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How to Use LM317 for Making a Variable Power Supply Circuit

How to Use LM317 for Making a Variable Power Supply Circuit

In this post we will elaborately discuss how to build a simple LM317 based adjustable power supply circuit using minimum number of external components.


Whether it’s an electronic noob or an expert professional, an adjustable power supply unit is required by everybody in the field. It is the basic source of power that may be required for various electronic procedures, right from powering intricate electronic circuits to the robust electromechanical devices like motors, relays etc.

A variable power supply unit is a must for every electrical and electronic work bench and it’s available in a variety of shapes and sizes in the market and also in the form of schematics to us.
These may be built using discrete components like transistors, resistors etc. or incorporating a single chip for the active functions. No matter what the type may be, a power supply unit should incorporate the following features to become a universal and reliable with its nature:

Essential Features

  • It should be fully and continuously adjustable with its voltage and current outputs.
  • Variable current feature can be taken as an optional feature because it’s not an absolute requirement with a power supply, unless the usage is in the range of critical evaluations.
  • The voltage produced should be perfectly regulated.
LM317 IC pinout specifications TO-220

With the advent of chips or ICs like LM317, L200, LM338, LM723, configuring power supply circuits with variable voltage output with the above exceptional qualities has become very easy nowadays.

How to Use LM317 for Producing a Variable Output

Here we’ll try to understand how to construct a simplest power supply circuit using the IC LM317. This IC is normally available in TO-220 package and has three pin outs.

The pin outs are very easy to understand, since it consists of an input, an output and an adjustment pins that just needs to be wired up with the relevant connections.

The input pin is applied with a rectified DC input, preferably with the maximum tolerable input, that’s 24 volts as per the specs of the IC. The output is received from the “out” pin of the IC while the voltage setting components are connected around the adjustment pin.

How to Connect LM317 in a Adjustable Voltage Power Supply Design

LM317 variable power supply circuit

As can be seen the diagram, the assembly needs hardly any components and is in fact a child’s play to get everything in place.

Adjusting the pot produces a linearly varying voltage at the output that may be right from 1.25 volts to the maximum level supplied at the input of the Ic.

Though the shown design is the simplest one and therefore includes only a voltage control feature, a current control feature can also be included with the IC.

Adding a Current Control Feature

LM317 current control circuit


The figure above  shows, how the IC LM317 can be effectively used for producing variable voltages and currents, as desired by the user. The 5K pot is used for adjusting the voltage, whereas the 1 Ohm current sensing resistor is selected appropriately to acquire the desired current limit.

Enhancing with High Current Output Facility

The IC can be further enhanced for producing currents higher than its rated values. The diagram below shows how the IC 317 can be used for producing more than 3 amps of current.

high current LM317 power supply circuit

LM317 Variable Voltage, Current Regulator

Our versatile IC LM317/338/396 may be used as an adjustable voltage and current regulator through simple configurations.

The idea was built and tested by one of the avid readers of this blog Mr. Steven Chiverton and used for driving special laser diodes which are known to have stringent operating specifications, and could be driven only through specialized driver circuits.

The discussed LM317 configuration is so accurate that it becomes ideally suitable for all such specialist current and voltage regulated applications.

Circuit Operation

Referring to the shown circuit diagram, the configuration looks pretty straightforward, two LM317 IC s can be seen, one configured in its standard voltage regulator mode and the other in a current control mode.

To be precise the upper LM317 forms the current regulator stage while the lower acts like a voltage controller stage.

The input supply source is connected across the Vin and ground of the upper current regulator circuit, the output from this stage goes to the input of the lower LM317 variable voltage regulator stage. Basically both the stages are connected in series for implementing a complete foolproof voltage and current regulation for the connected load which is a laser diode in the present case.

R2 is selected to acquire a range of around 1.25A max current limit, the minimum allowable being 5mA when the full 250 ohms is set in the path, meaning the current to the laser may be set as desired, anywhere between 5mA to 1 amp.

Calculating the Output Voltage

The output voltage of a LM317 power supply circuit could be determined with the following formula:

VO = VREF (1 + R2 / R1) + (IADJ × R2)

where is = VREF   = 1.25

Current ADJ is usually around 50 µA and therefore too negligible in most applications. You can ignore this.

Calculating Current Limit

The above is calculated by using the following formula:

R = 1.25/max allowable current

The current controlled voltage acquired from the upper stage is next applied to the lower LM317 voltage regulator circuit, which enables the desired voltage to be set anywhere from 1.25V to 30V, here the max range being 9V since the source is a 9V battery. This is achieved by adjusting R4.

