LM338K Adjustable 3-Terminal Positive Voltage Regulator

Overview

The LM338K is a member of the LM138 series of adjustable 3-terminal positive voltage regulators, designed to deliver high current output with exceptional precision and reliability. This component is capable of supplying more than 5A of output current over an adjustable voltage range of 1.2V to 32V. Its straightforward design requires only two external resistors to set the output voltage, making it highly versatile for a wide array of power supply applications. The LM338K is engineered to provide outstanding load and line regulation, rivaling the performance of many commercial power supplies.

Features

• High Output Current: Capable of delivering in excess of 5A continuously, with a guaranteed 7A peak output current.
• Adjustable Output Voltage: Output voltage can be precisely set from 1.2V to 32V using external resistors.
• Exceptional Regulation: Outstanding line and load regulation performance, comparable to commercial power supplies.
• Thermal Overload Protection: Built-in safeguards prevent damage due to excessive temperature.
• Short-Circuit Protection: Designed to withstand output short-circuits without failure.
• Wide Operating Temperature Range: Suitable for use in industrial and automotive environments.
• Easy to Use: Requires minimal external components for operation, simplifying circuit design.

Applications

The LM338K is widely used in applications requiring a robust, adjustable voltage regulator with high current capability. Common applications include:

• Bench Power Supplies: Provides stable and adjustable voltage for laboratory and testing equipment.
• Industrial Power Systems: Suitable for machinery and control systems requiring reliable voltage regulation.
• Battery Chargers: Used in high-current charging circuits for lead-acid, Li-ion, and other battery types.
• Motor Control: Delivers consistent voltage to DC motors and actuators.
• Audio Amplifiers: Ensures clean and stable power supply for high-fidelity audio systems.
• Automotive Electronics: Ideal for voltage regulation in automotive power systems and infotainment units.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM338K under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Input-Output Voltage Differential (V_IN - V_OUT): 35V
• Output Current (I_OUT): 5A (continuous), 7A (peak)
• Operating Junction Temperature (T_J): -40°C to +125°C
• Storage Temperature Range: -65°C to +150°C

Typical Performance Characteristics

• Line Regulation: 0.005%/V (typical)
• Load Regulation: 0.1% (typical)
• Reference Voltage (V_REF): 1.25V
• Dropout Voltage: 2.5V at 5A
• Ripple Rejection: 75dB (typical)

Package Information

The LM338K is available in a robust TO-3 metal can package, which provides excellent thermal performance and mechanical durability. The package dimensions and pin configuration are as follows:

TO-3 Package Details

• Package Type: TO-3 (2-15A)
• Mounting Style: Through-hole
• Pin Count: 3
• Pin Configuration:
  • Pin 1: Adjust (for setting output voltage)
  • Pin 2: Output (regulated voltage)
  • Pin 3: Input (unregulated voltage)
• Thermal Resistance (Junction-to-Case): 1.0°C/W
• Weight: Approximately 10 grams

Design Considerations

To ensure optimal performance and reliability, the following design guidelines should be observed when using the LM338K:

• Heat Sinking: Due to its high current capability, the LM338K may generate significant heat. A properly sized heat sink is essential to maintain safe operating temperatures.
• Input Capacitor: A 0.1µF capacitor should be placed close to the input pin to minimize noise and improve stability.
• Output Capacitor: A 10µF or larger capacitor is recommended at the output to enhance transient response and reduce output impedance.
• Adjust Pin Stability: To prevent oscillations, a small capacitor (1µF to 10µF) may be connected between the adjust pin and ground.
• PCB Layout: Keep traces short and wide for high-current paths to minimize voltage drops and thermal issues.

Conclusion

The LM338K is a highly reliable and versatile voltage regulator, offering exceptional performance for high-current applications. Its ease of use, combined with robust protection features, makes it an ideal choice for engineers designing power supplies, battery chargers, and other systems requiring precise voltage regulation. By adhering to the recommended design practices, users can maximize the performance and longevity of the LM338K in their applications.