Relay drive circuit

Abstract

The present invention discloses a relay driving circuit, including a PNP transistor Q1, a PNP transistor Q4, an NPN transistor Q2, an NPN transistor Q3, an NPN transistor Q5, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a diode D1, a diode D2, a diode D3, a diode D4, a capacitor C1, a relay KA, a positive power supply VCC, a negative power supply GND, and an input signal IN1. Beneficial effects: a single power supply is used to design the circuit, the circuit structure is simple, the difficulty of auxiliary power supply design can be reduced, and the control is simple, and only high-level and low-level signals need to be input to control the closing and disconnection of the relay, and the reliability is strong. When the control relay is closed, the voltage loaded on the relay coil is raised by the capacitor to accelerate the closing of the relay. After closing, the voltage on the relay coil automatically decays to the power supply voltage, maintaining the relay open, and achieving low power consumption.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a relay drive circuit. Background Art

[0002] Relay is an electrical control device, which is widely used in automatic control circuits. At present, the relay driving circuit mostly adopts constant voltage driving, PWM driving and dual power supply driving methods. The constant voltage method is simple, but the loss of the relay itself remains unchanged after closing, and it is generally suitable for relays with relatively small losses, such as signal relays. The PWM driving method uses constant voltage to turn on, and then adjusts the PWM duty cycle to output an equivalent low voltage to reduce the loss on the relay coil, but it will consume part of the CPU timer resources and the software control is complex. The dual power supply driving method is the mainstream method of power relay control at present. It is turned on by a high voltage power supply, and then switched to a low voltage power supply to power the relay coil, reducing the coil loss. The disadvantage of this method is that it requires the auxiliary power supply to have multiple power outputs, and the circuit design is complex.

[0003] Therefore, there is an urgent need for a relay driving circuit with a simple design that can both ensure fast relay closing and maintain low closing loss. Summary of the invention

[0004] In order to solve the above problems, especially to address the deficiencies in the prior art, the present invention provides a relay drive circuit capable of solving the above problems.

[0005] To achieve the above purpose, the present invention adopts the following technical means:

[0006] A relay driving circuit includes a PNP transistor Q1, a PNP transistor Q4, an NPN transistor Q2, an NPN transistor Q3, an NPN transistor Q5, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a diode D1, a diode D2, a diode D3, a diode D4, a capacitor C1, a relay KA, a positive power supply VCC, a negative power supply GND, and an input signal IN1;

[0007] The emitter of the PNP transistor Q1 is connected to the first end of the resistor R1 and the positive electrode VCC of the power supply;

[0008] The base of the PNP transistor Q1 is connected to the first end of the resistor R5;

[0009] The collector of the PNP transistor Q1 is connected to the first end of the resistor R2, the anode of the diode D1 and the first end of the capacitor C1;

[0010] The emitter of the NPN transistor Q2 is connected to the negative electrode GND of the power supply;

[0011] The base of the NPN transistor Q2 is connected to the second end of the resistor R1, the second end of the resistor R5 and the collector of the NPN transistor Q3;

[0012] The collector of the NPN transistor Q2 is connected to the second end of the resistor R2;

[0013] The emitter of the NPN transistor Q3 is connected to the negative electrode GND of the power supply;

[0014] The base of the NPN transistor Q3 is connected to the first end of the resistor R3;

[0015] The second end of the resistor R3 is connected to the first end of the resistor R6, the first end of the resistor R7 and the input signal IN1;

[0016] The emitter of the PNP transistor Q4 is connected to the positive electrode of the power supply VCC;

[0017] The base of the PNP transistor Q4 is connected to the second end of the resistor R6;

[0018] The collector of the PNP transistor Q4 is connected to the anode of the diode D2;

[0019] The cathode of the diode D2 is connected to the anode of the diode D3;

[0020] The cathode of the diode D3 is connected to the cathode of the diode D1, the second end of the capacitor C1, the first end of the resistor R4 and the first end of the relay KA;

[0021] The second end of the resistor R4 is connected to the cathode of the diode D4;

[0022] The anode of the diode D4 is connected to the collector of the NPN transistor Q5 and the second terminal of the relay KA;

[0023] The emitter of the NPN transistor Q5 is connected to the negative electrode GND of the power supply;

[0024] The base of the NPN transistor Q5 is connected to the second end of the resistor R7.

[0025] Beneficial effects of the present invention:

[0026] The present invention adopts a single power supply design circuit, the circuit structure is simple, the difficulty of auxiliary power supply design can be reduced, and the control is simple, and only high-level and low-level signals need to be input to control the closing and opening of the relay, and the reliability is strong. When the control relay is closed, the voltage loaded on the relay coil is raised by the capacitor to accelerate the closing of the relay. After closing, the voltage on the relay coil automatically decays to the power supply voltage, maintaining the relay open, and achieving low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 14 is a circuit diagram of a relay driving circuit of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Example

[0030] like Figure 1 As shown, the relay driving circuit includes PNP transistor Q1, PNP transistor Q4, NPN transistor Q2, NPN transistor Q3, NPN transistor Q5, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, diode D1, diode D2, diode D3, diode D4, capacitor C1, relay KA, positive power supply VCC, negative power supply GND, and input signal IN1;

[0031] The emitter of the PNP transistor Q1 is connected to the first end of the resistor R1 and the positive electrode of the power supply VCC;

[0032] The base of the PNP transistor Q1 is connected to the first end of the resistor R5;

[0033] The collector of the PNP transistor Q1 is connected to the first end of the resistor R2, the anode of the diode D1 and the first end of the capacitor C1;

[0034] The emitter of NPN transistor Q2 is connected to the negative electrode of the power supply GND;

[0035] The base of the NPN transistor Q2 is connected to the second end of the resistor R1, the second end of the resistor R5 and the collector of the NPN transistor Q3;

