1. To ignite the catalyst, it must be grounded polarly.
When the NPN transistor is driven: When the base of the transistor T1 is input high, the transistor is saturated and turned on, and the collector becomes low. Therefore, the relay coil is energized and the contact RL1 is closed.
When the base of the transistor T1 is input low, 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.
The role of each component in the circuit:
Transistor T1 can be regarded as a control switch. Generally, VCBO≈VCEO≥24V is selected, and the amplification factor β is generally selected between 120 and 240. . Resistor R1 mainly acts as a current limiter and reduces the power consumption of transistor T1, with a resistance value of 2 KΩ. The resistance R2 makes the transistor T1 cut off reliably, and the resistance value is 5.1KΩ. Diode D1 reverses freewheeling to suppress surges. Generally, 1N4148 can be selected.
2 Integrated circuit 2003 drive relay
Figures 1 to 7 on the left are signal input (IN), 10 to 16 are output signal (OUT), and 8 and 9 are integrated circuit power supplies.
2.1 Introduction to working principle
According to the input and output characteristics of integrated circuit driver 2003, some people call it "driver", "inverter", "amplifier", etc., and the commonly used model is now: TD62003AP. When the 2003 input is at high level, the corresponding output port outputs low level, the relay coil is energized, and the relay contacts are closed; when the 2003 input is at low level, the relay coil is de-energized and the relay contacts are disconnected; in 2003 The diode has been integrated to play the role of reverse freewheeling, so it can be directly used to drive the relay.
2.2 The method of repairing and judging the quality of 2003 is very simple. Use the DC gear of a multimeter to measure the voltage of the input and output terminals. If the input terminals 1～7 are low level (0V), the output terminals 10～16 must be high level (12V). ); On the contrary, if the input terminals 1～7 are high level (5V), the output terminals 10～16 must be low level (0V); otherwise, the driver is broken.
Test conditions: 1. Standby; 2. Turn on.
Test method: Adjust the multimeter to 20V DC, connect the negative test lead to the ground wire of the electric control board (7812 regulator block heat sink), and lightly touch the 2003 pins with the positive test lead.
3.1 Optocoupler drive relay circuit diagram
The relay switch module is composed of TLP521-4, ULN2803, SRD-12VDC and triode. The signal output by the microcontroller is sent to the TLP521-4 optocoupler chip through the switch circuit composed of triode and then amplified by ULN2803 Darlington. Drive the SRD-12DC relay, and then achieve the role of various switches that control the air conditioner, the relay switch control module and the microcontroller circuit
3.2 Optocoupler drive relay circuit diagram
Isolation drive circuit with photocoupler
In the interface circuit of the microcomputer, there are generally two ways to realize the isolation between the host and the peripherals: one is to use a relay; the other is to use a photocoupler.
The power consumption of the battery is the priority for the power consumption of the battery. The circuit in the figure uses a photocoupler as isolation. The current consumption of the battery can be as low as 50μA, but the current provided by the driver is greater than 1A.
This circuit has relatively high requirements for components. The photocoupler U1 can only use genuine components of the model of CNY17F-4. In the experiment, more than ten kinds of photocouplers have been tried. When the input current of this model is 50μA, the circuit can work, and the rest The driving current of the photocoupler needs to be several hundred microamperes or more.
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