A relay drive circuit

Abstract

The utility model relates to the field of charging pile control circuit especially relays drive circuit, include: power module, the power module includes first power supply and second power supply, first power supply and second power supply are connected with relay respectively and power supply for it, control module, its input end receives external trigger signal, and the output end generates drive signal and is connected to the control end of power switch device, voltage switching module, its input end connects first power supply, and the output end is connected with relay, and the parallel power supply path of first power supply and second power supply is established when the drive signal is turned on in response to it, and first power supply path is cut off after preset delay, protection module, wherein protection module includes freewheeling unit and energy absorption unit, and freewheeling unit is connected in parallel at both ends of relay, and energy absorption unit is connected across the two ends of relay contact, is used for inhibiting voltage peak when contact disconnects. The whole satisfies the engineering demand of simple structure, quick response, controllable cost.

Description

Technical Field

[0001] This utility model relates to the field of charging pile control circuits, and more particularly to a relay drive circuit. Background Technology

[0002] In the design of relay drive circuits for electric vehicle charging stations, traditional solutions commonly use a single power supply to directly drive the relay coil. This structure causes the relay to continuously withstand high voltage after it is energized, keeping the coil in a state of overcurrent for extended periods. Since the current required to maintain relay engagement is far lower than the starting current, continuous high-voltage power supply causes abnormal heating of the coil, accelerates the aging of insulation materials, and leads to creep of the contact metal materials. In practical applications, this design has been found to significantly shorten the relay's lifespan and increase the probability of charging station failures, especially under high-frequency switching conditions.

[0003] Existing circuits lack effective protection mechanisms when the relay is disconnected. When the drive transistor cuts off the coil current, the inductance inevitably generates a back electromotive force. Traditional solutions do not have a dedicated energy discharge circuit, and the high-voltage spike acts directly on the two ends of the drive transistor. When this electrical stress exceeds the device's tolerance limit, it causes the drive transistor to break down and be damaged, resulting in system failure or even a safety accident. Simultaneously, when the relay contacts disconnect loads such as large-capacity batteries, there is no absorption device to suppress the arc. Continuous arcing causes contact surface erosion, increases contact resistance, and ultimately leads to contact adhesion or open-circuit failure.

[0004] Some improvement solutions attempt to add independent protection circuits, but fail to address the core issue. For example, simply adding a Zener diode to absorb back EMF or using time-sharing control to switch the supply voltage requires additional control chips, leading to a significant increase in circuit complexity and excessive response delays. This complex structure not only raises manufacturing costs but also introduces new points of failure, making it difficult to implement in scenarios requiring high reliability for charging piles. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a relay drive circuit that dynamically reduces maintenance power consumption while ensuring reliable engagement, and incorporates a multi-level protection mechanism. Simultaneously, it meets the engineering requirements of simplified structure, rapid response, and controllable cost. This is precisely the core technical problem that this patent aims to solve.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is: a relay drive circuit, comprising: A power module, comprising a first power supply and a second power supply, wherein the first power supply and the second power supply are respectively connected to and supply power to a relay; The control module receives external trigger signals at its input terminal and generates drive signals at its output terminal, which are then connected to the control terminal of the power switching device. The voltage switching module has its input end connected to a first power supply and its output end connected to a relay. In response to the drive signal being turned on, it establishes a parallel power supply path between the first power supply and the second power supply, and cuts off the first power supply path after a preset delay. The protection module includes a freewheeling unit and an energy absorption unit. The freewheeling unit is connected in parallel across the relay to absorb the back electromotive force generated when the coil current is cut off. The energy absorption unit is connected across the relay contacts to suppress voltage spikes when the contacts are opened.

[0007] Furthermore, the voltage switching module includes a voltage divider unit and a charging / discharging unit; the voltage divider unit includes a first resistor R1, a third resistor R3, a switching device Q1, and a third diode D3; wherein one end of the first resistor R1 is connected to the first power supply and the drain (D) terminal of the switching device Q1, the other end of the first resistor R1 is connected to the gate (G) terminal of the switching device Q1 and one end of the third resistor R3, and the other end of the third resistor R3 is connected to a relay via the third diode D3; the charging / discharging unit includes a second resistor R2 and a third capacitor C3, wherein one end of the second resistor R2 is connected to the first power supply via the first resistor R1, the other end of the second resistor R2 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is connected to the other end of the third resistor R3.

[0008] Furthermore, the freewheeling unit is a second diode D2, with the anode of the second diode D2 connected to the first terminal of the relay and the cathode of the second diode D2 connected to the second terminal of the relay, forming a discharge circuit.

