Dual 3A DC-DC Voltage Regulated Power Supply LM317 LM337 BD139 BD140 TIP35C TIP36C

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Fig.1 – The dual 3A DC-DC voltage regulated Power Supply

Fig.1 – The dual 3A DC-DC voltage regulated PSU

Initially I built this PCB because I was fed up to hear the annoying low frequency noise from the speakers of an old amplifier. The issue came from the power supply that clearly wasn’t very good. The residual 50Hz signal from the AC line, technically called ripple, was so high that it generated an awful fixed background sound. By installing this PCB, after the existing PSU, I solved my issue.

Later, I decided to use the PCB as a general power supply to test my projects. It has always worked perfectly even if setting the voltage output by trimmers was not very comfortable. For that reason, if you are thinking of building it for that purpose, I suggest to substitute the trimmers with potentiometers by connecting them with wires to the board or, better, redraw the whole PCB mask.


A dual DC-DC PSU with discrete components

Nowadays there are integrated circuits for every purpose and to make a project with discrete components is becoming old-fashioned. Despite this, I found this approach more exciting because it enriches and consolidates your knowledge in electronics.

Fig.2 – The Dual 3A DC-DC voltage regulated Power Supply's schematic

Fig.2 – The Dual 3A DC-DC voltage regulated Power Supply’s schematic

The main characteristics are:

  • at least 3A continuously current output;
  • 3V to 30V voltage regulation output;
  • max 40V voltage input.

If you want to set a different voltage output range, find and change the value of R (that is R5+R7 for the positive section, R6+R8 for the negative one) according to the following formulas:

R = 176*VOUT  –  220     or     VOUT = (R + 220) / 176


Around the LM317

Probably you have already used this common IC and so you know as well how simple it is to make a 1A power supply even using the basic configuration. Starting from there, I added the transistor TIP35C and the BD140 to increase the power output as suggested on the typical applications section of the LM317‘s data sheet. That concerns the positive section of the circuit but, similarly I did the same thing for the negative one using the LM337, the TIP36C and the BD139.


Build the power supply’s PCB

Fig.3 - The power supply's PCB layout

Fig.3 – The PCB layout

Fig.4 - The power supply's PCB mask

Fig.4 – The PCB mask

If you make the project using my PCB mask pay attention to the polarity of the clamps because they are not specular, if you notice IN+ is on the right and OUT+ is on the left.

Every IC and transistor must be installed on a heat sink, isolated from it, by a mica each. In the picture on top I removed the heat sink to show you clearly how to do it.

Remember that is a DC-DC PSU, so you cannot directly connect the AC line form a transformer to the input.


Download the project

Pressing the button below you can download a compressed file with all the necessary material to build this project:

  • the LM317, the LM337, the BD139, the BD140, the TIP35C and the TIP36C data sheets;
  • the pictures of the final project, the schematic, the PCB mask and the PCB layout as shown in this post;
  • the schematic and the board files in Eagle format.

If you need some help please do not hesitate to contact me or leave your comments below. Enjoy it!

SP0002 (2.1 MiB, 818 downloads)


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Grazie di cuore, Andrea Dal Maso



This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

2 thoughts on “Dual 3A DC-DC Voltage Regulated Power Supply LM317 LM337 BD139 BD140 TIP35C TIP36C

  1. I’m impressed, I must say. Seldom do I come across a blog that’s both educative and entertaining, and let me tell you, you’ve hit the nail on the head. The issue is something that too few men and women are speaking intelligently about. Now i’m very happy that I found this in my hunt for something regarding this.

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