A control circuit for driving a relay to turn on and off quickly

Abstract

A control circuit for driving a relay to turn on and off quickly, comprising a relay. The first node of the relay coil is connected to a power supply through a boost circuit, and the second node of the relay coil receives a relay driving signal through a switch control circuit. The boost circuit includes a PNP-type triode, a first resistor, a second resistor, an energy storage capacitor, and a first diode. The emitter of the PNP-type triode and the positive pole of the first diode are connected to the power supply. The base of the PNP-type triode is connected to the power supply through the first resistor. The collector of the PNP-type triode and the negative pole of the energy storage capacitor are grounded through a third resistor. The negative pole of the first diode and the positive pole of the energy storage capacitor are connected to the first node of the relay coil. The switch control circuit includes an NPN-type triode and a fourth resistor. The base of the PNP-type triode is connected to the collector of the NPN-type triode and the second node of the relay coil through the second resistor and a voltage stabilizing diode. The base of the NPN-type triode receives the relay driving signal through the fourth resistor, and the emitter of the NPN-type triode is grounded.

Description

Technical Field

[0001] The present invention relates to the technical field of driving and controlling relays, and particularly relates to a control circuit for driving a relay to quickly turn on and off. Background Art

[0002] Relays play an important role in our daily lives and various industries. For example, in daily life, there are card-swiping power-on switches and touch doorbells, and in rail transit, there are driving of platform screen doors, controlling high voltage and large current with low voltage and small current in power equipment, pre-charge protection in inverter and active power filter circuits, etc. A relay consists of a coil and contacts, and has two working states: on and off. When turning on the relay, a relatively high voltage is required to provide sufficient energy for the contact to close during the process of contact closing. After the contact closes, only a relatively low voltage is needed to keep the contact closed. If a high voltage is maintained during and after the contact closing to ensure reliable opening of the relay, it is easy to cause serious heating of the relay coil, resulting in damage to the relay. In response to this situation, the currently common solutions are as follows:

[0003] Method 1: As Figure 3 shown, using the principle of short-circuit current continuous flow suction and hold when the relay is turned off, a high level is applied for several seconds during closing to ensure reliable closing of the relay. After the relay closes, PWM drive is adopted. When the PWM wave is at the trough, the relay remains closed due to the continuous flow characteristic of the coil. Although this method can reduce the heating of the relay coil and does not require dual voltage, it is necessary to connect a diode in parallel at both ends of the relay, which is likely to cause relay turn-off delay. If the relay cannot quickly turn off when a device fails, it is easy to cause damage to the device. Moreover, when using PWM to control the opening and closing of the relay, the driving time of the high and low levels of the PWM waveform needs to be the same. Therefore, the normal driving time is relatively long, and the requirements for the waveform of the PWM driving signal are relatively high.

[0004] Method 2: As Figure 4 shown, a dual-voltage driving method is adopted. The high driving voltage VH is connected to the energy storage capacitor C4 through the current-limiting resistor R8, and the low driving voltage VL is connected to the energy storage capacitor C4 through the diode D5. When the relay is not working, the high driving voltage VH charges the energy storage capacitor C4 to ensure that there is sufficient voltage to drive the contact of the relay to close. After the relay closes, the high driving voltage VH stops driving the relay under the action of the current-limiting resistor R8, and the low driving voltage VL continues to supply power to the relay, thereby reducing the heating of the relay coil. However, this method requires dual power supply, and the requirements for the power supply are relatively high. Summary of the Invention

[0005] The object of the present invention is to provide a control circuit for driving a relay to turn on and off quickly in view of the deficiencies of the prior art, which can achieve the quick turn-on and quick turn-off of the relay, and reduce the coil loss and coil heating of the relay.

[0006] The technical solution of the present invention is: A control circuit for driving a relay to turn on and off quickly, including a relay. The first node of the relay coil is connected to the power supply through a boost circuit, and the second node of the relay coil receives a relay driving signal through a switch control circuit. The boost circuit includes a PNP-type triode, a first resistor, a second resistor, a storage capacitor, and a first diode. The emitter of the PNP-type triode and the positive pole of the first diode are connected to the power supply. The base of the PNP-type triode is connected to the power supply through the first resistor. The collector of the PNP-type triode and the negative pole of the storage capacitor are grounded through a third resistor. The negative pole of the first diode and the positive pole of the storage capacitor are connected to the first node of the relay coil. The base of the PNP-type triode is connected to the switch control circuit through the second resistor and a voltage regulator diode in sequence. The switch control circuit includes an NPN-type triode and a fourth resistor. The collector of the NPN-type triode is respectively connected to the negative pole of the voltage regulator diode and the second node of the relay coil. The base of the NPN-type triode receives the relay driving signal through the fourth resistor, and the emitter of the NPN-type triode is grounded.