[0009] Furthermore, the energy absorption unit includes a first capacitor C1, a fourth resistor R4, a second capacitor C2, and a fifth resistor R5; the first capacitor C1 and the fourth resistor R4 are connected in series to form a first RC unit, and the second capacitor C2 and the fifth resistor R5 are connected in series to form a second RC unit, wherein the two ends of the first RC unit are connected across the two ends of the relay, and the two ends of the second RC unit are connected across the two ends of the relay.

[0010] Furthermore, the control module includes a seventh resistor R7 and a sixth resistor R6. One end of the sixth resistor R6 is used to receive an external trigger signal, and the other end is grounded through the seventh resistor R7. The power switching device is a second MOSFET Q2. The other end of the sixth resistor R6 is connected to the gate of the second MOSFET Q2. The source of the second MOSFET Q2 is grounded, and the drain of the second MOSFET Q2 is connected to the cathode of the third diode D3.

[0011] The beneficial effects of this utility model are as follows: 1. The relay drive circuit of this patent achieves multi-dimensional performance improvements through a unique circuit topology design. The dynamic voltage switching mechanism provides sufficient drive current during the initial relay engagement to ensure reliable contact closure, and then automatically switches to a low-voltage sustaining state. This fundamentally solves the coil overheating problem caused by traditional single high-voltage power supply, significantly reducing long-term operating temperature rise and extending relay lifespan. This intelligent power management avoids insulation aging and contact material deformation caused by overheating, greatly improving the stability of the device under frequent switching conditions.

[0012] 2. The freewheeling unit connected in parallel across the coil creates a low-impedance discharge circuit, clamping the reverse electromotive force to a safe range at the moment the drive tube is turned off, completely eliminating the risk of drive tube breakdown; the energy absorption unit across the two ends of the contact point effectively suppresses the destructive arc generated when the load is disconnected through the synergistic effect of capacitor energy storage and resistor energy dissipation, significantly slows down the melting rate of the contact material, maintains long-term stable contact resistance, and eliminates adhesion or open circuit failure from the source.

[0013] 3. This circuit accomplishes complex functions through a clever combination of basic components, eliminating the need for dedicated control chips required in traditional improvement solutions. This not only reduces manufacturing costs but also minimizes potential failure points. A single drive signal synchronously controls the power switch and delay logic, ensuring a response speed that fully meets the stringent time sequence requirements of charging piles. This efficient and concise design gives this solution a significant advantage in the cost-sensitive and high-reliability charging pile sector, providing the industry with an innovative solution that combines performance and practicality. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a relay drive circuit. Detailed Implementation

[0015] Please see Figure 1 As shown, this utility model relates to a relay driving circuit, comprising: a power supply module, which includes a first power supply of 12V and a second power supply of 7V, the first power supply and the second power supply being connected to and supplying power to the relay respectively; a control module, whose input terminal receives an external trigger signal, and whose output terminal generates a drive signal and is connected to the control terminal of a power switching device; a voltage switching module, whose input terminal is connected to the first power supply, and whose output terminal is connected to the relay, which establishes a parallel power supply path between the first power supply and the second power supply in response to the drive signal being turned on, and cuts off the first power supply path after a preset delay; and a protection module, wherein the protection module includes a freewheeling unit and an energy absorption unit, the freewheeling unit being connected in parallel across the relay to absorb the back electromotive force generated when the coil current is cut off; and the energy absorption unit being connected across the relay contacts to suppress voltage spikes when the contacts are opened.

[0016] In this specific embodiment of the relay drive circuit, the power supply module includes a first power supply of 12V and a second power supply of 7V, which are respectively connected to the common power supply terminal of the relay coil. When an external trigger signal (such as the charging pile CP signal voltage reaching a set threshold) is input to the control module, the module generates a drive signal (RELAY-OUT) and transmits it to the control terminal of the power switching device Q2, driving it to conduct. At this time, the voltage switching module responds to the drive signal to establish a power supply path: the first power supply of 12V turns on the switching device Q1 through a voltage divider resistor network (discussed in detail below), forming a power supply path from the first power supply to the relay coil; at the same time, the second power supply of 7V directly supplies power to the relay coil, forming a parallel power supply path of the first power supply and the second power supply, and the superimposed current ensures that the relay contacts reliably close.

