STMicroelectronics LM350K

Overview

LM350K from STMicroelectronics is a three-terminal adjustable positive voltage regulator delivering guaranteed 3 A output current, adjustable down to 1.2 V, with line regulation of 0.005 %/V and load regulation of 0.1 %, housed in a TO-3 metal package for high-power linear regulation in industrial power supplies and bench-top equipment.

For engineers reviewing the LM350K datasheet, LM350K pinout, LM350K application, or LM350K equivalent, key selection considerations include thermal resistance (R_thJC = 1.5 °C/W), reference voltage accuracy (1.19–1.29 V), minimum load current requirement (3.5–10 mA), and ripple rejection (65 dB at 120 Hz) in fixed- or adjustable-output configurations.

Technical Context

The LM350K operates as a floating-series-pass linear regulator using an internal bandgap reference and error amplifier to maintain output voltage via external resistor divider feedback. Its adjustment pin draws only 50–100 µA, minimizing error contribution while enabling precise 1.2 V to 25 V output programming.

It integrates thermal shutdown, current limiting (3–4.5 A), and safe-area protection. Unlike fixed-output regulators, it requires no output capacitor for stability but benefits from 1 µF solid tantalum on output and 0.1 µF ceramic on input to suppress transients and ensure loop stability across load and line variations.

Key Specifications

Pinout & Package

LM350K uses the standard TO-3 metal-can package (11.85 mm × 20.0 mm footprint, 39.5 mm height), designed for direct heatsink mounting with low thermal resistance (R_thJC = 1.5 °C/W). The case is electrically connected to the input terminal.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM350T, the LM350K offers superior thermal performance in metal-can form factor, while the LT1083CP delivers higher precision and lower thermal resistance - making LM350K optimal for cost-sensitive, high-current industrial supplies where proven reliability and TO-3 mechanical robustness are prioritized.

Availability

LM350K is available at Aetrix Electronics and suitable for industrial bench power supplies, programmable lab PSUs, high-current analog bias rails, and legacy equipment replacement requiring stable component supply and long-term availability planning.

Supply support for LM350K 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, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The LM350K belongs to ST's legacy linear regulator product line, engineered for rugged, high-current analog power delivery in environments demanding thermal resilience, long-term reliability, and compatibility with established TO-3 mechanical infrastructure.

FAQ

What is the minimum load current required for stable operation of the LM350K?

The LM350K requires a minimum load current of 3.5–10 mA depending on input-output differential and temperature. This is necessary because all quiescent current returns to the output; insufficient load causes output voltage to rise uncontrollably. A 240 Ω resistor from output to adjust pin typically satisfies this requirement for 1.25 V reference-based designs.

Can the LM350K be used without an output capacitor?

Yes - the LM350K is internally compensated and stable with zero output capacitance. However, adding 1 µF solid tantalum or 25 µF aluminum electrolytic improves transient response and suppresses ringing caused by parasitic inductance. Avoid 500 pF–5000 pF values, which may induce instability.

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 = V_REF(1 + R2/R1) + I_ADJ × R2. Since I_ADJ varies only ±5 µA over load and line, using R2 ≤ 1 kΩ limits this error to ≤5 mV - a key design constraint for high-accuracy applications.

Is the LM350K RoHS-compliant and lead-free?

Yes - the LM350K is supplied in ST's ECOPACK®-compliant TO-3 package with lead-free second-level interconnect, meeting JEDEC JESD97 standards. The inner box label and package marking indicate the lead-free status, and soldering profiles follow industry-standard Pb-free reflow guidelines.