The discussed circuit is assigned to handle not more than 1.5amps, if higher current is required, both the ICs may be replaced with LM338 for obtaining a max 5amp current or LM396 for a max of 10amp current.

The following lovely pictures were sent by Mr. Steven Chiverton, after the circuit was built and verified successfully by him.

Prototype Images

Upgrading LM317 with Push Button Voltage Control

So far we have learned how to configure an LM317 for producing adjustable output using a pot, now let's understand how push buttons may be used for enabling digitally controlled voltage selection. We eliminate the use of mechanical pot and replace it with a couple of push buttons for the up/down selection of the desired voltage levels.

The innovation converts the traditional LM317 power supply design into a digital power supply design, by eliminating the low tech potentiometer which might be prone to wear and tear in the long run resulting in erratic operations and incorrect voltage outputs.

The modified LM317 design which would be allow it to respond to the push button selections can be seen in the following diagram:

The R2 resistors associated need to be calculated with respect to R1 (240 ohms) for setting up the intended push button selected voltage outputs.

The R2 and the PNP BJT stage (using BC557) needs to be repeated 10 times for the integration with a LM3915 circuit configured with the intended push button stage, as shown below:

Pin#1 to pin#10 needs to be connected with the bases of the PNP associated with the LM317 circuit stage.

Once this is done, SW#1 and SW#2 could be used for implementing the digitally assigned up/down changeable outputs, as desired by the user.

The above push button circuit using LM3915 is specified with 10 outputs only, in order to get more selectable ranges, a couple of such IC LM3915 could be cascaded together for upgrading the design with 20 selectable voltage outputs.

The LEDs as shown in the design may be optional, however these can be useful for indicating the relevant voltage levels as per the preferred selections.

If you have anymore doubts regarding this LM317 push button operated power supply circuit, you can simply ask them through the comments.

References: http://www.ti.com/lit/ds/symlink/lm317.pdf


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

101 thoughts on “How to Use LM317 for Making a Variable Power Supply Circuit”

  1. thank you sir for your response, one more thing, pls what is cl fillter i saw this while reading other people’s comment concerning the 7modified sine wave inverter in your article.by the way thereare much changes in your website keep it up.

    • Thank you youngking, RC filter is a filter made by using capacitors and inductors to filter out harmonics to create the best possible sine waveform from a modified inverter. This is done at the secondary side of the transformer.
      I am trying to maximize my site performance and therefore trying out different website templates.

  2. hello sir, how are you doing .please sir can one connect the same
    mosfet on heat sink without any inslulator let say the upper and lower mosfet, will there be any effect because the gate will be tied together the same with the drain and the source as well .

    • Hello youngking, isolator is not required for mosfets within individual channels, since they have their similar pins joined together anyhow.

  3. sir i don’t understand what you mean in thisrepile you gave ( just make sure to have a large filter capacitor across the bridge rectifier of your source power supply.) are you refering to the first circuit because i didn’t see any rectifier

  4. sir, thank you for clearing my doubt, i will build this first circuit for my use but one more query can 104 capacitor be use as filter capacitor.

    • You are welcome youngking, please ignore the capacitors shown in the diagram. Just make sure to have a large filter capacitor across the bridge rectifier of your source power supply.

  5. sir i’m refering to this first circuit l.e variable power supply circuit using lm317 the place you indicate 28v as input , how can i modified it to 12volt. next query is that i build 1kva inverter but my problem is that i don’t have the money to purchase 12v 100ah battery, but according to the information i gather it said that automobile battery is meant for starting of vehicle and not for inverter . it also stated that inverter battery is deep cycle battery, now can you explain reason why automobile battery is not meant for inverter, because i have 75ah automobile battery at my disposal. sir i will be waiting for your response

    • younking, LM317/338 can be used with any input from 4.5V to 35V, so you can use 12V as the input.

      Your information is not correct, an automobile battery can be effectively used for all inverter applications. Whoever told you this probably has no experience or knowledge regarding batteries or inverters.

  6. Hi Swag,
    its possible to adjust the Current too?
    I wish to build variable bench power supply Voltage and Ampere can be adjustable.


  7. Hey I was thinking to make a power supply but which one is better and variable — LM317;LM723;L200 for my college project

    • Abhishek,

      please don’t send youtube links, instead you can send the video clip to my email, I’ll publish it in my site with your name in it 🙂

    • No I didn’t, I think it would be better to upload the diagram on some free image hosting site and provide the link to me here, I’ll look into it and reply you right here.

