⚡DIY Variable (1.2-24V) Power Supply Making

DIY Instructable: 1.2V to 24V Adjustable Power Supply with LM317T

A variable power supply is incredibly useful in electronics projects, allowing you to fine-tune voltage to meet your circuit’s requirements. In this guide, we’ll walk through building a 1.2V to 24V variable power supply using the LM317T voltage regulator IC, a 12-0-12 center-tapped transformer, and other essential components. This power supply can output anywhere from 1.2V to 24V (based on your transformer and other limitations), making it versatile for various electronics applications.

Get JLCPCB 6-layer PCBs for just $5! Register to get $80 Coupons: https://jlcpcb.com/?from=EST

Components Needed:

1. LM317T Voltage Regulator IC: Capable of outputting a regulated voltage from 1.2V to 37V. The heart of this power supply.
2. 1N5399 Diodes (2 pcs): To create a bridge rectifier for converting AC to DC.
3. 1000uF Electrolytic Capacitor: Smooths out the rectified DC voltage.
4. 104 Ceramic Capacitor: Filters high-frequency noise.
5. Variable Resistor (5K or 10K Potentiometer): Adjusts the output voltage.
6. Power Indicator LED: Shows when the power supply is on.
7. Resistor (330Ω for LED): Limits the current to the LED.
8. 12-0-12 Center-Tapped Transformer: Steps down AC mains voltage.
9. Heat Sink for LM317T: Dissipates heat from the regulator.
10. Wires and Soldering Supplies

Here's a basic outline of the circuit components:

1. Transformer: Steps down AC mains voltage to 12V AC.
2. Bridge Rectifier: Converts the AC output from the transformer to DC.
3. Filter Capacitors: Smooth out DC voltage.
4. LM317T IC: Regulates and adjusts the voltage.
5. Potentiometer: Allows output voltage control.
6. Indicator LED: Indicates when power is on.

Get JLCPCB 6-layer PCBs for just $5! Register to get $80 Coupons: https://jlcpcb.com/?from=EST

Connect Diodes: Arrange the 1N5399 diodes in a bridge rectifier configuration. Connect the AC terminals from the transformer’s secondary coil to the AC inputs on the bridge.

Connect the Capacitor: Place the 1000uF capacitor across the DC output of the bridge rectifier to filter out the rectified DC voltage.

1. The positive lead of the capacitor should connect to the positive output of the bridge, while the negative lead connects to the ground.

Connect Capacitors to LM317T: Place the 104 ceramic capacitor across the input and ground of the LM317T to filter high-frequency noise.

Attach Heat Sink: Secure a heat sink to the LM317T to manage heat during operation.

Connect the Potentiometer: Attach a 5K or 10K potentiometer to the "Adjust" pin of the LM317T, allowing the voltage to be varied.

1. Wire one end of the potentiometer to the “Output” pin, the other end to the ground, and the wiper (middle pin) to the “Adjust” pin on the LM317T. Rotating the potentiometer will now adjust the output voltage.

Connect LED & Resistor: Connect the LED with a 330Ω resistor between the output and ground to indicate when the power is on.

1. The longer leg (anode) of the LED should connect to the output via the resistor, and the shorter leg (cathode) should connect to ground.

Connect Primary Coil: Attach the primary coil of the transformer to the mains power supply.

Connect Secondary Coil: Connect the secondary (12-0-12) coil to the AC input of the bridge rectifier.

Check Connections: Ensure that all connections are correct, especially the polarities of diodes, capacitors, and the LED.

Power On and Measure: Switch on the power supply, and use a multimeter to measure the output voltage. Adjust the potentiometer to verify that the voltage ranges from around 1.2V to 24V.

Test Load: You can now test the power supply by connecting it to a load.

Get JLCPCB 6-layer PCBs for just $5! Register to get $80 Coupons: https://jlcpcb.com/?from=EST

Work in a Ventilated Area: Heat may accumulate around the LM317T, so ensure good airflow.

Insulate Exposed Wires: To avoid short circuits, use heat-shrink tubing or insulation tape around exposed wires.

Careful with Mains Power: The transformer’s primary side is connected to high voltage; ensure no direct contact with it when in use.

Congratulations! You now have a working variable power supply that can be adjusted to output between 1.2V and 24V (dependent on the transformer output). This project is ideal for powering small electronics, testing circuits, and charging batteries.