# Variable DC power supply schematic using LM317 voltage regulator

Variable voltage power supply is essential for any electronic hobbyist to begin their electronics lessons. For different applications you may need different voltages. So it becomes impossible to use multiple fixed power supplies all the time.Also this variable power supply circuit ensures the protection of other circuit parts from voltage fluctuations. So in this article we will teach you how to build a variable power supply on your own. Why to buy when you can make one of your own easily using very little components?Assemble this circuit on a PCB (Printed Circuit Board) and start your electronics projects. You can connect the output to a multimeter for displaying the voltage.

## How to make a variable power supply?

This supply unit uses a LM3 17 voltage regulator IC. The rectified output from the full wave bridge rectifier is fed to a LM317 regulator IC. By changing the value of potentiometer used in this circuit, the output voltage can be controlled easily.
Note: For safety, use this circuit to get a maximum of 30 volts.

## Variable DC power supply schematic

Click on the image for enlarged view

## Components Requiered

1. LM317 Regulator IC
2. Step down transformer (230V to 30V)
3. Resistor (1KΩ; 220Ω)
4. Potentio meter (5KΩ)
5. Capacitor (1µF; 35V)
6. Capacitor (2200µF, 0.1µF)
7. Bridge rectifier
8. 1N4007 Diode

## Working of Adjustable Power supply circuit

•  LM 317 provides output voltage that can be varied from 1.2V to 35V maximum by adjusting the potentiometer.
• Another striking thing is that lm317 has inbuilt current limiting and thermal shutdown features.
• A reference voltage of 1.25 V is maintained at the time of operation across the resistor R2.
• The 1uF capacitor across the output helps in getting better transient response.
• You can refer the basic configuration figure shown below for understanding the above said points.

• The voltage at the output is given by the relation:

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

See below how I have integrated this circuit to a multimeter to show instantaneous reading.  Let us know through the comment box below if you have any trouble in setting up a similar one.

## 45 thoughts on “Variable DC power supply schematic using LM317 voltage regulator”

1. Aiman Razali says:

whats the power of the transformer if i may ask ? thanks

• Yaseen says:

Hi Aiman Razali
Use 1A transformer.

2. Chamila says:

i need to simulate this circuit using a circuit simulator. i tried to use pspice , but i couldn’t find the correct regulator in there . can you tell me a good circuit simulator to find LM78XX series and LM317 so i can simulate the circuit.
Thank you

• Mohammed Maaz says:

Use Multisim, It has LM317 in it. But try a version above 11

• me says:

Id ask you to use proteus, but that’s too late

I did this project and it’s working perfectly thanks for the upload ^_^
I just want to ask why am I getting an output more that 30 V DC although I’m providing only 30 AC??

4. Wilson says:

@Khadija, when you rectify an Ac voltage to Dc, the dc value you get will be 1.414*transformer output. So you’ll be having about 42vdc from a 30v output trxfma. Hope this is helpful.

That makes sense now.. Thank you so much ^_^

5. Ray Brannam says:

The link to buy gives a 404 error. Apparently there is no DNS entry for services.circuitsgallery.com.

–Ray

6. Mohamed Asan says:

The 220 ohm resistor is burning in my circuit. Can anyone please tell me why it’s happening and what shoudl I do to overcome this problem?

• Yaseen says:

Hi Mohamed Asan

• MANOHAR SINGGH says:

USE ONE WATT RESISTENCE INPLACE OF QUARTER OR HALF WATTS OF 220 OHMS

7. mak says:

hi there! how much current this power supply can provide? In other words how much load it can carry?

8. how much amps will it give out?

9. zaima wajid says:

how do we find the fix resistance in regulator to find variable resistance ?

• Yaseen says:

Hi Zaima wajid
1. Use equation
2. After assembling the circuit set the required voltage by varying the POT, then measure the POT resistance and replace POT with a fixed resistor.

10. Zeeshanrz says:

I have transformer rating 220/30V and 3amperes .can I
use it in the circuit?????+

• Yaseen says:

Hi Zeeshanrz
You can use 220V/30V but, it will not give you 3 Amps.

• zeeshan says:

Ok and I have to ask something else that the potentiometer has 3pins ,two side pins will be used as input & output but what to do with the pin that is in center of that teo pins,please reply fast yaseen…….:-)

• Yaseen says:

Hi Zeeshan
Use center pin and any one of the side pin as input and output pins.

• jim says:

then how much amperes will it give?

11. Zeeshanrz says:

Thnx men…… 🙂

12. Zeeshanrz says:

Bro I want to ask that can I use 3200uF 50v capacitor in place of 2200uF 100v capacitor?????

• Yaseen says:

You can use 3200uF/50V capacitor.

13. Zeeshanrz says:

The 1kohm resistor and potentiometer is burning in my circuit. Can anyone please tell me why it’s happening and what shoudl I do to overcome this problem?

• Yaseen says:

Hi Zeeshanrz
Check diode D6 polarity.

14. Zeeshanrz says:

Polarities are all ok,every thing is according to the circuit diagram.
Don’t know what to do???

• Yaseen says:

Hi Zeeshanrz
Your Regulator IC may damaged, replace it, verify input and and output pin of LM317 is correct.

• Zeeshanrz says:

sorry yasin for trouble it was my fault, i made wrong connections of potentiometer,
now it is burnt but i dont know that diode D6 and IC would be working,what do you say are they also burnt or not?????????

15. Ahtisham says:

can i use a 12v 1A transformer.if i use 12v 1A transformer can i change the value of variable resistor.and what value of variable resistor i use?

16. ata says:

how much current this circuit provide???plz reply

17. ahir mayur says:

I can operate 25 watt load with this ckt??

i did this circuit but the output is varying frm 0.2 to 33 v can anyone tell me y i cant get the xact output

19. Anik says:

The registor R1 is getting heated up with a odour within seconds after tryin turning ou the circuit ON.

20. Nikhil says:

The circuit is working fine giving out 30volts on digital multimeter until the load is connected. As soon as the load is connected its directly dropping down to 2.5volts. Can someone please rectify this problem?

21. Moyosore says:

Hello there. How do I construct a 0-12V , 1A variable output power supply without using an IC?

22. Marlon says:

Hi! if I use Transformer 220v to 30 v with 5 amps how to can I maintain the 5 amps on dc output

23. Marlon says:

My Questions:
1. I have the 230v to 30 volts 3 amps transformer, how to maintain the 3 amps on dc output?
2. What will be the size of heat sink need to be use on LM317?
3. Where can I put the voltage and amp meter display?

24. M.ZAKIR BAIG says:

When we use 220 v to 60 v tranformer than the ckt may work or not???

25. aftab says:

this circuit is not working every time 5k pot burns out i have checked the components many time i dont know what to do

26. m zeeshan says:

i want to make a multi variable charger that have range from 3 to 12 volts using this circuit, that can charge a cell phone help me plzzzzzzzzzzzz

27. Mba Kalu Elijah says:

Please the correct pin output for LM 317 is as follows : 3 = input , 2 = output , 1 = adjust

28. Hamza says:

The circuit is not working properly…. every time variable resistor burns…..all the connections are ok….what should i do…kindly tell me??

29. Abraham says:

in this circuit design I discovered the Vref resistor connected between Vin and Vout is the one making the LM317 hot and voltage dropping

so if I remove the resistor it stop heating what is the implication of removing it pls

30. Ibrahim saeed says:

HI Yaseen
I have 30v transformer 2Amp can I use this circuit diagram