          • Hi Swagatam,

            It works very well. However when I put a 2A load on the output at 12V, the TIP34C and LM317HV gets extremely hot. I have mounted them on large heatsinks.
            The input voltage to the circuit is 26.5VDC.
            Is it normal that these two components should get so hot or is there perhaps a design fault in my circuit.

            Thank you for your assistance.

            • Hi Jan, yes it s normal due to the small package of the TIP and LM317 (TO-220), if you use a TO-3 kind of BJT then probably the heat will be little less, so anyway using a large heatsink is the only remedy for the present situation…..

  8. Hi Swagatam,
    I have been posting messages to you, but I dont think you received them. I want to send you a circuit diagram of the variable power supply which I have an overheating problem with. Please give me an email where I can send it.


    • Hi Jan, I was busy with the maintenance work of my site therefore could not attend the comments, no problem you can send it to my email
      homemadecircuits @ gmail.com, I’ll check it out

  9. Hi. Swagatam,
    Re: High Current Adjustable Regulator
    I have difficulty sourcing the LM195/LM395 in my country. Is there any other product that I can use that will do the job?

    • Hi Jan,

      But I think you can get LM338 easily, if you get LM338 you can apply it in the last circuit which is shown the above article, and upgrade the transistor rating and achieve the required high output current.

    • sorry, actually the last circuit itself utilizes the LM195….to eliminate this you can change the configuration and connect the lower BJT in a different method as shown in the following article


      consider the 78XX as your LM338 or LM317, adn apply the BJT as recommended in the article

    • Hello Matt, no that's not possible, because LM337 is rated to handle a maximum of 38V input, and moreover it's a negative voltage regulator

  10. Sir swagatam hello again..pls. advice me wat to do abwt my power bank..it is charging to my samsung galaxy but remain to its voltage percentage not increasing..I am using a 9 packs of battery in serries connection, Ni-MH AA1500mAh 1.2V.
    I took my circuit from a car charger..pls.pls. pls.mr swagatam I need your expertise especially me still learning in this

    • Hi Mark, I think I have already answered this question in another post, I'll repeat it again, your power bank output capacity must be significantly higher than your phone battery capacity, especially the AH rating, otherwise the performance will never be at the optimal level

      ….and make sure the power bank bats are fully charged before using them for the intended purpose

  11. So it needs a very low resistance? The higher the value..the lower the current? and vice versa?…

    and where is the negative of the output? base or emitter?

  12. I've seen some ckt on Google…they have a diode that is connected betwwen the Vin and Vout of the regulator..whats that for? can you explain? tnx

    • that's for protecting the IC in a situation where the output of the might have a filter capacitor, and the input of the IC is shorted to ground, which is never possible under normal conditions.

  13. Ooh…thanks Sir…

    Also I thinking that if I use two IC(LMLM317 or LM338) in parallel than have any chance to reduce the heat ??

  14. Sir,
    I have done this …
    It working well..
    But one problem… the IC LM317 is too heating when some load (like a 6 volt dc motor) is connecte. I also used a medium size heat sink.

    So please tell me how can reduce the heating problem…
    Thank you…

    • Narottam, Linear ICs like 317 and 338 will always heat up even with normal loads…it cannot be avoided, you can try LM338 instead and see the response

      or try reducing the input voltage

  15. Well…. Sir….we hav a project to design a 40mA power supply with transformer…. So basically I could be using either of these IC's…. But since we have just entered our branch I do not have knowledge to the depth…. Could you please suggest me what changes is to be done in the values of the passive components so as to get a 40mA power supply

  16. Well…. Sir….we hav a project to design a 40mA power supply with transformer…. So basically I could be using either of these IC's…. But since we have just entered our branch I do not have knowledge to the depth…. Could you please suggest me what changes is to be done in the values of the passive components so as to get a 40mA power supply

    • you can try the first circuit with IC LM317….no changes in the component values is required, use a 50mA transformer in order to restrict the output current to the specified limit

  17. Dear Mr Swagatam,
    is there a possibility that a 5Amps 50Hz transformer be combined with timer to regulate the Vout? I've successfully built a variable bench power supply with ic L200 and a few power transistors, but I don't think it's efficient enough.

