EMC experiment practical case ESD electrostatic experiment

For any one EMC experiment , I like to use Sun Tzu's art of war “ Enemy and know yourself , you can fight a hundred battles with no danger of defeat ” this sentence , Because in and products EMC In this war . As long as we know ourselves and the enemy , I think I will be invincible .
EMC Not a cunning opponent , It showed us all its cards , If we can't overcome it , Then we have to think about our own problems , What is his card ？GB/T 17626！ If you don't know the standard , Rectification EMC How to start with ？
The front is pure gossip , Get to the point .

1：ESD Basic introduction to electrostatic experiment

Electrostatic experiment （GB/T 17626.2） Little friends who don't know suggest Baidu .
Here are two pictures that need your attention
The first picture is as follows

The most important information conveyed by this diagram is the interference source ,EMC One of the three elements of the problem , The discharge head is the gun that discharges the product , Round head for air discharge , Tip for contact discharge . The connection point of the discharge circuit is the clamp , This clip is usually clamped directly on the ground , good , Then according to the principle that the signal returns to its source , The protective device is directly connected to the connection point between the discharge place and the discharge circuit , Then the general direction of solving the electrostatic problem is set , This problem 80% resolved .

The second picture

This is the discharge waveform we usually use , Then the important information provided by this figure is to select the response time of the protection device , Electrostatic protection suggestions ps level , commonly ESD Devices and TVS Can effectively protect .

Two ： Examples of rectification
A while ago, I received a ESD Rectification project , It's a controller , Its general structure is as follows ：

Draw roughly , The experimental phenomenon is air discharge 8kv, The discharge position is at the button and LED It's about , The controller crashes or keeps resetting .

The reason for the preliminary investigation is the button and LED The control pin is not placed with any ESD Protective devices , Static electricity enters directly MCU Cause restart or crash .

Rectification plan ： On buttons and LED Control pin increase ESD Protective devices .

Retest experiment passed .

The problem of knowing yourself and the enemy is simple , You didn't add any ESD The protection device wants to experiment ？ Tell the truth , In fact, whether to do the experiment , The results are very obvious . Fought unprepared battles , Even if you win, you will be confused .

3、 ... and ： Experience induction and summary
1： The key signal of discharge position needs to be added ESD Protective devices .
2： Sensitive signal wiring should be away from electrostatic discharge points .
3： Sensitive signals are filtered by software and hardware .
4： The relief circuit of protective devices should be as wide and short as possible .
There are two ways of electrostatic interference ： Conduction and coupling , For conduction 1 Method , Coupled use 2,3 Method .