# Variable power supply using LM317

Here is an LM317 Adjustable power supply circuit. If you are a beginner in electronics.

You want a good variable power supply. This may be the best project for you.

It can supply the output voltage 1.2V to 30V at the max current of 1.5A.

## Variable power supply using LM317, 1.2V to 30V at 1A

This is the first DC power supply in my life that made to use in many projects. It is ideal for those who want to adjust voltage from 1.25V to 30V and currents up to 1A.

Which is sufficient for normal use. For example, It is a power supply instead of a one 1.5V AA battery.

When you want to listen to music from a 30 watts amplifier that required a voltage of 24V 1A, it can be done easily.

Before we commonly used the transistor regulator that is very difficult, large, and probably more expensive ICs.

But this circuit can be created with a single IC is lm317 based variable power supply.

The LM317 or LM117 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 1.5A over a 1.2V to the 37V output range,

And has many special features that I like are :

• Output Voltage Tolerance 1%
• Line Regulation 0.01%
• Prevent the deposition temperature.
• Short-circuit protection.
• Ripple is eliminated with a ratio of 80dB
• Maximum input voltage 40V

## How it works

Followed circuits below.

Here is the step by step process:

First, the transformer T1 is changed an AC 220V down as AC 24V to the bridge diode rectifier D1(1N4001) to D4(1N4001).

There is DC voltage into the filter capacitor C1 equal to DC35V.

The output voltage from IC1 Depending on the Voltage Adj pin of the IC, or to adjust the VR1.

The VR1 is controlled the output DC voltage 1.25V  to 30V (32V) or 37V maximum voltage at 1.5A max all range.

Note: If you want to start at Zero volts (0V) Look Here

Let’s set output voltage with:

Calculate the LM317 output voltage

And we can calculate output voltage equal to:

Vout = 1.25 x {1+ (Rp/R1)

• Vref = 1.25V
• Typically R1 is 220Ω or 240Ω as a datasheet. I use the 220Ω.
• Normally as a datasheet, I see them use VR= 5K (Potentiometer) But I have VR-10K only since it easy to use.Rp = {(VR1 x R2) / (VR1 + R2)}

Then we test it, Suppose, rotate VR1 to lowest resistance cause Rp = 0Ω. put it in the formula above:

Vout = 1.25 x {1+(0/220)}
= 1.25V

But, when adjusting VR1 to a maximum resistance of VR1 and R2 are parallel together.

Rp = 5.46K = 5460Ω.

Test it in formula above:

Vout = 1.25 x {1+(5460/220)}
= 32.2V

Then the capacitor C3 is Better performance filter of IC1.
The diode D5 and D6 ( both is 1N4007) is the protector from external voltage to reverse to makes the damage to the IC1.

### How it builds

If you want to see the PCB layout and component layout and fully content.

This is first ebook.

You like my sites want to support me by buying this E-book.

Many begin friends tell me this project difficult to adjust voltage output. so I add potentiometer 1K and parallel 1K-resistor together. then connects them to VR1 as Figure below.

You will see that we can adjust the voltage at VR2 (new) is 4volts since resistance sum of 500Ω approximately.

For example, I set voltage is 9V with rotate VR1 is 8.00V and rotate VR2 easily to control the output voltage of 9.00V.

View in the video below

I assemble in the universal box to use easily.

### Apply the transformer

I have old a transformer 12V CT 12V output. It should have a total voltage of 24V.

But I measure it as 30.9V too much voltage. It may cause overvoltage DCV as 30.9V x 1.414 = 43.7V.

Which can be damaged to IC1 by too much current.

So I modify another transformer 12V CT 12V and 0V 6V 9V 12V output into 21-volts.
as Figure below

This circuit perfectly works, as the video below. I can adjust voltage output is 1.25V to 27V since I use the 21V output transformer.

If you can adjust 24V or 12V CT 12V. It causes output up to 30V. But IC overheat when a short circuit or overload.

I test circuit with the 12V 8W lamp as a load. A steady (DC) Voltage will not be transferred from 12V.

We can add LED voltmeter to show a voltage level of output.
Mr. Ali Mohammed, ask me how to use 3 wires voltmeter, red, black, and yellow.

