An electromagnet control circuit

Abstract

The utility model discloses an electromagnet control circuit. The electromagnet control circuit includes the switch circuit based on electronic switch for controlling the on-off of the coil of electromagnet, and the electromagnet control circuit further includes timing circuit for making the switch circuit conductive for a fixed time and then turn off after power on, and the timing circuit includes resistance R3~R7, capacitor C2, capacitor C3, MOS tube VT1 and MOS tube VT2. The utility model adopts the timing circuit composed of two MOS tubes and a set of resistance and capacitor to control the on-off of electronic switch, and then realizes the accurate control of the coil energizing time, and compared with the prior art scheme using differential circuit, the utility model has obvious improvement in high-temperature energizing starting reliability, high-voltage starting reliability and component reliability, and compared with other timing control circuits composed of single-chip microcomputer, operational amplifier circuit and other devices, the circuit structure is simple and reliable, and the power consumption and cost are lower.

Description

Technical Field

[0001] This utility model relates to an electromagnet control circuit. Background Technology

[0002] Currently, most circuit breaker electric control uses electromagnets, such as for electric closing and opening, various trip units, and remote reset. Conventional electromagnets typically use electronic switch-based circuits to control the on / off state of their coils. For certain applications, such as electromagnets used for electric closing and opening, they do not need to remain in an engaged state for an extended period after being energized; they only need to be engaged and held engaged for a short time after power-on. Existing technology for controlling such electromagnets usually involves setting a differentiating circuit at the electronic switch control terminal of the switching circuit. This differentiating circuit converts a high-level square wave signal into a gradually decreasing signal with an exponential trend, enabling the electronic switch to automatically turn off after a period of time.

[0003] To ensure reliable electromagnet engagement, the switching circuit of the control coil typically has a long conduction time, usually >50ms. This results in a slow decline of the gradient signal output by the differentiating circuit, allowing sufficient energizing time for the coil. As is well known, common electronic switches such as MOSFETs and bipolar transistors must first pass through an amplification state when transitioning from the on to the off state. When such electronic switches operate in the amplification state, under the control of the gradient signal, their on-resistance gradually increases from the on-state resistance to the off-state resistance. The slow decline of the control signal further prolongs the amplification state period, causing the on-resistance to increase dramatically. Under the influence of the coil current, this results in significant power consumption and a rapid rise in the core temperature of the electronic switch. This is especially problematic for coils controlling low voltage and high current; under such conditions, the core temperature can exceed the maximum operating temperature, leading to overheating and damage. Furthermore, the conduction time of an electronic switch is determined by comparing the gradual signal with the threshold voltage of the electronic switch. Different models or different batches of the same model of electronic switches have large variations in threshold voltage, which leads to large variations in the conduction time of the electronic switch. Therefore, the conduction time of the electronic switch must be lengthened to ensure the minimum energization time of the coil, which further lengthens the time from the switch being on to the switch being off, exacerbating the heating of the electronic switch core and reducing the reliability of the electronic switch. This phenomenon is particularly common under high-temperature operating conditions. Utility Model Content

[0004] The technical problem to be solved by this utility model is to overcome the shortcomings of the prior art and provide an electromagnet control circuit. The timing circuit is used to control the electronic switch, which can effectively reduce the core temperature of the electronic switch during the process of switching from conduction to cutoff. At the same time, it can accurately control the energizing time of the electromagnet coil. Moreover, the timing circuit does not require the use of a timing chip, has a simpler structure, and lower implementation cost.

[0005] The present invention specifically adopts the following technical solution to solve the above-mentioned technical problems: An electromagnet control circuit includes an electronic switch-based switching circuit for controlling the on / off state of the electromagnet coil; the electromagnet control circuit further includes a timing circuit for first turning on the switching circuit for a fixed period of time after power-on and then turning it off; the timing circuit includes resistors R3 to R7, capacitors C2 and C3, MOSFETs VT1 and VT2, the positive terminal of the DC control power supply is connected to one end of resistor R3 and one end of resistor R5, the other end of resistor R3 and one end of resistor R4 are connected to the drain of MOSFET VT1, the other end of resistor R5, one end of capacitor C3, and the drain of MOSFET VT2 are connected to the control terminal of the electronic switch, the other end of resistor R4, one end of capacitor C2, and one end of resistor R7 are connected to the gate of MOSFET VT2, the other end of capacitor C3 and one end of resistor R6 are connected to the gate of MOSFET VT1, and the other end of capacitor C2, the other end of resistor R6, the other end of resistor R7, the source of MOSFET VT1, and the source of MOSFET VT2 are all connected to the negative terminal of the DC control power supply.

