# Variable DC power supply circuit using LM317

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

#### Schematic

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)

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.

#### sandeep

Hobbiest Electrical DIY project passionate

### 4 thoughts on “Variable DC power supply circuit using LM317”

• 7th June 2017 at 2:06 am

Awesome! Its actually amazing paragraph, I have got much clear idea regarding from this piece of writing.

• 7th June 2017 at 6:48 pm