Help! Building of 12 V 2A and 5V 2A Power Supply!

Thread Starter


Joined Jul 9, 2017
I need a power supply for Arduino Uno and GSM-900 module with 12V 2A and 5V 2A respectively.
I'm searching on how I'm to build power supply with a transformer input of 220Vac and have variations of output of 3V, 6V, 9V, and 12V but the result shows only already built chargers/power supply.

Can you help or even suggest what components I need to have a stable output of 12V and 5V respectively.

It's different circuit for 12V 2A and 5V 2A. Just using the same transformer.



Joined Nov 4, 2013
If you went with a 12 volt 3 amp system you could use a common automotive USB adapter to get the 5 volts 2 amps from it.

Everything else depends on how regulated you need the other voltages to be and at what current limits plus what overall efficiency you want to work with at each one.


Joined Feb 20, 2016
An old PC supply is a good idea.
Another way is to use a 19V laptop supply and feed a couple of these..

One set at 12V and another at 5V.
A student in my electronics class just made a power supply with one of them and it came out well. The trim pot was pulled off and a 100K pot with a switched 47K series resistor was added. (I could not get a 150K pot.)

He added a voltmeter and pot and 2 range switch so it goes from 0.8V to 14V.
These regs are 3A.
The result is a very handy power supply for one's tool box.
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Joined Aug 1, 2013
There are a ton of power supplies on ebay, in both kit form and fully assembled modules. If you surf there and select a few, we can comment on whether or not they are appropriate for your project.

Separate from that, I disagree with dendad. I think an old PC power supply is not appropriate. First, it has a minimum load requirement that could be greater than your entire project's power needs. Second, it rarely is a good idea to connect a 2 amp load to a 20-40 amp power source. If your project has a problem, the internal protections in the supply never will kick in and your parts will fry. Better to use a supply that is inherently power-limiting to something closer to your needs.

There are several ways to achieve your power requirements. The most simple is a standard switch-fuse-transformer-bridge-filter capacitor to make what is called the bulk supply. That filtered DC at 15 V or more can then be regulated down to 12 V and 5 V with either linear or switching circuits. Switchers are more complex, generate very little heat, generate more high-frequency noise on the output, and should be purchased as an ebay module. A linears regulator easy to design and build by hand, has very low output noise, but needs a heatsink for the "pass" device, either an integrated regulator chip, or a power transistor controlled by a regulator circuit.



Joined Jan 28, 2017
Little higher then the output you wanted. However maybe it is adjustable However this one will do both 12v and 5v with dual output and cost isn't to far over what one may expect for something under these specs. Under 8 USD

I know you wanted help building and again I am not saying that you need to buy for the project but maybe buy for reference to your own build. Again the cost is far less then the parts to build one. Unless you have all the parts already.


Joined Mar 2, 2011
An off the shelf 220 to 24 VAC transformer; a big rectifier diode and cap will get you the bulk DC input.
Then go to the Linear Tech or TI sites and pick a DC to DC PWM controller. There will be several choices to do the job, and there will be reference designs and instructions on setting the output voltage and selecting the 3 or 4 external components required.
For this power level, the two DC-DC circuits will fit on a PCB about the size of a saltine cracker...

Good Luck!