Instructables

12v to USB adapter \ 12v to 5v transformer (great for cars)

Picture of 12v to USB adapter \ 12v to 5v transformer (great for cars)
This will show you how to make a 12v to USB (5v) adapter. The most obvious use of this is for 12v car adapters, but anywhere you have 12v you can use it! If you need 5v for anything other than USB, simply skip the steps about adding the USB ports ;)

You will need
 
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sportative2 months ago

Hi, I wonder if someone can help.

I made this circuit and it is running a bluetooth receiver in my car perfectly. However, I have split the output to two USB cables; one for the bluetooth receiver and one for a phone charger. Whenever I plug my phone in to charge, the bluetooth device stops.
I think the circuit doesn't output the correct amps to run both. Any ideas of how to increase the output beyond 2Amps?

Many thanks!

julienrl (author)  sportative2 months ago
It may be worth just making a second circuit; the components cost pennies, and I know that the 12v can take it for sure.

On a side note, are the two USB in parallel or in series? It would be important that they not be in series and could definately cause problems.
coventrian4 months ago

I've made it using this voltage regulator

http://cpc.farnell.com/jsp/search/productdetail.js...

I used this one as I want something that is high output, however it's only giving me 0.44 amps. Any idea why i'm not getting a higher output? What factors would affect the output current apart from the voltage regulator it's self?

julienrl (author)  coventrian4 months ago
http://cpc.farnell.com/stmicroelectronics/l4940v5/ic-v-reg-ldo-5-0v-4940-to-220-3/dp/SC10587

How are you measuring this? Is there a load on the circuit? Are you measuring at the input (12v) or output (5v)?

I was measuring with an ammeter in series between the voltage regulator and my phone. I also have an app which I can use to compare different chargers, although this reads lower because the phone is consuming some of the power.

I have also found the solution. I noticed that in the phones status it shows as USB charging (same if it's plugged in to a PC), where as I want AC charging. The phone thinks it is connected to and AC power source if the data pins are connected / shorted (they are the two in the middle). This is known as the USB "dumb specification". I now have full speed charging :) . If you decide to do this, be sure that the voltage regulator can supply MORE than the max charge rate of your device, and that you adjust the fuses accordingly. My phone is android, I seem to remember that iPhones will not charge at full speed unless there is a chip at the other end, therefore this may not work.

Thanks julienrl for a great post and quick responses.

julienrl (author)  coventrian3 months ago

nice find! Thanks for sharing!

julienrl (author)  coventrian4 months ago
The link you sent me gives me an error. Can you give me the product numer?

Thanks
Jedrokivich10 months ago
This is great, thanks :) Used it to add bluetooth to a speaker system I'm building
julienrl (author)  Jedrokivich10 months ago
cool, I guess you used a bluetooth device that listens and outputs to a standard audio output that needed 5v?
mole69993 years ago
Do you think a 2 amp fuse would be ok?
julienrl (author)  mole69993 years ago
(removed by author or community request)
Do you know of any resettable fuses or a regular fuse I can use that can be put on a breadboard. Been loooking on digikey and there are so many options I am lost.
julienrl (author)  mole69991 year ago
I am not sure if resettable fuses come in that size, but if they are fast blowing, then why not! I added a list of fuse values in my instructables that can go with different transistors.
I built this 12v to 5v transformer. I bought all of the parts you specified. I built it exactly as your instructions implied. After I finished it was working great. I put it on a shelf in my locker. I went back about a week later. For some reason the 12v is going in, but nothing is coming out. I decided to build another one. the EXACT same thing happened. would there be a certain reason why after not using the 12v to 5v transformer for a week it would short out?

Thanks
julienrl (author)  thirdGEARchirp1 year ago
use a lower amperage fuse. I revised my instructables. With my old fuse values, it was possible to fry the transistor (the 5v device was safe given the max output of the transitor).
julienrl (author)  thirdGEARchirp1 year ago
strange, I have never heard of this. Could it be that it got a static shock? Static electricity will RUIN electronics (I fried my 50 000v capable multimeter with a static shock once).

