There are three options for commonly used surge protection circuits: First, the use of traditional lightning protection components combined into anti-surge circuits, such as TVS tube (TVS diode), gas discharge tube, PTC (Thermistor) and so on. The price of these lightning protection components is very low. Second, optical coupling circuit. (optical isolation devices, lower prices, TPL521-4 price is about 2 yuan.) Third, magnetic coupling circuit. Magnetic isolation is ADI's patented iCoupler technology and is based on chip-level transformer isolation technology. Using the relevant chips produced by the company can greatly simplify the circuit and reduce the area of ​​the PCB. (The price of adm2483 is about 10 yuan, and the price of adm3251e is between 10 yuan and 20 yuan.) The source of the surge: Surge is usually caused by the thunder of nature, the switch of the power system (especially with heavy inductive load), and the surge will bring huge transient transient over-voltage or over-current, for example, Induced transient interference caused by lightning on the RS-485 transmission line, whose energy can instantaneously burn down all the components that connect the transmission line. Generally referred to as anti-surge, there are two pressure indicators, one is common mode, and the other is differential mode. The surge generated by lightning or high-current switching in nature is generally considered to be common mode, and the surge in differential mode is often caused by the high-voltage line passing near the data cable, and the data cable and the high-voltage line are generated due to poor insulation. The voltage and current generated by the former are much smaller than those of the former, but it does not remain as short as a few milliseconds as in the former, but it will exist stably for a long time in the data communication network. The nominal withstand voltage of an optocoupler or a magnetic coupling device is common mode, that is, the withstand voltage between the front end and the rear end. If this pressure is exceeded, the front and rear ends are all burned together; the device will not be rated differential pressure resistance. This is determined by the design of the circuit. If this voltage is exceeded, the front end will burn and the back end will not burn out. Surge protection circuits are usually divided into isolation and evasion: First, the isolation method Optical coupling (need to isolate power supply) Optical coupler (optical coupler, OC), also known as optoelectronic isolator, referred to as optocoupler. Optocouplers use light as the medium for transmitting electrical signals. It has a good isolation effect on the input and output electrical signals, so it is widely used in various circuits. At present, it has become one of the most versatile and versatile optoelectronic devices. Optocouplers generally consist of three parts: light emission, light reception, and signal amplification. The input electrical signal drives a light emitting diode (LED) to emit a certain wavelength of light, which is received by the photodetector to generate a photocurrent, which is further amplified and output. As long as the voltage amplitude generated by the surge does not exceed the nominal value of the optocoupler device (usually 2500V), the optocoupler will not be damaged, even if the surge voltage exists for a long time will not damage the isolated device. It is worth noting that the optocoupler can only suppress the surge in the common mode and can not suppress the surge in the differential mode. Optocoupler isolation is widely used in RS485 or RS232 communications. The advantage of using optical isolation is that electrical or magnetic noise can be avoided. The disadvantage is that the transmission speed is limited by the LED's switching speed, high power scattering and wear, and an isolated DC-DC power supply is also required. Second, magnetic coupling Magnetic coupling is based on Analog Devices iCoupler magnetic isolation patented isolation device, also known as the secondary isolator. Since the purpose of the magnetic coupling is to isolate the input and output signals, the primary side of the transformer and the secondary side of the transformer must be on isolated chips. The transformer itself can be placed on any chip. Take ADI's ADM2682E (for RS485) as an example to illustrate the role of magnetic coupling in surge protection. The ADM268E2 is a fully integrated 5kV rm signal and power isolated data transceiver with ±15kV ESD protection for high speed communications applications on multipoint transmission lines. The ADM2682E integrates a 5kV rms isolated DC/DC power supply, eliminating the need for an external DC/DC isolation module. Compared with the optocoupler, the magnetic coupling not only lacks an isolated DC-CD power supply, but also has a level-shifting chip, which can greatly reduce the PCB area. Second, the evasion method The ground of the main equipment is connected together to form a single point of grounding. Once a surge occurs, it can safely transfer the surge energy. In addition, it is necessary to add some devices to suppress the surge. The device that can discharge the harmful current generated by the surge before it reaches the data port and discharges it to the ground loop. There are mainly TVS tubes, varistors, and gas discharge tubes. They all have a clamp voltage, once the clamp is exceeded. The bit voltage, the device will produce a low impedance between the connection point, thus transferring harmful currents, the specific circuit is as follows: However, these devices cannot be maintained for a long time due to the large amount of energy transferred. Generally, these devices are installed between the data line and the ground. For RS485 or RS422 systems, devices with a rated voltage of 6~8V should be selected. At the same time, they usually bring some capacitive load to the data lines. Therefore, the system is designed. It is necessary to consider reducing the length of the entire system data line. When installing the device, it should be as close to the protected device as possible. In addition, the user must ensure that the impedance between the grounding point of the protected device and the ground is very small, and the line connecting the grounding point to the ground is preferably thick and short. Beyond 1m, use copper wire or cable. (1) Single-stage protection Only one TVS is required for the data cable. (2) Level 3 protection The first stage is the gas discharge tube, which can discharge the amplified current. Because the surge produces a very high peak voltage at the same time, the gas discharge tube is too slow to protect the solid state circuit behind; the second stage is a small resistance, on the other hand, the current can be limited. On the one hand, a voltage drop occurs in the first and third stages; the third stage is a TVS tube, which can protect the solid state circuit behind quickly enough to clamp the voltage at a safe level to protect the data line. If the isolation method and the evasion method are combined, the system can be better protected. The specific circuit is shown above. In the figure, the signal ground is connected to the ground. With the isolation device, the main device is not affected by the voltage drop that may be generated at the ground point. In addition, the circumvention device can suppress the surge protection isolation device on the one hand, and can also suppress the differential mode surge generated on the data line on the other hand. In Fig. 8, the signal ground is not connected to the ground. The bypass device can suppress the differential mode surge generated on the data line, and the differential mode surge is balanced and converted into the common mode surge. The isolation device is just inhibited. It protects the master device. 72V20Ah Lithium Ion Battery,Electric Scooter Lifepo4 Battery Pack,Lithium Battery For Electric Motorcycle,Lithium Battery For Electric Bike Jiangsu Zhitai New Energy Technology Co.,Ltd , https://www.zt-tek.com
