What is the working principle and function of the relay?

June 14,2022

smartlife relay,8CH RS485 relay,8CH 10ARelay module

Relays are generally used when low-voltage controllers control high-voltage electrical appliances. When you want to control 220V voltage devices such as lamps, you can use a relay. Generally, a relay can be imagined as a switch that can be controlled by a smartlife relay or a single-chip microcomputer.

1. Electromagnetic relays.

When the circuit of the low-voltage power supply is disconnected, the electromagnet is not magnetic, then the high-voltage circuit of the lamp is connected, and the lamp is lit. Because, when the low-voltage circuit does not provide current, the switch of the high-voltage circuit is closed, so it is also called "normally closed".

When the circuit of the low-voltage power supply is closed, the electromagnet becomes magnetic, and the armature is sucked down, then the high-voltage circuit of the motor is connected, the motor starts to work, and the light goes out at the same time. Because, when the low-voltage circuit does not provide current, the switch of the high-voltage circuit (the lower right part of the above figure) is disconnected, so it is also called "normally open".

Since it is a mechanical device, there will be some unique shortcomings such as: 1. The service life is relatively short. 2. The switch is noisy. 3. The switching speed is relatively slow.

Second, solid state relays. The solid-state 8CH 10ARelay module is also compatible with the pins of the common electromagnetic 8CH RS485 relay, but its internal structure is completely different. A solid state relay consists of three parts: input circuit, isolation (coupling) and output circuit.

The input circuit is generally voltage matched. For example, it will generally match the TTL or CMOS level. For limiting the input current or protecting it when the input is too large, different relays are different, and you need to read the specifications. The isolation circuit is generally isolated by an optocoupler or a transformer to isolate the input and output, thus preventing the high voltage at the output from affecting the low voltage at the input.

The output circuit is generally composed of high-power transistors (switch-transistor), one-way thyristor (Thyristor or SCR), two-way thyristor (Triac), power field effect transistor (MOSFET), insulated gate bipolar transistor ( IGBT) composition. In short, it is a power tube with high current and high voltage.

The equivalent circuit diagram of the solid-state smartlife relay is roughly like this: From the above introduction, it can be seen that a relay needs to be connected to the 8CH RS485 relay, and a lot of peripheral circuits are required.

One is to protect the relay (the electromagnetic relay itself has a coil, and a discharge circuit is required after a power failure, otherwise the coil may be damaged)
The second is to amplify the signal of the pin, because the current required by the coil of the 8CH 10ARelay module may be relatively large, and the pin cannot provide it, so the circuit will be added to amplify the pin current.

The third is to do some peripheral circuits to illustrate the status of the relay, which is usually some indicator LEDs.

K is the relay. The diode D2 is used to discharge the relay coil. Q is the transistor used to amplify the pin current. D1LED is used to indicate the working status of the relay. D3LED is used to indicate whether the power is on. Therefore, the existence of the module is to facilitate the connection of the Arduino to the relay, which is purely for lowering the threshold.

smartlife relay, 8CH RS485 relay, 8CH 10ARelay module For more inquiries, you can contact us.