This project is a variable DC voltage regulator built around the LM317T IC.
It converts an unregulated DC or AC input into a smooth, adjustable DC output using a bridge rectifier, filter capacitors, and precision voltage control components.
The design is ideal for powering microcontroller circuits, sensors, and embedded systems where variable regulated power is required.
- Input: 12V–24V DC or AC (via bridge rectifier)
- Output: Adjustable 1.25V to ~12V DC (using potentiometer)
- Current: Up to 1.5A (with proper heatsink)
- Built-in short-circuit and thermal protection
- Clean output with low ripple and noise
- Compact, single-sided PCB layout suitable for hobby or lab use
| Name | Value | PCB Label | Description / Function |
|---|---|---|---|
| J1 | Screw_Terminal_2Pin | IN | DC Input terminal (AC or DC supply) |
| D1 | B40C2300-1500A | BR1 | Bridge rectifier – converts AC to DC |
| C1 | 1000µF / 25V | C1 | Input filter capacitor – smooths rectified voltage |
| C2 | 0.1µF | C2 | Ceramic decoupling capacitor (stabilizes LM317 input) |
| U1 | LM317T | U1 | Adjustable voltage regulator IC |
| C3 | 10µF / 25V | C3 | Capacitor between Adj & GND – improves regulation |
| RV1 | 5kΩ / 10kΩ | VR1 | Potentiometer – adjusts output voltage |
| R1 | 220Ω / 240Ω | R1 | Fixed resistor – sets reference voltage with VR1 |
| C4 | 0.1µF | C4 | Ceramic capacitor at output – reduces noise |
| C5 | 470µF / 25V | C5 | Output filter capacitor – smooth DC output |
| J2 | Screw_Terminal_2Pin | OUT | DC Output terminal (regulated output) |
The bridge rectifier (BR1) converts AC input into DC, filtered by C1 and C2.
The LM317T (U1) regulates the voltage, with R1 and VR1 forming an adjustable divider to set the output voltage.
C3, C4, and C5 provide additional stability and reduce output ripple.
Output voltage can be varied using the potentiometer VR1: Vout = (Vin × R2) / (R1 + R2)
- Embedded and IoT development boards
- Sensor testing and prototyping
- Variable bench power supply
- Educational / DIY electronics labs
- Use a heat sink with the LM317 if load current > 500 mA.
- Ensure capacitors have voltage ratings at least 25–35% higher than the input voltage.
- Connect all grounds to a common GND plane on the PCB for stability.
💡 Designed with KiCad 9 — clean schematic, simple routing, and ready for fabrication.