[0017] Within a preset delay period after the relay engages, the RC charging / discharging electronic module of the voltage switching module triggers a state switch: after the drive signal is turned on, the first power supply (12V) charges the delay capacitor through the current-limiting resistor; after the capacitor is fully charged, the discharge path raises the control electrode potential of the switching device Q1, causing it to turn off and cut off the first power supply path. Thereafter, the relay coil is maintained by only the second power supply (7V) to maintain engagement, achieving a dynamic reduction in the operating voltage. This mechanism fundamentally avoids the coil overheating problem caused by continuous high-voltage power supply in traditional solutions, significantly delaying material aging.

[0018] Furthermore, the voltage switching module includes a voltage divider unit and a charging / discharging unit; the voltage divider unit includes a first resistor R1, a third resistor R3, a switching device Q1, and a third diode D3; wherein one end of the first resistor R1 is connected to the first power supply and the drain (D) terminal of the switching device Q1, the other end of the first resistor R1 is connected to the gate (G) terminal of the switching device Q1 and one end of the third resistor R3, and the other end of the third resistor R3 is connected to a relay via the third diode D3; the charging / discharging unit includes a second resistor R2 and a third capacitor C3, wherein one end of the second resistor R2 is connected to the first power supply via the first resistor R1, the other end of the second resistor R2 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is connected to the other end of the third resistor R3.

[0019] In the voltage divider unit of the voltage switching module, one end of the first resistor R1 is connected to the first power supply 12V and the drain of the switching device Q1, and the other end is connected to the gate of the switching device Q1 and one end of the third resistor R3. The other end of the third resistor R3 is grounded through the third diode D3. In the charging and discharging unit, one end of the second resistor R2 is connected to the common junction of the first resistor R1 and the first power supply 12V, and the other end is connected to the positive terminal of the third capacitor C3; the negative terminal of the third capacitor C3 is connected to the common junction of the third resistor R3 and the third diode D3.

[0020] When the drive signal turns on the power switch Q2, the 12V power supply current acts through two paths: firstly, it divides the voltage through the first resistor R1 and the third resistor R3, causing the gate potential of the switch Q1 to be lower than its source potential, thus turning it on and establishing a power supply path from the 12V power supply to the relay coil; secondly, it charges the third capacitor C3 through the second resistor R2. When the third capacitor C3 is saturated, it discharges through the discharge path formed by the third resistor R3 and the third diode D3, raising the gate potential of the switch Q1 to near its source voltage, causing it to turn off. At this time, the 12V power supply path is cut off, and only the second 7V power supply maintains power to the coil.

[0021] By utilizing the physical characteristics of current-limiting charging by the second resistor R2 and energy storage and discharging by the third capacitor C3, precise control of preset delay is achieved, eliminating the need for an additional timing chip. The voltage divider structure of the first resistor R1 and the third resistor R3 ensures that the switching device Q1 conducts only within the safe gate voltage range, avoiding overdrive damage. Furthermore, the unidirectional conduction characteristic of the third diode D3 ensures that the current flows unidirectionally through the third resistor R3 when the third capacitor C3 discharges, avoiding voltage feedback interference. The charging and discharging rate of the third capacitor C3 matches the relay pull-in time constant, ensuring that the voltage switching timing precisely matches the contact state changes.

[0022] Furthermore, the freewheeling unit is a second diode D2, with the anode of the second diode D2 connected to the first terminal of the relay and the cathode of the second diode D2 connected to the second terminal of the relay, forming a discharge circuit.

[0023] The freewheeling unit is composed of a second diode D2, whose anode is connected to the first terminal of the relay coil (i.e., the drain terminal of the power switching device Q2), and whose cathode is connected to the second terminal of the relay coil (i.e., the input terminal of the second power supply 7V). This physical connection forms a closed discharge circuit across the relay coil, and its working principle is as follows: When the control module outputs a drive signal to turn on the power switch Q2, the second diode D2 is in a reverse-biased cutoff state, which does not affect the normal pull-in current path of the relay. At the instant the drive signal fails and causes the power switch Q2 to turn off, the relay coil generates a reverse electromotive force (EMF) due to a sudden current change. At this moment, the potential at the first terminal of the relay coil drops sharply, while the potential at the second terminal rises, forcing the second diode D2 to switch from reverse bias to forward conduction. The reverse EMF drive current continuously discharges along a closed loop: "first terminal of coil → anode of second diode D2 → cathode of second diode D2 → second terminal of coil → first terminal of coil," converting the inductor's stored energy into heat dissipation. This process continues until the coil energy is completely released, causing the reverse EMF to return to zero.

