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.

Variable Powersupply using LM317

  • 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. 

Variable power supplyMini power supply unit

Components Pin out

LM317 pin out

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

  1. 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

  2. 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??

  3. @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.

  4. 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?

    • 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.

  5. 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?

      • 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?????????

  6. 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?

  7. 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?

  8. 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?

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

  10. 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

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

  12. 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

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