A DC adjustable 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 an Adjustable 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 | LM317 | 1 |
| 5. | Bridge Rectifier Diode | 3A 50v | 1 |
| 6. | Diode | 1N4002 | 2 |
| 7. | Resistor | 100 ohms | 2 |
| 8. | Potentiometer | 5.1k | 1 |
| 9. | Electrolytic Capacitor | 220uF,100uF,10uF | 1, 1, 1 |
| 10. | Ceramic Capacitor | 0.33uF | 1 |
LM317 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of LM317
Adjustable 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.
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