Electronic – 3 Contact Laptop Power Supply

power supply

So I'm wondering if anyone has any information about the Dell power supplies which have 3 contacts on the barrel.

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I know the 3 are power, ground, and some sort of communication link. Does anyone know what the communication line is for and/or what kind of protocol it uses?


EDIT The reason I ask is I'm considering trying to build my own semi-advanced charger (not for a laptop but something else… it's a long story) and while I'm sure I could figure out a charging circuit given the internet as a resource, I was wondering what they use the communication line for and if it's necessary for my purposes. It seems the answer is no since I will be the only one using my device and thus don't need to worry about people plugging in not kosher chargers…

Best Answer

The protocol is 1-wire; it's used to read a DS2501 write-once memory chip: http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed

I have no idea what data is in the chip, but you can probably read the data out of a working power supply and see if you can decipher it.

The data might contain information about the max current the supply can output.