LM317 Voltage Regulator circuit


In this project, I have made a simple adjustable voltage DC power supply using the LM317. This circuit has an inbuilt bridge rectifier, so I can directly supply 220V or 110V AC supply at the input of the LM317 circuit. The circuit converts 230V / 110V AC to 0v – 12v DC.

LM317 Voltage Regulator circuit thumbnail

I can also monitor the output voltage on the digital voltmeter, connected with the circuit. I can use this circuit as a variable DC power supply for different electronics projects.

Circuit of LM317 variable DC power supply:

LM317 Voltage Regulator circuit

Please refer to this circuit diagram for the LM317 adjustable DC power supply. I have mentioned all the required component’s rating in the circuit diagram.

First, the step-down transformer reduces the voltage from 220V/110V to 15V AC.

Then the inbuilt bridge rectifier converts 15 volt AC to 15 volt DC.

To get the maximum 12volt DC at the output, I need to supply 15volt DC at the input of the LM317 IC.

The output voltage can be adjusted by the potentiometer.

Required Components for LM317 circuit:

LM317 variable power supply components
  1. LM317 IC with heat sink 1no
  2. 220-ohm resistor 1no
  3. 1k resistor 1no
  4. 5k potentiometer 1no
  5. 10 uF Capacitor 1no
  6. 1000 uF Capacitors 2no
  7. 0.1uF Capacitors 2no
  8. 5-mm LED 1no
  9. 1N4007 Diodes 6no
  10. Step Down Transformer 220/110V to 15V
  11. Digital Voltmeter 0-100V Three Wire (Optional)
  12. Connectors
  13. Zero PCB

LM317 IC pinout:

LM317 pinout

Now, before working with the LM317 voltage regulator, we should know the pros & corns of the LM317.
So in this video, I have explained the following topic of LM317 IC which gives you a clear idea about the LM317 regulator

Operating Condition of LM317 IC from the Datasheet [voltage, current, temperature rating, etc]
Explained with voltage equation, how the LM317 circuit works [ use of resistors, capacitors in circuit]
Pinout of LM317t ic [Adjust pin, output pin & input pin]
How to make an adjustable DC power supply with LM317 IC on the breadboard
LM 317 circuit analysis by measuring the input & output voltage using a multimeter.
Using LM317 as a fixed voltage regulator with circuit [LM317 as 7806]
How to calculate the power dissipation in LM317 regulator [ When the heat sink should be used with LM317 IC]
Protections for LM 317 circuit for different applications from LM317 datasheet

I have explained all the features of the LM317 variable voltage regulator with practical experiments, like an LED dimmer, motor speed controller, etc.

Testing LM317 Circuit on Breadboard:

Testing LM317 circuit

Before designing the PCB, I have made the circuit on the breadboard for testing.

The maximum current limit for this circuit is 1.5Amps and the maximum output voltage is 12 volt DC.

The input voltage will be always greater than the output voltage, as the LM317 is a linear voltage regulator. The efficiency of the circuit decrease with the increases in the difference between input & output voltage.

Tutorial video for the LM317 project:

PCB layout for LM317 Power Supply:

LM317 power supply PCB layout

After testing the circuit on Breadboard, I have designed the PCB for this LM317 DC Power Supply which I will use as a power source for different electronics projects.

Download the PCB layout and print it on A4 page. Then stick the layout on Zero PCB and place the components as mentioned.

Placed all the Components on PCB

place components on PCB

Now, place all the components on the PCB as shown in the PCB layout.

Place the Diodes, LED, DC Capacitors, and LM317 IC on PCB as per the polarity mentioned in the PCB layout.

Solder the Components on the LM317 PCB

Solder the Components

Now, solder all the components as marked on the PCB.

Connect the step-down transformer. Then connect the primary and secondary of the transformer as mentioned in the circuit.

Please take proper precautions while working with the high voltage (110V or 220V AC).

Finally, LM317 Power Supply is ready

Controlling LED brightness
Controlling LED brightness with LM317 circuit
Controlling motor speed
Controlling motor speed with LM317 circuit

The Adjustable LM317 power supply is ready. Now, I can connect small DC loads like DC motors, LEDs, etc at the output.

The maximum current limit is 1.5Amp and the maximum output voltage is 12Volt DC for this circuit.

Please share your feedback on this mini-project and also let me know if you have any queries.

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I hope you have liked this projects, Thank you for your time.

This Post Has 4 Comments

  1. Haseeb Nassar

    I dont know whats wrong,right after the in4007 diode rectifier bridge,its giving 15 volts, but when i chk the voltage before lm317 (V in) its giving 0.5 volts. What can be the problem?all the capacitors are 35v

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