STMicroelectronics LM337K

Overview

LM337K from STMicroelectronics is an adjustable three-terminal negative voltage regulator in TO-3 metal package, delivering up to −1.5 A over −1.2 V to −37 V output range, with −1.25 V reference voltage, 0.01%/V typical line regulation, and 77 dB ripple rejection at 120 Hz - used in lab power supplies and industrial bias rails.

For engineers reviewing the LM337K datasheet, LM337K pinout, LM337K application, or LM337K equivalent, key selection criteria include guaranteed −1.5 A output current, thermal regulation of 0.003%/W, minimum load current of 2.5 mA, and compatibility with standard TO-3 heatsinking solutions.

Technical Context

The LM337K implements a bandgap-referenced error amplifier driving a PNP pass transistor, with internal current limiting, thermal shutdown, and safe-area protection active even if the adjustment pin is open. Its feedback loop uses two external resistors to set VO = −VREF × (1 + R2/R1) − IADJ × R2.

It operates with input–output differential up to 40 V and junction temperature from 0 °C to 125 °C. Thermal resistance junction-to-case is 4 °C/W (TO-3), enabling high-power dissipation with minimal derating when mounted on a heatsink.

Key Specifications

Pinout & Package

LM337K is housed in a TO-3 metal can package with isolated tab, rated for 0 °C to 125 °C operating junction temperature and designed for direct mounting to heatsinks via the case (pin 2).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM337K, LM337SP trades thermal performance for compactness, while LT1033CN offers superior noise and drift control but requires external thermal management - making LM337K optimal for rugged, high-current industrial supplies needing self-protected operation.

Availability

LM337K is available at Aetrix Electronics and suitable for laboratory power supplies, bipolar op-amp bias rails, and industrial sensor signal conditioning requiring stable component supply and long-lifecycle support.

Supply support for LM337K 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, specializing in power management, analog, microcontrollers, and automotive ICs.

The LM337 series belongs to ST's legacy linear regulator product line, engineered for high-reliability industrial and test equipment where robustness, thermal resilience, and full internal protection are critical.

FAQ

What is the maximum input–output voltage differential for LM337K?

The absolute maximum input–output voltage differential is 40 V. Exceeding this risks permanent damage. For reliable operation, maintain ≤35 V differential with adequate heatsinking, especially at high output currents where power dissipation (|VO − VI| × IO) must stay within thermal limits defined by RthJC = 4 °C/W and ambient constraints.

Can LM337K be used in parallel for higher current?

No - LM337K lacks built-in current-sharing circuitry. Direct paralleling causes unequal current distribution due to VREF and IADJ mismatches, risking thermal runaway. For >1.5 A, use a single higher-rated regulator or implement external ballast resistors with careful thermal coupling and derating per ST Application Note AN2279.

Is the TO-3 case electrically connected to any internal node?

Yes - the TO-3 metal case (pin 2) is internally connected to the output terminal (VO). It must be electrically isolated from the heatsink unless the output is referenced to chassis ground. Failure to insulate may cause short circuits or ground loops in floating-output configurations.

What capacitor values are mandatory for stability?

A minimum 1 µF solid tantalum or 10 µF aluminum electrolytic capacitor is required between input and ground (C1) for stability. Output capacitor (C2) is optional but recommended: 1 µF solid tantalum if regulator is >10 cm from bulk filter; 10 µF improves ripple rejection. Larger values require protection diodes per Figure 18 in the datasheet.