the current in the maintaining coil also changes accordingly. This causes the current of the maintaining coil to be larger when the power supply voltage is high, the maintaining suction of the electromagnet is larger, the power consumption of the maintaining coil is larger, and the temperature rise is higher. When the power supply voltage is low, the current of the maintaining coil is smaller, the suction of the electromagnet is smaller, and the reliability of the electromagnet maintaining the attraction is reduced. In addition, since the maintaining coil is applied with full voltage, the enameled wire of the maintaining coil has to use a thinner wire diameter and more turns, resulting in a higher wire breakage rate of the enameled wire during coil winding, and there is a higher risk of strain. In addition, the tensile strength of the thinner enameled wire is smaller, and the thermal expansion and contraction caused by temperature changes can easily cause the coil to break, reducing working reliability. Utility Model Content

[0005] The utility model aims to overcome the deficiencies of the prior art and provide a double-coil electromagnet control circuit, which can effectively improve the electromagnet pull-in reliability, reduce the burden of the starting coil, and has a simple and reliable circuit and low implementation cost.

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

[0007] A double-coil electromagnet control circuit, the double-coil electromagnet comprising a holding coil and a starting coil; the double-coil electromagnet control circuit comprising:

[0008] A first switch circuit is connected in series with the holding coil and is used to control the power on and power off of the holding coil;

[0009] A second switch circuit is connected in series with the starting coil and is used to control the power on and power off of the starting coil;

[0010] A unidirectional circuit, two ends of which are respectively connected to the common end of the first switch circuit and the holding coil and the common end of the second switch circuit and the starting coil, so that the conduction of the second switch circuit can simultaneously energize the holding coil and the starting coil, while the conduction of the first switch circuit can only energize the holding coil;

[0011] A rectifier circuit is used to rectify the grid voltage Ui into a DC voltage U1 as the working power supply voltage for the holding coil and the starting coil;

[0012] A power supply circuit, used for performing voltage reduction and filtering on the DC voltage U1 to generate a lower DC voltage U2;

[0013] A voltage sampling circuit is used to divide the DC voltage U1 to generate comparison voltages U3 and U4, and U3>U4;

[0014] An oscillating circuit, used to use the DC voltage U2 as a working power supply to generate an oscillating voltage Uo4 and output it to the control end of the first switch circuit;

[0015] A comparison circuit, used to use the DC voltage U2 as a working power supply and generate a control level Uo1 according to the input comparison voltages U3 and U4;

[0016] A differential circuit, used for converting the control level Uo1 into a conduction control signal Uo3 which is input into the control end of the second switch circuit, and converting the conduction control signal into a shutdown control signal after the preset time;

[0017] The third switch circuit has two ends connected to the control end of the first switch circuit and the control level Uo1 respectively, and is turned on when the control level Uo1 is lower than the oscillation voltage Uo4.

[0018] In one embodiment, the sampling circuit includes resistors R3 to R6, a diode D6 and a capacitor C2; resistors R3 and R4 are connected in series, 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; the common end of the resistors R5 and R6 is the output end of the comparison voltage U4, one end of the capacitor C2 is connected to the cathode of the diode D6 and the other end of the resistor R5 and serves as the output end of the comparison voltage U3, and the other end of the capacitor C2 and the other end of the resistor R6 are grounded.

[0019] In one embodiment, the comparison circuit includes a resistor R8, a capacitor C5, a MOS tube VT5 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 resistor R8 is connected to the DC voltage U2, and the other end is connected to the drain of the MOS tube VT5; pin 3 of the integrated circuit IC1 is connected to the gate of the MOS tube VT5; one end of the capacitor C5 is connected to pin 5 of the integrated circuit IC1; the other end of the capacitor C4, the source of the MOS tube VT5, and pin 1 of the integrated circuit IC1 are grounded together.

