Adjustable Power Supply

Whether you're working on electronics projects or need a reliable power source for your bench, this adjustable power supply circuit offers a flexible solution. With a simple design, it can easily convert 220V AC to a smooth, adjustable DC voltage ranging from 1.25V to 22V at 1.5A.

Components List

The following components are required to make this project.

Designation	Parts	Quantity
U1	IC LM317 adjustable three-terminal positive-voltage regulator	X1
R1	220Ω 1/4W Resistor	X1
R2	5kΩ Potentiometer	X1
T1	24V 2A / 220V 50Hz Step Down Transformer	X1
D1, D2, D3, D4	1N5408 Diode	X4
C1	4700uF 50V Electrolytic Capacitor	X1
C2	0.1uF polyester film capacitor	X1
C3	0.22uF polyester film capacitor	X1
C4	1uF 50V Electrolytic Capacitor	X1

Circuit Diagram

The schematic of an adjustable power supply circuit using lm317 is shown below.

Circuit Explanation

The transformer (T1) steps down the 220V AC to a lower AC voltage of 24V at 2A. This stepped-down AC voltage is fed into a bridge rectifier made of four diodes (D1 to D4), which convert the AC to pulsating DC. A capacitor (C1) smooths the pulsating DC, reducing ripple and providing a more stable DC voltage. This smoothed DC voltage is then supplied to the input (IN) of the LM317 voltage regulator IC (U1).

A fixed resistor (R1) and a potentiometer (R2) are used to set the output voltage by develops and maintains a nominal 1.25 V reference (Vref) between its output and adjustment terminals.

The output voltage Vout is dependent on values R1 and R2, according to the following formula: Vout = 1.25 (1 + R2/R1)

The LM317 can regulate and provide an adjustable output voltage ranging from 1.25V to 22V DC with a maximum current of 1.5A. Additional capacitors (C2, C3, and C4) are included to further stabilize the output voltage and reduce noise.