EMC surge protection and decoupling design

Level III surge protection and decoupling design

Level III surge protection and decoupling design

Surge (surge) Also known as surge 、 Transients (voltagetransient), It is a short circuit 、 The sudden phenomenon that the current exceeds the peak value of the stable value instantaneously caused by power switching or large engine switching , It usually refers to a kind of spike that occurs in a few millionths of a second , It usually includes surge voltage and surge current .

Surge protection principle

Surge is very harmful , The circuit can be burnt out instantly , And surge protection is to use linear components to protect high frequency ( Surge ) The sensitive design of the protection circuit , Simple and commonly used are shunt capacitors and series inductors . For commercial equipment , The sudden peak energy is generally absorbed by the product with surge blocking device , Protect connected equipment from surge damage .

In circuit design , Generally follow “ Multi level protection 、 Step by step reduction ” Principles , Combine and use a variety of protection components , Realize system level 、 Highly reliable surge protection .

First level protection

In most protective circuits , The first level is the port that is easiest to introduce lightning spikes .

For building inlets 、AC Power input port and other applications , In these occasions, large current protection devices such as gas discharge tubes are selected , Such as GDT、SPG、TSS、 Signal lightning protection module (SPD) etc. . High arc extinguishing voltage can be applied to DC circuit GDT, Similar to leimao electron 2R350-8LH, It can be used for DC24V Direct bridging of ,

Two level surge protection scheme

For power port applications , For the first level protection, clamp type large current protection devices that can withstand high voltage or large current are generally selected . If the switch type protection device is selected at the power port , In case of overvoltage, the voltage of switching device is low after it is turned on , It affects the supply voltage of the system , On the other hand, the system voltage may remain in the on state and cannot be disconnected normally , The system passes a large current for a long time ( Such as A Stage current ) May cause fatal injury to the circuit board , Even cause a fire .

MOV Add GDT Protection plan

For the first stage clamping overvoltage protection device of power port , Generally, metal oxide varistors are selected (MOV)、 Super power TVS(hyperfix), Or the lightning protection module composed of these devices (SPD) etc. . Of course , The low-speed signal port can also select clamping devices for the first level of protection , But the premise is that the junction capacitance of the clamping device can not affect the normal communication of the communication line .

Second level protection

The second level of protection is similar to the first level of protection , Generally, the device with fast reaction speed and low clamping voltage is selected TVS、ESD etc. .

At the second level , The too prominent spike pulse has been cut off by the first stage , Only interference signals smaller than the first threshold are left 、EMI And the secondary noise . among ,ESD Specially designed for door anti-static components , By multiple diodes or TVS It's a combination of , Suitable for high-speed data lines ESD protective , Such as HDMI、USB3.0、IEEE1394 etc. .

Decoupling components

The decoupling element has a certain impedance , The function is to ensure that the two-stage overvoltage protection devices work together . Because the types of overvoltage protection devices adopted by the first level protection device and the second level protection device are different , The breakdown voltage is different , Different response times , It has to be matched by decoupling elements .

In design , The second level overvoltage protection device generally adopts the small through current low-voltage device with fast response speed , When the surge voltage surges, the pilot will be switched on , Decoupling device has certain internal resistance , When passing large surge current , It will increase the voltage before the decoupling element to above the breakdown voltage of the first stage overvoltage element , After the first stage element is turned on, it can discharge and amplify the surge current , Thus sharing the pressure of the second stage protection device . If there is no decoupling device between two-stage overvoltage protection devices , In this way, the second stage protection device will always be in the pilot on state , When the surge current exceeds the capacity of the second level components, it will be damaged .

When selecting decoupling devices , It should be selected according to the working current of the circuit , For example, the working current of some signal circuits is small , Under the condition of ensuring normal communication, power type resistor or self recovery fuse can be selected (PPTC), Decoupling resistance is generally selected 10Ω within . From the perspective of surge protection , The greater the decoupling resistance, the better , But not too big , Otherwise, the normal working current of the line will be affected , Engineers should consider comprehensively in circuit design .

For some low-frequency lines with large input current , Inductance can be selected for decoupling , The calculation formula of inductance impedance is Z=2πfL, When the decoupling impedance value is determined , The inductance used can be calculated from the formula .

single TVS Protection plan

Similar to 5G The lightning protection design circuit of the base station , For electricity VC Clamping voltage requirements are very high , You can also use single TVS Protection plan for , It uses leimao electronic AK series TVS, similar AK10 AK15 protective 10KA Grade TVS, This type of scheme is characterized by very low residual pressure .

This article comes from the Internet ：《 Level III surge protection and decoupling design 》