Picture of Make a simple 12 volt power supply
Have you ever needed a 12 volt power supply that can supply maximum 1 amp? But trying to buy one from the store is a little too expensive?

Well, you can make a 12 volt power supply very cheaply and easily!

I needed a 12 volt power supply for my project, the SSTC (Solid State Tesla Coil), and also made this instructable because it might be use full to someone...
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Step 1: Things that you will need...

Picture of Things that you will need...
Things that you will need to make this power supply is...

  • Piece of veroboard
  • Four 1N4001 diodes
  • LM7812 regulator
  • Transformer that has an output of 14v - 35v AC with an output current between 100mA to 1A, depending how much power you will need. (I found a 16v 200mA transformer in a broken alarm clock.)
  • 1000uF - 4700uF capacitor
  • 1uF capacitor
  • Two 100nF capacitors
  • Jumper wires (I used some plain wire as jumper wires)
  • Heatsink (optional)

You should be able you get most (maybe all) of the parts at Radio Shack or Maplin.

Step 2: And the tools...

Picture of And the tools...
Also you will need the tools to make this power supply...

  • Soldering iron
  • Wire cutters
  • Wire strippers
  • A thing you can cut veroboard tracks.
  • Hot glue (To hold components down and make the power supply physically strong and sturdy.)
  • And some other tools that you might find helpful.

Okay, I think that is about it, lets get to work!

Step 3: Schematic and others...

Picture of Schematic and others...
If you want a 5 volt power supply, just simply replace the LM7812 to a LM7805 regulator.
Datasheet for LM78XX

If you are going to pull out about 1 amp from this power supply, you will need a heatsink for the regulator, otherwise it will generate very high temperatures and possibly burn out...
However, if you are just going to pull out a few hundred milliamps (lower than 500mA) from it, you won't need a heatsink for the regulator, but it may get a little bit warm.

Also, heres the schematic...
I also add in an LED to make sure the power supply is working. You can add in an LED if you want.
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arukshan20 days ago

will I get 12v 10a from this circuit if I use 12v 10a stepdown teansformer

connect more transistor in parallel get more current.......high power transistor...and also used heat sink for all ic and transistor....

mathewriver16 days ago

What should I change to use batteries (24volts) instead of the transformer and get 1A out and what is the efficiency of the circuit?

ursm21 days ago

if planning to use any power supply for motors you should add a protection diode between output and input on the regulator

Can you give me a schematic and materials for 12V input voltage with an output 5V and 2A ..thank you in advance..

BUT you should reduce the transformer output to 7.5 volts.

otherwise you create too much heat reducing the input voltage

Just use 7805 voltage regulator. It gives 5v output and max of 1.5Amps.

AntonioP31 month ago

I need to convert 115volt AC 12volt 4AMP
for a refrigerator water dispenser

eli2411 year ago

hey :) what if i use a power supply with 3 amps? what do i do? do i keep the same capacitor values?

tehcmn eli2412 months ago

1uF per mA is a good rule of thumb.

I am sorry if I sound new at this, but I am. I just blew a capacitor and burned my finger (lol). Instead of using a transformer I used a 12vdc adapter. I am looking to pull about 1A and your comment says 1uF/mA. What capacitors are you talking about in this comment? Could you give me some direction as to how to wire from a 12VDC adapter?

So you will want a 1000uF electrolytic on both the input and the output pins, with the - stripe to ground, with a 25V (or 16V) working voltage (WV). I'd be willing to bet you either put the cap in backwards or used one with a WV that was too small.

Use the circuit diagram in the article but chop off the diodes and transformer. If you are dropping 12V to 5V at 1A (I assume this is what you are doing) you'll need a heatsink. 7805s do not smell nice when they are burning ;)

If you are trying to keep 12V as 12V a Zener diode might be a better option, but that's a different implementation entirely.