[0020] In one embodiment, the oscillation circuit includes a resistor R7, a resistor R9, a resistor R12, a capacitor C3, a capacitor C4, a diode D7, 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 resistor R7, an anode of the diode D7, and pin 7 of the integrated circuit IC2 are connected, the other end of the resistor R12 is connected to the DC voltage U2, the other end of the resistor R7, the cathode of the diode D7, and one end of the capacitor C3 are connected to pins 2 and 6 of the integrated circuit IC2, 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 grounded together, pin 3 of the integrated circuit IC2 is connected to one end of the resistor R9, and the other end of the resistor R9 is the output end of the oscillation voltage Uo4.

[0021] In one embodiment, the differential circuit includes a capacitor C6 and a resistor R11 connected in series, the other end of the capacitor C6 is connected to the control level Uo1, the other end of the resistor R11 is grounded, and the common end of the capacitor C6 and the resistor R11 serves as the output end of the conduction control signal Uo3.

[0022] In one embodiment, the first switch circuit includes a MOS transistor VT3 and a diode D9, the diode D9 is connected in parallel with the maintaining 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 transistor VT3, the gate of the MOS transistor VT3 is connected to one end of the third switch circuit and the oscillation voltage Uo4, and the source of the MOS transistor VT3 is grounded.

[0023] In one embodiment, the second switch circuit includes a MOS tube VT4 and a diode D11, the diode D11 is connected in parallel with the starting coil, 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 output end of the differential circuit, and the source of the MOS tube VT4 is grounded.

[0024] In one embodiment, the third switch circuit includes a diode D8, an anode of the diode D8 is connected to the control end of the first switch circuit, and a cathode of the diode D8 is connected to the control level Uo1 output end of the comparison circuit.

[0025] In one embodiment, the unidirectional circuit includes a diode D10, a cathode of the diode D10 is connected to a common end of the second switch circuit and the start coil, and an anode of the diode D10 is connected to a common end of the first switch circuit and the maintain coil.

[0026] Based on the above double-coil electromagnet control circuit, the following technical solutions can also be obtained:

[0027] An undervoltage release includes a double-coil electromagnet and a double-coil electromagnet control circuit, wherein the double-coil electromagnet includes a holding coil and a starting coil; and the double-coil electromagnet control circuit is the double-coil electromagnet control circuit described in any of the above technical solutions.

[0028] Compared with the prior art, the utility model has the following beneficial effects:

[0029] When the electromagnet needs to be attracted, the control circuit of the utility model controls the starting coil and the maintaining coil to be in a full voltage application state, thereby increasing the starting suction force of the electromagnet and improving the starting reliability. When the electromagnet needs to remain attracted, the starting coil current is turned off, and the maintaining coil is operated in a PWM current state, thereby reducing the power consumption of the maintaining coil, thereby reducing the temperature rise of the coil. In addition, the working PWM current of the maintaining coil can be further automatically adjusted with the size of the grid voltage. When the grid voltage changes, the maintaining suction force of the electromagnet also changes accordingly, thereby improving the anti-vibration reliability of the electromagnet when it remains attracted. The utility model realizes adaptive control completely by means of hardware circuits, and the circuit is simple and reliable, and the implementation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the structural principle block diagram of the utility model;

[0031] Figure 2 It is a specific implementation circuit of the utility model;

[0032] Figure 3 This is a schematic diagram of the control process principle of the utility model. DETAILED DESCRIPTION

[0033] In order to facilitate public understanding, the following takes the double-coil electromagnet control in the undervoltage release as an example, and describes the technical solution of the utility model in detail in combination with the accompanying drawings:

[0034] The undervoltage release of this embodiment is as follows Figure 1As shown, it includes a double-coil electromagnet having a holding coil and a starting coil and a double-coil electromagnet control circuit; the double-coil electromagnet control circuit includes:

[0035] A first switch circuit is connected in series with the holding coil and is used to control the power on and power off of the holding coil;

