Introduction

The LM317 is an adjustable voltage regulator that provides a stable output voltage that can be varied between 1.25V and 37V using external resistors. This tutorial will guide you through building a simple adjustable power supply using the LM317.

Materials Required

• LM317 Adjustable Voltage Regulator
• Resistors (R1 = 240Ω, R2 = Variable Resistor 5kΩ)
• Capacitors (C1 = 0.1μF, C2 = 1μF)
• Input power source (10V to 40V DC)
• Breadboard and jumper wires
• Multimeter (for voltage measurement)

No Ads Available.

Circuit Diagram

The following diagram shows how to connect the LM317 as an adjustable voltage regulator:

Pin Configuration of the LM317

• Pin 1 (ADJ): Adjustment pin for setting the output voltage.
• Pin 2 (VOUT): Output voltage pin.
• Pin 3 (VIN): Input voltage pin.

Steps for the Experiment

1. Place the LM317 regulator on the breadboard.
2. Connect the input power supply (10V to 40V DC) to Pin 3 (VIN).
3. Connect Pin 2 (VOUT) to the output line where you will measure the voltage.
4. Connect Pin 1 (ADJ) to the junction of two resistors: R1 (240Ω) and a variable resistor R2 (5kΩ).
5. Connect the other end of R1 to Pin 2 (VOUT).
6. Connect the other end of the variable resistor R2 to ground.
7. Add a capacitor (C1) (0.1μF) between Pin 3 (VIN) and ground for input filtering.
8. Add another capacitor (C2) (1μF) between Pin 2 (VOUT) and ground to stabilize the output.
9. Use a multimeter to measure the output voltage and adjust the variable resistor R2 to change the output voltage.

Explanation

The output voltage of the LM317 can be adjusted using the resistors connected to its adjustment pin (ADJ). The output voltage (V_OUT) is determined by the following formula:

V_OUT = 1.25V × (1 + R2 / R1)

By varying the resistance of R2, the output voltage can be adjusted from 1.25V up to the maximum input voltage minus a small dropout voltage.

Results and Observations

After setting up the circuit and powering it, you should observe:

• A variable output voltage between 1.25V and 37V, depending on the input voltage and the adjustment of the variable resistor R2.
• Stable voltage regulation at the output, with minimal ripple or fluctuation.

Applications of the LM317 Adjustable Voltage Regulator

The LM317 can be used in various applications, such as:

• Building adjustable power supplies for testing circuits and devices.
• Regulating voltage in battery chargers or portable electronics.
• Providing stable voltage in DIY electronics projects requiring precise voltage control.

Conclusion

This experiment demonstrates how to use the LM317 as an adjustable voltage regulator. By adjusting the resistance of R2, you can easily vary the output voltage for different applications, providing a flexible and stable power supply for your projects.