[0024] This design offers several advantages: 1. The low-impedance discharge circuit constructed by the second diode D2 clamps the reverse electromotive force to a typical value of 0.7V within its forward conduction voltage drop range, ensuring that the voltage across the power switching device Q2 is always below its withstand threshold, thus completely eliminating the risk of breakdown. 2. The discharge circuit allows for the orderly release of coil energy, avoiding electromagnetic interference (EMI) caused by voltage oscillations in traditional solutions and ensuring the signal integrity of the charging pile control circuit. 3. Only a single diode is needed to achieve critical protection functions, reducing the number of components compared to traditional transient suppression solutions such as a TVS diode + resistor combination by two.

[0025] Furthermore, the energy absorption unit includes a first capacitor C1, a fourth resistor R4, a second capacitor C2, and a fifth resistor R5; the first capacitor C1 and the fourth resistor R4 are connected in series to form a first RC unit, and the second capacitor C2 and the fifth resistor R5 are connected in series to form a second RC unit, wherein the two ends of the first RC unit are connected across the two ends of the relay, and the two ends of the second RC unit are connected across the two ends of the relay.

[0026] The energy absorption unit consists of a first capacitor C1, a fourth resistor R4, a second capacitor C2, and a fifth resistor R5. The first capacitor C1 and the fourth resistor R4 are connected in series to form a first RC unit, and the second capacitor C2 and the fifth resistor R5 are connected in series to form a second RC unit. The two RC units are connected in parallel across the two conductive terminals of the relay contacts, forming a symmetrical protection network. When the relay contacts open, the accumulated charge on the load side creates a high-voltage electric field in the contact gap. The first capacitor C1 and the second capacitor C2 immediately absorb the charge deposit, slowing down the voltage surge rate; simultaneously, the fourth resistor R4 and the fifth resistor R5 convert the energy stored in the capacitors into heat energy for continuous dissipation. This synergistic mechanism of "capacitor temporary storage + resistor dissipation" ensures that the voltage between the contacts is always limited within a safe threshold.

[0027] Furthermore, the control module includes a seventh resistor R7 and a sixth resistor R6. One end of the sixth resistor R6 is used to receive an external trigger signal, and the other end is grounded through the seventh resistor R7. The power switching device is a second MOSFET Q2. The other end of the sixth resistor R6 is connected to the gate of the second MOSFET Q2. The source of the second MOSFET Q2 is grounded, and the drain of the second MOSFET Q2 is connected to the cathode of the third diode D3.

[0028] The control module constructs a signal conditioning path using a sixth resistor R6 and a seventh resistor R7. One end of the sixth resistor R6 receives an external trigger signal, such as a charging pile CP signal, and the other end is connected to the common junction of the gate G of the second MOSFET Q2 and the seventh resistor R7; the other end of the seventh resistor R7 is grounded to form a fixed potential reference. The source S of the second MOSFET Q2 is directly grounded, and the drain D is connected to the cathode of the third diode D3 and the relay coil circuit.

[0029] When an external trigger signal CP=6V is input, current flows through the sixth resistor R6 to drive the gate of the second MOSFET Q2, causing it to conduct and establishing a current path for the relay coil. The seventh resistor R7 acts as a pull-down resistor, forcibly clamping the gate potential to ground when the trigger signal fails, ensuring that the second MOSFET Q2 is momentarily turned off. The direct connection between the drain D of the second MOSFET Q2 and the cathode of the third diode D3 creates a physical cascade between the coil circuit and the protection module, automatically activating the energy discharge path of the freewheeling unit at the moment of turn-off.

[0030] The overall working principle is as follows: When an external trigger signal, such as the charging pile CP voltage, reaches the set threshold and is input to the control module, the sixth resistor R6 transmits the signal to the gate of the second MOSFET Q2, causing it to conduct. At this time, the seventh resistor R7 maintains a stable gate potential. The conduction of the second MOSFET Q2 establishes a current loop for the relay coil, simultaneously triggering the voltage switching module to start working. The first power supply 12V, through the first resistor R1 and the third resistor R3 of the voltage divider unit, turns on the switching device Q1, forming a power supply path from the first power supply to the coil; at the same time, the second power supply 7V directly supplies power to the coil. The parallel connection of the two power supplies provides a large pull-in current to ensure reliable contact closure.

[0031] Within a preset delay period after the relay is engaged, the second resistor R2 of the charging and discharging unit charges the third capacitor C3. Once fully charged, it discharges through the discharge path formed by the third resistor R3 and the third diode D3, raising the control electrode potential of the switching device Q1 to the cutoff threshold. This process automatically cuts off the first power supply path, ensuring that the relay coil is maintained in the engaged state only by the second power supply 7V, thus eliminating the coil overheating problem caused by traditional continuous high-voltage power supply.

