STMicroelectronics LM317LZ-AP

Overview

LM317LZ-AP from STMicroelectronics is a TO-92 packaged, adjustable positive voltage regulator delivering up to 100 mA output current with 1.2 V to 37 V output range, 1.25 V internal reference, and built-in thermal/short-circuit protection. It operates in floating configuration for high-voltage applications such as lab bench supplies and programmable bias sources.

For engineers reviewing the LM317LZ-AP datasheet, LM317LZ-AP pinout, LM317LZ-AP application, or LM317LZ-AP equivalent, key selection criteria include minimum load current (3.5–5 mA), line regulation (0.01% typ.), load regulation (5–70 mV), adjustment pin current (50–100 µA), and thermal resistance (200 °C/W junction-to-ambient).

Technical Context

The LM317LZ-AP implements a monolithic bandgap-referenced error amplifier driving an NPN pass transistor, with all quiescent current returned to the output to maintain regulation stability. Its floating architecture enables operation with input-to-output differentials up to 40 V, independent of ground potential.

Internal safe-area compensation prevents secondary breakdown during overload, while the 1.25 V reference is trimmed at production to ±2% tolerance over temperature (0–125°C). Output noise is 0.003% (10 Hz–10 kHz) and supply voltage rejection reaches 80 dB with 10 µF adjust-to-ground capacitor.

Key Specifications

Pinout & Package

LM317LZ-AP is supplied in TO-92 plastic package (Ammopack variant), with leads formed for through-hole mounting and standardized mechanical dimensions per ST DocID2168 Rev 7.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317LZ-AP, LM317LDR2G offers improved thermal behavior and reference accuracy in surface-mount form, while TLV1117-ADJ trades floating capability and wide voltage range for higher current and lower dropout-making each optimal in distinct system constraints.

Availability

LM317LZ-AP is available at Aetrix Electronics and suitable for programmable power supplies, industrial sensor biasing, LED current regulation, and microcontroller I/O translation requiring stable component supply and long-term manufacturability.

Supply support for LM317LZ-AP 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, designing and manufacturing analog, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The LM317L series belongs to ST's legacy linear regulator product line, engineered for robustness, ease of use, and compatibility with decades-old designs-targeting cost-sensitive, reliability-critical analog power applications.

FAQ

What is the minimum load current required for stable regulation with LM317LZ-AP?

The LM317LZ-AP requires a minimum load current of 3.5–5 mA to maintain regulation, as specified in ST DocID2168 Rev 7 Table 5. This stems from its architecture returning all quiescent current to the output pin; insufficient load causes output voltage to rise uncontrollably. A 240 Ω resistor from OUT to ADJ provides exactly 5.2 mA at 1.25 V, satisfying this requirement.

Can LM317LZ-AP be used in a high-side floating configuration?

Yes-LM317LZ-AP operates as a floating regulator, meaning it regulates based solely on the voltage difference between its IN and OUT pins (up to 40 V), not ground. This enables high-side configurations, such as generating +100 V bias from a +137 V supply with 37 V drop across the device, provided thermal limits are observed.

How does the adjustment pin current affect output voltage accuracy?

The adjustment pin draws 50–100 µA, contributing an error term of I_ADJ × R2 in the output equation VO = 1.25(1 + R2/R1) + I_ADJR2. Using R2 ≤ 2.4 kΩ keeps this error under 0.24 V; selecting R1 = 240 Ω and R2 = 1.2 kΩ yields 6.25 V nominal with <2% added error, well within typical design margins.

What thermal considerations apply to LM317LZ-AP in TO-92 package?

With R_thJA = 200 °C/W (TO-92, no heatsink), power dissipation above ~150 mW raises junction temperature significantly in still air. For example, at 12 V input and 5 V output delivering 50 mA, PD = (12−5)×0.05 = 350 mW → ΔT = 70°C rise. Use copper pour or clip-on heatsinks for sustained >100 mW operation, especially above 85°C ambient.