STMicroelectronics LM137K

Overview

LM137K from STMicroelectronics is a three-terminal adjustable negative voltage regulator in TO-3 metal package, delivering up to −1.5 A output current across −1.2 V to −37 V output range with −1.25 V reference voltage, 0.02%/V typical line regulation, and 77 dB ripple rejection at 120 Hz. It serves as the main negative supply regulator in dual-rail analog power systems, lab bench supplies, and industrial instrumentation requiring wide output adjustability and robust thermal protection.

For engineers reviewing the LM137K datasheet, LM137K pinout, LM137K application, or LM137K equivalent, key selection considerations include guaranteed −1.5 A output current at junction temperatures from −55 °C to +150 °C, low thermal regulation (0.02 %/W), adjustable output via two external resistors, and full on-chip protection including current limit, thermal overload, and safe-area safeguarding-even with open adjustment pin.

Technical Context

The LM137K implements an internally compensated bandgap reference and precision error amplifier driving a high-current PNP pass transistor, enabling stable negative output regulation without external compensation. Its architecture supports direct feedback from the output node through R1–R2 divider to the ADJ pin, with I_ADJ held tightly at 65–100 µA for predictable setpoint accuracy.

Thermal regulation is minimized by monolithic integration of sensing and control circuitry on a single silicon die with optimized thermal layout; the TO-3 package provides 4 °C/W junction-to-case thermal resistance, enabling sustained −1.5 A operation under forced-air or heatsink-cooled conditions without derating below 125 °C ambient.

Key Specifications

Pinout & Package

LM137K is housed in a hermetically sealed TO-3 metal can package with center-tab mounting, rated for −55 °C to +150 °C operating junction temperature and offering low 4 °C/W junction-to-case thermal resistance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM337K and LM337SP, the LM137K uniquely delivers guaranteed −1.5 A output across −55 °C to +150 °C with tighter reference tolerance and lower thermal regulation-making it the sole choice for high-reliability, wide-temperature, high-current negative regulation where TO-3 ruggedness and hermetic sealing matter.

Availability

LM137K is available at Aetrix Electronics and suitable for industrial power supplies, test & measurement equipment, process instrumentation, and medical signal conditioning requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for LM137K 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 analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The LM137 series belongs to ST's legacy linear regulator product line, engineered specifically for high-current, wide-output-range negative voltage regulation in mission-critical analog power systems where reliability, thermal resilience, and protection integrity are non-negotiable.

FAQ

What is the minimum load current required for stable regulation with LM137K?

The LM137K requires a minimum load current of 2.5 mA (typical) to maintain regulation when |V_I − V_O| ≤ 40 V. This ensures sufficient bias for internal circuitry and prevents output voltage drift or oscillation. For outputs below −5 V, maintaining ≥5 mA load is recommended to guarantee full spec compliance across temperature.

Can LM137K be used in parallel for higher output current?

No-LM137K is not designed for parallel operation. Its internal current-limit circuitry lacks built-in current-sharing capability, and mismatched thermal gradients between devices cause unequal current distribution and potential thermal runaway. For >−1.5 A requirements, use a discrete pass transistor with external current-sense feedback or select a higher-current regulator IC.

What capacitor values are mandatory for stability with LM137K?

A minimum 1 µF solid tantalum (or 10 µF aluminum electrolytic) capacitor is required at the input pin for stability. Output capacitance is not mandatory but recommended: 1 µF solid tantalum improves transient response, while ≥10 µF enhances ripple rejection. Larger output capacitors (>20 µF) require protection diode D1 per Figure 18 in the datasheet.

Does LM137K support electronic shutdown or remote sensing?

The LM137K does not integrate electronic shutdown, but Figure 19 in the datasheet shows a proven method using an NPN transistor to pull the ADJ pin to ground, forcing output to −1.3 V (minimum). Remote sensing is not supported-the ADJ pin senses only local feedback; for remote load regulation, external op-amp error amplifiers with sense lines must be added.