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Here is the circuit diagram and description of a 1A variable power supply for any electronics project application. Output voltage can be adjusted from 1.2V – 30V. LM317 3-terminal voltage regulator IC is the main head of this electronics project. The main features of this IC are 0.1 % line and load regulation, Floating operation for high voltages, 1% tolerance of output voltage etc.  This IC is also able to supply more than 1.5A at 1.2 to 37V. 

Working of 1A Variable Power Supply:

220V AC supply is converted to 24V AC by the transformer T1. Use 1A or 4A rated transformer. Output of transformer is given to a bridge rectifier. With the help of diodes in the rectifier, AC voltage is converted into DC. Capacitor C1 is a filtering capacitor and C2 is used for proper regulation. Variable Resistor VR1 will vary the output voltage from LM317. Diodes D5 and D6 are protection diodes. Mount the voltage regulator IC on a heat sink. This heat sink is used to absorb the heat dissipated by voltage regulator. Create a fine tuning system by adding another 1K variable resistor to improve the efficiency of varying output voltage. After assembling the circuits perfectly check the circuit using a multimeter. Try to tackle the problems if any occurs in the power supply circuit.

1A-Variable-Power-Supply-(1.2-30V DC) for electronics projects

Circuit Diagram of 1A-Variable-Power-Supply-(1.2-30V DC)

Variable DC Power supply can be used to power wide range of electronics projects according to its need. This is very apt circuit for students to test their electronics mini projects giving different range of voltage.

Electronic Components:


  • R1 – 12K Resistor (1/4W)
  • R2 – 220 Ω Resistor (1/4W)
  • VR1 - 10K Potentiometer


  • C1 - 1000uF 50V Electrolytic Capacitor
  • C2 - 0.1uF 63V Polyester Capacitor
  • C3 - 10uF 35V Electrolytic Capacitor
  • C4 - 470uF 35V Electrolytic Capacitor



  • T1 - 21-24V 1A/2A Transformer 

Most of the electronics hobbyists always need this circuit for a variety of applications. It is very useful for students to study about power supply and voltage regulators. So this DIY project is very effective as a variable power supply.

User Review (8)

v vlady  

this linear regulator/supply is Ok, but wastes power. An alternative that is just as easy and inexpensive to make is a step-down (buck) switch mode power supply based upon the LM2596. The following link is a site that has full details on how to make such a power supply

Reply  Report Abuse   07 May,2017 07:05

Koustav Mondal   Kalyani,West Bengal

this circuit can modified by adding two 1N4148 diode in the input terminal of the LM317 ic, after the adding those diode then this circuit can regulate 0V to 30V

Reply  Report Abuse   13 May,2016 10:05

leomar agyamoc  

Hello, can you please provide me with a schematic diagram for this?(EAGLE) thank you!

Reply  Report Abuse   22 October,2014 11:10

Kris Santiago  

is it okay that the diodes are 1 A and my transformer is 2 A? and my potentiometer does not change the output voltage of the circuit

Reply  Report Abuse   12 October,2014 06:10


I recommend 1A transformer..... If your transformer can supply 2A, there will be circumstances that it will. So for security add fuse to the mains side, 150mA to 200mA slow blow (more resistant to transients at switch on). In the event of a disaster, the 1N4001 will pass higher current, and the transformer will supply it - but the fuse will burn out.

Reply   Report Abuse   21 October,2014 04:10


If it is difficult to adjust the output voltage add two 1k resistors parallel and connect it with VR1. Will update that part in the article soon. thanks

Reply   Report Abuse   22 October,2014 11:10

Nima Kiran   Kerala

very helpful notes....

Reply  Report Abuse   07 July,2014 02:07

Kris Santiago

is it okay that the diodes are 1 A and my transformer is 2 A?

Reply   Report Abuse   12 October,2014 06:10
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