Is there any way to build a simple dc-dc converter to power a 19V laptop in a car? Ideally, I would prefer one that went to ~25V, so I could regulate it as well. The laptop needs 3A at 19V. All of the designs on the internet either seem to use some part that I can't get. I need to get all of the parts at maplins, but already have pcbs and connectors. Otherwise, would a mains inverter work (I hear laptop power supplies can mess them up.)
proteus design file {you can download the demo to view this design} www.labcenter.co.uk yes you can do this simply by adding split charging circuit {a diode in series} from the battery you already have this way you can charge / get more power / get the voltages you need all from one three position switch its the safest way to do it and recomended instead of flapping electronics you can wire a nice bay on the radio dash,,, one solution anyway and will save you a packet.... just be warned the supply from a car system is 13.8 v not 12 so you will get 25.8 volts not 24 out as i have in the design above when its running
Maybe a stupid question, but any reason you just don't buy one? I got one for my dell for I believe $25 usd.
I see what you're saying, to a point. For me, I've been working on my laptop pc for over six months now (electronics ,software and fabrication) and still no end in sight. So for me, it was a nobrainer to spend the money and tkae care of the easy things.
sorry man ye your right i am a little too crytical of others ive just been into electronics too long to buy stuff ready made i like to wind my own coils and transformers, make my own tools and have many many of my own methods after 15 years at the bench after 10 years at solid study for this i am sorry its sometimes best to buy a ready made unit sometime i should anyway whats up with your laptop maybe i can help
Not at all. For me, with my limited skills at this time, building the power supply is just one more thing to put everything off as I hunt for parts or wait for mouser to deliver what I need. Then it's one more potential source of problems. Suppose it's the same reason I bought a PIC programmer instead of making one (yet). I figured for me, it would be best to start with something that was likely to work. Otherwise, I wouldn't be sure if any problems I had were with the circuit or the programmer.
the first pic i re-programmed was for paket in a chip on a pic16c74 in 1983 i used a bbc micro i didnt re-program another one till the pic16c84 in 1995 i used a noppp no parts parallel programmer its the experiance in dos some people dont have and the dos panel becomes a fight if you know that any dos command like copy.exe has switches and you can get help on any command by using /? or /HELP like copy /? or nopp /? format /? del /? etc... a big mistake is the name pic programmer becouse the pic is at zero when its made in hardware this is a program so it should be called a re-programmer not a programmer anyone selling a programmer is stupid or insulting already so not worthy of buying there devices however i got a cheep PICALL the other year for ease and the newer pic18 no re-programming circuits were avalible for at the time i do agree its not worth reinventing the wheel sometimes
wtf? Even Microchip, Atmel, TI etc. themselves call the devices Programmers. Does that mean you're going to not buy any of their devices? Fishcake was looking for a form of 12-19V DC-DC converter. I doubt he has two 12V batteries in his car, so your solution would not work. In addition, semiconductor devices should never be paralleled (with the exception of FETs) because of their manufacturing intolerances. You'd need some 0.1R resistors in series with each device. Fishcake, there's no problem with using a laptop power supply with a mains inverter. Just be sure to find an inverter with a sinewave output as some of the cheaper ones just produce a 50Hz squarewave which is fine for lamps etc, but will not work with switching power supplies as you noted.
Actually, most switching supplies will work with square waves and maybe DC. I actually have an inverter for a laptop that's merely a 12v to 170v DC/DC converter.
Depends on if the PSU has a universal input voltage. A squarewave input won't rectify to the same voltage as a sinewave which is what causes some PSU's not to work. The high frequency component of a squarewave is also not welcome depending on the filtering of the PSU.
Thanks everyone, really useful, I will probably have to buy one. Would it work though, if I made a 555 sine wave generator switching a high frequency transistor connected to a tranformer? Would I be able to make a true sine wave, or would a smoothed-square wave work? Also, would I connect the transformer between the emmitor of the transistor and 6V, to make it truly AC?
The issue with simple 555 converter would work, provided it could provide 3a (you'd need an external power transistor), and had some form of regulation. I believe there are ways to accomplish that using only a 555with few external components. However, the best idea would probably to simply buy a purpose made dc-dc converter IC. The resulting circut would probably be cheaper and simpler, and they generally have fairly substantial onborard transistors eliminating the need for an external power transistor. The bigissue that i can forsee is that therearetwo types of switching converters. Boost, and Buck. Boost increases voltage, and buck decreases. Doing both with the same circut, so that the input voltage can vary above and below the output is quite difficult. It might be best to first boost the voltage to ~30v, and than drop it back down to 19v. That would probably give you an input range up to 25v. As for vsmlibs, uhhh.... Out of your 23posts, the 15 or so i've seen have contained no useful information at all, not to mention the fact that a number of them were actually incorrect. I think you need to do a little fact checking. That, and proofread you're posts.
Thanks for that, would I be able to buy the boost chip from maplins? I could buy from elesewhere but maplins is easiest for me. I assume I will need some sort of inductor of tranformer? again, maplins would be nice. If I can get the voltage to ~30V, then I will have no problem regulating it to 19V.
You should be able to get it from maplins (assuming they carry a decent compliment of ICs). The biggest issue is determining what IC you want. Here are some good application notes, with theory: http://www.maxim-ic.com/appnotes.cfm/appnote_number/2031 I suspect the hardest part to get may not be the ic, but the inductors. Asfor the regulation down to 19v, i do sugest you use a DC-DC converter as well (buck converter), as using something like a lm317 would be excessively wastefull (you'd be burning up something like 30w).
http://www.powerstream.com/12v-index.htm here is the idiots link however i think overall 15/23 is ok judging by the students here and better one than none a spare 12v gel cell would suffice in series with a cigar lighter socket and a switch for charging lasting some 12 - 20 hrs or more before the voltage on the gel cell depreciates the diodes were as a demostration that lower voltage is possible with more than main cell {150 aph } total system would last 128hrs up convert when intermittent use is needed prolonged use... personaly i always regulate its less to go wrong up converting is never pretty in a melt down and costs heeps and a spare big 12v cell is always welcome so i beleve your all wrong about psu for any device in a big car you always want some spares better a pile up of ideads than a pile up of idiots sometimes however thats what happens
Err, what did that last post mean vsmlibs, I (and many others) are getting frustrated as to your lack of clarity and information in your posts. I believe cpemma has warned you a fair few times... Also, didn't SteveyG point out that I didn't want abnother battery in my car?
