What is the difference between the GND of a 3-pin power supply and the GND of a 2-pin power supply?

Nubility

What is the difference between the GND of a 3-pin power supply and the GND of a 2-pin power supply? [Copy link]

 

The outputs of common 3-pin and 2-pin power supplies only have positive and negative poles (GND). In the case of isolated power supplies, there should be no risk of electric shock. What is the function of the extra ground on the 3-pin power supply? We all know that it is for safety and anti-interference, but we can't just ignore it.

I once accidentally plugged a 3-pin laptop (metal case) into a 2-pin power strip, and felt a stinging sensation on the touchpad, but it was not an electric shock. I replaced it with a 3-pin power strip, and the stinging sensation disappeared.

My guess: There is still a certain voltage between the GND of the isolated power supply and the earth, and touching it with your hand can make people feel tingling. The GND of the 3-pin power supply is connected to the earth in some way, so there will be no tingling sensation when touching the metal shell.

Is there any big shot in the power supply industry who can tell me if this is the actual practice?

maychang

[Personal guess: There is still a certain voltage between the GND of the isolated power supply and the earth, and touching it with your hand can make people feel tingling. The GND of the 3-pin power supply is connected to the earth in some way, so there will be no tingling sensation when touching the metal shell with your hand]

Your guess is wrong.

Nubility

maychang posted on 2024-6-8 18:54 [Personal guess: There is still a certain voltage between the GND of the isolated power supply and the earth, and people can feel tingling when touching it with their hands. The G of the 3-pin power supply ...

How to do it specifically?

maychang

The switching power supply in the picture above uses a three-pin plug for the AC input. The longer pin of the three-pin plug is plugged into the protective ground wire (of course, the premise is that the corresponding hole of the socket has been connected to the ground). The switching power supply in the picture below uses a two-pin plug for the AC input, and the protective ground wire pin of the three-pin plug is missing.

Nubility

maychang posted on 2024-6-8 18:54 [Personal guess: There is still a certain voltage between the GND of the isolated power supply and the earth, and people can feel tingling when touching it with their hands. The G of the 3-pin power supply ...

The USB metal shell of the mobile phone charger also feels the same tingling sensation when it touches the skin

maychang

Nubility posted on 2024-6-8 18:58 The USB metal shell of the mobile phone charger also feels the same tingling sensation when it touches the skin

[The USB metal shell of the mobile phone charger also causes the same stinging sensation when it touches the skin]

Mobile phone chargers all have two pins, I've never seen a three pin one.

maychang

Nubility posted on 2024-6-8 18:56 How to do it specifically?

Specifically, no matter which type (the three-pin power supply and the two-pin power supply you mentioned), its output end (which you call GND, which is wrong) is insulated from the AC mains and has voltage resistance requirements. However, there is a capacitor (many articles call it Y capacitor) between the output end of the switching power supply and the AC mains. The so-called two-pin power supply, its Y capacitor is connected to one line of the AC mains (a two-pin plug, which may be the phase line or the neutral line) or one end after the bridge rectification. If it is the former, then when you feel something when touching the output end, just turn the two-pin plug in reverse. If it is the latter, it is useless to turn the two-pin plug in reverse.

maychang

Nubility posted on 2024-6-8 18:56 How to do it specifically?

For the so-called three-pin switching power supply, the Y capacitor must be connected to the long pin in the middle of the plug. If the corresponding hole of the socket is connected to the ground, there will be no feeling when touching the output end. If the corresponding hole of the socket is not connected to the ground, the feeling of touching the input end is also very weak, much weaker than the latter case described on the 8th floor. If the corresponding hole of the socket is not connected to the ground, only the primary and secondary distributed capacitance of the transformer in the switching power supply will work, and the capacitance between the primary and secondary is much smaller than the Y capacitor.

Nubility

maychang posted on 2024-6-8 19:14 For the so-called three-pin switching power supply, the Y capacitor must be connected to the long pin in the middle of the plug. If the corresponding hole of the socket is connected to the ground, the contact output end will not...

Is this the way it is done in the product? Is there a schematic diagram I can refer to?

Nubility

maychang posted on 2024-6-8 19:09 Specifically, no matter which one (the three-pin power supply and the two-pin power supply you mentioned), its output terminal (which you call GND, which is wrong) is connected to the AC mains...

