On 21 June 2010 18:52, Wojciech Zabolotny wrote: > I use the HP/Compaq nx7300, which I need to power from the car power > supply. Unfortunately, this laptop uses a nonstandard power supply > jack. > It features the inner and outer ring, which provide the high current > power supply, and also the thin central pin, which is used for ??? > I have three hypotheses: > 1. It may be used to control the operation of the AC charger from the > laptop (forcing the "power down mode"?) > 2. It may be used as a feedback connection to provide better voltage control > 3. (the conspiracy theory ;-) ) It may be a kind of serial interface > used to authenticate the original HP power supply to prevent using > other, cheaper adapters. > > Does anybody know what is the real function of this central pin? > The original power supply looks like this: > http://www.topfreebiz.com/product/469522/Original-New-Laptop-Adapter-For-HP-18.5v-3.5a-Center-Pin.htm > -- > TIA & Regards, > WZab > -- It's along the lines of option 3. The computer checks with the power supply and limits some functions depending on the reply. - and possibly the computer type. IIRC the battery should still charge with a non-standard supply but only at a low rate, and there may be a limit on charging while having the laptop turned on. YMMV Richard P -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist