Variable bench power supply v2

20 Oct

This is a follow up (version 2) of my previous design of the Digital power supply that can be found at :

Instructables link:

This one is an improved version with the following features:

  1. When powered ON,it does not switches the load automatically so that you don’t burn your load(specially working with voltage sensitive applications).It displays the terminal voltage and then asks you switch on the load so that you can adjust the terminal voltage to suit your application.
  2. Load ON/OFF function to switch ON/OFF the load without disconnecting it from the terminals with LOAD status indication.
  3. Switches LOAD ON/OFF from software(PC application).

The circuit diagrams for the power section and display section both have been revised:



Version 2 of this power section are as similar to the version 1.Only some minor improvements are made like we have increased two more 4700uf,50V filtering capacitors,and added 100nf ceramic caps after LM7805 and LM7812 for stability purpose. Now earlier,we were directly feeding >25v DC to the inputs of LM7805 and LM7812 regulators which was not a good idea because the power (as heat) dissipated from the regulator is directly proportional to the voltage difference across it and current taken from the regulator, so to minimise the power dissipation, we have to minimise the voltage difference across the regulators. So we have included a series array of 1N4002 (or any general purpose diode) to make an appropriate voltage drop before it goes to the two fixed voltage regulators.So after diode D18, we will get a nominal voltage of 16v which feed the LM7812 and a nominal voltage of 10v after D26 which feeds the LM7805. Although this is not the best way to do it, you can also use a dual secondary core transformer with lower voltage at the second secondary to feed the LM7805 or LM7812.

Interface and display circuit v2:


Version 2 circuit is also shown (I recommend to build this).This one has additional features to switch ON/OFF load and more features.Sorry the description of v2 is not done,but is actually the same as v1(which you can read below with reference to the version 1 circuit above) with some minor amendments.

PCBv2 files for display section:

Atmega8 mcu v2 code:

Some pics of the modified case:
DSC01538 (Large)

DSC01539 (Large)DSC01540 (Large)DSC01545 (Large)DSC01541 (Large)DSC01544 (Large)DSC01496 (Large)DSC01497 (Large)


Posted by on October 20, 2013 in AVR, Microcontrollers


2 responses to “Variable bench power supply v2

  1. vigneshskp

    October 3, 2015 at 2:37 am

    Hi this is indeed a great project especially for hobbyists. I am impressed with the simplicity of the design. And do you have codes for arduino as I do not have any AVR programmer and only arduino board. Please reply.

  2. vigneshskp

    October 28, 2015 at 7:17 am

    Please reply me.


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