[0006] Furthermore, the electromagnet control circuit also includes: A rectifier circuit is used to convert the mains voltage into DC voltage to serve as the operating power supply voltage for the coil. The power supply circuit is used to step down the DC voltage to a low-voltage DC voltage, which serves as the DC control power supply.

[0007] Preferably, the power supply circuit includes a resistor R1 and a Zener diode D5. One end of the resistor R1 is connected to the positive output terminal of the rectifier circuit, and the other end of the resistor R1 is connected to the cathode of the Zener diode D5 to serve as the positive terminal of the DC control power supply. The anode of the Zener diode D5 is connected to the negative output terminal of the rectifier circuit to serve as the negative terminal of the DC control power supply.

[0008] Preferably, the switching circuit includes a MOSFET VT3 and a diode D7. The cathode of the diode D7 is connected to one end of the coil and the positive terminal of the coil's operating power supply voltage. The anode of the diode D7 is connected to the other end of the coil and the drain of the MOSFET VT3. The source of the MOSFET VT3 is connected to the negative terminal of the coil's operating power supply voltage. The gate of the MOSFET VT3 serves as the control terminal of the electronic switch and is connected to the timing circuit.

[0009] Compared with the prior art, the technical solution of this utility model has the following beneficial effects: This invention employs a timing circuit consisting of two MOSFETs and a set of resistors and capacitors to control the on / off state of the electronic switch, thereby achieving precise control of the coil energizing time. Compared to existing schemes that use a differentiating circuit to directly control the on / off state of the electronic switch to control the coil energizing time, this invention significantly improves the reliability of high-temperature energization startup, high-voltage startup, and component operation. Compared to other timing control circuits composed of microcontrollers, operational amplifiers, and other components, the timing circuit proposed in this invention has a simpler and more reliable circuit structure, lower power consumption, and lower cost. Attached Figure Description

[0010] Figure 1 This is a circuit diagram of a specific embodiment of the present invention; Figure 2 The output waveform diagram is shown in the specific embodiment. Detailed Implementation

[0011] To address the shortcomings of existing technologies that use differentiating circuits to directly control the on / off state of electronic switches to control the coil energizing time, this invention proposes a timing circuit consisting of two MOS transistors and a set of resistors and capacitors to control the on / off state of the electronic switches, thereby achieving precise control over the coil energizing time.

[0012] The electromagnet control circuit proposed in this utility model includes a switching circuit based on an electronic switch for controlling the on / off state of the electromagnet coil; the electromagnet control circuit also includes a timing circuit for first turning on the switching circuit for a fixed period of time after power-on and then turning it off; the timing circuit includes resistors R3 to R7, capacitors C2 and C3, MOSFETs VT1 and VT2, the positive terminal of the DC control power supply is connected to one end of resistor R3 and one end of resistor R5, the other end of resistor R3 and one end of resistor R4 are connected to the drain of MOSFET VT1, the other end of resistor R5, one end of capacitor C3, and the drain of MOSFET VT2 are connected to the control terminal of the electronic switch, the other end of resistor R4, one end of capacitor C2, and one end of resistor R7 are connected to the gate of MOSFET VT2, the other end of capacitor C3 and one end of resistor R6 are connected to the gate of MOSFET VT1, and the other end of capacitor C2, the other end of resistor R6, the other end of resistor R7, the source of MOSFET VT1, and the source of MOSFET VT2 are all connected to the negative terminal of the DC control power supply.

[0013] Furthermore, the electromagnet control circuit also includes: A rectifier circuit is used to convert the mains voltage into DC voltage to serve as the operating power supply voltage for the coil. The power supply circuit is used to step down the DC voltage to a low-voltage DC voltage, which serves as the DC control power supply.

[0014] Preferably, the power supply circuit includes a resistor R1 and a Zener diode D5. One end of the resistor R1 is connected to the positive output terminal of the rectifier circuit, and the other end of the resistor R1 is connected to the cathode of the Zener diode D5 to serve as the positive terminal of the DC control power supply. The anode of the Zener diode D5 is connected to the negative output terminal of the rectifier circuit to serve as the negative terminal of the DC control power supply.

