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pschoen@xxxxxxxxxx wrote:
> mrdarrett@xxxxxxxxx wrote:
> > mrdarrett@xxxxxxxxx wrote:
> > > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external
> > > (switching?) power supply. (It didn't have a battery with it when I
> > > bought it - got it 2 years ago for about $200.)
> > >
> > > I recently built an external battery pack, powered by 16 Energizer 1.2V
> > > 2500mAh NiMH AA cells, to power my laptop in lieu of the external power
> > > supply, and it does work. So far I have been able to run the laptop
> > > for about an hour and a half, and still going strong. (Decided to stop
> > > stress-testing at 1:15am, since I had work the next morning.) A far
> > > cry from paying $150 for a "new" laptop battery, when the laptop only
> > > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" at
> > > anyone who glances at it... ;-)
> > >
> > > For my next project, a DC-DC converter.
> > >
> > > So... I'd like to convert 12VDC from a jump-start car battery to
> > > 18.5VDC, at 3A.
> > >
> > > After reading a recent thread about avoiding Maxim like the plague, I
> > > went over to TI's website, entered my parameters (Input V: 12VDC;
> > > output V: 18.5 VDC; current: 3A.)
> > >
> > > I found this from the search result:
> > >
> > > http://focus.ti.com/lit/ds/symlink/tps5430.pdf
> > >
> > > but I was a bit confused why this would have been suggested, since it
> > > seems to be a step-DOWN regulator.
> > >
> > > Any suggestions...?
> > >
> > > Thanks,
> > >
> > > Michael
> >
> >
> > Eh, no response from sci.electronics.basics; belatedly cross-posting to
> > SED. Better than multiposting... ;-)
> >
> > Michael
>
> You could use an isolated 12 V to 6 V DC-DC converter and add the
> output to your 12 volts from the battery. You could probably run it
> with a full square wave without regulation to simplify feedback. Just a
> high frequency transformer driven by something like a UC3526 and a
> couple MOSFETs, and a simple rectifier and filter on the isolated
> output in series with the battery voltage to get what you need. You
> could use the PWM to make it regulated if you want.
>
> Paul
Oh, that's elegant! Thanks!
Michael
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