ITX PSU (12V Brick + DC-DC PCB) weird GND/earth connection - Page 1
Forum section: electronics / beginners

author: neo2001
author_rank: Contributor
timestamp: July 04, 2023, 10:35:18 am
content: Over a longer period of time, I got some power supplies, from different sources, that are supposed to be used with small (Mini-ITX) cases. The external part is a power brick with a DC output of 12 V (some use 19 V or more). Inside the case is a small PCB, which creates the other voltages needed (5 V, 3.3V,...). These come either already installed with the case or can be bought separately.Both parts are connected using a regular barrel jack (5.5/2.5) on the backside of the case, which is connected internally to the mentioned PCB. The PCB itself provides the ATX connector(s) usually needed.The barrel connector has 3 contacts: tip, sleeve and insertion detection. Insertion detection is connected to sleeve as long as no plug is disconnected. If a plug gets connected, the insertion detection pin is mechanically disconnected from the sleeve.Now the weird thing is, that all these PSU combos use a green/yellow wire that is connected to this insertion detection pin and are supposed to (or simply are) connected to the metal case. But I don't understand why? I would understand, if this wire would be permanently connected to the sleeve, for a better GND/earth connection to the case, but this way it actually gets disconnected when the plug is inserted. In the end, it doesn't matter, since DC GND is connected to PE/Earth anyway through the power brick and the standoffs of the PCB. But there are multiple devices that do this, so I don't think it's a mistake of a single device.What could be the reason for this connection?

author: agehall
author_rank: Frequent Contributor
timestamp: July 05, 2023, 11:10:30 am
content: You can’t really have PE in a standard barrel jack since it only has two connections (+ and GND). Makes me wonder if this is some sort of contraption to counter ESD when the computer isn’t plugged in..?

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 05, 2023, 11:26:25 am
content: This is PicoPSU (clone?) kind of thing right? Why do you assume they know what they're doing?

author: neo2001
author_rank: Contributor
timestamp: July 05, 2023, 11:28:07 am
content: Yes, some power "bricks" (if they even have earth connection) seem to connect GND to PE/Earth either directly or with a certain resistance in between.I think connecting the case to the detection pin is either some kind of genius move I don't understand or simply makes no sense, and they just copied this from each other without understanding why.

author: neo2001
author_rank: Contributor
timestamp: July 05, 2023, 11:42:53 am
content: Quote from: ArdWar on July 05, 2023, 11:26:25 amSome of them are sold by reputable brands, like Chieftec:https://www.chieftec.eu/products-detail/192/Adapter___DC_to_DC_SERIEShttps://www.inter-tech.de/productdetails-155/ITX-601_EN.htmlBut there are also cheaper ones on AliExpress and eBay with a "simplified" layout. But they probably can get away with this, because it's only a DC to DC conversion and the system powered by those usually only need 15-20 W tops anyway. For the AC part, I tend to use a known (laptop)brand.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: July 06, 2023, 02:19:10 am
content: Since you don't need to switch from battery power (and detect it) there is an extra wire. It's a good idea to ground your case. So why not save some money and use the spare wire? There might even be a bit of EMI benefit by keeping this connection away from the PCB.