STMicroelectronics LM217K

Overview

LM217K from STMicroelectronics is a monolithic adjustable positive voltage regulator in TO-3 metal can package, delivering ≥1.5A output current with 1.2V to 37V adjustable output range, 0.1% line/load regulation, and integrated thermal shutdown, current limiting, and SOA protection. It operates as a floating regulator for high-voltage applications such as lab power supplies and industrial DC rails.

For engineers reviewing the LM217K datasheet, LM217K pinout, LM217K application, or LM217K equivalent, key selection considerations include its −25°C to +150°C operating junction temperature, 40V max input-output differential, 1.25V internal reference, minimum 3.5mA load requirement, and TO-3 thermal resistance of 4°C/W junction-to-case.

Technical Context

The LM217K implements a bandgap-referenced error amplifier driving a series pass transistor, with all quiescent current returned to the output to enable precise resistive feedback control. Its floating architecture allows regulation of outputs far above ground potential, provided Vi–Vo ≤ 40V.

It features three-stage protection: foldback current limiting active below 1.5A, thermal shutdown at ~150°C junction temperature, and safe operating area (SOA) control that dynamically limits power dissipation under high Vi–Vo conditions.

Key Specifications

Pinout & Package

LM217K uses a TO-3 metal can package with 3 terminals: Input (collector of pass transistor), Output (emitter), and Adjustment (error amplifier inverting input). The case is electrically connected to the Input terminal and must be isolated from chassis ground unless referenced to input potential.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317K and LM217T, the LM217K uniquely supports −25°C cold-start operation and delivers full 1.5A with minimal heatsink due to TO-3's 4°C/W junction-to-case thermal resistance-critical for ruggedized power modules and high-reliability test equipment.

Availability

LM217K is available at Aetrix Electronics and suitable for lab power supplies, battery chargers, industrial motor drive bias rails, and programmable sensor excitation circuits requiring stable component supply across extended temperature ranges.

Supply support for LM217K 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, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The LM217K belongs to ST's legacy linear regulator product line, engineered for high-reliability analog power management in harsh environments where extended temperature operation and robust protection are mandatory.

FAQ

What is the minimum load current required for stable regulation with LM217K?

The LM217K requires a minimum load current of 3.5mA to maintain regulation. This is due to its architecture returning all quiescent current to the output pin. If load current falls below this threshold-such as during light-load or standby conditions-the output voltage will rise uncontrollably. A bleeder resistor from output to ground is mandatory in no-load or micro-power applications.

Can LM217K be used in a negative voltage configuration?

No. The LM217K is designed exclusively as a positive adjustable regulator. Its internal circuitry, including the 1.25V reference between output and adjustment pins, assumes positive polarity. For negative regulation, ST's LM337 family (complementary negative-adjustable regulator) must be used, which shares identical topology but inverted pinout and reference polarity.

How does the TO-3 package affect thermal design compared to TO-220 versions?

The TO-3 metal can package provides 4°C/W junction-to-case thermal resistance-significantly lower than TO-220's 35°C/W. This allows the LM217K to dissipate more power with smaller heatsinks or operate at higher ambient temperatures. However, the TO-3 case is electrically connected to the input pin, requiring insulated mounting hardware when the heatsink is grounded or at a different potential.

What capacitor values are recommended for optimal ripple rejection and transient response?

For best performance: a 0.1µF ceramic capacitor at the input, a 10µF tantalum (or 25µF aluminum electrolytic) from adjustment pin to ground to improve ripple rejection by ~15dB, and a 1µF tantalum (or 25µF aluminum) at the output to enhance transient response. Protection diodes (1N4002) are also recommended across input/output to prevent damage during capacitor discharge events.