It is a good idea. It’s accurate and more convenient.

Block diagram of adding a voltmeter to the first power supply

In the circuit diagram, it needs an External DC power supply. We have to build a 9V DC regulator for it.

We connect a bridge diode (D1 through D4) to SEC (0 and 12V) of a transformer. Then we connect the measure voltage wire in yellow (+) to the output LM317 power supply. And Ground to (-).

If you use other AC voltage such as 24 volts. You must change:

• C1 = 1,000uF 50V Electrolytic capacitor
• R1 = 1K 0.5W resistor

This so saves and easy circuit.

## Why does it not work and FAQ

• C2 — you can use a 0.1μF electrolytic capacitor instead of 0.1uF 63V or 50V ceramic or mylar type. But we need to be careful to be correct lead.
• Transformer size—You should use 2A transformer to full current up to the 1.5A output. However, 1A transformer also works well lower current.
• WVDC All capacitors, You can use voltage of  50V. Specifically, Electrolytic capacitor!
• Why R1 is coal?—If Diode-D5 is the wrong terminal. It causes an input high voltage across LM317. Then, comes to R1 to VR1 and R2 to ground. So, They get high current and burned. Please check all diode terminal in a right way only.
•  If you put the D6 polarity incorrect, The VR10K will burn.
• You can solder the components on Perforated or universal PCB Board.
• Why use C3-470uF? It is a filter capacitor. You can use 1uF tantalum capacitor same in the datasheet.   But I use this because I have it. It also works well.
• Why is the output 1.5A?—The current is not constant at 1.5A throughout all voltage ranges.
If you need high current more.
• Please look at: LM317 2N3055  high current regulator.
• Electronic devices with polarity Must be put correctly.  For example, Diodes, Electrolytic capacitors, LM317 etc.

### Use an LM317 as 0 to 30V adjustable regulator

There are many ways to do 0 to a 30V adjustable regulator.  But this is easiest with helping of two diodes.
When the current flows the diodes. It always has a voltage across it of 0.65V to 0.7V.

If we connect the two diodes in series. They have 1.3V across them. In normal LM317, start voltage at 1.2V. But this voltage is in both diodes. So, the output starts at 0V.

But it has a disadvantage. The current is slightly reduced by the resistance in diodes

## Sample circuit of LM317 power supply Others

Besides this circuit, We also have other interesting circuits. Choose a simple first.

## LM317 adjustable voltage regulator 1.2V to 10V

This is also LM317 based variable power supply and Low noise, adjustable voltage output: 1.25V to 10VDC (0-12V) from 12V battery source, so simple circuit

If you have a 12V battery. But you have a load to use the voltage 1.5V to 10V at 0.75A. You should reduce the noise as well.

In this circuit, it will converter DC low voltage, 12V  to be out of 1.25V to 10VDC.  by can give current topmost get about 1.5A.

You should use an IC number LM317K(on TO-03). Because it has powered more than LM317T (on TO-220).

While it works. It is so hot too. So, need a heat sink that large-sized.

Others parts function

• The R4 use to adjust the output voltage level.
• The C1-470uF 25V (electrolytic capacitors)  acts like a miniature battery that supplies power during the spike.
• C3-0.1uF 63V (Ceramic Capacitor or Mylar Capacitor)  reduces  noise
• C2-22uF 25V to decrease all noise well. The others detail, Read in the circuit.

## Simplest LM317 Adjustment power supply, 1.25-15V

This is the simplest LM317 based variable power supply. We can adjust the output voltage of 1.25V to 15V. An output current level of each voltage is different.

For example: If you adjust the voltage of 12V, the current level will be 0.5A. When you set the voltage of 15V, it causes the output current of 0.2A.

Simplest LM317 Adjustment power supply, 1.25-15V

In the circuit diagram, When the voltage from 220V AC main reach transformer. It reduces voltage AC220V into 18VAC.

Then, this low AC voltage flows to a full wave rectifier, D1, D2.

Next, DC voltage flows into C1.  It is a filter capacitor to smooth and increase the DC voltage of 20V as unregulated voltage.

