CN111883388A - Control circuit for driving relay to be switched on and off rapidly - Google Patents

Abstract

A control circuit for driving a relay to turn on and off quickly, comprising a relay, a first node of the coil of the relay is connected to a power supply through a booster circuit, a second node of the coil of the relay receives a relay drive signal through a switch control circuit, and the booster circuit comprises a PNP type triode, The first resistor, the second resistor, the energy storage capacitor, the first diode, the emitter of the PNP triode and the anode of the first diode are connected to the power source, and the base of the PNP triode is connected to the power source through the first resistor, The collector of the PNP triode and the negative electrode of the energy storage capacitor are grounded through the third resistor. The negative electrode of the first diode and the positive electrode of the energy storage capacitor are connected to the first node of the coil of the relay. The switch control circuit includes an NPN triode and a fourth resistor. , the base of the PNP triode is connected to the collector of the NPN triode and the second node of the relay's coil through the second resistor and the voltage regulator tube, the base of the NPN triode receives the relay drive signal through the fourth resistor, and the transmission of the NPN triode pole ground.

Description

A control circuit for fast on-off of a driving relay

technical field

The present invention relates to the technical field of drive control of relays, in particular to a control circuit for driving relays to quickly switch on and off.

Background technique

Relays play an important role in our daily life and in all walks of life, such as plug-in card access switches, touch doorbells, and the drive of screen doors in rail transit, and the control of low-voltage, small-current, and high-voltage in power equipment. Pre-charge protection of current, inverter and active power filter circuits, etc. The relay is composed of a coil and a contact, and has two working states: on and off. When the relay is turned on, a higher voltage is required to provide enough energy for the contact to pull in during the process of the contact pull-in, while the contact pull-in After closing, only a low voltage is needed to keep the contacts in the closed state. If, in order to ensure the reliable opening of the relay, the high voltage is maintained when the contacts are closed and after the contacts are closed, it is easy to cause the coil of the relay to heat up. serious, resulting in damage to the relay. In response to this situation, the commonly used solutions are as follows:

Method 1: As shown in Figure 3, using the short-term freewheeling pull-in principle of the coil when the relay is closed, the relay can be reliably pulled in through a high level that lasts for several seconds when the relay is closed. After the relay is closed, it is driven by PWM. When the PWM wave is in the valley, the relay is still kept in the pull-in state by the freewheeling characteristic of the coil. Although this method can reduce the heating of the relay coil and does not require the use of dual voltages, it is necessary to connect diodes in parallel at both ends of the relay, which will easily lead to a delay in turning off the relay. Moreover, when the PWM control relay is turned on and off, the driving time of the high and low levels of the PWM waveform is required to be the same, so the normal driving time is longer, and the waveform of the PWM driving signal is required to be higher.

Method 2: As shown in Figure 4, 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 enough voltage to drive the contacts of the relay to close; after the relay is closed, the high driving voltage VH stops driving the relay under the action of the current limiting resistor R8 , the low driving voltage VL continues to supply power to the relay, thereby reducing the heating of the relay coil, but this method requires dual power supply, and has higher requirements on the power supply.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a control circuit for fast on-off of the relay, which can realize the fast turn-on and turn-off of the relay, and reduce the coil loss and coil heating of the relay.

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

The first diode is a Schottky diode.

A second diode is connected in parallel between the collector and the emitter of the NPN triode, the anode of the second diode is connected to the emitter of the NPN triode, and the cathode of the second diode is connected to the collector of the NPN triode. electrode connection.

The energy storage capacitor is an electrolytic capacitor.

The NPN type triode can be an N type field effect transistor, the gate of the N type field effect transistor is connected to the relay drive signal, the drain of the N type field effect transistor is connected to the second node of the coil of the relay, and the N type field effect transistor is connected to the second node of the coil of the relay. The source is grounded.

An RC filter circuit is connected in parallel between the base of the NPN transistor and the ground, and the RC filter circuit is composed of a fifth resistor and a second capacitor connected in parallel.