[0036] The collector of the NPN transistor Q2 is connected to the second end of the resistor R2;

[0037] The emitter of the NPN transistor Q3 is connected to the negative electrode of the power supply GND;

[0038] The base of the NPN transistor Q3 is connected to the first end of the resistor R3;

[0039] The second end of the resistor R3 is connected to the first end of the resistor R6, the first end of the resistor R7 and the input signal IN1;

[0040] The emitter of the PNP transistor Q4 is connected to the positive electrode of the power supply VCC;

[0041] The base of the PNP transistor Q4 is connected to the second end of the resistor R6;

[0042] The collector of the PNP transistor Q4 is connected to the anode of the diode D2;

[0043] The cathode of diode D2 is connected to the anode of diode D3;

[0044] The cathode of the diode D3 is connected to the cathode of the diode D1, the second end of the capacitor C1, the first end of the resistor R4 and the first end of the relay KA;

[0045] The second end of the resistor R4 is connected to the cathode of the diode D4;

[0046] The anode of the diode D4 is connected to the collector of the NPN transistor Q5 and the second terminal of the relay KA;

[0047] The emitter of NPN transistor Q5 is connected to the negative electrode of the power supply GND;

[0048] The base of the NPN transistor Q5 is connected to the second end of the resistor R7.

[0049] Relay disconnection principle

[0050] When the input signal IN1 is low level, the relay KA is disconnected. The principle is as follows: PNP transistor Q4 is turned on, NPN transistor Q3 is turned off, the collector of NPN transistor Q3 outputs high level, PNP transistor Q1 is turned off, NPN transistor Q2 is turned on, and NPN transistor Q5 is turned off. During the disconnection of relay KA, the power supply charges capacitor C1 through the PNP transistor Q4, diode D2, diode D3, capacitor C1, resistor R2, and NPN transistor Q2 loop. The polarity of the capacitor is negative at the top and positive at the bottom. When charging is completed, the voltage across capacitor C1 is VC1 = VCC-VCE4-VD2-VD3-VCE2. Changing the number of diodes D2 and D3 can change the maximum value of VC1. Avoid excessive voltage on the relay coil during the later opening process, which may damage the relay.

[0051] Relay high voltage switching principle

[0052] When the input signal IN1 is high level, the relay KA is closed. The principle is as follows: the PNP transistor Q4 is disconnected, the NPN transistor Q3 is turned on, the collector of the NPN transistor Q3 outputs a low level, the PNP transistor Q1 is turned on, the NPN transistor Q2 is disconnected, and the NPN transistor Q5 is turned on; at the moment when the input signal IN1 is high level, the voltage applied to the coil of the relay KA is VCC+VC1-VCE1-VCE5, and the maximum coil voltage is approximately twice VCC, realizing high voltage opening; as the capacitor C1 discharges, the voltage difference across the capacitor C1 decreases to zero, and VCC reversely charges the capacitor C1, and the voltage polarity of the capacitor C1 is reversed, with the positive pole on the top and the negative pole on the bottom. When the voltage difference is greater than 0.7V, the diode D1 is turned on, bypassing the capacitor C1, and the voltage applied to the coil of the relay KA is VCC-VCE1-VD1-VCE5, realizing low voltage maintenance.

[0053] The capacitance of capacitor C1 is determined by the high voltage on time T0. The relay coil is equivalent to a resistor R KA , the transistor saturation voltage drop is 0.1V, the diode conduction voltage drop is 0.7V, and the capacitor C1 calculation formula is as follows:

[0054]

[0055] I0 is the peak coil current when the relay high voltage is turned on, N is the number of series diodes in the C1 charging circuit, and I1 is the coil current when the relay is held at low voltage.

[0056] The examples given in the present invention are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A relay drive circuit, characterized in that: Including PNP transistor Q1, PNP transistor Q4, NPN transistor Q2, NPN transistor Q3, NPN transistor Q5, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, diode D1, diode D2, diode D3, diode D4, capacitor C1, relay KA, positive power supply VCC, negative power supply GND, input signal IN1; The emitter of the PNP transistor Q1 is connected to the first end of the resistor R1 and the positive electrode VCC of the power supply; The base of the PNP transistor Q1 is connected to the first end of the resistor R5; The collector of the PNP transistor Q1 is connected to the first end of the resistor R2, the anode of the diode D1 and the first end of the capacitor C1; The emitter of the NPN transistor Q2 is connected to the negative electrode GND of the power supply; The base of the NPN transistor Q2 is connected to the second end of the resistor R1, the second end of the resistor R5 and the collector of the NPN transistor Q3; The collector of the NPN transistor Q2 is connected to the second end of the resistor R2; The emitter of the NPN transistor Q3 is connected to the negative electrode GND of the power supply; The base of the NPN transistor Q3 is connected to the first end of the resistor R3; The second end of the resistor R3 is connected to the first end of the resistor R6, the first end of the resistor R7 and the input signal IN1; The emitter of the PNP transistor Q4 is connected to the positive electrode of the power supply VCC; The base of the PNP transistor Q4 is connected to the second end of the resistor R6; The collector of the PNP transistor Q4 is connected to the anode of the diode D2; The cathode of the diode D2 is connected to the anode of the diode D3; The cathode of the diode D3 is connected to the cathode of the diode D1, the second end of the capacitor C1, the first end of the resistor R4 and the first end of the relay KA; The second end of the resistor R4 is connected to the cathode of the diode D4; The anode of the diode D4 is connected to the collector of the NPN transistor Q5 and the second terminal of the relay KA; The emitter of the NPN transistor Q5 is connected to the negative electrode GND of the power supply; The base of the NPN transistor Q5 is connected to the second end of the resistor R7.

Images