[0015] Preferably, the switching circuit includes a MOSFET VT3 and a diode D7. The cathode of the diode D7 is connected to one end of the coil and the positive terminal of the coil's operating power supply voltage. The anode of the diode D7 is connected to the other end of the coil and the drain of the MOSFET VT3. The source of the MOSFET VT3 is connected to the negative terminal of the coil's operating power supply voltage. The gate of the MOSFET VT3 serves as the control terminal of the electronic switch and is connected to the timing circuit.

[0016] To facilitate public understanding, the technical solution of this utility model will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings: The electromagnet control circuit in this embodiment includes a rectifier circuit, a power supply circuit, a timing circuit, and a switching circuit; its specific circuit structure is as follows: Figure 1 As shown.

[0017] like Figure 1 As shown, the rectifier circuit includes diodes D1 to D4, which are used to rectify the mains input voltage Ui into a DC voltage U1, which serves as the operating power supply voltage for the electromagnet coil L1.

[0018] like Figure 1 As shown, the power supply circuit includes a resistor R1 and a Zener diode D5. One end of the resistor R1 is connected to U1, and the other end of the resistor R1 is connected to the cathode of the Zener diode D5. The cathode of the Zener diode D5 is U2. The anode of the Zener diode D5 is grounded. The function of the power supply circuit is to reduce the DC voltage U1 to the DC control power supply voltage U2 of the timing circuit.

[0019] like Figure 1As shown, the timing circuit includes resistors R3 to R7, capacitors C2 and C3, MOSFETs VT1 and VT2. The DC control power supply voltage U2 is connected to one end of resistor R3 and one end of resistor R5. The other end of resistor R3 and one end of resistor R4 are connected to the drain of MOSFET VT1. The other end of resistor R5, one end of capacitor C3, and the drain of MOSFET VT2 are connected and serve as the output terminal of control voltage Uo1. The other end of resistor R4, one end of capacitor C2, and one end of resistor R7 are connected to the gate of MOSFET VT2. The other end of capacitor C3 and one end of resistor R6 are connected to the gate of MOSFET VT1. The other end of capacitor C2, the other end of resistor R6, the other end of resistor R7, the source of MOSFET VT1, and the source of MOSFET VT2 are all connected to ground.

[0020] like Figure 1 As shown, the switching circuit includes a MOSFET VT3 and a diode D7. Diode D7 is connected in parallel with coil L1. The cathode of diode D7 is connected to DC voltage U1, and the anode of diode D7 is connected to the drain of MOSFET VT3. The gate of MOSFET VT3 is connected to control voltage Uo1, and the source of MOSFET VT3 is grounded. The function of the switching circuit is to control the on / off state of coil L1.

[0021] Figure 1 The working process and principle of the circuit shown are as follows: (1) After the grid voltage Ui is energized, the grid voltage Ui is rectified by the rectifier circuit and becomes DC voltage U1. The DC voltage U1 is stepped down by the power supply circuit to obtain low-voltage DC voltage U2, which provides the working power for the timing circuit.

[0022] (2) DC voltage U2 is connected to the timing circuit. One path of DC voltage U2 is applied to the gate of MOSFET VT2 through resistors R3 and R4, and the other path is applied to the gate of MOSFET VT1 through resistor R5 and capacitor C3. Due to the effect of capacitor C2, the establishment of the gate voltage of MOSFET VT2 lags behind the establishment of the gate voltage of MOSFET VT1, causing MOSFET VT1 to turn on before MOSFET VT2. After MOSFET VT1 turns on, the voltage at point A becomes low, and the gate of MOSFET VT2 is kept low through resistor R4. MOSFET VT2 is turned off, and the output control voltage Uo1 is high, controlling the switching circuit to turn on, the coil is energized, and the electromagnet is attracted. At this time, capacitor C3 in the timing circuit charges, causing the voltage at the gate of MOSFET VT1 to gradually decrease, and gradually causing MOSFET VT1 to exit the conducting state, gradually changing from the conducting state to the cutoff state, and causing the voltage at point A to gradually rise. The voltage at point A, through resistor R4, causes the gate voltage of MOSFET VT2 to gradually decrease. As the gate voltage gradually increases, MOSFET VT2 gradually changes from the off state to the on state, causing the control voltage Uo1 to decrease. The control voltage Uo1, through capacitor C3, further decreases the gate voltage of MOSFET VT1, accelerating VT1's cutoff. This causes the voltage at point A to rise rapidly, which, through resistor R4, accelerates the rise of the gate voltage of MOSFET VT4, accelerating MOSFET VT2's turn-on. This, in turn, causes the control voltage Uo1 to decrease rapidly, creating a chain reaction process. Ultimately, this results in MOSFET VT1 rapidly turning off, MOSFET VT2 rapidly turning on, and the control voltage Uo1 rapidly dropping to a low level. This cuts off the control switching circuit, de-energizes the coil, and releases the electromagnet. Due to the chain reaction effect of the timing circuit, the control voltage Uo1 can quickly transition from a high level to a low level, significantly shortening the time for the MOSFET in the switching circuit to change from on to off. This greatly reduces the core temperature of the MOSFET during the transition from on to off, improving the MOSFET's operational reliability. The charging circuit composed of capacitor C3 and resistors R5 and R6 determines the duration t1 of the high level of the control voltage Uo1, achieving the timing function of controlling the coil's energization time.

