This article will discuss the LM338 voltage regulator, including its working principle, pin configuration, specifications, features, application circuit, alternatives, comparisons with other regulators, and typical applications.

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LM338 Voltage Regulator

The LM338 Adjustable 5A Voltage Regulator is a high-current, three-terminal linear regulator designed to provide a stable and adjustable DC output. Unlike fixed regulators, it allows users to set the output voltage from about 1.25V up to 32V using two external resistors. With a maximum output current of 5A, it is suitable for power-hungry applications that require reliable voltage control.

This regulator includes built-in protection features such as thermal shutdown, current limiting, and short-circuit protection, ensuring safe and stable operation. Because it is a linear regulator, excess voltage is dissipated as heat, so a proper heatsink is recommended for high-current use. The LM338 is commonly used in adjustable power supplies, battery chargers, and industrial control circuits where precise voltage regulation is required.

If you are interested in purchasing the LM338 adjustable 5A voltage regulator, feel free to contact us for pricing and availability.

LM338 Voltage Regulator CAD Models

LM338 Voltage Regulator Pinout Details

Alternatives & Equivalent Model

• LM350

• LM350T

• LT1083

• LT1084

• MC338

• LM338HV

• LT3083

• LM317

• LM317HV

• TL783

Functional Block Diagram

The LM338 block diagram shows how the regulator controls voltage and current internally. At the center of the circuit is the precision reference source, which generates a stable reference voltage of about 1.25V. This reference is compared with a portion of the output voltage taken from the adjustment pin. The internal error amplifier continuously compares these two signals and adjusts the pass transistor to maintain a constant output voltage.

The large output transistor section on the right side acts as the series pass element. It controls how much current flows from the input (VIN) to the output (VOUT). When the load increases, the transistor allows more current to pass. When the output voltage rises too high, it reduces conduction to stabilize the voltage.

The diagram also includes current limiting and thermal protection circuits. These protection blocks monitor output current and chip temperature. If the current exceeds safe limits or the device overheats, the internal circuitry reduces output drive to protect the regulator from damage.

LM338 Technical Specifications

LM338 Voltage Regulator Features

• 5A Continuous Output Current – Delivers up to 5 amps of steady output current, making it suitable for high-power linear regulation applications.

• 7A Peak Output Current – Supports short-duration peak currents up to 7A, useful during startup or sudden load changes.

• Adjustable Output Voltage (1.2V to 32V) – Output voltage can be set using two external resistors, allowing flexible power supply design.

• High Reference Accuracy (≈1.25V Reference) – Provides stable and precise reference voltage for reliable output regulation.

• Excellent Line Regulation – Maintains stable output voltage even when input voltage changes.

• Good Load Regulation – Keeps output voltage constant despite variations in load current.

• Thermal Regulation Protection – Minimizes output voltage drift caused by internal temperature changes.

• Built-In Current Limiting – Protects the regulator and load by limiting excessive output current.

• Temperature-Compensated Current Limit – Current limiting remains stable across operating temperature ranges.

• Short-Circuit Protection – Automatically limits current during output short conditions to prevent device damage.

• Safe Operating Area (SOA) Protection – Internal circuitry prevents damage from high voltage and high current combinations.

• Wide Input Voltage Range (Up to 40V Differential) – Handles a broad input-to-output voltage difference safely.

• Low Output Noise – Produces relatively low ripple and noise for cleaner DC output.

• High Ripple Rejection – Effectively reduces AC ripple from the input supply.

• TO-220 and TO-3 Package Options – Available in multiple packages for different thermal and mounting requirements.

• Simple Three-Terminal Design – Requires minimal external components for operation, simplifying circuit design.

LM338 Voltage Regulator Application Circuit

The diagram shows the basic adjustable application circuit of the LM338 voltage regulator. The input voltage (VIN) is applied to the input pin, and the regulated output voltage (VOUT) is taken from the output pin. To set the desired output voltage, two external resistors, R1 and R2, are connected between the output, adjustment (ADJ), and ground terminals.

The LM338 maintains a constant reference voltage (VREF ≈ 1.25V) between the output and adjustment pin. Resistor R1 sets a constant current through the adjustment network, while R2 determines how much the voltage is scaled down to ground. By changing the value of R2, the output voltage can be adjusted according to the formula:

V_OUT = 1.25V × (1 + R2/R1) + I_ADJ × R2

The small adjustment pin current (IADJ) is usually minimal and often ignored in simple calculations. This simple resistor network allows precise control of output voltage from about 1.2V up to 32V, making the LM338 easy to use in adjustable power supply designs.

LM338 Voltage Regulator Applications

• Adjustable bench power supplies

• Battery chargers

• High-current DC power supplies

• Laboratory power supplies

• Industrial control systems

• Motor speed control circuits

• LED driver circuits

• Audio amplifier power supplies

• Variable voltage regulators

• Linear post-regulators for switching supplies

• Power supplies for communication equipment

• Microcontroller and embedded system power regulation

• Automotive power regulation systems

• Test and measurement equipment

• DC voltage stabilizers

Comparison: LM338 vs Other Voltage Regulator

Mechanical Dimensions

Conclusion

With accurate reference voltage, strong line and load regulation, and built-in protection features such as thermal shutdown and current limiting, LM338 provides both performance and safety in high-power applications. From its internal block diagram and electrical specifications to its practical application circuit and comparison with similar regulators, the LM338 demonstrates versatility and ease of use. Whether used in bench power supplies, battery chargers, or industrial control systems, it offers stable voltage regulation with straightforward implementation, making it a dependable solution for adjustable high-current DC power designs.