power supply

[mike havens]

Thanks for the tutorial. It was very informative! I took the battery out the
moment you told me to test that . So far no crashes but I've had it go days
without crashing so I suppose it is just a wait and see type of thing.

On 10/19/09, Jim March <1.jim.march at gmail.com> wrote:
>
> On Mon, Oct 19, 2009 at 8:03 AM, mike havens <bmike1 at gmail.com> wrote:
>
> > so the prick is the power supply? Thanks for the help.... I am so
> thankful I
> > found you guys. You all are so helpful and friendly.
>
>
> Well mostly :).  OK, here's how power management really works in a laptop.
>
> The "brick" turns AC wall power into DC.  I just picked up a Dell
> brick off my floor, it's putting out 19.5v DC.  That's the main power
> supply, what most people just call "the power supply".  Like most of
> these bricks, my Dell brick can take in foreign-spec AC (220v at 50
> cycles) in addition to US-spec.
>
> Once DC gets into the laptop, a much much smaller DC-to-DC power
> supply turns it into 12v, 5v and usually 3.3v or so.  Sometimes 2.8v.
> It's very, VERY uncommon for that part to break, because it's not
> under as much stress.  The reason the main power supply (AC-to-DC
> "brick") is external at all is because it heats up from the amount of
> work it does...and because they blow up a lot, the makers want to be
> able to quickly swap them with no screwdriver involved.  By the time
> power gets all the way into the laptop past the brick, a lot of the
> "heavy lifting" power conversion is already done by the brick.  The
> laptop is being spoon-fed something very easy to digest.
>
> If the DC-to-DC internal power supply blows, you're screwed - it's
> part of the motherboard most of the time.  But you're also having an
> astonishingly unlucky day if that happens, I've never seen it myself.
>
> There's one more circuit involved: the "battery charge controller".
> This takes DC in and spoon-feeds it in and out of the batteries,
> detecting when the batteries are full and chopping power when they
> are.  Good ones slowly back off the power as it gets close to full.
> That circuit is built into the battery pack itself, so swap batteries
> and you swap that.  The laptop can run without it, and if that charge
> controller goes bonkers it can cause problems such as you're having.
> Hence as a test run it without the battery, eliminate that as an
> issue.
>
> The reason you have the charge controller in the battery is to allow
> different capacity battery packs.  You can order three different
> grades of battery off of Dell for example for my laptop, and each will
> have different charge controller settings for their respective
> internal battery arrays.
>
> That's how laptop power works.
>
> Desktop power supplies are simpler: they take AC in, put out the
> various DC types the system needs.  Even then most motherboards will
> have a small DC-to-DC power supply on board to feed very clean and
> precise stuff to the CPU and in many cases vary the CPU voltage under
> software control.
>
>
> Jim
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-- 
:-)~MIKE~(-:
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