What is the principle of single-chip microcomputer control relay?
First look at the drive of the relay
This is a typical relay drive circuit diagram. Such diagrams can be found everywhere on the Internet, and standard textbooks are generally also such circuit diagrams.
Why understand the principle of this diagram?
The single chip microcomputer is a weak current device. Under normal circumstances, most of them work at 5V or even lower. The drive current is below the mA level. It is obviously not feasible to use it in some high-power applications, such as controlling motors. Therefore, there must be One link to connect, this link is the so-called "power drive". Relay drive is a typical and simple power drive link. Here, relay drive has two meanings: one is to drive the relay, because the relay itself is for the microcontroller It is a power device; there is also a relay to drive other loads. For example, a relay can drive an intermediate relay and can directly drive a contactor. Therefore, the relay drive is the interface between the microcontroller and other high-power loads. This is very important, because it has been Our electrical engineers (I mean those who have not learned the corresponding electronic technology) are puzzled: How can a small chip have such a powerful power to control a powerful thing like an electric motor?
How to understand this circuit diagram?
To understand this circuit, it is actually relatively easy. Then please follow my thinking, there should be no problem:
First of all, the triode inside is very important. The triode is a very important component in the electronic circuit. How to understand the triode?
In simple terms, the triode has two functions, one is the amplification function, and the other is the switching function. (Strictly speaking, the switching function is the limit of the amplification function, but it does not matter. Separating the two is easier to understand its working principle). Here, we only understand its switching function related to this circuit.
First think of the triode as a faucet.
The upper Vcc is the pool, the relay is a hydraulic turbine, and the lower GND is any point lower than the pool. As mentioned earlier, the triode is the faucet, and its handle is the pin with the resistor.
Now, a certain output pin of the single-chip microcomputer that needs to control this relay circuit is a "hand". When this pin of the single-chip microcomputer outputs a low level, it is like the "hand" turning on the triode "faucet", and the water is When the flow goes from top to bottom, the relay "turbine" starts to rotate. On the contrary, if the output is high, the "hand" starts to turn off the "faucet", and the relay "turbine" stops because there is no water flowing down.
This is the switching function of the triode.
The simple understanding and memory is: the triode is a switching device, in fact, you can really regard it as a switch, but it is not controlled by hand, but controlled by voltage (current), so there are some triodes It is also called an electronic switch (different from a mechanical switch).
There is another thing on the picture, it is the protection diode. If you don't need to understand it in depth, you don't have to chase why it exists, but you must remember that as long as the relay is driven by a triode, it usually exists. Special attention should be paid to its connection method: the cathode of both ends of the relay must be connected to Vcc in parallel
Attached is the relay module circuit on the STC8052RC microcontroller I learned
Oh, it turns out that this is a relay. This is my first feeling after checking the schematic diagram of the relay on the encyclopedia. It turns out that we have already learned physics in junior high school, but there is no such specific understanding at all, so I can take the exam.
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