[0007] The first diode is a Schottky diode.

[0008] A second diode is connected in parallel between the collector and the emitter of the NPN-type triode. The positive pole of the second diode is connected to the emitter of the NPN-type triode, and the negative pole of the second diode is connected to the collector of the NPN-type triode.

[0009] The storage capacitor is an electrolytic capacitor.

[0010] The NPN-type triode can be replaced by an N-type field effect transistor. The gate of the N-type field effect transistor is connected to the relay driving signal. The drain of the N-type field effect transistor is connected to the second node of the relay coil, and the source of the N-type field effect transistor is grounded.

[0011] An RC filter circuit is connected in parallel between the base of the NPN-type triode and the ground. The RC filter circuit is composed of a fifth resistor and a second capacitor connected in parallel.

[0012] Adopt the above technical solution: The first node of the relay coil is connected to the power supply through a boost circuit, and the second node of the relay coil receives the relay drive signal through a switch control circuit, that is, the opening and closing of the relay are realized through these two circuits. The boost circuit includes a PNP-type triode, a first resistor, a second resistor, an energy storage capacitor, and a first diode. The emitter of the PNP-type triode and the positive pole of the first diode are connected to the power supply. The base of the PNP-type triode is connected to the power supply through the first resistor. The collector of the PNP-type triode and the negative pole of the energy storage capacitor are grounded through the third resistor. The negative pole of the first diode and the positive pole of the energy storage capacitor are connected to the first node of the relay coil. Through this boost circuit, the energy storage capacitor can be charged to reserve enough large energy for turning on the relay, and after the relay is turned on, the relay is kept in the on state by a low voltage. The base of the PNP-type triode is sequentially connected to the switch control circuit through the second resistor and the voltage regulator diode. The switch control circuit includes an NPN-type triode and a fourth resistor. The collector of the NPN-type triode is respectively connected to the negative pole of the voltage regulator diode and the second node of the relay coil. The base of the NPN-type triode receives the relay drive signal through the fourth resistor. The emitter of the NPN-type triode is grounded. This switch control circuit controls the opening and closing of the relay by receiving the relay drive signal. Since an NPN-type triode is used, when the relay drive signal is at a low level, the NPN-type triode is turned off, and the energy storage capacitor is charged through the boost circuit. When the relay drive signal is at a high level, the NPN-type triode is turned on, and the instantaneous voltage at the first node of the relay coil rises, so that the relay is quickly turned on, and the voltage at the first node of the relay coil drops simultaneously after the relay is turned on, so that the relay is kept in the on state at a lower voltage. When the relay drive signal changes from a high level to a low level, the NPN-type triode is turned off, and the relay is also turned off. Since the voltage regulator diode is connected between the second resistor and the second node of the relay coil, the voltage regulator diode can block the flyback effect of the coil when the relay is turned off, thereby accelerating the turn-off of the relay. It can be seen from this that this control circuit can realize the quick opening and closing of the relay, and after driving the relay to turn on through a high voltage, it can keep the relay in the on state at a low voltage, reduce the coil loss and heating of the relay, and prevent the back electromotive force when the relay is turned off from impacting the NPN-type triode, playing a protective role for the circuit components. In addition, this control circuit only needs to be powered by a single power supply, greatly simplifying the power supply circuit.

[0013] The first diode adopts a Schottky diode with a fast switching speed. When the relay coil is powered off, a flyback channel can be quickly established to prevent the coil's excessive back electromotive force from impacting the NPN-type triode.

[0014] A second diode is connected in parallel between the collector and the emitter of the NPN transistor. The positive electrode of the second diode is connected to the emitter of the NPN transistor, and the negative electrode of the second diode is connected to the collector of the NPN transistor, preventing the NPN transistor from conducting in the reverse direction and playing a role in protecting circuit components.

[0015] A RC filter circuit is connected in parallel between the base of the NPN transistor and the ground. The RC filter circuit is composed of a fifth resistor and a second capacitor connected in parallel, which filters the relay drive signal.

