Variable DC power supply

Denis's picture


Joined: Apr 17, 2020

Replies: 0
Variable DC power supply
April 17, 2020 - 12:43am



because i am a beginner i need a little bit of help from you guys. I have fixed power supply model PS1303 it was fixed to 13.8V and i have added to it ammeter and in inside was small pottentiometer 470k for adjusting voltage from 12 to 16V. I replaced that with B500K and now i can adjust my voltage from 6.8 to 25V.I also for good measure replaced caps that were 100uF 25V to 100uF 35V.The question is can i somehow make it adjustable from 0-25V and what would be next step to do. Power supply uses transformer and a small board that converts AC to DC, also one 2N3055 transistor.

Thank you wery much for your help and opinions. 

jaksonlee's picture


Joined: Nov 07, 2019

Replies: 124

The bridge rectifier gives a continuous pulsating DC signal. Then capacitors are used to filter the pulsating signal into a smooth non-pulsating DC. Finally, the voltage is regulated using a regulator IC.
A variable dc power supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A.

Sourav Gupta's picture


Joined: Feb 12, 2018

Replies: 646

Can you provide any schematic or the internal circuit pictures? (Schematic is what that is mainly required).

But it is best to use proper buck-boost regulator additionally across the output for configuring it to a 0-25V power supply unit.


However, it can be done as far as transistor based switching device is concerned. It will be helpful if you provied proper schematic, if possible.

Technical Shahzad's picture


Joined: May 23, 2020

Replies: 48

According to me directly using a variable resistor or potentiometer is not a good practice, because same thing you can do with a fan regulator. For this you need to attach a power supply regulator LM317, which is commonly used in DC variable power supply. Other thing you can do is that you can purchase a DC to DC buck converter for getting variable voltage supply. I suggest you to get more assistance from Sierra Software Ltd. technical support team about products and techniques.

McPoel's picture


Joined: Jun 01, 2020

Replies: 1

Well, LM317 is also the way to go I thought (

But I've been having heat issues with this component. In theory those LM317 are a nice option.

I think if thermally stable, they are ideal.