Equipment is to use a dc power supply equipment, metal shell, no battery, metal shell not connected to the earth, the equivalent of metal shell is a floating empty metal cover, there would like to ask the internal circuit board of the cathode GND (i.e., the power of the cathode), should be connected to the metal case? Why is that?

CodePudding user response:

This was because the ground knowledge don't understand, look to the ground knowledge,

CodePudding user response:

Metal case for safety is normally need to shell access to the earth, and to prevent electric shock or ESD interference to the PCB, but this product is special, the shell can't ground to the earth, and the power input is adapter, power supply, no ground, so here to discuss the "ground", actually is the GND of the PCB,
Actually mainly consider the ESD problems, don't worry about getting an electric shock (dc low voltage input), if you don't pick up PCB GND shell, there is a problem, is the metal shell is empty, the accumulation of static electricity is released, the accumulated to a certain amount, can produce arc discharge to PCB or even I will PCB with shell distance is far, to let it is not enough to produce arc discharge, but also worry that the PCB with the electrostatic field caused by signal caused by EMI interference, this is my worry about a problem, but if the shell to the GND of PCB, the ESD is to discharge directly to the GND on PCB, it will cause the negative potential was higher, also can lead to abnormal PCB work, so I don't know how to deal with, also please warrior to give directions, thank!

CodePudding user response:

Then put the adapter and equipment together, not the adapter to connect mains? That had the land.

CodePudding user response:

1: battery such as mobile phone, tablet, early walkman, radio, etc., outside the batteries do not need to check the power supply, if there is a metal case will need to connect the battery and the shell (usually a battery cathode), such enclosures and equipment circuit is potential, can improve the anti-interference, prevent electrostatic damage to equipment,
2: two lines of power supply of home appliance equipment (wire line, zero line 2 no ground wire), the device inside a AC/DC power supply (early some color TV with AC/DC isolated power supply), metal shell grounding in the form of this equipment is more,
3: with ground communication power supply equipment, earthing is necessary,

Ground also has several,
1: the GND PCB board and shell "zero resistance connection,"
2: PCB board GND connected with the shell "resistance",
3: the GND PCB board and the shell "small capacitance" connection,
4: the GND PCB board and the shell "small capacitance/big resistance" in parallel connection,
Small capacitance 1000 pf/3000 v, big resistance is greater than 1 m ohm resistance (greater than 1 w), big resistance electric shock security is to consider the human body, capacitance is to provide anti-interference,

A battery-powered device, most of the ground 1 way,
220 v two-wire power supply equipment, 1, 2, 3, 4 the grounding of several, 4 way more ground, mainly considering safety, the power of the AC/DC isolation, 1 4-trichlorobenzene is common, for safety is not recommended 1.

CodePudding user response:

@ qq_708907433 thank you for your advice!
But still have some questions:
1. You said that the two lines of power supply equipment, power supply with isolated power, choose 1/2/4 scheme, you here say "equipment", the metal shell is also floated didn't pick up the right of the earth?
2. It is recommended to use 2/4 scheme, and is not recommended 1 solution, whether for ESD discharge through 0 r resistance, can instantly to the cathode potential rise? While by 2/4 scheme with big resistance buffer effect, to the cathode potential fluctuation is small?

CodePudding user response:

Also have a question not understand, is based on the electrostatic voltage reference, so the electrostatic discharge path should be where to go the low impedance of the earth, so my equipment is AC/DC isolated power input, namely with the earth also is completely isolated, electrostatic accumulated to the metal case, the PCB is also can't walk? On the earth can only form a static electric field, the electrostatic field disturbance in the PCB?
If shell with PCB GND via resistance connection, also can only transfer electrostatic to PCB, without the formation of a current path, there is no current path, before there is no worry about the negative potential of raising the problem, instead of electrostatic accumulated on the PCB will be a greater impact on PCB, don't know me analysis of right, also looks correct, thank you.

CodePudding user response:

220 v power supply, there is no ground equipment (metal shell is floated didn't pick up the earth), the security point of view, there are no reliable grounding device is not safe, there is leakage, the risk of electric person,
High resistance grounding, is to prevent equipment damage caused by static electricity, high resistance, but also to reduce the risk of human body electric shock,
Said electrostatic refers to equipment at work here, the air friction, the body touch small current from high voltage electrostatic, high resistance can effectively release the electrostatic, make between metal shell and circuit board equipotential body,
If the metal casing floating empty, in the surface of the shell is easy to produce a few kv high-voltage electrostatic, and there is also a high potential difference between circuit boards, will produce the harm of the electrostatic discharge can damage circuit,
ESD discharge experiment, small current, high resistance of pressure drop is small, also will not damage the circuit board,
0 ohm resistance, be helpful for ESD etc. Through the experiment, but no reliable grounding, is a potential safety hazard,
Financially aware, safety is the most important, it is a good isolation power supply isn't guaranteed to water, fire, lightning, mechanical shock causes such as leakage, earth is dangerous,

CodePudding user response:

Metal case there is no potential difference between circuit board and can guarantee the safety of the circuit board, metal shell may be on the high tension line of high pressure tower, it doesn't matter, no difference between him and the circuit board, as long as the PCB with the surrounding the conductor potential difference (metal shell) no, no discharge, don't strike a light won't damage, ESD high pressure can't bad, how to play circuit safety, the safety of the people see,

CodePudding user response:

@ qq_708907433
You mean, if you don't consider the risk of electric shock, single from ESD consideration, 0 r resistance is better, the shell with the PCB GND to reliable connection to eliminate the potential difference, avoid discharge between shell and the PCB, so in fact that is equivalent to GND with electrostatic gun directly on the PCB, so whether there will be a problem? The electrostatic discharge path in where?

CodePudding user response:

Does not consider the safety of the people, PCB GND 0 ohm shell, electrostatic gun to GND, test of AC/DC power supply, electrostatic discharge is also see the power of the isolation degree, insulation good electrostatic didn't release channel also won't damage the circuit,
With good insulation isolation power supply, with a metal shell protection circuit board, it doesn't matter no electrostatic discharge passage,
Usually shell after the earth is the safest and most simple and lowest cost,
Industrial electronic equipment, we do 220 v + ground power supply, the shell by the earth, and the PCB GND 0 ohm after the earth is one of the most common and effective practice,
But in the countryside, no ground in some places, the electronic equipment is relatively easy to damage,

CodePudding user response:

Learning has been I don't have to how to use this