[0023] (3) After the power supply voltage Ui is de-energized, the control circuit returns to the de-energized state. When the power supply voltage Ui is energized again, the above (1) and (2) processes are repeated.

[0024] The waveform changes of Ui, U2, Uo1, and I1 during the above process are as follows: Figure 2 As shown.

[0025] As described above, after the control circuit is powered on, it calculates the time it takes for the voltage of capacitor C3 to charge until MOSFET VT2 is turned off by setting the parameters of resistors R5 and R6 and capacitor C3. This allows for precise control of the electromagnet's energization time. Furthermore, the timing circuit directly controls the switching circuit's MOSFET VT3 to turn on and off, avoiding the overheating problem of MOSFET VT1 caused by slow changes in the control signal.

Claims

1. An electromagnet control circuit, comprising an electronic switch-based switching circuit for controlling the on / off state of the electromagnet's coil; characterized in that, The electromagnet control circuit also includes a timing circuit, used to first turn on the switch circuit for a fixed period of time after power-on and then turn it off; the timing circuit includes resistors R3 to R7, capacitors C2 and C3, MOSFETs VT1 and VT2, the positive terminal of the DC control power supply is connected to one end of resistor R3 and one end of resistor R5, the other end of resistor R3 and one end of resistor R4 are connected to the drain of MOSFET VT1, the other end of resistor R5, one end of capacitor C3, and the drain of MOSFET VT2 are connected to the control terminal of the electronic switch, the other end of resistor R4, one end of capacitor C2, and one end of resistor R7 are connected to the gate of MOSFET VT2, the other end of capacitor C3 and one end of resistor R6 are connected to the gate of MOSFET VT1, and the other end of capacitor C2, the other end of resistor R6, the other end of resistor R7, the source of MOSFET VT1, and the source of MOSFET VT2 are all connected to the negative terminal of the DC control power supply.

2. The electromagnet control circuit as described in claim 1, characterized in that, Also includes: A rectifier circuit is used to convert the mains voltage into DC voltage to serve as the operating power supply voltage for the coil. The power supply circuit is used to step down the DC voltage to a low-voltage DC voltage, which serves as the DC control power supply.

3. The electromagnet control circuit as described in claim 2, characterized in that, The power supply circuit includes a resistor R1 and a Zener diode D5. One end of the resistor R1 is connected to the positive output terminal of the rectifier circuit, and the other end of the resistor R1 is connected to the cathode of the Zener diode D5 to serve as the positive terminal of the DC control power supply. The anode of the Zener diode D5 is connected to the negative output terminal of the rectifier circuit to serve as the negative terminal of the DC control power supply.

4. The electromagnet control circuit as described in claim 1, characterized in that, The switching circuit includes a MOSFET VT3 and a diode D7. The cathode of the diode D7 is connected to one end of the coil and the positive terminal of the coil's operating power supply voltage. The anode of the diode D7 is connected to the other end of the coil and the drain of the MOSFET VT3. The source of the MOSFET VT3 is connected to the negative terminal of the coil's operating power supply voltage. The gate of the MOSFET VT3 serves as the control terminal of the electronic switch and is connected to the timing circuit.

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