Texas Instruments LM317AH/NOPB

Overview

LM317AH/NOPB from Texas Instruments is a 1% accurate, adjustable 3-terminal positive-voltage linear regulator delivering up to 1.5 A over a 1.25 V to 37 V output range. It features 0.005%/V line regulation, −40°C to 125°C operation, and input-output differential up to 40 V. It serves as a post-regulator in switching power supplies and precision current source in battery chargers.

For engineers reviewing the LM317AH/NOPB datasheet, LM317AH/NOPB pinout, LM317AH/NOPB application, or LM317AH/NOPB equivalent, key selection considerations include output voltage adjustability via two external resistors, no mandatory output capacitor requirement, thermal and short-circuit protection integrity with ADJ pin disconnection, and TO-220 package suitability for heatsinked 1.5 A continuous operation.

Technical Context

The LM317AH/NOPB operates as a floating regulator that senses only the input-to-output differential voltage, enabling high-voltage supply regulation (e.g., hundreds of volts) as long as the 40 V max differential is not exceeded. Its internal 1.25 V reference is stable across temperature and load, with adjustment pin current held constant at 50–100 μA to minimize error in resistor-divider-based output programming.

Protection circuitry-including current limiting, thermal shutdown, and safe-area control-remains fully functional even if the ADJ pin is open. The device achieves 65–80 dB ripple rejection depending on ADJ pin bypass capacitance (0 μF vs. 10 μF), and supports constant-current operation by fixing a resistor between VOUT and ADJ pins.

Key Specifications

Pinout & Package

LM317AH/NOPB is supplied in a TO-220 (NDE) package with 3 leads and an electrically connected metal tab serving as the output terminal. Thermal performance is optimized when the tab is mounted to a heatsink using thermally conductive interface material.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable linear regulator applications.

Compared with LM317T and LM317L-N, the LM317AH/NOPB delivers superior accuracy (1%), higher current capability (1.5 A), and better thermal performance in TO-220, making it optimal for industrial and automotive applications demanding robustness and precision.

Availability

LM317AH/NOPB is available at Aetrix Electronics and suitable for automotive LED lighting, battery chargers, and post-regulation for switching supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM317AH/NOPB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, specializing in analog, embedded processing, and digital signal processing technologies.

The LM317A product line was designed for high-reliability linear regulation in industrial, automotive, and test equipment applications where accuracy, thermal resilience, and protection integrity are essential.

FAQ

What is the maximum input-output differential voltage for LM317AH/NOPB?

The LM317AH/NOPB supports a maximum input-output differential voltage of 40 V. Exceeding this rating risks internal short-circuit failure. This specification allows use in high-input-voltage applications such as 48 V industrial buses regulated down to 5 V or 12 V, provided the differential remains within limit. Always verify VIN – VOUT ≤ 40 V under worst-case operating conditions for the LM317AH/NOPB.

Can LM317AH/NOPB operate without an output capacitor?

Yes, the LM317AH/NOPB is internally compensated and stable with no output capacitor required. This simplifies designs and reduces component count. However, adding a 1–1000 μF aluminum or tantalum capacitor improves transient response and output impedance. Avoid capacitors between 500 pF and 5000 pF, which may cause ringing. The LM317AH/NOPB's stability is preserved across its full operating range without mandatory external capacitance.

How do I configure LM317AH/NOPB as a constant-current source?

Configure the LM317AH/NOPB as a constant-current source by connecting a single resistor R_SET between the VOUT and ADJ pins. Since the internal reference maintains 1.25 V across R_SET, output current equals 1.25 V / R_SET. For example, a 1.25 Ω resistor delivers 1 A. Ensure R_SET power rating exceeds I²R dissipation and that input voltage provides sufficient headroom. This configuration is widely used in LM317AH/NOPB-based LED drivers and battery charge termination circuits.

Does LM317AH/NOPB require a heatsink at 1.5 A output current?

Yes, the LM317AH/NOPB requires a heatsink when delivering 1.5 A continuously. With θ_JA = 23.3°C/W and a maximum junction temperature of 125°C, even at 25°C ambient, power dissipation >2.3 W (e.g., 12 V input → 5 V output @ 1.5 A = 10.5 W) necessitates thermal management. Use a heatsink with thermal resistance ≤5°C/W for reliable operation. Derate output current if heatsinking is insufficient. The LM317AH/NOPB's TO-220 tab is electrically connected to VOUT and must be insulated if mounted to a grounded heatsink.

What is the role of the ADJ pin current in LM317AH/NOPB output accuracy?

The ADJ pin draws 50–100 μA, which flows through R1 in the voltage divider and introduces a small error in output voltage calculation. To maintain 1% accuracy, R1 should be ≤ 100 Ω (so 100 μA × 100 Ω = 10 mV error ≈ 0.8% of 1.25 V reference). Higher R1 values increase error proportionally. The LM317AH/NOPB's design minimizes ADJ current variation with line/load, but proper resistor selection remains essential for achieving datasheet-specified 1% tolerance in final LM317AH/NOPB implementations.