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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.

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