[0016] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments. Description of the Drawings

[0017] Figure 1 is the circuit schematic diagram of the present invention;

[0018] Figure 2 is the circuit schematic diagram of an embodiment of the present invention;

[0019] Figure 3 is the circuit schematic diagram of the existing PWM-driven relay;

[0020] Figure 4 is the circuit schematic diagram of the existing dual-voltage-driven relay. Detailed Embodiments

[0021] See Figures 1 to 2, a control circuit for driving a relay to quickly turn on and off, including a relay Y1. The first node of the coil of the relay Y1 is connected to the power supply through a boost circuit, and the second node of the coil of the relay Y1 receives a relay drive signal through a switch control circuit, that is, the turn-on and turn-off of the relay Y1 are jointly realized through the boost circuit and the switch control circuit. The boost circuit includes a PNP-type triode Q1, an energy storage capacitor C1, a first diode D1, and a first resistor R1 and a second resistor R2 for voltage division. The emitter of the PNP-type triode Q1, the positive electrode of the first diode D1 are connected to the power supply. The base of the PNP-type triode Q1 is connected to the power supply through the first resistor R1. The collector of the PNP-type triode Q1, the negative electrode of the energy storage capacitor C1 are grounded through a third resistor R3. The third resistor R3 plays a role in limiting the current of the PNP-type triode Q1 to avoid damage to the PNP-type triode Q1 caused by excessive current. The negative electrode of the first diode D1, the positive electrode of the energy storage capacitor C1 are connected to the first node of the coil of the relay Y1. The base of the PNP-type triode Q1 is sequentially connected to the switch control circuit through the second resistor R2 and a voltage regulator diode D3. Through the action of the first resistor R1 and the second resistor R2, the PNP-type triode Q1 can be turned on. Then, the PNP-type triode Q1, the first diode D1, and the energy storage capacitor C1 cooperate to realize the bootstrap boost function, thereby increasing the instantaneous voltage on the first node of the coil of the relay Y1. Therefore, through this boost circuit, the energy storage capacitor C1 can be charged to reserve enough large energy for turning on the relay Y1, realizing the turn-on of the relay Y1 with high voltage, and after the relay Y1 is turned on, it is maintained in the on state by a low voltage. The energy storage capacitor C1 is an electrolytic capacitor with a large capacity and a high rated withstand voltage. An aluminum electrolytic capacitor with a lower price can be used to reduce the device cost.

[0022] The switch control circuit includes an NPN transistor Q2 and a fourth resistor R4 for current limiting. The collector of the NPN transistor Q2 is connected to the negative electrode of a zener diode D3 and the second node of the coil of a relay Y1 respectively. The positive electrode of the zener diode D3 is connected to a second resistor R2. The base of the NPN transistor Q2 receives the driving signal of the relay Y1 via the fourth resistor R4, and the emitter of the NPN transistor Q2 is grounded. This switch control circuit controls the turn-on and turn-off of the relay Y1 by receiving the driving signal of the relay Y1. Since an NPN transistor Q2 is used, when the relay driving signal is at a low level, both the NPN transistor Q2 and the PNP transistor Q1 are in the off state. In the boost circuit, the power supply charges the energy storage capacitor C1 through the first diode D1, so that the energy storage capacitor C1 stores a large enough voltage for turning on the relay Y1. When the relay driving signal is at a high level, both the NPN transistor Q2 and the PNP transistor Q1 are in the on state. At this time, the instantaneous voltage on the first node of the coil of the relay Y1 rises, meeting the high driving voltage required by the relay Y1, enabling the relay Y1 to turn on quickly. Moreover, after the relay Y1 is turned on, the voltage on the first node of the coil of the relay Y1 drops synchronously, and the relay Y1 is kept turned on by a low voltage. When the relay driving signal changes from a high level to a low level, the NPN transistor Q2 turns off, and the relay Y1 also turns off accordingly. Since the coil of the relay Y1 is equivalent to a large inductor, a reverse voltage will be induced when it turns off. To prevent the high reverse electromotive force of the coil of the relay Y1 from impacting the NPN transistor Q2, the first diode D1 is a Schottky diode with a fast switching speed, which can quickly establish a freewheeling path when the coil of the relay Y1 is powered off. And in this control circuit, a zener diode D3 is connected between the second resistor R2 and the second node of the coil of the relay Y1. Therefore, when the relay Y1 is turned off, the zener diode D3 can block the freewheeling effect of the coil of the relay Y1, thereby accelerating the turn-off of the relay Y1 and achieving the purpose of quickly turning off the relay Y1.