[0032] When the drive signal fails, the control module pulls the gate potential of the second MOSFET Q2 down to ground potential through the seventh resistor R7, causing it to turn off momentarily. At this time, the relay coil generates a reverse electromotive force due to the sudden change in current, and the second diode D2 immediately switches from reverse bias to forward conduction, forming a closed discharge circuit of "coil → second diode D2 → coil", converting the inductor energy into heat dissipation, ensuring that the voltage of the second MOSFET Q2 is always within a safe range.

[0033] At the instant the contacts break, the energy absorption unit connected between the two conductive terminals activates: the first capacitor C1 and the second capacitor C2 work together to absorb the accumulated charge, while the fourth resistor R4 and the fifth resistor R5 convert the stored energy into heat energy for continuous dissipation. This synergistic mechanism of capacitive storage and resistive dissipation effectively suppresses voltage surges and destructive arcs, significantly slowing down the melting rate of the contact material.

[0034] The entire circuit achieves intelligent control through a pure hardware topology: a single drive signal synchronously coordinates power switching and voltage switching; a voltage divider and charge / discharge network provide precise delay control; dual protection mechanisms address coil back EMF and contact arcing respectively; and a symmetrical energy absorption unit ensures system fault tolerance. This innovative design achieves an optimal balance of reliability, energy efficiency, and cost under the high-frequency switching conditions of charging piles.

[0035] The above embodiments are merely preferred embodiments of the present utility model and are not intended to limit the scope of the present utility model. Various modifications and improvements made to the technical solutions of the present utility model by those skilled in the art without departing from the spirit of the present utility model should fall within the protection scope defined by the claims of the present utility model.

Claims

1. A relay drive circuit, characterized in that, Includes a power supply module, a control module, a voltage switching module, and a protection module: A power module, comprising a first power supply and a second power supply, wherein the first power supply and the second power supply are respectively connected to and supply power to a relay; The control module receives external trigger signals at its input terminal and generates drive signals at its output terminal, which are then connected to the control terminal of the power switching device. The voltage switching module has its input end connected to a first power supply and its output end connected to a relay. In response to the drive signal being turned on, it establishes a parallel power supply path between the first power supply and the second power supply, and cuts off the first power supply path after a preset delay. The protection module includes a freewheeling unit and an energy absorption unit. The freewheeling unit is connected in parallel across the relay to absorb the back electromotive force generated when the coil current is cut off. The energy absorption unit is connected across the relay contacts to suppress voltage spikes when the contacts are opened. The voltage switching module includes a voltage divider unit and a charging / discharging unit. The voltage divider unit includes a first resistor (R1), a third resistor (R3), a switching device (Q1), and a third diode (D3). One end of the first resistor (R1) is connected to the first power supply and the drain (D) terminal of the switching device (Q1), and the other end of the first resistor (R1) is connected to the gate (G) terminal of the switching device (Q1) and one end of the third resistor (R3). The other end of the third resistor (R3) is connected to a relay through the third diode (D3). The charging / discharging unit includes a second resistor (R2) and a third capacitor (C3). One end of the second resistor (R2) is connected to the first power supply through the first resistor (R1), and the other end of the second resistor (R2) is connected to one end of the third capacitor (C3). The other end of the third capacitor (C3) is connected to the other end of the third resistor (R3). The freewheeling unit is a second diode (D2). The anode of the second diode (D2) is connected to the first terminal of the relay, and the cathode of the second diode (D2) is connected to the second terminal of the relay, forming a discharge circuit. The energy absorption unit includes a first capacitor (C1), a fourth resistor (R4), a second capacitor (C2), and a fifth resistor (R5); the first capacitor (C1) and the fourth resistor (R4) are connected in series to form a first RC unit, and the second capacitor (C2) and the fifth resistor (R5) are connected in series to form a second RC unit, wherein the two ends of the first RC unit are connected across the two ends of the relay, and the two ends of the second RC unit are connected across the two ends of the relay. The control module includes a seventh resistor (R7) and a sixth resistor (R6). One end of the sixth resistor (R6) is used to receive an external trigger signal, and the other end is grounded through the seventh resistor (R7). The power switching device is a second MOSFET (Q2). The other end of the sixth resistor (R6) is connected to the gate (G) of the second MOSFET (Q2). The source (S) of the second MOSFET (Q2) is grounded, and the drain (D) of the second MOSFET (Q2) is connected to the cathode of the third diode (D3).

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