STMicroelectronics LM250K

Overview

LM250K from STMicroelectronics is a three-terminal adjustable positive voltage regulator delivering guaranteed 3 A output current with adjustable output down to 1.2 V, ±1% reference voltage (1.19–1.29 V), 0.005%/V typical line regulation, and –25°C to +150°C operating junction temperature range. It is used in industrial power supplies requiring stable high-current biasing for analog circuitry, motor drivers, and test equipment.

For engineers reviewing the LM250K datasheet, LM250K pinout, LM250K application, or LM250K equivalent, key selection considerations include thermal resistance (1.5°C/W junction-to-case), minimum load current (3.5–5 mA), ripple rejection (65–86 dB), and TO-3 package mechanical compatibility with heatsink mounting requirements.

Technical Context

The LM250K implements a bandgap-referenced error amplifier driving a Darlington-pass transistor stage with internal current limiting and thermal shutdown. Its 1.25 V nominal reference is developed between output and adjustment terminals, enabling precise external resistor-based output programming via VO = 1.25 V × (1 + R₂/R₁) + I_adjR₂.

Line and load regulation are measured at constant junction temperature; thermal regulation (0.002–0.01 %/W) and long-term stability (0.3–1 % at 125°C) are separately specified to isolate heating effects. The device maintains constant current limit over temperature and features internally limited power dissipation up to 30 W.

Key Specifications

Pinout & Package

LM250K uses the standard TO-3 metal-can package with case-isolated collector (output) terminal, requiring electrically insulated mounting hardware when the case is not tied to output potential.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM350K, LM250K provides wider low-temperature capability (–25°C vs. 0°C) and tighter regulation; compared with LM150K, it trades extended cold rating for lower cost while retaining identical thermal and electrical performance above –25°C.

Availability

LM250K is available at Aetrix Electronics and suitable for industrial power supplies, test equipment bias rails, motor driver bias networks, and embedded controller auxiliary rails requiring stable component supply with legacy TO-3 mechanical compatibility.

Supply support for LM250K 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, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The LM250K belongs to ST's legacy linear regulator product line, engineered specifically for high-current, high-reliability linear regulation in thermally constrained industrial power systems where simplicity, ruggedness, and proven field performance are prioritized over modern switching efficiency.

FAQ

What is the minimum load current required for stable regulation with LM250K?

The LM250K requires a minimum load current of 3.5–5 mA to maintain regulation. This is due to internal quiescent current returning to the output; insufficient load causes output voltage to rise uncontrollably. A 240 Ω resistor from output to adjustment pin satisfies this requirement when set for outputs ≥1.25 V.

Can LM250K be used without an output capacitor?

Yes, the LM250K is stable with no output capacitor, unlike many other regulators. However, adding 1–100 µF aluminum or tantalum electrolytic capacitance improves transient response and output impedance. Avoid 500 pF–5 nF values, which may cause ringing.

How does the adjustment pin current affect output accuracy?

The LM250K's adjustment pin draws 50–100 µA, introducing error in the R₂ resistor of the feedback divider. This error is minimized by keeping R₁ = 240 Ω and selecting R₂ to limit I_adjR₂ voltage drop to <1% of VO-e.g., R₂ ≤ 2 kΩ for 5 V output.

Is a protection diode needed when using an output capacitor?

No protection diode is required for output capacitors ≤100 µF at output voltages ≤15 V. For >25 V outputs or >100 µF capacitance, a reverse-biased diode from output to input prevents capacitor discharge through internal junctions during input short events.