[0023] A second diode D2 is connected in parallel between the collector and the emitter of the NPN transistor Q2. The positive electrode of the second diode D2 is connected to the emitter of the NPN transistor Q2, and the negative electrode of the second diode D2 is connected to the collector of the NPN transistor Q2, preventing the NPN transistor Q2 from conducting in the reverse direction and playing a role in protecting the circuit components. The NPN transistor Q2 can also be an N-type field effect transistor. The gate of the N-type field effect transistor is connected to the driving signal of the relay Y1, the drain of the N-type field effect transistor is connected to the second node of the coil of the relay Y1, and the source of the N-type field effect transistor is grounded.

[0024] A RC filter circuit is connected in parallel between the base of the NPN transistor Q2 and the ground. The RC filter circuit consists of a fifth resistor R5 and a second capacitor C2 connected in parallel, which filters the driving signal of the relay Y1. Moreover, the driving signal of the relay Y1 is divided by the fifth resistor R5 and the fourth resistor R4, so that the base voltage of the NPN transistor Q2 meets the conditions for turning on and off.

[0025] In this embodiment, a relay Y1 with a rated voltage of 24V, a breaking current of 30A, a coil resistance of 200Ω, and a release voltage of 2.4V is taken as an example to specifically analyze this control circuit. According to the parameters of the relay Y1, the design of other circuit components is as follows.

[0026] A 24V power supply is selected, and the high level of the relay driving signal is designed to be 15V and the low level is 0V.

[0027] In the switch control circuit, to avoid damage to the NPN transistor Q2 caused by the back electromotive force after the coil of the relay Y1 is powered off, the NPN transistor Q2 is selected as the model TIP41C with a high withstand voltage. That is, the parameters of the NPN transistor Q2 are I CM = 10A, V CE = 1.2V, V BE = 1.8V, V CEO = V CBO = 100V. The second diode D2 uses a common diode 1N4148. According to the NPN transistor Q2, a fourth resistor R4 with a resistance value of 2kΩ is selected, the resistance value of the fifth resistor R5 is 50kΩ, and the second capacitor C2 is selected as a capacitor with a withstand voltage of 63V and a capacitance value of 0.1uF.

[0028] In the boost circuit, since the larger the capacitance value of the energy storage capacitor C1, the longer the high voltage can be maintained when the relay Y1 is turned on, which is more likely to promote the turn-on of the relay Y1. However, if the relay Y1 is frequently turned on and off, it cannot ensure that the energy storage capacitor C1 has enough charging time, making it difficult to ensure the subsequent rapid turn-on of the relay Y1. Moreover, the larger the capacitance value, the higher the cost of the energy storage capacitor C1. Therefore, in this embodiment, according to the actual situation, an electrolytic capacitor with a capacitance value of 47uF and a withstand voltage of 50V is selected. The model of the PNP transistor Q1 is 2N4920. That is, the parameters of the PNP transistor Q1 are I CM = 3A, V CE = 0.6V, V BE = 1.3V, V CEO = V CBO = 80V. The first diode D1 is selected as a Schottky diode of model MUR120. That is, the parameters of the first diode D1 are that the maximum reverse impact voltage is 200V, the average current conduction is 1A, and the forward voltage drop VFM = 0.875V. The resistance value of the third resistor R3 for current limiting is selected as 10 kΩ. For the selection of the first resistor R1 and the second resistor R2, if the resistance values of both are too large, when the relay Y1 coil is powered off, the generated current cannot quickly form a freewheeling current through the zener diode D3, the first resistor R1, the second resistor R2, and the first diode D1. At this time, although the relay Y1 will quickly disconnect, the reverse electromotive force generated by the relay Y1 coil is very large and will damage the NPN-type triode Q2. If the resistance values of both are too small, although the freewheeling current will be accelerated, the disconnection time of the coil will be extended, and at this time, the larger current will also damage the NPN-type triode Q2. Therefore, in this embodiment, the resistance values of the first resistor R1 and the second resistor R2 are selected as 200 Ω. The model of the zener diode D3 is selected as BZX84C16, and the regulated voltage is 16V.

[0029] The specific working process of the control circuit in this embodiment is as follows:

[0030] When initially powered on, when the relay drive signal is at a low level, the NPN-type triode Q2 is turned off, the relay is in the off state, and the PNP-type triode Q1 is also in the off state because the base voltage is about 24V. The power supply charges the energy storage capacitor C1 through the first diode D1, so that the voltage of the energy storage capacitor rises from 0 to about 24V - 0.875V = 23.125V, storing voltage for turning on the relay.