If it happens again, I would consider returning the transistors you bought.
somabva4 years ago
Cool project. Just a couple of questions julienrl: Under no load, my circuit works great. Once I add a typical load to the circuit, it gets very, very hot. Is this to be expected? The spec sheet seems to allow for operating temps up to 150 deg C, but I had planned to enclose this circuit in my car's dash and am now hesitant. I don't want to light my dashboard on fire. The chip was definitely hot enough to melt your hot glue casing, so I'm assuming I did something wrong. The only thing I could think of as I read the spec sheet was that perhaps I had put the capacitor in the wrong place. If I followed your directions correctly, the capacitor went over the ground and output pins. But the spec sheet seems to indicate that the capacitor should be placed over the input and ground pins to insure stable operation under load. Or am I misunderstanding the purpose of the capacitor in your circuit? I don't do this sort of thing very much...
julienrl (author)  somabva4 years ago
putting a capacitor simply helps to prevent peaks. Circuits that require more precision usually just put 2 capacitors instead of one (one that goes input-ground and one that goes output-ground); in this circuit, putting the capacitor on the output is what was intended. As for heat, these transistors are cheap and abundant, however, if you can get your hand on a slightly better quality one (we are still only talking about 5-10 bucks max), you can get much more efficient ones. If I remember correctly, the transistor used is only efficient at 40 or 60% or something (meaning the rest is converted to heat). You can get solid state transistors which have much less tolerance for error but that have 80+% efficiency ratings (bringing the temp down). Operating temperature means that this chip can function in such temperatures (so if you have a lot of them in a small enclosed area for example, they would still function), however, in this use, it should not reach those temperatures. You can however expect the hot glue that is directly on the transistor to melt away if you used low-heat glue like I did; this is okay since the glue prevents proper heat dissipation and is only really wanted on the contacts to prevent shorts. You will notice that in my picture I had no glue on the actual transistor (well a bit of over spill, but that is not really an issue). Although the transistor can get hot enough to hurt you if you touch it, it should not damage things around it; that being said, don't go sticking it in a bundle of wires! When you think about it, they don't get hot enough to de-solder themselves. It should be easy enough to put it in a space where it has 1-2cm of breathing room around it, and if you want extra precautions, you can use a standard project box. These boxes can absolutely withstand the heat this transistor produces; you can also use a heat sink (with or without the box). These heat sinks are readily available and made just for this kind of use; they screw on the hole on the metal plate (that's what that hole in the built-in heat sink is for!) If you need more clarification, feel free to ask! :)
hello,
I am currently building a dual port setup for installation into the dash of my pickup. that said i have had an issue finding the capacitor you list locally at all. that said you say just about any capacitor will work. If i am going to sub-statue a cap what value should I try to carry over to the new cap. Also i am interested in lower heat as this is going in the dash. I've attached an aluminium heat-sink to the transistor with some thermal paste. dropped the heat to a level where i can touch the transistor and or heat-sink without getting burnt.

Also you say that for more precision you'd use 2 capacitors one on the input to ground and one on the output to ground.. would you recommend this for an automotive in-dash install?? I charge some very expensive objects off the 5v USB ports i just want to be sure its clean power and not likely to damage my devices.

Thanks in advance
James
julienrl (author)  jgosselin2 years ago
having the two capacitors will never hurt. The risk of a dangerous spike is near nothing once you have your first capacitor, the second one would be important for precision circuits such as measurement instruments. Then again you lose nothing at doing it!

If you want less heat, there are also more efficient transistors I have talked about before. They are a few dollars more, but will drop the heat down significantly, but a heatsink would still be useful.

As for the caps, just make sure that they are higher than your car battery can spike to, this is normally 13-14 volts when fully charged, that is way a 16+v cap is recommended. you can use one as big as you want, jsut make sure you don't end up with something that arcs in your car! I would say don't go over 60v-ish to be safe (that is about what telephone wiring has) since you will probably have exposed wires in close proximity.
i went and scoured radio shack and the only 220uf caps they had where 35v will those work ok?
julienrl (author)  jgosselin2 years ago
they will work perfectly
Wow, that's a really detailed reply. Thanks for the insights! I was really more concerned with the voltage drop that the heat spike seemed to produce, but as you point out, it is a really cheap transistor, can't expect too much. I actually ended up screwing it into the contact side of an old CPU heat sink from my parts bucket. Overkill perhaps, but it works like a charm and I get a rock solid 5V now.
julienrl (author)  somabva4 years ago
good to ehar a heatsink helped!
julienrl (author)  julienrl4 years ago
ps. sorry for the 12 day delay!
here is what i have 470uf 16v x3, 470uf 25v x2, 1000uf 16v, 47uf 200v will any of these work
julienrl (author)  josephthorpwausau2 years ago
anything around 200-500uf and 14-30v is a very safe choice. In fact almost any capacitor could work just fine.
i did find a 220uf 25v maybe that will work if you could let me know that would be greatly appreciated
is there a different Capacitor i could use maybe a 220uf 35v Capacitor
mmeeker3 years ago
I mad one of these for my house the tricky part was coming from 120V to 12V then to 5V but with your instructions it wasn't to bad. You're very detailing instructions helped me out tons
julienrl (author)  mmeeker3 years ago
what did you do to go form 120AC to 12DC?
there are plenty of ways, i went the easy route and found an old 120Vac to 12Vdc and took it apart and put it insdie my enclosure then i connected the + coming from the adapter to the 5v transistor then to whatever i hooked it up to i wired mine up to power hard drives and cd drive
julienrl (author)  mmeeker3 years ago
okok, that's usually what I do (use an existing AC to DC transformer). I was just wondering if you had made that by yourself too.
i'm sure it wouldn't be to hard to do its just what i had on hand lol my first project actually. it got me back into electronics its kinda like being a kid all over again haha
Phil B4 years ago
It is good to find someone else who uses hot glue as a "project case."  It is very helpful that you identified the pins in the USB socket for power connections.  Thank you.
Hycro Phil B3 years ago
Sometimes I use cloth duct tape, when it's something where it just needs to be protected from shorts, and a little protection from the elements, and does not heat up much, if at all...
julienrl (author)  Phil B4 years ago
glad i could be of help