After that, the unregulated voltage flows to the DC Regulator circuit. Which use an LM317, R1, and VR1.

This circuit provides a constant voltage to the load. Which we can adjust many voltage levels of 1.2V to 15V by adjusting VR1.

By the way, C2 is a 0.1μF capacitor to filter out the transient noise which can be induced into the supply by stray magnetic fields.

## More great LM317 Power supply circuits

In addition, You maybe not like this. But you may modify these circuits work well too. Below.

And now you can see

## 3A Adjustable Regulators using LM350T

Sharing is caring!

## GET UPDATE VIA EMAIL

I always try to make Electronics Learning Easy.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Subscribe
Notify of
mystic

(My first Variable DC Power Supply 1.2V to 30V 1A by LM317) R1 was be coal. 🙁 I wonder why?

electro

Yes same prob Admin! and made much coal, i guess atleast a full truck load of R1 coal. R1 is attached from Vout to Adj of LM317.

ElecCircuit.com

Thank you @electro.

styles

(My first Variable DC Power Supply 1.2V to 30V 1A by LM317)
does this really work? because i had a hard time in doing it successfully. the one that i built doesn’t work. 🙁 my output doesn’t have an output of 30v and the 10k potentiometer i can’t figure out how to work it properly. please help me.

styles

gab

help.. the output is correct but when i connect it to a desired circuit it will low the voltage.. why?????? 🙁

envire

very nice projects for learner thanx a lot sir

ElecCircuit.com

Hello, slyles
This projects is works, please see others:
https://www.eleccircuit.com/lm317-linear-power-supply-regulator-selector-15v3v45v5v6v9v-15a/

We use LM317 on a lot of project :https://www.eleccircuit.com/tag/lm317/

Hi everyone..
Recently i bought an ac-dc power adaptor in which i have an option to vary my output from 1.5v to 12v.
But when i adjust the knob to 4.5v and check the output using digital multimeter the out put is varying by 3-4volts..
say for 1.5v it gives 3.6v or somehthing..
just tell me whether the problem is with my device or with m y understanding????????????

entoy

is the output of this is adjustable from 0-30volts?

maine

admin can i use 0.1uf 50V electrolytic capacitor insteda of 0.1uf 63V polyester. because im having a hard time finding that capacitor.

Rob

Dear sir.
I have copied your schematic and drawn out the pcb i have located all the parts on the pcb except one which you show directly below the 10k pot. i have checked and rechecked the schematic and the pcb all to no avail i can not trace this item what ever it is. Sir would you be so kind and explain it to me. thank you in return. Rob

chris

May I ask if I can actually build this circuit in a universal PCB?

patrick

what will I use in transformer, 1A or 2A? thank you Sir.

Derrick

can I use 2A 24V transformer??

BIlal zahid

i m not gettting output voltage ….is circuit digaram ok??…..i have tried many times

aanya

what if… instead of 24 v..i use 30 volts???
i mean if less or more than 24 V is used then ???

Hitman

How do you calculate output voltage ???

ElecCircuit.com

Hi, Hitman

ElecCircuit.com

@styles, all diode normally works.
@maine, You can use it but be careful about polarity electrolytic capacitors.

@Rob, The pcb is correct but you can use universal PCB it cheaper and faster.

Fernand

I just finished my first 1.24 to 15V dc power with 2 LM317 voltage regulators but every time I connect my transformer (AC) its producing a smoke on the rectify area . When I use A Dc voltage supply it works fine …can’t figure out the problem. here is the schematic

rahul

admin bhai……how the potentiometer being connected in proj.

ElecCircuit.com

Hi, rahul
I solder potentiometer on PCB and Figure the components layout.

Des

The LM317 will shutdown if more than 1.5amp is passed through it.

It seems a number of people leaving messages of failure to their project are missing this vital safety feature of the LM317.

MR OHM 1970

Pin 1,2,3 Adjust,,, Vout,,, Vin,,,One Tiny Error Can Screw Up This Whole Circuit,,,Please Be Careful Everyone!!! This Circuit Works For Me!!! Thanks admin

TtotheI

What if I need to supply power from 3-25 V using the same structure here? How can I start with a minimum of 3 V output? I tried using zener diodes but they do not function as desired.