[0036] A second switch circuit is connected in series with the starting coil and is used to control the power on and power off of the starting coil;

[0037] A unidirectional circuit, two ends of which are respectively connected to the common end of the first switch circuit and the holding coil and the common end of the second switch circuit and the starting coil, so that the conduction of the second switch circuit can simultaneously energize the holding coil and the starting coil, while the conduction of the first switch circuit can only energize the holding coil;

[0038] A rectifier circuit is used to rectify the grid voltage Ui into a DC voltage U1 as the working power supply voltage for the holding coil and the starting coil;

[0039] A power supply circuit, used for performing voltage reduction and filtering on the DC voltage U1 to generate a lower DC voltage U2;

[0040] A voltage sampling circuit is used to divide the DC voltage U1 to generate comparison voltages U3 and U4, and U3>U4;

[0041] An oscillating circuit, used to use the DC voltage U2 as a working power supply to generate an oscillating voltage Uo4 and output it to the control end of the first switch circuit;

[0042] A comparison circuit, used to use the DC voltage U2 as a working power supply and generate a control level Uo1 according to the input comparison voltages U3 and U4;

[0043] A differential circuit, used for converting the control level Uo1 into a conduction control signal Uo3 which is input into the control end of the second switch circuit, and converting the conduction control signal into a shutdown control signal after the preset time;

[0044] The third switch circuit has two ends connected to the control end of the first switch circuit and the control level Uo1 respectively, and is turned on when the control level Uo1 is lower than the oscillation voltage Uo4.

[0045] 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 maintenance 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 of the comparison circuit and the oscillation circuit. U2 is also used as a reference voltage. The oscillation circuit works immediately after being powered on, and outputs a PWM pulse voltage Uo4, which is output to the input ends of the first switch circuit and the third switch circuit. 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 output end of the comparison circuit outputs a control voltage Uo1 that works together with the pulse voltage Uo4 to control the opening and closing of the first switch circuit, so that the maintenance coil works in the PWM state or loses power. The other output of the comparison circuit is connected to the differential circuit, which converts the high-level square wave signal into a gradual decrease according to the exponential law. Signal Uo3, if the grid voltage value is greater than the set value (the comparison voltage U3 is greater than the pull-in reference voltage), the output end of the comparison circuit outputs a high level control voltage Uo1, so that the PWM pulse voltage Uo4 output by the oscillation circuit is applied to the first switch circuit to control the maintenance coil to work in the PWM current state. At the same time, the control voltage Uo1 controls the second switch circuit to open through the differential circuit output control signal Uo3, and the start coil is energized to make the undervoltage releaser pull in. When the gradual signal output by the differential circuit is lower than the minimum opening level of the second switch circuit, the second switch circuit is closed, and the unidirectional circuit disconnects the power supply of the start coil. At this time, the maintenance coil works in the PWM state, and the undervoltage releaser remains in the pull-in state; if the grid voltage value is less than the set value (the comparison voltage U4 is less than the release reference voltage), the output end of the comparison circuit outputs a low level, so that the PWM pulse voltage Uo4 output by the oscillation circuit is bypassed by the third switch circuit, and the pulse voltage Uo4 cannot be applied to the first switch circuit, the maintenance coil loses power, and the undervoltage releaser is released.

[0046] Figure 2 A specific implementation circuit is shown, which uses two low-power time base circuits 7555 to control the maintaining coil and the starting coil respectively, and has the advantages of simple circuit structure, low power consumption, and stable suction of the electromagnet.

[0047] like Figure 2 As shown, the rectifier circuit includes diodes D1 to D4, which are used to convert the power input voltage Ui into a DC voltage U1.