    • Dear imanul, i have no idea how a timer can be used for voltage/current regulation, one of the best options is shown in the above article first diagram, an LM338 may be used instead of Lm317 for a 5amp input

    • I'm sorry, not a timer, i mean some controller that's designed for smps, like pwm.
      When using a linear regulator like LM317 I can feel a lot of heat on the heatsinks both from the ic and power transistors, and I believe that's a wasted power.
      I googled the formula of the wasted heat, (Vin – Vout) x Amps.
      eg. (18V – 6V) x 3A = 36Watts of wasted heat.
      So if you could please teach me how I can get high efficiency by using alternative other than linear regulator. Building a complete smps, with ferrite core, is too hard for me.

    • the formula and the calculations that you have shown is true for resistors and zeners, not for these sophisticated power regulator ICs. These ICs may dissipate say about 10% of the total power, which is quite reasonable.

      You can try LM338 circuit for your application, or if you are interested to get 99% efficiency then ferrite cored smps is the only way to go..

    • Thank you Mr. Swagatam, a new lesson learned today.
      Anyway I'd like to stock up common diodes at home, like 1n4001. Most people recommend the 1n4007-the highest voltage rating ones. With their particularly equal price, why do the manufactuter still make the lower ones? When I go to the retailer and ask for 1n4001 they give me 1n4007 instead, and saying "its the same". I dont think it's true, a "marking" means "something", right. And what about 1n5819 Schottky diodes, should I stock them up for my everyday electronics? Can they be used as the substitute for the 1n400x series?
      Thank you in advance Mr. Swagatam for your advice.

    • Thanks Imanul, yes the numbers definitely indicate a lot of things, 1N4007 is much better than 1N4001 in terms of reverse voltage handling capability, and nowadays all other variants are slowly getting obsolete except 1N4007.

      1N5819 may be considered an enhanced version of 1N4007 in terms of speed and forward voltage drop but as far as voltage rating is concerned its far inferior just around 30V

  18. Hi, I am trying to build a variable PSU using a 24 v smps and LM338. The circuit works but the output current is very low. The same circuit works with LM317. Could you advise me if any changes are needed in components for LM338. I have used the first circuit as shown here on top.

    • Hi, please provide all the info regarding what exactly you are trying to include in your power supply, and what are the input/output amp specs

    • I am trying to build a benchtop variable supply. I just require variable output using LM338, 5k wirewound potentiometer which will be used to vary the voltage.Input amperes is 3A and same is needed at output. The 24v SMPS is a ready made manufactured by meanwell. Hope this info is helpful.

    • The IC LM338 is designed to provide in excess of 5amps at its output, so if the input is 3amps you should get 3 amps full at the output of the IC, across the whole variable voltage range, if this is not happening your IC could be faulty(duplicate) or not connected correctly.

      A 10k pot would work better than 5k

    • Hi i tried the same circuit using 10k pot, still i get the same result. Now for the resistor between ADJ and Vout, do we need it to be of higher wattage, currently i am using 220 ohms 1/4 watt.

    • Hi Swagatam, As you said, the LM338 turned out to be faulty. I ordered same ICs from Texas Instruments samples and they worked perfectly.
      Now another issues is do LM338 have short circuit protection ? If not can i use your suggested circuit which uses relay to protect the SMPS from damage ?

  19. Hi sir,
    I came across your work on “​Bicycle Dynamo Battery Charger Circuit” in Homemade circuit design blog. It was really informative. I would like to ask something regarding that article. I am working on a hexapedal robot with battery switching mechanism. Once the primary battery gets beyond a preset voltage, secondary battery will power up the robot’s system. My concern is not regarding the switching circuit. Together with this, I am working on energy generation by attaching a generator to each motor. The current generated is intended to be used to recharge 30C 11.1V 2200mAh 3 cell LiPo battery. I am aware that the circuit mentioned in “Bicycle Dynamo Battery Charger Circuit” will not be useful for my purpose. Can you give me any other option pertaining my issue. I just need to know on how to modify the circuit to make it LiPo compatible. Thanks, looking forward for a reply.

    Arun Prashan

    • Hi Arun, yes I'll post the required design in this blog soon, may be by tomorrow, so please be in touch

      By the way if you are assuming that you would be able to charge the battery with the same energy which is being used for operating the robot, that may be not feasible….the output will be always less than the input

  20. I checked with 24V supply:

    R1=180, R2=5K POT, Output 24V at low R2 and high R2, POT frying.
    R1=180, R2=10K POT wire wound, Output 1.5V at low R2, 24V at slight increase in R2, R1 heating up.

    I have tried the fifth and last LM317…………all behaving similarly.

    • Hi Abu-Hafss,

      You decide how this can be possible, LM317 can be never wrong, its datasheet cannot be wrong, the indicated part values cannot be wrong.

