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In need of circuit: 12V Car Battery - > 22V 2A Laptop

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Does anyone know where to get a circuit diagram of a DC DC converter,
I ve been looking for this for several weeks, without any result.
I have a laptop that draws lots of amps, and I am trying to use it while
working out of home (its litium battery is death :cry: )
Thanks in advance

Hi Aldo,

Sierra Solar Systems do a 12 to 24 volt step up
converter for $54

**broken link removed**
These are pricey, four to six hundred somethings,
probably dollars.
these are all over a hundred dollars.

just put this:
"12 to 24" volt
into google, 1710 hits

If you want to build your own, see:
**broken link removed**

A 12 to 24 volt unit which was made for a solar panel,
but looks about right for a laptop.

Best of luck, John :)
Aldo - I was surfing thru the National Semiconductor website and stumbled on to their design area. It would appear that they have a way to help select a device and from the applications guide there are schematic diagrams. I was left with the impression that for many common applications the on-line design center would literally give you the values and sources for all of the critical parts. I was pleasantly surprised that with one design (similar to your needs) that the most critical part was the inductor and it was a 2 dollar item.
Hi guys,
thanks for your replies,
I ve been looking at the diagram that you John provides,
it looks not so difficult, I m gonna search for the IC the author
Thanks you Stevez for your help, I m gonna take a look on that
web site,
Thanks a lot guys,
Have a great day

HAHAH i dont know HOW manny times i see this on forums all over... and everyone edns up spending way to much time, money, and headaches trying to figure itu out! and it can cost you somewhere between 20-40 dollars! not $600 dollars. just get a simple DC-AC inverter, then just use you rAC adapter in the car.. i got my 60 watt inverter at Walmart for just $22 dollars. my friend got a 300 watt for a measly $60 dollars at a computer fair... its alot cheaper, and has WAY more uses! (IE radios and small Tv's, full computers and LCD monitors..ect..)
Hi Jaw174,

That sounds like a very practical suggestion.
I have a small inverter,
but i have never tried it on any computer stuff,
ive always thought the output was a bit too rough.

As for running it through the laptops charger-pack
or AC-adapter that comes with the laptop,
i am a little wary of doing that.

I may put a dummy load on the adapter, to see how
it behaves from the inverter.

Certainly worth checking out,

Cheers, John :)
This is a possible solution...


  • boost.gif
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Hi there TheDisturbedOne,

Yes, its that sort of thing.
An inverter (typically)gives a square wave into a transformer
from a battery, and the transformer steps up to mains voltage.

Its ok for lots of stuff, but it can upset some electronic goods.

Maybe they do units now that give better waveforms.

Regards, John :)
I use an inverter to power the laptop from 12V (boat) batteries. It is about the simplest solution for this application. The cheaper inverters (like my 150W unit) output what's called a modified sine wave, it looks like a stepped square wave. Since this is fed into the laptop's mains power supply, which is usually of the switching variety, it is this and NOT the laptop that gets the modified sine wave. There appears to be no problem with my inverter to power the laptop's power supply. My laptop is a 18V unit, so it draws about 1/3rd more Amps than stated on its power supply from the boats 12V batteries.
Hi ,
you guys are posting very good ideas,
porbably an inverter is not that expensive, but
what 's going to happen if I like to keep the laptop on while
turning off and on the engine?
I know there is always some surge from the alternator,
Is there any way to eliminate most of the surges and provide safe
operation to the laptop even with frequent on and offs?
Thanks a lot 8)

I'm sure, no need inverter. If You build the boost converter ( my previous post ) with serial diode and high capacitor on input, it will work.
why would you spend the time on a circuit if u can get an inverter much faster, as well as cheaper. ypu dont need to worry about the sine wave issue, as its going into another transformer to the laptop, which is further smoothed out by the capacitors in the AC-adaper. if you are worried about back surges and the like, most if not all inverters are prepared to handle that, as my cheap one even is, but if you witsh, you could add a surge supressor/ UPS and further lengthen the ability to supress teh minute surges that MAY occur. i have been using my inverter for 2 years with several cars, in a 97' mercury villager, an 87' honda civic, and a 74' ford pickup. iv had No problems whatsoever in any of these vehicles, and neither should you... and if you DO then its probably because you are exceding the wattage ratings, if ur using like a oven or somethijng, not becasue of surges of not the correct wave forms. AC out of the wall isnt always perfect either, the wave forms can be "deformed" as well. i know my friend lives in an old are of town and needs this box thing hooked up to his monitor to reconvert the signal from whatever it is to a since/square wave otherwise he gets lots of "fuzz".
Hi guys,
I can see that the circuit posted by Sebi is not that difficult to build,
the problem is where I live, I don't have any electronics shop to go and buy the components, even the IC ( I think is a National Semicond) this one is not expensive, but like Jaw says, yeah, is faster to get one from Walmart,
I m gonna take a look there,
now I have another question, but it s related to the laptop lcd,
I m gonna post it in the right forum,
Thanks a lot guys, very useful ideas....and don't get mad!! be :wink: :lol:

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