TtotheI

Also how is ripple voltage calculated ?

SEUN

Pls sir help out, i built an amp with TDA2030, but it hums, what could be the reason? It happens to all TDA circuit I hv ever build, I use filter cap of 6800uf still it hums

priyanka

how can i use this circuit for gettin pure dc of 0-10 volt which will vary according to variation in input 0-230 volt ac ??

akshay bhakhar (ddit)

that good projet……
because that application……….
any project in case all dc project have most of in 30v…….
thanks….

Kegan

I just want to know which on of the 217 and 337 transistors outputs has a negative voltage and a positive voltage. Would be appreciated

Kegan

sorry 337

VINCE

when i connect it to a 24 v car battery it is overheating and suddenly shut down.

ElecCircuit.com

Hi, Kegan.
You can use LM337 negative dc regulator replace with LM317 IC. But you change voltage polarity to negative way.

In next time I will assemble them because I have more many ICs-LM337.

ElecCircuit.com

Hi, Vince

You can use this circuit to 24V car battery source.

Please you check the circuit again some part may not correct.

Kumar

I have made this circuit, its working perfectly.
I’ve used 15V 1A transformer as input, 100ohm and 10Kohm resistors for 220ohm and 12K resistors respectively. Used both 10K and 1K pots as per the circuit. I am getting 12V dc output. I have also installed a Digital panel voltmeter to the circuit. Its working fine.

Karim

The project works very good but without the VR 10k…….whenever I connect it and turn the circuit on it starts to burn.
please I need help because I want it a variable power supply

ElecCircuit.com

Hi, Kumar

Thanks for feedback.

ElecCircuit.com

Hi,Karim.

I am sorry for your project do not work.
In particular,Diode-1N4002 at between Output and ADJ of IC1.
If you switched lead of diode in wrong polarity.
It may will cause too much current flow through it to VR-10k with too much current until the potentiometer burned.

ElecCircuit.com

Hi,Kegan
Please wait me in the future I will show you the project that use LM337 in main parts.

Ashok

i make this circuit i used all 1n4007 diode & 24 v 1.5amp transformer but R1 get burnout & also 10k pot also plz tell me what is poblem

ElecCircuit.com

Hi,Ashok.
I am sorry you that your project not work.

Diode-1N4007 across IC1- IN and OUT lead. It may have problem or position of lead not correct. It cause high current flow through it to R1 and VR1 to ground.
Which make they are burned.

Ashok

sir i chk those connection but problem is still thr plz help me

ElecCircuit.com

@ Ashok
I think IC1, D-1N007 may be damaged. cause too much current to R1 and VR1.
But you can test the circuit by follows step below.
2.remove VR1 and D5,D6 before.
3. Hold the voltmeter at output.
4.Then short between ADJ and Ground.
5. Apply AC-power line
6. If OK the voltage output must be 1.25V
and R1 not overheat.

Some times D5,D6 may error. Please check them again.

Goodluck.

Ashok

Sir

which type of Variable resistor is used for adjusting voltage, as i used it when i move these it burns so it have any amperage for control? as per your instruction i will do it after printing PCB board.

Ashok

in your above comment in 3 point you said hold voltmeter at output & GND right and ADJ is directly connected to GND that is remove R2? What about R1? I used C2 electrolytic Capacitor as you said polyster?

ElecCircuit.com

Hi,Ashok

I think IC1, D-1N007 may be damaged. so test circuit as above.
In testing we don’t adjust voltage output.
We check IC1.
You remove VR1 then short ADJ and Ground of circuit by may be use wire jumper.
So you don’t need remove R2 because resistance across it is zero now.
if the circuit is normal it will be 1.25V at output.

But R2 burned again indicate that voltage too high which IC1 and D5 are damaged.

Therefore You check lead of any parts in correct only.
For example D5,IC1 and more.

C2 isn’t prblem you can use any type.

Rajan

how to select transformer using KVA ratings.
if i want 230V 50Hz ac to down convert it into 24V ac.

vivek