      I am suspecting that the entire lot of your LM317 could be duplicate and faulty… assuming your connections to be perfectly correct as per the diagram.

      a wire wound pot is not required, even a preset should work here.

    • Hi Abu-Hafss,

      the sparking of the pot itself suggests that the ADJ pin is shorted with the input pin which is probably causing the input supply to short to ground through the pot making all those sparks inside the pot.

  21. As per datasheet the output voltage range is 1.5 – 37V. And input voltage must be 1.5V higher than the output, which means to get 37V at output the input should be 38.5V ! However, in my case the input is not 36V, it is 32V.

    Ok, I will try with 220R (240R not have) and 10k POT.

  22. Hi Swagatam

    I need your help to get rid of the frustration I am experiencing with my first LM317 circuit.

    As the configuration is quite simple, I soldered the components on PCB straightaway. The value of the resistor was selected based on the value of the POT and the required output voltage (30V). The step down transformer is about 500mA

    Initially the 30V-analog voltmeter would show more than 30V. When I adjusted the POT, I noticed some spark or flash inside the POT. And then the output remains within 28V-32V. The current consumption of the load is hardly 100mA.

    I assembled fresh components on a breadboard but same results. I checked the circuit on the simulator, it works perfectly…………….so where am I wrong???

    • Hi Abu-Hafss,

      R1 could be 240 ohms or a 120 ohms, it won't make any difference as long the pot is selected for satisfying both the values… in other words a 10K pot would be just enough.

      so R1 is not so crucial.

      There's hardly anything one can suggest regarding the troubleshooting of the first circuit, because it's as simple as can be.

      Only two things which you probably know that could be causing the problems are, incorrect pin connections, or faulty (duplicate) devices. there's nothing else that could blow these devices of as these devices have a thorough and very robust internal protection circuitry.

    • I have updated the connection diagram. Please re-check. That is how I am connecting the components.

      I have tried another IC (4th one). When the POT is providing very low resistance the voltmeter shows about 5V. When trying to rotate the shaft of the POT, I can see light inside the POT which means it cannot withstand the current flowing thru it. Do I have to use a wire-wound POT?

    • Hi Abu-Hafss,

      use a new IC and try with a 24V supply, I think the 36V input could be damaging the IC….and it should 240 ohms for R1 and 10k for R2 ideally.

    • Just fried the 220 ohms resistor when used with 10k wire-wound POT.
      Supply is 32V. And there is no load, no C2 only a 30V analog voltmeter.

      I assume, earlier the carbon film of 5K POT could not withstand the I(adj) and now the 220 ohms resistor failed to withstand that current. Why I(adj) is so high?

  23. Hello Mr. Majumdar. What have to be done differently to adjust the output current to a specific value? I mean I would like to make the available current adjustable to that it could go through a digital ammeter before the terminal. Also, for the high current circuit, how should the circuit be fused? Thank you.

  24. 50mA per second is huge, it's the problem of your clock not the battery configuration, I don't think any external circuit can help to reduce this.

    If you increase the voltage from 1.5 to 1.8 would force the clock to consume even more current so that's not a correct approach, and the opamp has no role in the situation.

    One method could be to use LM317 with an input of 2.4V and output of 1.25V supplying the clock

    Another possible way could be to use a joule thief circuit.

  25. Dear sir
    Aap ne jo 7805 ke help se charger banane ki idea diya hai thanx for that . maine kal wo banake dekha . to successfully run hua . but wo 12v 12amp pe chalane ke bad hot ho raha tha . to plz usake liye koi solution batawo . sir muze actually muti pin charger aur sibhi automobile battery ke liye (motorcycle , car , truck )ke liye charger banana tha . so plz help me sir

    • Dear Shrikant,

      Use a large aluminum heatsink with the 7805 IC for preventing it from getting hot.

      For using the circuit with many cell phiones you can try the folowing design


  26. hello sir, I want to ask that for the above circuit which dynamo would be suitable as we want to charge our laptop from dynamo by using it in our bike wheel. and to charge a laptop e will require atleast 24v and from dynamo I don't know this much power can be generated or not and if it can be done then which dynamo will be used as there are different types of dynamo.
    so should we use a d.c. motor as an input source or dynamo can work here. and please specify the ratings and type of d.c. motor or dynamo.
    Thank you.

    • Hello concor,

      you can use any small dynamo rated at around 28V/2amp for the project, the dealer will be able to advise you better with the product.

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