Variable DC power supply circuit using LM317


About the article

Variable DC power supply is required frequently for any hobbyist,

Different level of voltage sources needed in many different projects so it is next to impossible to arrange all type of fixed voltage source, at same time it is too expensive to buy those kits from market so why not we make a variable DC power source of our own.

So in this article I will give idea about how to build your own variable DC power source in very cheap and using easily available components and it is also safe to use for you delicate projects.

So let see how to make Variable DC power supply



Here we used LM317  voltage regulator IC

In this IC supply voltage is connected to its terminal (3) and the output voltage on terminal (2) can regulate by the potentiometer connected to the terminal (1)

This IC can varies DC voltage from 1.2V to 37V  for more information click here read the data sheet of LM317

Note:- for safety reasons use this circuit only upto 30V DC

Component List

  1. 230V / 30V 1Amp Ac Transformer
  2. LM317 voltage regulator IC
  3. Resistor 1KΩ & 220Ω
  4. Potentiometer 5KΩ
  5. Capacitor 1uF 35V
  6. Capacitor 2200uF & 0.1uF 100V
  7. Diode 1N4001 (qty-4)
  8.  Diode 1N4007 ((qty-1)

Working principle

First input voltage (230V AC ) get step down to 30V AC via stepdown transformer, then full wave bridge ratifier convert this AC voltage into DC voltage

This DC voltage feed to LM317 IC then LM 317 provides output voltage that can be varied from 1.2V to 35V maximum by adjusting the potentiometer.

A reference voltage of 1.25 V is maintained at the time of operation across the resistor R2.

Diode D1 is a protection diode that prevents the C3 from discharging into the regulator IC caused by short circuit of input to ground.

The 1uF capacitor across the output helps in getting better transient response.

Output voltage is depends on following relation

so that’s it friends comment below if you have any doubt or query thank you.



Low cost PCB on PCBWay - only $5 for 10 PCBs and FREE first order for new members

PCB Assembly service starts from $88 with Free shipping all around world + Free stencil 

PCBWay 2nd PCB Design Contest



Hobbiest Electrical DIY project passionate

4 Responses

  1. Wow, amazing blog format! How lengthy have you been running a blog for? you make running a blog look easy. The full look of your site is magnificent, let alone the content!

Leave a Reply

Your email address will not be published. Required fields are marked *

Enter Captcha Here : *

Reload Image

Post comment