Variable bench power supply 5A(1.2 – 25V) +1A(5V)+1A(12V)

31 Mar

See version 2 at:

Instructables page:

Also at:

Power supply is an utmost essential tool for an electronic lab. It comes in handy for powering up various applications and circuits. However a fixed voltage, fixed current power supply is sufficient for basic needs but a variable one is good to have because different circuits and components operate at different voltages and consumes different current. When it comes to an electronic hobbyist’s lab, a good power supply is must to have. Also if the power supply boosts additional features like onboard voltage and current display, it comes in handy as one can know the exact voltage at the output terminals and also the current drawn by the load. But in the electronic market, those power supplies are not economic are meant for industrial purpose majorly. Here in this article I present an economical and cost effective yet efficient variable bench power supply that is capable of providing 1.2 to 25 Volt variable supply upto 5 Ampere through one channel while 5 Volt, 1 Ampere and 12 Volt, 1 Ampere supply through other two channels thus having one variable and two fixed supply channels. It also displays the voltage on the output terminals and also the current and instantaneous power drawn by the load on an onboard LCD disply. Not only this one can connect this power supply to his personal computer via the serial port and can see the voltage, current and power drawn by the load graphically. The project  is portable and simple to build that even a newcomer can build this power supply with ease and add into his lab. The project uses component that are easily and cheaply available. The project is composed of  two modules, one is main power module that consists of linear voltage regulators with rectification and filtering circuitry for supply generation and regulation while the other is composed of a microcontroller which is used to sense and display the current and voltage across the variable supply channel. The second section only provides an additional functionality of displaying current and voltage, however one can build the power supply even skipping the second section leaving it functional but without the display feature.For more info read this project in EFY magazine(August,2013).

The simple windows monitoring application:


The gauge meter type windows monitoring application:


The advanced chart recorder windows monitoring application:

The hardware:


Block diagram:fig5 main.bmp mcu.bmp

The Circuit diagrams:



The PCB:





The Downloads:

1.The microcontroller code for atmega8:

2.The PCB files in eagle:

3.The simple windows software:

4.The advanced windows software:


Posted by on March 31, 2012 in Microcontrollers


10 responses to “Variable bench power supply 5A(1.2 – 25V) +1A(5V)+1A(12V)

  1. Abhishek Kumar

    August 22, 2013 at 1:38 pm

    David,in the magazine if you consider the figure no 4 in the article one and figure no 5,first of all both the circuit will share the same ground at one point,and as u asked about the shunt one terminal of it will go to the ground (which is shown as -ve in block diag figure 3,which is the common ground of both the circuit sections) and the other terminal will come out of the supply to power the load(as shown point A in fig 3).Thus the load ground will be in series with that shunt (called as low side current sensing),and this point will also go to the point A in fig 5 so that the voltage drop across resistor (as proportional to current) will be sensed by the microcontroller circuit in fig 5.Thus out external load will not be directly connected to our power supply’s ground but will be above the shunt resistor.

    And one more thing guys,either you use the super precise 0.3 ohm,10watt resistor as the shunt (as i used in my circuit)or if you change the value as 0.03 ohm shunt will not be readily available,please do change the shunt value in the microcontroller code before compiling in BASCOM,else you will get different current value on the display.The code is quite simple and well commented.The value at line number xx in the code should be changed according to the shunt value you choose in your project.

    And,you guys may be wondering where is the crystal in the microcontroller circuit.So,just to save money,i used the internal 4MHz RC oscillator prebuilt in the ATMEGA8 MCU.So you have to change the fuse bits to run the ATMEGA8 on internal 4MHz RC oscillator.

    If you have any problem regardin the project,please feel free to comment at my blog.The project is fully correct here on this page

  2. Masood Nayaz

    October 3, 2013 at 8:07 am

    I am unable to download the code etc as the mediafire has already deleted them. So help me by sending them to my email directly..

    • embeddedfortheevil

      October 4, 2013 at 9:40 am

      I checked it,each and every mediafire link is working and they haven’t deleted them,u can also get the source code on EFY page.

  3. goher

    February 7, 2016 at 4:53 pm

    a great work. any way is it safe to use for laptop motherboard trouble shooting as there is no current limiting feature.

  4. goher

    February 8, 2016 at 2:45 pm

    Dear Abhishek
    can i use it to troubleshoot laptop motherboard as there is no current limiting feature? will this have any adverse impact while checking the motherboard or the motherboard will draw it required current automatically.

  5. gowhar khan

    February 8, 2016 at 2:50 pm

    Dear Abhishek
    this is a great work, can i use this power supply to trouble shoot laptop motherboards as there is no current limiting feature or the motherboard will draw its required current itself. will this have any adverse impact on the motherboard.

  6. goher

    February 9, 2016 at 10:43 am

    what are the changes required if i dont want fixed outputs of 12v & 5v.

  7. gowhar khan

    February 9, 2016 at 12:46 pm

    Dear Sir,
    could you please post the revised version in EFY as in the first version every detail was nicely elaborated and pcb files were downloaded smoothly with complete details.


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