STMicroelectronics LM238K

Overview

LM238K from STMicroelectronics is a three-terminal adjustable positive voltage regulator delivering up to 5 A continuous output current over 1.2 V to 32 V, with guaranteed thermal regulation, time-dependent current limiting (7 A peak), and ±1% reference voltage (1.19–1.29 V). It operates from –25 °C to 150 °C and is used in high-reliability industrial power supplies requiring stable, programmable DC output.

For engineers reviewing the LM238K datasheet, LM238K pinout, LM238K application, or LM238K equivalent, key selection considerations include its TO-3 package thermal performance (R_thJC = 1.4 °C/W), adjustable output via two external resistors, 0.005 %/V typical line regulation, and built-in safe-area and thermal overload protection-critical for high-current linear regulation where transient load handling and junction temperature control are essential.

Technical Context

The LM238K implements a floating architecture that regulates based solely on input-to-output differential voltage (max 35 V), enabling use in high-voltage applications such as lab bench supplies or motor drive pre-regulators. Its internal bandgap reference and error amplifier drive an NPN pass transistor with time-dependent current limiting-allowing 12 A peak for ≤0.5 ms while reducing to 5–8 A under sustained load.

Thermal shutdown activates at ~150 °C junction temperature and remains functional even if the adjustment pin is disconnected. The device requires no mandatory external capacitors but supports optional 10 µF adjustment-pin bypass for ≥75 dB ripple rejection and 1–100 mF output capacitance for transient stability-both validated in ST's typical application circuits.

Key Specifications

Pinout & Package

LM238K is housed in a hermetically sealed TO-3 metal can package with center-tab mounting, optimized for mechanical robustness and thermal conduction to heatsinks. The case serves as the output terminal, simplifying thermal design and eliminating PCB trace resistance in high-current paths.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM338K and LT1083CP, the LM238K uniquely balances extended temperature operation (–25 °C), robust 7 A peak current delivery, and TO-3 thermal performance-making it optimal for industrial systems where cold-start reliability and transient load resilience are non-negotiable.

Availability

LM238K is available at Aetrix Electronics and suitable for industrial bench power supplies, high-current sensor excitation circuits, motor drive pre-regulators, and legacy equipment voltage retrofits requiring stable component supply and long-lifecycle support.

Supply support for LM238K 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 ICs, analog components, and MEMS sensors for industrial, automotive, and consumer markets.

The LM238K belongs to ST's legacy linear regulator product line, engineered specifically for high-reliability, high-current analog power applications where thermal robustness, transient immunity, and extended temperature operation are critical design requirements.

FAQ

What is the maximum input-to-output voltage differential for LM238K?

The absolute maximum input-output differential voltage is 35 V, as specified in Table 2 of the ST datasheet. Exceeding this value risks permanent damage to the internal pass transistor, regardless of power dissipation. This rating applies across the full operating temperature range (–25 °C to 150 °C) and is independent of output current or heatsink performance.

Can LM238K operate without external capacitors?

Yes-LM238K is internally compensated and stable with no external capacitors. An input bypass (0.1 µF ceramic) is recommended only if the device is located >6 inches from bulk input capacitance. Output capacitance is optional and used solely to improve transient response; values from 1 mF to 100 mF (tantalum or aluminum) are validated in ST's application notes.

How does the time-dependent current limit function?

The LM238K delivers up to 12 A for ≤0.5 ms under short-circuit or heavy transient conditions, then reduces to 5–8 A for sustained loads. This behavior is implemented via on-chip thermal time constants and does not require external circuitry. It enables reliable startup into large capacitive loads while preventing thermal runaway during continuous overload.

Is the metal case electrically connected to any internal node?

Yes-the TO-3 metal case is internally connected to the output (emitter) terminal. When mounted to a heatsink, electrical isolation (e.g., mica washer + insulating sleeve) is required unless the heatsink is intentionally tied to the output rail. Failure to isolate may cause short circuits or ground loops in multi-rail systems.