The above technical scheme is adopted: the first node of the coil of the relay is connected to the power supply through the boost circuit, and the second node of the coil of the relay receives the relay drive signal through the switch control circuit, that is, the two circuits are used to realize the opening and closing of the relay. The booster 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 anode of the first diode are connected to the power supply. The PNP transistor The base is connected to the power supply through the first resistor, the collector of the PNP transistor and the negative electrode of the energy storage capacitor are grounded through the third resistor, the negative electrode of the first diode and the positive electrode of the energy storage capacitor are connected to the first node of the coil of the relay, The energy storage capacitor can be charged through the booster circuit to reserve enough energy for turning on the relay, and after the relay is turned on, the low voltage keeps the relay turned on. The base of the PNP transistor is connected to the switch control circuit through the second resistor and the Zener tube in turn. The switch control circuit includes an NPN transistor and a fourth resistor. The collector of the NPN transistor is connected to the negative pole of the Zener tube, The second node of the coil of the relay, the base of the NPN triode receives the relay drive signal through the fourth resistor, the emitter of the NPN triode is grounded, the switch control circuit controls the on and off of the relay by receiving the relay drive signal, Since the NPN transistor is used, when the relay drive signal is at a low level, the NPN transistor 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 transistor is turned on, and the relay's The instantaneous voltage of the first node of the coil rises, so that the relay is turned on quickly, and the voltage of the first node of the coil drops at the same time after the relay is turned on, so that the relay remains on at a lower voltage. When the relay drive signal changes from high level to low level, the NPN transistor is turned off, and the relay is also turned off. Since the voltage regulator tube is connected between the second resistor and the second node of the coil of the relay, when the relay is turned off, the The Zener tube can block the freewheeling effect of the coil, thereby speeding up the shutdown of the relay. It can be seen from this that the control circuit can realize the rapid turn-on and turn-off of the relay, and after the relay is turned on by driving the relay with a high voltage, the relay can be kept turned on at a low voltage, thereby reducing the coil loss and heating of the relay, and preventing the The reverse electromotive force when the relay is turned off causes an impact on the NPN triode and protects the circuit devices. In addition, the control circuit only needs to be powered by a single power supply, which greatly simplifies the power supply circuit.

The first diode adopts a Schottky diode, and the switching speed is fast. When the relay coil is powered off, a freewheeling channel can be quickly established to prevent the excessive reverse electromotive force of the coil from impacting the NPN triode.

A second diode is connected in parallel between the collector and the emitter of the NPN triode, the anode of the second diode is connected to the emitter of the NPN triode, and the cathode of the second diode is connected to the collector of the NPN triode. The electrode is connected to avoid reverse conduction of the NPN triode, which plays the role of protecting the circuit device.

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, and plays a filtering role on the relay drive signal.

The present invention will be further described below with reference to the accompanying drawings and specific embodiments of the description.

Description of drawings

Fig. 1 is the circuit schematic diagram of the present invention;

2 is a schematic circuit diagram of an embodiment of the present invention;

Fig. 3 is the circuit schematic diagram of the existing PWM drive relay;

FIG. 4 is a schematic circuit diagram of a conventional dual-voltage drive relay.

Detailed ways

Referring to Figures 1 to 2, a control circuit for driving a relay to quickly turn on and off includes 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 is received through the switch control circuit. The relay drive signal, that is, the turn-on and turn-off of the relay Y1 is realized through the boost circuit and the switch control circuit. The boost circuit includes a PNP transistor 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 transistor Q1, The anode of the first diode D1 is connected to the power supply, the base of the PNP transistor Q1 is connected to the power supply through the first resistor R1, the collector of the PNP transistor Q1 and the cathode of the energy storage capacitor C1 are grounded through the third resistor R3. The third resistor R3 plays a current limiting role on the PNP transistor Q1 to avoid damage to the PNP transistor Q1 due to excessive current. The cathode of the first diode D1 and the anode of the energy storage capacitor C1 are connected to the first node of the coil of the relay Y1 , the base of the PNP transistor Q1 is connected to the switch control circuit through the second resistor R2 and the voltage regulator D3 in turn, and the PNP transistor Q1 can be turned on through the action of the first resistor R1 and the second resistor R2, then the PNP transistor Q1 It cooperates with the first diode D1 and the energy storage capacitor C1 to realize the bootstrap boost function, thereby increasing the instantaneous voltage on the first node of the coil of the relay Y1. Therefore, the energy storage capacitor C1 can be charged through the boost circuit to turn on The relay Y1 reserves enough energy to realize the high voltage driving the relay Y1 to turn on, and after the relay Y1 turns on, the low voltage maintains the turn-on state of the relay Y1. The energy storage capacitor C1 is an electrolytic capacitor with a large capacity and a high rated withstand voltage value, and a lower-priced aluminum electrolytic capacitor can be used to reduce the cost of the device.