SivaA22 months ago

how to identfy the primary and secondary winding

chrisrickers11 months ago

Some of you posters need to stay from electricity before you electrocute yourselves. Your questions prove that your are inept working with it. As for the person asking about the pinout, yes, the regulator pinout is WRONG. Hopefully anyone building this is smart enough to check the datasheet. {Pin 1 is the input, Pin 2 is ground, and Pin 3 is output).

I agree.
A universal rule for the NatSemi 78xx is that with the model number & batch # / datecode facing toward you, every so often IGO and play with linear regulators.

merv.gower.52 months ago

hi, i have a power supply that is producing 20.00 volts and is rated at 13.8 volts x 4amps

TGRIMEAU1 year ago
I am planning to make wood portable laptops cooling fan and 12 volt power supply change to 2 volt ( red led ) and i did calculater of formula R=V/I R=( 12-2 ) / 0.015 R=( 10) / 0.015 R= 666.67 ohm resistor but no light red led with switch so try reduce to 325 ohm resisor but still weak light red led and agian try reduce to 265 ohm resistor to work bright light red led but 265 ohm resistor is still hot . Do you have any idea ??
PaulJ7 TGRIMEAU4 months ago

You need to know 2 items. The turn on voltage of the LED and the current consumption. The dropping resistor is based on both. Also make sure it is and LED and not some other lamp type.

aa salam1 year ago
Is it correct the pin out of ic 7812?
PaulJ7 aa salam4 months ago

You can find the correct information from the manufactures documentation at::

Azam-Jamal8 months ago

Can this circuit provides a stable filtered current like I designed one with IN4001 diodes and 12 v transformer and 330micro farad capicitor a power regulator but when ever the supply is working suddenly if any one switch on the side way switch like a bulb etc .The power fluctuate and its make the hole system attached to it off.can any one help me about the filterd current supply plz.and design etc

PaulJ7 Azam-Jamal4 months ago

Please check the current draw of the circuit you are powering. This reads as if you have exceeded the ability of the regulator. You can find these limitations in the manufactures documentation at::

Jez3655 months ago

Looks great but Ive got one question before I make it... What is the lowest voltage you can charge it at? Or what voltage do you charge it at?

PaulJ7 Jez3654 months ago

If the question is:: What is the min / max voltage that can be applied to get a regulated 12vDC output the answer is in the manufactures documentation for the part. For the LM7812 the specs are found at::

if i want say 11v at output. would it be sare to include 11v zener? pls answer needed urgent

Yes. However a 1 volt drop from a zener (ie 11vZ) can be hard to find as well as (compare) expensive to a dropping resistor. Using Ohm's law R= V / I gives you the resistance drop. P=((I*I)*r) or P=Isq times R. There are many dropping resistor calculators available on the web for free.

funkyshakeel4 months ago
Can i use 103nF replace of 100nF ???


fkhan143 years ago
Can i Use Bridge in Replace of diode........????????? please answer me as soon as possible

Yea, you can, just make sure the bridge rectafier is rated for more then your transformer output.

how to decide capacitor and resistor values at input and output sides?
xyndaen1 year ago
i think you will also need a cooler to protect 7812.

its very nice, simple and has helped me a lot in completing my project.......
thanks a lot.....!!!!!
DeShark1 year ago
I know this was over 5 years ago, but you probably wanted to use a different transformer to reduce the voltage further. This would cause the power dissipation of the voltage regulator, keeping it cooler..
he bro you should use breadboard first to make pre-circuit....p
no problem one of my friend also burnt his transformer in lab :P and he has to submit power supply project and he buy new one dn't be disheart :P
i burnt my transformer when i made this supply...i dont know what went was really disheartning
chetan_m.p3 years ago
what is the voltage of those capacitors..
The "voltage" of a capacitor usually refers the the maximum working voltage before the capacitor components degrade. The rectifier outputs about 16V, so use capacitors rated for at least 30V for safety
The rectifier will actually output a bit more. The rms value (average value) of the transformer is 16 volts, however during rectification the voltage output is actually the peak voltage of the AC input which would be the rms value x 1.41 or around 22 volts :)
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