Principle of relay drive circuit Relay drive circuit precautions
1. The transistor is used to drive the relay, and the emitter of the transistor must be grounded. The specific circuit is as follows:
Relay drive circuit principle Relay drive circuit precautions
When NPN transistor is driven: when the base of transistor T1 is input high level, The transistor is saturated and turned on, and the collector becomes a low level, so the relay coil is energized, and the contact RL1 is pulled in.
When the base of transistor T1 is input with a low level, the transistor is turned off, the relay coil is de-energized, and the contact RL1 is disconnected.
The PNP transistor drive circuit is not currently used, so it will not be introduced here.
1.2 The role of each component in the circuit:
Transistor T1 can be regarded as a control switch, generally choose VCBO≈VCEO≥24V, and the magnification β is generally selected between 120～240 . . Resistor R1 mainly plays the role of current limiting and reduces the power consumption of transistor T1, and the resistance value is 2 KΩ. Resistor R2 makes transistor T1 cut off reliably, and the resistance value is 5.1KΩ. Diode D1 reverse freewheeling to suppress surge, generally choose 1N4148.
2 IC 2003 Drive Relay
The left figure 1~7 is the signal input (IN), 10~16 is the output signal (OUT), 8 and 9 are the IC power supply. The picture on the right is the internal schematic diagram of the integrated block.
Relay drive circuit principle Relay drive circuit precautions
Relay drive circuit principle Relay drive circuit precautions
2.1 Introduction to the working principle
According to the input and output characteristics of the IC driver 2003, some people call it “driver”, “inverter”, “amplifier”, etc., and the commonly used model is: TD62003AP. When the input terminal of 2003 is high level, the corresponding output port outputs low level, the relay coil is energized, and the relay contact is closed; when the input terminal of 2003 is low level, the relay coil is powered off and the relay contact is disconnected; in 2003 The diode for reverse freewheeling has been integrated inside, so it can be used to drive the relay directly.
2.2 The method of overhauling and judging the quality of 2003 is very simple. Use the DC gear of the multimeter to measure the voltage of its input and output terminals respectively. If the input terminals 1~7 are low level (0V), the output terminals 10~16 It must be high level (12V); on the contrary, if input terminals 1 to 7 are high level (5V), output terminals 10 to 16 must be low level (0V); otherwise, the driver is broken.
Test conditions: 1. Standby; 2. Power on.
Test method: adjust the multimeter to 20V DC, connect the negative test lead to the ground wire of the electric control board (7812 voltage stabilizer block heat sink), and touch the positive test lead to each pin of 2003 lightly.
