LM117H

LM117H: Adjustable 3-Terminal Positive Voltage Regulator

Overview

The LM117H is a member of the LM117 series of adjustable 3-terminal positive voltage regulators. Designed for high-performance applications, this regulator is capable of supplying in excess of 1.5A over an adjustable output voltage range of 1.2V to 37V. The LM117H is exceptionally easy to use, requiring only two external resistors to set the output voltage. It offers superior line and load regulation compared to standard fixed regulators, making it an ideal choice for precision voltage regulation in a wide range of applications. The device is packaged in standard transistor packages, ensuring ease of mounting and integration into various circuit designs.

Features

• Adjustable Output Voltage: The output voltage can be set from 1.2V to 37V using two external resistors.
• High Output Current: Capable of delivering more than 1.5A of continuous output current.
• Excellent Regulation: Superior line and load regulation compared to fixed regulators.
• Guaranteed Output Tolerance: The LM317A variant guarantees a 1% output voltage tolerance.
• Thermal Overload Protection: Built-in protection prevents damage due to excessive heat.
• Short-Circuit Protection: Internal circuitry safeguards the regulator against short-circuit conditions.
• Standard Transistor Packages: Available in packages that are easy to mount and suitable for various applications.
• Wide Operating Temperature Range: Designed to operate reliably across a broad temperature spectrum.

Applications

The LM117H is versatile and can be used in a wide array of applications, including but not limited to:

• Power Supplies: Ideal for adjustable and fixed voltage power supply designs.
• Industrial Equipment: Suitable for use in industrial control systems and automation.
• Consumer Electronics: Used in devices requiring precise voltage regulation, such as audio amplifiers and display units.
• Automotive Systems: Can be employed in automotive electronics where stable voltage is critical.
• Test and Measurement Equipment: Provides accurate voltage references for precision instruments.
• Battery Chargers: Used in circuits that require adjustable voltage for charging batteries.
• Embedded Systems: Suitable for microcontroller and FPGA power regulation.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the LM117H under typical operating conditions (unless otherwise specified):

• Output Voltage Range: 1.2V to 37V
• Output Current: >1.5A
• Line Regulation: 0.01%/V (typical)
• Load Regulation: 0.1% (typical)
• Dropout Voltage: 1.5V at 1A (typical)
• Reference Voltage: 1.25V (typical)
• Operating Junction Temperature: -40°C to +125°C
• Thermal Resistance (Junction-to-Ambient): 50°C/W (typical)

Package Information

The LM117H is available in a TO-39 metal can package, which provides excellent thermal performance and durability. Below are the key details of the package:

• Package Type: TO-39 (Metal Can)
• Pin Configuration:
  • Pin 1: Adjust
  • Pin 2: Output
  • Pin 3: Input
• Dimensions: 9.81mm diameter, 5.2mm height (excluding leads)
• Weight: Approximately 2.5 grams
• Mounting Style: Through-hole
• Material: Metal casing for enhanced heat dissipation

Typical Application Circuit

A basic application circuit for the LM117H involves connecting two resistors to set the desired output voltage. The formula for calculating the output voltage (V_out) is:

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

Where:

• R1 and R2 are the external resistors.
• I_ADJ is the adjustment pin current (typically 50µA).

For stable operation, it is recommended to place a capacitor (typically 10µF) at the output to improve transient response and reduce noise.

Thermal Considerations

Due to its high current capability, the LM117H may generate significant heat during operation. Proper heat sinking is essential to maintain the junction temperature within safe limits. The thermal resistance of the chosen heat sink should be calculated based on the maximum power dissipation (P_D), which can be estimated using:

P_D = (V_in - V_out) × I_out

Where:

• V_in is the input voltage.
• V_out is the output voltage.
• I_out is the output current.

Ensure that the heat sink is adequately sized to dissipate the calculated power without exceeding the maximum junction temperature.

Conclusion

The LM117H is a highly reliable and versatile adjustable voltage regulator that offers superior performance in a compact package. Its ease of use, combined with robust features like thermal and short-circuit protection, makes it an excellent choice for a wide range of applications. Whether used in industrial, automotive, or consumer electronics, the LM117H delivers precise voltage regulation and high current capability, ensuring stable and efficient operation.