In this project
A DC variable power supply is an integral part of any power supply unit used in electronic equipment. It serves as an interface between a wall outlet and common power electronic equipment. In this project, we are going to design a simple adjustable power supply circuit using an LM317 voltage regulator IC.
LM317 is a three-terminal voltage regulator IC, with a high output current value of 1.5A. The LM317 IC has many features such as current limiting, thermal protection, and safe operating area protection. It can also provide a float function for high voltage uses. If we disconnect the adjustable terminal still, LM317 will be helpful in overload protection.
Hardware Components
The following components are required to make a Variable Power Supply Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Breadboard | - | 1 |
| 2. | Connecting Wires | - | 1 |
| 3. | Stepdown Transformer | 230/28v,3A,50 Hz | 1 |
| 4. | Voltage Regulator IC | LM317T | 1 |
| 5. | Diode | 1N4002, 1N4007 | 2, 4 |
| 6. | Potentiometer | 10k | 2 |
| 7. | Resistor | 100 ohm | 2 |
| 8. | Electrolytic Capacitor | 2200uF, 100uF, 10uF | 1 |
| 9. | Ceramic Capacitor | 0.33uF | 1 |
LM317 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of LM317T
Variable Power Supply Circuit
Working Explanation
An input voltage of 230V is applied at the primary of a non-CT transformer which steps it down to 28V 3A through mutual induction of the primary & secondary windings while maintaining the frequency at 50Hz. After which the 28V AC signal goes through a bridge rectifier that converts the AC signal into a rippling DC signal.
The rectified voltage is then fed into the input of an adjustable voltage regulator LM317. This three-terminal voltage regulator has an output voltage operating range from 1.2V to 37V DC with a maximum load current of up to 1.5A. The diodes D1 & D2 are used to protect the regulator from excess flowing through it if a battery or any other voltage source is connected across the output terminals of the regulator. The output voltage range is controlled by connecting a 5.1KΩ pot at the ADJ pin of the regulator. The DC signal then passes through a smoothing capacitor of 100μF before going on towards the output.
Applications
- A Variable power supply can be used in applications such as applying a variable voltage to DC motors.
- Commonly used in testing & troubleshooting small electronic projects.
Discussion
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