[0031] When the relay drive signal changes from a low level to a high level, the NPN-type triode Q2 conducts, and the voltage of the second node of the relay coil is about 1.2V. Then, the base voltage of the PNP-type triode Q1 is about 24 - (24 - 0.7 - 1.2) / 2 = 13V, as shown in I2 in Figure 2 At this time, the PNP-type triode Q1 conducts, and the voltage of the first node of the relay coil instantaneously rises to 24 - 1.3 + 23.125 = 45.8V, thus realizing driving the relay to turn on through a high voltage. After the relay is turned on, the voltage of the first node of the relay coil drops from 45.8V to 23.125V, that is, keeping the relay in a stable on state through a low voltage, as shown in I1 in Figure 2

[0032] When the relay drive signal changes from a high level to a low level, the NPN-type triode Q2 is turned off. Since the relay coil is a large inductor, it will induce a reverse electromotive force, thus forming a freewheeling current with the zener diode D3, the first resistor R1, the second resistor R2, and the first diode D1, as shown in Figure 4 ​As shown in I3, since the blocking voltage of the voltage stabilizing diode D3 is 16V, the freewheeling state will only be entered when the reverse voltage induced by the relay coil is greater than the blocking voltage of 16V. Therefore, the voltage stabilizing diode D3, the first resistor R1, and the second resistor R2 play a role in blocking the freewheeling of the relay coil. When the voltage of the relay Y1 is greater than 16V, since the first diode D1 uses a Schottky diode, a freewheeling current can be quickly formed to avoid the impact of the reverse voltage on the NPN-type triode Q2. When the voltage of the relay coil drops to 16V, the relay can be turned off, thus accelerating the closing speed of the relay Y1.

[0033] From the above analysis, it can be seen that this control circuit realizes the fast opening and closing of the relay through the cooperation of the boost circuit and the switch control circuit. After the relay is turned on by high voltage, the relay can be kept in the on state at low voltage, reducing the coil loss and heat generation of the relay, and preventing the impact of the back electromotive force when the relay Y1 is turned off on the NPN-type triode Q2, playing a protective role for the circuit components. In addition, this control circuit only needs to be powered by a single power supply, which can greatly simplify the power supply circuit.

Claims

1. A control circuit for driving a relay to quickly turn on and off, comprising a relay, characterized in that: The first node of the coil of the relay is connected to a single power supply through a boost circuit, and the second node of the coil of the relay receives a relay driving signal through a switch control circuit. The boost circuit includes a PNP transistor, a first resistor, a second resistor, an energy storage capacitor, and a first diode. The emitter of the PNP transistor and the positive pole of the first diode are connected to the power supply. The base of the PNP transistor is connected to the power supply through the first resistor. The collector of the PNP transistor and the negative pole of the energy storage capacitor are grounded through a third resistor. The negative pole of the first diode and the positive pole of the energy storage capacitor are connected to the first node of the coil of the relay. The base of the PNP transistor is sequentially connected to the switch control circuit through the second resistor and a voltage stabilizing diode. The switch control circuit includes an NPN transistor and a fourth resistor. The collector of the NPN transistor is respectively connected to the negative pole of the voltage stabilizing diode and the second node of the coil of the relay. The base of the NPN transistor receives the relay driving signal through the fourth resistor. The emitter of the NPN transistor is grounded.

2. The control circuit for driving a relay to quickly turn on and off according to claim 1, characterized in that: The first diode is a Schottky diode.

3. The control circuit for driving a relay to quickly turn on and off according to claim 1, characterized in that: A second diode is connected in parallel between the collector and the emitter of the NPN transistor. The positive pole of the second diode is connected to the emitter of the NPN transistor, and the negative pole of the second diode is connected to the collector of the NPN transistor.

4. The control circuit for driving a relay to quickly turn on and off according to claim 1, characterized in that: The energy storage capacitor is an electrolytic capacitor.

5. The control circuit for driving a relay to quickly turn on and off according to claim 1, characterized in that: The NPN transistor can be an N-type field effect transistor. The gate of the N-type field effect transistor is connected to the relay driving signal. The drain of the N-type field effect transistor is connected to the second node of the coil of the relay. The source of the N-type field effect transistor is grounded.

6. The control circuit for driving a relay to quickly turn on and off according to claim 1, characterized in that: An RC filter circuit is connected in parallel between the base of the NPN transistor and the ground. The RC filter circuit is composed of a fifth resistor and a second capacitor connected in parallel.

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