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 respectively connected to the negative electrode of the voltage regulator tube D3 and the second node of the coil of the relay Y1. The anode of the pressure tube D3 is connected to the second resistor R2, the base of the NPN transistor Q2 receives the driving signal of the relay Y1 through the fourth resistor R4, and the emitter of the NPN transistor Q2 is grounded. The switch control circuit controls the opening and closing of the relay Y1 by receiving the drive signal of the relay Y1. Since the NPN transistor Q2 is used, when the relay drive signal is low, the NPN transistor Q2 and the PNP transistor Q1 Both 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 reserves enough voltage to turn on the relay Y1. When the relay drive signal is at a high level, the NPN Both the type transistor Q2 and the PNP type transistor Q1 are in the open state. At this time, the instantaneous voltage on the first node of the coil of the relay Y1 rises to meet the high driving voltage required by the relay Y1, so that the relay Y1 is turned on quickly, and 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 on by the low voltage. When the relay drive signal changes from high level to low level, the NPN transistor Q2 is turned off, and the relay Y1 is also turned off. Since the coil of the relay Y1 is equivalent to a large inductance, a reverse voltage will be induced when it is turned off. In order to prevent the relay The high reverse electromotive force of the Y1 coil impacts the NPN transistor Q2. The first diode D1 adopts a Schottky diode, which has a fast switching speed. When the relay Y1 coil is powered off, a freewheeling channel can be quickly established. Moreover, in this control circuit, a voltage regulator 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 voltage regulator D3 can block the freewheeling effect of the coil of the relay Y1. Thus, the turn-off of the relay Y1 is accelerated, and the purpose of quickly turning off the relay Y1 is achieved.

A second diode D2 is connected in parallel between the collector and the emitter of the NPN transistor Q2, the anode of the second diode D2 is connected to the emitter of the NPN transistor Q2, and the cathode of the second diode D2 is connected to the emitter of the NPN transistor Q2. The collector of the NPN triode Q2 is connected to avoid reverse conduction of the NPN triode Q2, so as to protect the circuit device. The NPN transistor Q2 can also use an N-type field effect transistor, the gate of the N-type field effect transistor is connected to the drive 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 N-type field effect transistor is connected to the second node of the coil of the relay Y1. The source of the FET is grounded.

An RC filter circuit is connected in parallel between the base of the NPN transistor Q2 and the ground. The RC filter circuit is composed of a fifth resistor R5 and a second capacitor C2 connected in parallel. The fifth resistor R5 and the fourth resistor R4 divide the driving signal of the relay Y1, so that the base voltage of the NPN transistor Q2 satisfies the conditions of being turned on and off.

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 used as an example to specifically analyze the control circuit. And according to the parameters of the relay Y1, other circuit devices are designed as follows.

Select 24V power supply, design the high level of the relay drive signal as 15V and the low level as 0.

In the switch control circuit, in order to avoid damage to the NPN transistor Q2 caused by the reverse electromotive force after the relay Y1 coil is powered off, the NPN transistor Q2 selects the model TIP41C with high withstand voltage, that is, the parameters of the NPN transistor Q2 are, I _CM =10A, _VCE =1.2V, _VBE =1.8V, _VCEO = _VCBO =100V. The second diode D2 adopts a common diode 1N4148. According to the NPN transistor Q2, the 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 with a withstand voltage of 63V and a capacitance value of 0.1uF.

In the boost circuit, due to the larger capacitance value of the energy storage capacitor C1, when the relay Y1 is turned on, the high voltage can be maintained for a longer time, and it is easier to cause the relay Y1 to turn on. The energy storage capacitor C1 has sufficient charging time, so it is difficult to ensure the subsequent rapid turn-on of the relay Y1, and the larger the capacitance value is, the higher the cost of the energy storage capacitor C1 is. 50V electrolytic capacitor. The model selected for 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 a Schottky diode with the model MUR120, that is, the parameters of the first diode D1 are the reverse impulse voltage, the maximum value is 200V, the average current is 1A, and the forward voltage drop _VFM =0.875 V. The resistance value of the third resistor R3 for current limiting is selected as 10kΩ. For the selection of the first resistor R1 and the second resistor R2, if the resistance values of the two are too large, the current generated when the coil of the relay Y1 is powered off will not be able to quickly pass through the voltage regulator tube D3, the first resistor R1, the second resistor The resistor R2 and the first diode D1 form a freewheeling current. At this time, although the relay Y1 will be disconnected quickly, the reverse electromotive force generated by the coil of the relay Y1 will cause damage to the NPN transistor Q2. If the resistance values of the two are too small, Although it will speed up the freewheeling, it will prolong the disconnection time of the coil, and the larger current will also damage the NPN transistor Q2. Therefore, in this embodiment, the resistance value selected by the first resistor R1 and the second resistor R2 is 200Ω . The model selected for the voltage regulator tube D3 is BZX84C16, and the voltage regulator voltage is 16V.

