Variable Power Supply with LM7812

  • Spiliopoulos Kwstas
  • 23478
  • moderate
  • Non tested


This project is a simple variable power supply using the famous LM7812 regulator IC. It consists of two boards, the main board which includes the regulator, capacitors, bridge rectifier and potentiometer and a second board that includes the mains tranformer, the fuse and a switch.


I designed this variable power supply which is based on the famous series of voltage regulator LM78xx. The electrical characteristics can be found here. LM78xx can be easily found in stores with electronic materials.

On this project I use the LM7812 in TO-220 footprint, which can be screwed to the rear of a heatsink for better heat dissipation. You will get better heat conduction if you use thermal paste between the heatsink and LM78xx before screwed together.

The bridge rectifier is a classic 2KVV. You may choose the appropriate bridge rectifier according to your requirements.

The variable resistor R3 varies the output voltage (Vout). The R3 can be placed in your project box and can be replaced with a potentiometer of similar price.

The second board is for the transformer, the board contains the base for the primary fuse and one on-off switch for 220V mains voltage.


Regulator board



Transformer board






Power Supply_1

Power Supply_2

Power Supply_3



  • Gundeep

    Now be honest Spili! You didn’t design this circuit but just simply copied it from an electronics book because it’s a very common circuit that many hobbyists just like you have tried to say that they alone designed. ;^)

    5 years ago
  • Gundeep,
    This schemetic comes from LM78xx datasheet I’ll will never said that belong to me…
    If you check the datasheet on page 17/34 or 20/34,you see some schematics concern different applications.
    I try to apply some of them on my breadboard test some and after design them at Cadsoft EAGLE…thats all!
    Thanks for your comments.

    5 years ago
  • Franco

    This has given me a start and is better then many others I have seen. @Gundeep, if you don’t like, don’t comment. If you can do better, create your own site! Everobody on the internet has copied it from somewhere. @ Admin, thank you for this.

    3 years ago

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