🔌 DIY Variable Power Supply (5V to 18V) Using Transformer

🔌 DIY Variable Power Supply (5V to 18V) Using Transformer

A variable power supply is essential for any electronics hobbyist. In this project, we’ll build a 5V–18V adjustable power supply using a step-down transformer, diodes, and a voltage regulator.

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🔧 Components Required

Component	Specs / Notes
Step-down Transformer	220V to 18V (center tap optional)
Diodes (1N5408 x 4)	For bridge rectifier (3A)
Electrolytic Capacitor	1000µF – 2200µF / 35V
LM317 Regulator IC	Adjustable output
Potentiometer	5k or 10k to adjust voltage
Heat Sink	For LM317
Resistors	220Ω & 2.2kΩ (for LM317 config)
Output Terminals	Banana jack or screw terminals
Enclosure	For safety and neatness

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⚙️ How It Works

1. Transformer steps down 220V AC to 18V AC.

2. Bridge rectifier converts AC to DC.

3. Capacitor smooths the DC voltage.

4. LM317 regulates and lets you vary voltage from ~1.25V to 18V using a potentiometer.

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🖼️ Basic Circuit Diagram (Text View)

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[220V AC]
   │
   ▼
[Step-down Transformer 220V → 18V]
   │
   ▼
[Bridge Rectifier → DC ~18V]
   │
   ▼
[Filter Capacitor]
   │
   ▼
[LM317 + Potentiometer]
   │
   ▼
[Output: Adjustable 5V–18V DC]

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🔋 Output Adjustment

• Use a potentiometer connected to LM317’s adjust pin.

• Adjust knob to get the required voltage.

• You can add a voltmeter panel for monitoring output.

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✅ Features

• Smooth adjustable DC output

• Handles up to 1.5A current with LM317 + heatsink

• Useful for powering Arduino, breadboard projects, LED strips, etc.

• Add over-voltage protection or fuse for safety

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⚠️ Safety Note

• Transformer and AC parts must be properly insulated.

• Use a fuse at the input and keep the circuit in a ventilated plastic/metal box.

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🏠 Applications

• Electronics lab bench power

• Battery charging (manually monitored)

• Running DC motors, LEDs, microcontrollers

• Testing circuits with different voltages

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🧠 Final Words

This variable supply is easy to build and cost-effective. It gives you the flexibility to run different low-voltage electronics devices safely from a single setup.