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.
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