[Specifically, no matter which type (the three-pin power supply or the two-pin power supply you mentioned), its output terminal (which you call GND, which is wrong) is insulated from the AC mains and has voltage resistance requirements.]

This statement still cannot solve the problem that the positive and negative poles of the two-pin power supply will cause tingling sensation when they touch the human body

maychang

Nubility posted on 2024-6-8 19:35 [Specifically, no matter which type (the three-pin power supply and the two-pin power supply you mentioned), its output terminal (which you call GND, which is wrong) is connected to the AC mains...

[This statement still cannot solve the problem that the positive and negative poles of the two-pin power supply will cause a tingling sensation when they touch the human body]

To solve the tingling sensation caused by the 2-pin power output terminal touching the human body, there are two ways:

One is that the human body is not grounded, such as standing on an insulated stool.

Second, do not use a two-pin power supply, only use a three-pin power supply, and make sure the socket is connected to a protective ground wire.

Nubility

maychang posted on 2024-6-8 19:39 [This statement still cannot solve the problem that the positive and negative poles of the 2-pin power supply will cause tingling when they touch the human body] To solve the problem of the 2-pin power supply output terminal touching the human body...

That brings us back to the original question: Is the output of the 3-pin power supply directly or indirectly connected to the ground of the AC power supply?

maychang

Nubility posted on 2024-6-8 19:42 That brings us back to the original question, is the output end of the 3-pin power supply directly or indirectly connected to the ground of the mains?

[That brings us back to the original question. Is the output terminal of the 3-pin power supply directly or indirectly connected to the ground of the mains? ]

You didn't say [directly or indirectly] at first.

maychang

Nubility posted on 2024-6-8 19:28 Is this how it is done in the product? Is there a schematic diagram I can refer to?

The schematic diagrams of a switching power supply with low-power AC mains input and low-voltage DC output are everywhere. You can search for them. If you don't understand them, you can post a question on the forum.

乱世煮酒论天下

Is there a resistor-capacitor circuit between the output gnd and the pe of the distribution network to release the generated static electricity? If there is no grounding, the charge will accumulate on the pcb board and cannot be released, which will cause electric shock.

Nubility

乱世煮酒论天下published on 2024-6-8 20:11 Is there a RC circuit between the output GND and the PE of the distribution network to release the generated static electricity? If there is no grounding, the charge will accumulate on the PCB board...

Static electricity will disappear after just a touch. When using a 2-pin socket, there is a constant numbness and tingling sensation when touching the touchpad. This is because there is voltage between the metal case and the ground.

乱世煮酒论天下

Nubility posted on 2024-6-8 22:52 Static electricity will disappear after touching it. When using a 2-pin socket, there will be a constant numbness and tingling when touching the touchpad. This is because there is voltage between the metal casing and the ground

There is no induced electricity when using a three-pin socket, but there is when using a two-pin socket. Is this the case? Could it be that the induced electricity is in the metal shell? The switching frequency of the switching power supply is still relatively high. When the metal shell is not grounded, the human skin surface is relatively moist and it is easy to feel it. Otherwise, it is leakage.

Nubility

乱世煮酒论天下published on 2024-6-8 23:28 There is no problem with a three-pin socket, but there is with a two-pin socket. Is that right? Could it be that the induced electricity is in the metal casing? The switching frequency of the switching power supply is still relatively high...

It's possible. I've seen the PCB of a laptop, and the metal screw hole is connected to GND. If the metal shell is connected to the ground when using a 3-pin socket, then the connection should be completed inside the power adapter.

tagetage

One time, I accidentally plugged the 3-pin power supply of my laptop (metal case) into a 2-pin power strip. Did you make this power strip yourself? Have you seen any regular power strips you bought? Which one has a 2-pin input? Your power strip is not regular, no wonder you got electrocuted.

maychang

tagetage posted on 2024-6-9 10:36 Once I accidentally plugged the 3-pin power supply of a notebook (metal shell) into a 2-pin plug strip-------this plug strip was made by yourself, you can see it when you buy it...

[You made this power strip yourself. Your power strip is not standard, no wonder you got electrocuted]

Yes.