The specific work flow of the control circuit of this embodiment is as follows:

At the initial power-on, when the relay drive signal is at a low level, the NPN transistor Q2 is turned off and the relay is in an off state. Since the base voltage of the PNP transistor Q1 is about 24V, it is also in the off state. The diode D1 charges the energy storage capacitor C1, so that the voltage of the energy storage capacitor rises from 0 to about 24V-0.875V=23.125V, which reserves the voltage for opening the relay.

When the relay drive signal changes from low level to high level, the NPN transistor Q2 is turned on, the second node voltage of the relay coil is about 1.2V, and the base voltage of the PNP transistor Q1 is about 24-(24-0.7 -1.2)/2=13V, as shown by I2 in Figure 2, at this time, the PNP transistor Q1 is turned on, and the voltage of the first node of the relay coil instantly rises to 24-1.3+23.125=45.8V, so that the high voltage can be passed through. The drive relay is turned on. After the relay is turned on, the voltage of the first node of the coil of the relay drops from 45.8V to 23.125V, that is, the low voltage keeps the relay in a stable on state, as shown by I1 in Figure 2.

When the relay drive signal changes from high level to low level, the NPN transistor Q2 is turned off. Since the relay coil is a large inductance, it will induce a reverse electromotive force, which is connected with the voltage regulator tube D3, the first resistor R1, and the second resistor R2. , The first diode D1 forms a freewheeling current, as shown in I3 in Figure 4, since the blocking voltage of the Zener tube D3 is 16V, only when the reverse voltage induced by the relay coil is greater than the blocking voltage 16V will it enter the continuous flow Therefore, the freewheeling current of the relay coil is blocked by the voltage regulator tube D3, the first resistor R1, and the second resistor R2. When the voltage of the relay Y1 is greater than 16V, due to the It can quickly form a freewheeling current and avoid the impact of reverse voltage on the NPN transistor Q2. When the voltage of the relay coil drops to 16V, it can be turned off, thereby speeding up the closing speed of the relay Y1.

It can be seen from the above analysis that the control circuit realizes the rapid turn-on and turn-off of the relay through the cooperation of the boost circuit and the switch control circuit, and after the relay is turned on by the high voltage drive, the relay can be kept on at a low voltage, reducing the relay's voltage. Coil loss and heat generation can also prevent the reverse electromotive force from the NPN transistor Q2 when the relay Y1 is turned off, and protect the circuit devices. In addition, the control circuit only needs to be powered by a single power supply, which can greatly simplify the power circuit.

Claims (6)

1. A control circuit for fast on-off of a drive relay, comprising a relay, characterized in that: the first node of the coil of the relay is connected to a power supply through a boost circuit, and the second node of the coil of the relay receives the relay drive 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 anode of the first diode are connected to the power supply, and the PNP The base of the type triode is connected to the power supply through the first resistor, the collector of the PNP type triode and the negative electrode of the energy storage capacitor are grounded through the third resistor, and the negative electrode of the first diode and the positive electrode of the energy storage capacitor are connected to the first coil of the relay. Node, the base of the PNP transistor is connected to the switch control circuit through the second resistor and the voltage regulator in turn, the switch control circuit includes an NPN transistor and a fourth resistor, and the collectors of the NPN transistor are respectively connected to the voltage regulator tube. The negative pole, the second node of the coil of the relay, the base of the NPN triode receives the relay driving signal through the fourth resistor, and the emitter of the NPN triode is grounded. 2 . The control circuit for fast on-off of a driving relay according to claim 1 , wherein the first diode is a Schottky diode. 3 . 3 . The control circuit for fast on-off of a driving relay according to claim 1 , wherein a second diode is connected in parallel between the collector and the emitter of the NPN transistor, and the second diode 3 . The anode of the second diode is connected to the emitter of the NPN triode, and the cathode of the second diode is connected to the collector of the NPN triode. 4 . The control circuit for fast on-off of a driving relay according to claim 1 , wherein the energy storage capacitor is an electrolytic capacitor. 5 . 5. A control circuit for fast on-off of a driving relay according to claim 1, characterized in that: the NPN-type triode can adopt an N-type field effect transistor, and the gate of the N-type field effect transistor and the relay driving signal Connection, the drain of the N-type field effect transistor is connected to the second node of the coil of the relay, and the source of the N-type field effect transistor is grounded. 6 . The control circuit for fast on-off of a driving relay according to claim 1 , wherein an RC filter circuit is connected in parallel between the base of the NPN transistor and the ground, and the RC filter circuit is composed of a parallel connection of the first RC filter circuit. 7 . Five resistors and a second capacitor are formed.

Images