Help me with AC to DC converter!

AmareX · Oct 10, 2012

Hello,

I am new to this forum, it looks like a great place and I am hoping to stick around.

I need to build an AC to DC converter for an AC power adapter (output rated at : 12V 3Amp).

Now as far as my limited knowledge allows about this, I know I need a bridge rectifier with 4 diodes, a capacitor for filtering and an specific IC for accurate 12V output. I have no idea about the whole design though

Now if anyone can please provide a circuit diagram for a high quality 12V 3Amp AC to DC converter which will provide as accurate output as possible, I'll be very grateful.

Thank You.

CocaCola · Oct 10, 2012

You need in excess of [email protected] to get a regulated [email protected] out... As it stands by the time you rectify the 12VAC and than allow for whatever kind of regulation you are likely only looking at about 9VDC out at 3A, if you boost back up to 12V you will have less Amperage to work with...

There is likely a better approach to your problem, more details would be helpful...

AmareX · Oct 10, 2012

Hi Cocacola, I am happy if the conversion reduces the amp a little bit, I don't actually need exactly 3Amp .. but I need a proper 12V. Could you please provide me a diagram with regulated IC?

The AC Power adapter came with a creative 2:1 speaker, recently the Power Adapter of my Wimax modem got busted, so my plan is to convert the creative adapter to 12v dc. The power requirement for my Wimax modem is 12V 1.5 Amp. I just want the circuit as stable and accurate as possible because I run my modem 24/7. The Creative speaker adapter is pretty heavy and well made .. now I need an excellent AC to DC converter for it.

Thanks a lot for your reply.

CocaCola · Oct 10, 2012

It's cheaper and less hassle to just get the proper wall wart vs making the one you have work...

You don't identify your location but for example, just over $6 delivered...

http://www.ebay.com/itm/AC-Power-Ad...=Laptop_Adapters_Chargers&hash=item2a1d7e37a9

AmareX · Oct 10, 2012

Thanks for your suggestion. I can buy one from local market (ebay is not an option) but I was thinking with a quality rectifier, the AC adapter I have would be a stable choice. If I can find a diagram I can definitely make it .. and wheres the spirit of making something by yourself?

CocaCola · Oct 10, 2012

AmareX said:

and wheres the spirit of making something by yourself?
Click to expand...

Making it yourself only goes so far, why re-invent the wheel at a cost of $30 when you can purchase one for $10, the thrill of doing it yourself only extends so far...

You need to rectify the AC and feed that into a DC to DC boost converter, since the rectification will drop the voltage... Also if the AC out of the wall wart you have is not regulated you might have other issues... And back at square one, I wouldn't bother making the boost converter when you can purchase one for less than the cost of the parts to build it...

There are other ways to do it as well, but again I'm not into wasting my time an energy reinventing the wheel when I can get a proper solution for a few bucks...

AmareX · Oct 10, 2012

I see your point. I have already made the bridge rectifier with filtering capacitor and its running my modem so far. I am only worried about unregulated output damaging my modem .. thats why I am looking for a design with regulated IC. So All I need to do now is buy a regulator IC and two extra capacitor probably, solder a few joints and I am done. The problem is I forgot the 3 pin IC number and capacitor values, and I cant find a damn circuit diagram for this simple thing on the massive sea of knowledge (Internet). I used to have a book for basic electronics, lost it !!

Is that adapter is really 2Amp? Its made in China (well what isn't !!) but can we really trust its printed ratings and how about stability? Already lost the original adapter came with the modem (another excellent example of chiness electronics) .. filtering cap is busted, regulator IC burned.

CocaCola · Oct 10, 2012

AmareX said:

thats why I am looking for a design with regulated IC. So All I need to do now is buy a regulator IC and two extra capacitor probably, solder a few joints and I am done. The problem is I forgot the 3 pin IC number and capacitor values, and I cant find a damn circuit diagram for this simple thing on the massive sea of knowledge (Internet). I used to have a book for basic electronics, lost it !!
Click to expand...

What you describe is a linear regulator, and it has horrible efficiency... To get 12VDC out you need about 14V in on a normal one, there are low dropout the will operate with less headroom but they all require more in than you get out... So if you want 12V out you can't do it this way... You bridge rectifier is already dropping about 1.4V on average so you only have about 10.5VDC to work with... That means to get a stable 12VDC out of an AC regulator you will need about a 16V AC source, not the 12V one you have... This goes back to what I said about only getting 9VDC out of that adapter after you rectify and regulate it to DC, this is possible with a low dropout linear regulator...

This is why you would use a DC to DC boost regulator in this type of application, it will take the lower voltage in and boost it to the appropriate output level...

A regulator similar to this...

http://www.ebay.com/itm/LM2577-Boos...387?pt=LH_DefaultDomain_0&hash=item3f1a5150e3

BUT, If your AC adapter is not regulated to start with that means that you can experience irregularities on the output of the DC to DC boost converter output... In short you need an additional regulator somewhere, doing it this way...

Do you see how trying to reinvent the wheel is getting overly complicated all the sudden?

Is that adapter is really 2Amp? Its made in China (well what isn't !!) but can we really trust its printed ratings and how about stability?
Click to expand...

Generally I have found them to be rated pretty well, but like anything you never push to the the limits... You said you needed 1.5A thus the reason I directed you to a 2A version as that gives you headroom... You can just as easily find a 2.5A or 3.0A wall wart if you are concerned...