STMicroelectronics LM338K

Overview

LM338K from STMicroelectronics is a three-terminal adjustable positive voltage regulator delivering up to 5 A continuous output current over a 1.2 V to 32 V range, featuring 1.24 V nominal reference voltage, 0.005 %/V typical line regulation, and thermal/overcurrent/safe-area protection. It operates from 0 °C to 125 °C and is used in high-current bench power supplies, battery chargers, and industrial DC power systems.

For engineers reviewing the LM338K datasheet, LM338K pinout, LM338K application, or LM338K equivalent, key selection considerations include guaranteed 5 A output, time-dependent current limiting (7 A peak), TO-3 package thermal resistance (1.4 °C/W junction-to-case), and adjustment pin current stability (45–100 µA) under load and line variation.

Technical Context

The LM338K implements a floating architecture where only the input-to-output differential voltage (max 35 V) is seen by the internal pass transistor, enabling high-voltage input operation with low-voltage outputs. Its bandgap-derived 1.24 V reference is impressed across R1 to generate a stable programming current, while the adjustment pin draws minimal, temperature-stable current (≤100 µA) to minimize error in output voltage setting.

Current limiting is time-dependent: short-duration peaks up to 12 A are permitted for transient loads, while sustained current drops to 5–8 A to prevent thermal runaway. Internal thermal shutdown activates at ~150 °C junction temperature, and safe-area protection prevents second breakdown during overload conditions - all functional even if the adjustment pin is disconnected.

Key Specifications

Pinout & Package

LM338K is housed in a hermetically sealed TO-3 metal can package with integral heat sink tab, designed for direct mounting to external heatsinks. The case is electrically connected to the input terminal, requiring insulation when mounted on grounded heatsinks.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM338K, LM350K offers lower thermal resistance but reduced current capacity, while LT1083CP provides higher current and tighter regulation in surface-mount form but requires additional protection circuitry and layout care to match LM338K's robustness.

Availability

LM338K is available at Aetrix Electronics and suitable for laboratory power supplies, battery charging systems, industrial motor interface circuits, and high-reliability DC power modules requiring stable component supply across long production lifecycles.

Supply support for LM338K 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 LM338K belongs to ST's legacy linear regulator product line, engineered specifically for high-current, high-reliability industrial power applications where ruggedness, thermal resilience, and fault tolerance outweigh integration density.

FAQ

What is the maximum input-to-output voltage differential for LM338K?

The absolute maximum input-output voltage differential is 35 V, as specified in Table 2 of the datasheet. Exceeding this value risks permanent damage to the internal pass transistor, regardless of power dissipation or thermal management. This rating applies across the full operating temperature range (0 °C to 125 °C).

Can LM338K operate without an output capacitor?

Yes - the LM338K is internally compensated and stable with no output capacitor. However, adding a 1 mF solid tantalum or 25 µF aluminum electrolytic capacitor improves transient response and suppresses ringing caused by parasitic inductance in output traces, especially under dynamic load changes above 1 A/ms.

How does the adjustment pin current affect output accuracy?

The adjustment pin draws 45–100 µA, which flows through R2 and introduces an error term in the output equation: VO = 1.24 V × (1 + R2/R1) + I_ADJ × R2. For R2 = 2.4 kΩ, this adds up to ±0.24 V error - mitigated by using lower R2 values or including I_ADJ in design calculations.

Is thermal shutdown reversible, and how quickly does it recover?

Yes - thermal shutdown is fully reversible and non-latching. Once junction temperature falls below ~135 °C (hysteresis ~15 °C), regulation resumes automatically within milliseconds. Recovery time depends on heatsink thermal mass and ambient airflow; typical cooldown from 150 °C to 135 °C takes 2–10 seconds under natural convection with a 1°C/W heatsink.