On Mon, 2010-06-21 at 08:52 +0200, 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.

AFAIK it's actually #3, it's often used to confirm "authenticity",
although in some cases it's used to determine how strong a supply it is
(on some Dells for example there are two supplies available, one is
strong enough just to power the laptop, while the second can power the
laptop and charge the battery, or something like that).

TTYL

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