[0048] The power supply circuit includes a resistor R1, a resistor R2, a capacitor C1, a voltage regulator diode D5, and a MOS tube VT1. One end of the resistor R1 and the resistor R2 are connected to U1, and the other end of the resistor R1 and the cathode of the voltage regulator tube D5 are connected to the gate of the MOS tube VT1; the other end of the resistor R2 is connected to the drain of the MOS tube VT1; the source of the MOS tube VT1 is the output end of the voltage U2; one end of the capacitor C1 is connected to the voltage U2, and the other end of the capacitor C1 and the anode of the voltage regulator tube D5 are grounded; the function of the power supply circuit is to reduce the DC voltage U1 to the low-voltage working power supply U2.

[0049] The 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 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 D6 and the other end of the resistor R5, and the other end of the capacitor C2 and the other end of the resistor R6 are grounded. The voltage sampling circuit obtains two voltages U3 and U4 through resistor voltage division, and the common connection end of the resistor R5 and the cathode of the diode D6 outputs the voltage U3; the common connection end of the resistors R5 and R6 outputs the voltage U4.

[0050] The comparison circuit includes a resistor R8, a capacitor C5, a MOS tube VT5 and an integrated circuit IC1, wherein the integrated circuit IC1 is a time base circuit 7555; U2 is connected to pins 4 and 8 of the integrated circuit IC1; U3 is connected to pin 6 of the integrated circuit IC1; U4 is connected to pin 2 of the integrated circuit IC1; one end of the resistor R8 is connected to U2, and the other end is connected to the drain of the MOS tube VT5; the pin 3 of the integrated circuit IC1 is connected to the gate of the MOS tube VT5; one end of the capacitor C5 is connected to pin 5 of the integrated circuit IC1; the other end of the capacitor C4, the source of the MOS tube VT5 and pin 1 of the integrated circuit IC1 are grounded together.

[0051] The oscillation circuit includes resistor R7, resistor R9, resistor R12, capacitor C3, capacitor C4, diode D7, and integrated circuit IC2. Integrated circuit IC2 is a time base circuit 7555; voltage U2 is connected to pins 4 and 8 of integrated circuit IC2; one end of resistor R12, one end of resistor R7, an anode of diode D7 and pin 7 of integrated circuit IC2 are connected, the other end of resistor R12 is connected to U2, the other end of resistor R7, a cathode of diode D7, and one end of capacitor C3 are connected to pins 2 and 6 of the integrated circuit, one end of capacitor C4 is connected to pin 5 of integrated circuit IC2, the other end of capacitor C3, the other end of capacitor C4 and pin 1 of integrated circuit IC2 are grounded together, pin 3 of integrated circuit IC2 is connected to one end of resistor R9, and the other end of resistor R9 is the output end of voltage Uo4.

[0052] The differential 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 tube VT4, and the other end of the resistor R11 is grounded; the function of the differential circuit is to convert the input high-level signal into a gradual signal that decreases according to the exponential law.

[0053] The first switch circuit includes a MOS tube VT3 and a diode D9. The diode D9 is connected in parallel with the maintaining 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 output end of the voltage Uo4 of the third switch circuit. 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 maintaining coil L1.

[0054] The second switch circuit includes a MOS tube VT4 and a diode D11. The diode D11 is connected in parallel with the starting coil. 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 output end of the differential 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.

[0055] The third switch circuit includes a diode D8, an anode of the diode D8 is connected to the gate of the MOS transistor VT3 in the first switch circuit, and a cathode of the diode D8 is connected to the output terminal of the output voltage Uo1 of the comparison circuit.

[0056] The unidirectional circuit includes a diode D10, a cathode of the diode D10 connected to a common end connected to an anode of a diode D11 in the second switch circuit and a drain of a MOS tube VT4, and an anode of the diode D10 connected to a common end connected to an anode of a diode D9 in the first switch circuit and a drain of a MOS tube VT3.

[0057] Figure 2 The working process and principle of the circuit shown are as follows Figure 3 As shown, the details are as follows:

[0058] 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.

[0059] After the low-voltage DC voltage U2 is established, the oscillation circuit starts to work and outputs the PWM pulse voltage Uo4, which is output to the gate of the MOS tube VT3 of the first switch circuit. Since the charging resistor R12 of the oscillation circuit is connected to the high voltage U1, the high voltage U1 is used as the charging power supply of the oscillation circuit, so the output pulse width can change with the size of the high voltage U1, that is, it changes accordingly with the change of the power supply voltage Ui.

[0060] The DC voltage U1 is divided by resistors R3 and R4, and then smoothed 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 When the 3rd pin of the integrated circuit IC1 and IC2 changes from high level to low voltage, the MOS tube VT5 is cut off because of no control high level. At this time, the low-voltage DC voltage U2 outputs the control voltage Uo1 through the resistor R8, thereby controlling the oscillation circuit to output the PWM pulse voltage Uo4 to the gate of VT3 to make VT3 periodically turned on and off, so that the maintenance coil works in the PWM current state, the maintenance coil is energized to generate electromagnetic attraction, and the diode D9 continues the current, so that the maintenance coil continues to have current; the other way of the control voltage Uo1 charges the capacitor C6 in the differential circuit, and outputs the control voltage Uo3, so that the control pole of the MOS tube VT4 is energized, VT4 is turned on, and the start coil is energized During the conduction period of MOS tube VT4, due to the effect of diode D10, the maintenance coil does not work in the PWM current state and is continuously energized, which increases the electromagnetic attraction. The electromagnet is attracted under the combined effect of the electromagnetic attraction generated by the maintenance coil and the starting coil. After C6 is charged, the VT4 control electrode loses power, VT4 is cut off, the starting coil loses power and stops working, and the maintenance coil resumes working in the PWM current working state. At this time, due to the unidirectional conduction effect of diode D10, the starting coil is not controlled by the working state of MOS tube VT3 and generates coil current, and is still in the de-energized state. The electromagnet only maintains the attracted state under the effect of the electromagnetic attraction generated by the maintaining attraction coil.

[0061] When the undervoltage releaser is in the energized state, the maintenance coil maintains a low-power working state under the control of the PWM control signal generated by the oscillation circuit, generates less heat, and can work for a long time without overheating and damage. Moreover, the PWM control signal generated by the oscillation circuit changes accordingly with the change of the power supply voltage Ui (the larger the power supply voltage Ui, the smaller the PWM duty cycle, and the smaller the power supply voltage Ui, the larger the PWM duty cycle), so that the current of the maintenance coil changes accordingly with the change of the power supply voltage. On the one hand, the power consumption at high voltage can be controlled, thereby controlling the temperature rise of the maintenance coil not to be too high, thereby increasing the service life of the coil. On the other hand, it can avoid the suction force of the electromagnet from being significantly reduced when the power supply voltage is small, so that the suction force change of the electromagnet is controlled within a suitable range, thereby improving the vibration resistance of the undervoltage releaser.

[0062] The power supply voltage Ui drops, causing the sampling voltages U3 and U4 to drop accordingly. When the sampling voltage U4 drops below When the MOS tube VT5 is turned on, the output voltage Uo1 changes to a low level, and the capacitor C6 of the differential circuit is discharged to prepare for the next charging process. At the same time, the output voltage Uo1 passes through the diode D8 to turn the gate of the MOS tube VT3 to a low level, and the MOS tube VT3 is turned off, the maintenance coil is de-energized, and the electromagnet is released.

