LM317LZ Adjustable Positive Voltage Regulator

Overview

The LM317LZ is a versatile, 3-terminal adjustable positive voltage regulator designed to deliver a stable output voltage ranging from 1.2V to 37V with a maximum output current of 100mA. This component is widely recognized for its simplicity, requiring only two external resistors to configure the output voltage. The LM317LZ offers superior line and load regulation compared to standard fixed regulators, making it an excellent choice for applications demanding precise voltage control. The device is available in a TO-92 package, which is compact and suitable for through-hole PCB mounting.

Features

• Adjustable Output Voltage: The output voltage can be precisely set from 1.2V to 37V using external resistors.
• High Accuracy: Provides excellent line and load regulation, ensuring stable output under varying conditions.
• Low Quiescent Current: The device maintains low power consumption, making it suitable for battery-operated applications.
• Thermal Overload Protection: Built-in safeguards prevent damage due to excessive temperature.
• Short-Circuit Protection: The regulator is designed to withstand output short-circuits without failure.
• Wide Operating Temperature Range: Functions reliably across industrial temperature ranges.
• TO-92 Package: Compact and easy to integrate into through-hole PCB designs.

Applications

The LM317LZ is suitable for a broad range of applications, including but not limited to:

• Power Supplies: Used in adjustable linear power supplies for low-current applications.
• Battery Chargers: Ideal for designing simple and efficient battery charging circuits.
• Voltage References: Provides a stable reference voltage for precision analog circuits.
• Consumer Electronics: Commonly found in portable devices, audio equipment, and other low-power electronics.
• Industrial Control Systems: Used in control circuits requiring adjustable voltage rails.
• DIY Projects: A popular choice for hobbyists due to its ease of use and flexibility.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM317LZ under typical operating conditions (unless otherwise noted):

• Output Voltage Range: 1.2V to 37V
• Output Current: Up to 100mA
• Input-Output Voltage Differential: 3V to 40V
• Line Regulation: 0.01%/V (typical)
• Load Regulation: 0.1% (typical)
• Quiescent Current: 5mA (typical)
• Operating Temperature Range: 0°C to +125°C
• Thermal Resistance (TO-92): 160°C/W (junction-to-ambient)

Typical Performance Curves

The LM317LZ exhibits consistent performance across its operating range. Key performance characteristics include:

• Output Voltage vs. Temperature: The output voltage remains stable with minimal drift over the specified temperature range.
• Load Regulation vs. Output Current: The regulator maintains tight voltage regulation even as the load current varies.
• Dropout Voltage: The minimum input-output differential required to maintain regulation is typically 2V at full load.

Package Information

The LM317LZ is available in a TO-92 package, which is a widely used through-hole package for low-power devices. Key package details include:

• Package Type: TO-92 (3-pin)
• Pin Configuration:
  • Pin 1 (Adjust): Connected to the voltage divider network to set the output voltage.
  • Pin 2 (Output): Provides the regulated output voltage.
  • Pin 3 (Input): Connected to the unregulated input voltage supply.
• Dimensions: Approximately 4.95mm x 4.95mm x 3.68mm (excluding leads).
• Weight: Typically 0.35 grams.
• Mounting Style: Through-hole, suitable for hand soldering or wave soldering.

Recommended PCB Layout Guidelines

To ensure optimal performance and reliability, follow these PCB layout recommendations:

• Place the input and output capacitors as close as possible to the regulator pins to minimize parasitic inductance.
• Use a ground plane to improve thermal dissipation and reduce noise.
• Ensure adequate trace width for the input and output connections to handle the expected current.
• For high-temperature environments, consider additional heat sinking or ventilation.

Conclusion

The LM317LZ is a highly reliable and flexible voltage regulator suitable for a wide range of low-power applications. Its adjustable output, robust protection features, and compact TO-92 package make it an excellent choice for both hobbyists and professional engineers. By adhering to the recommended design guidelines, users can achieve stable and efficient voltage regulation in their circuits.