STMicroelectronics LM317LZ-TR

Overview

LM317LZ-TR from STMicroelectronics is a monolithic adjustable positive voltage regulator in TO-92 package, delivering up to 100 mA output current with 1.2 V to 37 V adjustable output range, 1.25 V internal reference voltage, and built-in thermal overload and short-circuit protection. It enables floating operation for high-voltage applications such as lab bench supplies and industrial sensor biasing.

For engineers reviewing the LM317LZ-TR datasheet, LM317LZ-TR pinout, LM317LZ-TR application, or LM317LZ-TR equivalent, key selection criteria include minimum load current (3.5–5 mA), line regulation (0.01% typical), load regulation (0.1% typical), and thermal resistance (200 °C/W junction-to-ambient in TO-92).

Technical Context

The LM317LZ-TR operates as a three-terminal floating linear regulator, using an internal 1.25 V bandgap reference between OUT and ADJ pins to set output voltage via external resistive divider. Its quiescent current flows entirely into the output terminal, requiring ≥3.5 mA minimum load to maintain regulation.

It features safe-area compensation for output transistors, enabling stable operation under transient overloads. Protection circuitry includes thermal shutdown triggered at ~150 °C junction temperature and current limiting that folds back above 100 mA to prevent device damage.

Key Specifications

Pinout & Package

LM317LZ-TR uses the TO-92 plastic package (ECOPACK® compliant), with leads formed for through-hole mounting and tape-and-reel delivery. The package provides mechanical robustness and cost-effective assembly for low-power analog designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317LZ-TR, LM317LDR2G offers superior thermal performance and higher current in SO-8, while TLV1117-ADJ trades floating operation for ultra-low dropout and high current-but cannot replace LM317LZ-TR in high-voltage or floating configurations.

Availability

LM317LZ-TR is available at Aetrix Electronics and suitable for lab power supplies, industrial sensor biasing, LED current sources, and remote voltage references requiring stable component supply across long-lifecycle embedded programs.

Supply support for LM317LZ-TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power management ICs, analog chips, and MEMS sensors for industrial, automotive, and consumer markets.

LM317LZ-TR belongs to ST's legacy linear regulator product line, engineered for simplicity, reliability, and wide operating range in cost-sensitive analog power applications where programmability and protection are essential.

FAQ

What is the minimum load current required for stable regulation?

The LM317LZ-TR requires a minimum load current of 3.5 mA (typical) to 5 mA (max) to maintain output regulation. This is due to its design where all quiescent current returns to the output pin. If load falls below this threshold-e.g., in high-impedance monitoring circuits-a 240 Ω resistor from OUT to GND ensures compliance and prevents output voltage rise.

Can LM317LZ-TR be used in floating or high-side configurations?

Yes. As a floating regulator, LM317LZ-TR regulates based solely on the voltage difference between IN and OUT pins-not referenced to ground. This allows it to operate with inputs up to 40 V above the output node, enabling high-side switching, battery chargers, and negative-output configurations when combined with external components.

How does the adjustment pin current affect output accuracy?

The adjustment pin draws 50–100 µA, which flows through the R2 resistor in the voltage divider, adding an error term (I_ADJ × R2) to the ideal V_O = 1.25 V × (1 + R2/R1). For R2 = 2.4 kΩ, this introduces ≤0.24 V error-reduced by using lower R2 values or compensating in divider design.

What thermal considerations apply in TO-92 package?

In TO-92, R_thJA is 200 °C/W. At 100 mA output and 12 V drop (1.2 W dissipation), junction temperature rises ~240 °C above ambient-exceeding safe limit. Derating is mandatory: max continuous power is ~625 mW, requiring ≤6.25 V drop at 100 mA or reduced current at higher differentials.