Claims

1. A double-coil electromagnet control circuit, the double-coil electromagnet comprising a holding coil and a starting coil; characterized in that: The double-coil electromagnet control circuit comprises: A first switch circuit is connected in series with the holding coil and is used to control the power on and power off of the holding coil; A second switch circuit is connected in series with the starting coil and is used to control the power on and power off of the starting coil; A unidirectional circuit, the two ends of which are respectively connected to the common end of the first switch circuit and the holding coil and the common end of the second switch circuit and the starting coil, so that the conduction of the second switch circuit can simultaneously energize the holding coil and the starting coil, while the conduction of the first switch circuit can only energize the holding coil; A rectifier circuit is used to rectify the grid voltage Ui into a DC voltage U1 as the working power supply voltage for the holding coil and the starting coil; A power supply circuit, used for performing voltage reduction and filtering on the DC voltage U1 to generate a lower DC voltage U2; A voltage sampling circuit is used to generate comparison voltages U3 and U4 after dividing the DC voltage U1, and U3>U4; An oscillating circuit, used to use the DC voltage U2 as a working power supply to generate an oscillating voltage Uo4 and output it to the control end of the first switch circuit; A comparison circuit, used to use the DC voltage U2 as a working power supply and generate a control level Uo1 according to the input comparison voltages U3 and U4; A differential circuit, used for converting the control level Uo1 into a conduction control signal Uo3 which is input into the control end of the second switch circuit, and converting the conduction control signal into a shutdown control signal after a preset time; The third switch circuit has two ends connected to the control end of the first switch circuit and the control level Uo1 respectively, and is turned on when the control level Uo1 is lower than the oscillation voltage Uo4.

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

3. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The comparison circuit includes a resistor R8, a capacitor C5, a MOS tube VT5 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 resistor R8 is connected to the DC voltage U2, and the other end is connected to the drain of the MOS tube VT5; the pin 3 of the integrated circuit IC1 is connected to the gate of the MOS tube VT5; one end of the capacitor C5 is connected to pin 5 of the integrated circuit IC1; the other end of the capacitor C4, the source of the MOS tube VT5, and pin 1 of the integrated circuit IC1 are grounded together.

4. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The oscillation circuit includes a resistor R7, a resistor R9, a resistor R12, a capacitor C3, a capacitor C4, a diode D7, 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 resistor R7, an anode of the diode D7, and pin 7 of the integrated circuit IC2, the other end of the resistor R12 is connected to the DC voltage U2, the other end of the resistor R7, the cathode of the diode D7, and one end of the capacitor C3 are connected to pins 2 and 6 of the integrated circuit IC2, 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 grounded together, pin 3 of the integrated circuit IC2 is connected to one end of the resistor R9, and the other end of the resistor R9 is the output end of the oscillation voltage Uo4.

5. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The differential circuit includes a capacitor C6 and a resistor R11 connected in series, the other end of the capacitor C6 is connected to the control level Uo1, the other end of the resistor R11 is grounded, and the common end of the capacitor C6 and the resistor R11 serves as the output end of the conduction control signal Uo3.

6. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The first switch circuit includes a MOS tube VT3 and a diode D9, the diode D9 is connected in parallel with the maintaining 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 one end of the third switch circuit and the oscillation voltage Uo4, and the source of the MOS tube VT3 is grounded.

7. The double-coil electromagnet control circuit according to claim 1, characterized in that: The second switch circuit includes a MOS tube VT4 and a diode D11, the diode D11 is connected in parallel with the starting coil, 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 output end of the differential circuit, and the source of the MOS tube VT4 is grounded.

8. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The third switch circuit comprises a diode D8, an anode of the diode D8 is connected to the control end of the first switch circuit, and a cathode of the diode D8 is connected to the control level Uo1 output end of the comparison circuit.

9. The double-coil electromagnet control circuit as claimed in claim 1, characterized in that: The unidirectional circuit includes a diode D10, a cathode of the diode D10 is connected to a common end of the second switch circuit and the start coil, and an anode of the diode D10 is connected to a common end of the first switch circuit and the maintain coil.

10. An undervoltage release, comprising a double-coil electromagnet and a double-coil electromagnet control circuit, wherein the double-coil electromagnet comprises a holding coil and a starting coil; characterized in that: The double-coil electromagnet control circuit is the double-coil electromagnet control circuit as claimed in any one of claims 1 to 9.

Images