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Last updated: December 2, 2025

Adjustable Voltage Regulator LM338 Circuit DIY Guide

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Adjustable Voltage Regulator LM338

Learn how to use LM338 to build an adjustable voltage regulator. DIY guide with circuit diagram, components, working principle, and applications explained.

What is LM338 Adjustable Voltage Regulator?

LM338 is a three-terminal adjustable voltage regulator IC with the capacity of maintaining a constant output voltage of 1.2 V to 32 V. In home electronics, it is commonly used in non-professional electronics innovations to drive circuits where controlled voltage is needed.

Regulated voltage supply using LM338

LM338 Adjustable Voltage Regulator is a common IC in making DIY voltage regulation circuits to realize an electronics project. It offers a variable output of 1.2V to 32V, and it can supply as much as 5A current with appropriate heat sinking. LM338 is an improved design of LM317 with increased current-carrying ability and protection provisions.

This IC is appropriate for hobbyists and students to create regulated power supplies, battery chargers, as well as test circuits in which adjustable voltage is desired. This tutorial is a description of the module, principle of operation, circuit layout, and step-by-step process of construction of an adjustable voltage regulator using LM338 safely and efficiently.

Features and Specifications of LM338

  • Adjustable output voltage: 1.2V–32V
  • Maximum output current: 5A
  • Input voltage up to 35V
  • Built-in current limiting
  • Thermal overload protection
  • Short-circuit protection
  • Low dropout voltage

Components Required for LM338 Voltage Regulator Circuit

  • LM338 voltage regulator IC
  • Resistors (for voltage adjustment)
  • Potentiometer (for fine tuning)
  • Capacitors (0.1μF, 1μF for filtering)
  • Heat sink for LM338
  • DC input power supply (12V–35V)
  • Wires, PCB, or breadboard
  • Load device (LED, motor, electronics)

Working Principle of LM338 Adjustable Voltage Regulator

Voltage Adjustment Mechanism

The output voltage is set using a resistor and a potentiometer between the adjustment pin and the output pin. The formula is:

Vout = 1.25 × (1 + R2/R1) + Iadj × R2

Current Limiting Feature

LM338 includes internal current limiting to protect both the IC and the load from excessive current flow.

Heat Dissipation and Protection

A heat sink is essential for safe operation at higher currents. Built-in thermal overload protection ensures the IC shuts down if temperatures exceed safe limits.

Circuit Diagram of LM338 Adjustable Voltage Regulator

  • Connect the LM338 input pin to the DC voltage source.
  • Connect the output pin to the load and resistor network.
  • Use a potentiometer for fine voltage adjustment.
  • Add input/output capacitors for filtering.
  • Mount IC on a proper heat sink.

Step-by-Step DIY Construction Guide

  1. Mount LM338 on PCB or breadboard with heat sink.
  2. Connect input/output capacitors (0.1μF & 1μF).
  3. Install resistors and a potentiometer.
  4. Connect DC input to LM338 input pin.
  5. Connect load to output.
  6. Measure output voltage using a multimeter.
  7. Adjust potentiometer to set voltage.
  8. Ensure IC temperature remains stable.

Applications of LM338 Adjustable Voltage Regulator

  • DIY regulated power supply
  • Battery charging circuits
  • LED drivers
  • Electronics testing
  • Adjustable voltage lab power supply

Safety Precautions

  • Always use a heat sink to prevent overheating.
  • Ensure input voltage does not exceed 35V.
  • Do not short output terminals.
  • Verify resistor/potentiometer wiring.
  • Avoid touching components when powered.

Troubleshooting Common Issues

Output Voltage Not Stable

  • Check potentiometer and resistor connections.
  • Ensure sufficient input voltage.

LM338 Overheating

  • Attach a larger heat sink.
  • Reduce load current.

Short Circuit Protection

  • Verify wiring connections.
  • LM338 will shut down automatically if the output is shorted.

Frequently Asked Questions - Adjustable Voltage Regulator LM338:

What is LM338 IC used for?

LM338 is an adjustable voltage regulator IC used for building regulated power supplies.

What is the maximum current of LM338?

It can deliver up to 5A output current with proper heat sinking.

What is the output voltage range?

Adjustable from 1.2V to 32V depending on resistor network.

Do I need a heat sink?

Yes, especially for high current applications to prevent overheating.

Can I use LM338 to charge batteries?

Yes, suitable for lead-acid and lithium-ion battery charging with proper setup.

How do I adjust output voltage?

Using a resistor and potentiometer between the adjustment and output pins.

Is LM338 protected against short circuits?

Yes, it has built-in short circuit and thermal overload protection.

What input voltage is required?

Up to 35V DC input is allowed, depending on desired output.

Can I use it for LED drivers?

Yes, LM338 can be used for regulated LED driving circuits.

Is it suitable for beginners?

Yes, with careful wiring and heat sink installation, beginners can use it safely.

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Rojony Khatun

Rojony Khatun

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Rojony Khatun is the creator of a free online tools website designed to simplify everyday and engineering-related calculations for students, professionals, and hobbyists. The platform offers a wide variety of basic and advanced calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators, helping users solve problems quickly and accurately.