onsemi LM317MT

Overview

LM317MT from STMicroelectronics is a monolithic adjustable positive voltage regulator in TO-220 package, delivering up to 500 mA output current with 1.2–37 V adjustable output range, 1.25 V internal reference voltage, and built-in thermal overload and short-circuit protection. It enables simple floating high-voltage regulation in power supplies for test equipment and industrial instrumentation.

For engineers reviewing the LM317MT datasheet, LM317MT pinout, LM317MT application, or LM317MT equivalent, key selection criteria include output voltage adjustability via two-resistor divider, load regulation ≤25 mV (typ.), line regulation ≤0.04 %/V (typ.), minimum load current of 3.5–10 mA, and thermal resistance of 3 °C/W (junction-to-case) in TO-220.

Technical Context

The LM317MT operates as a floating three-terminal linear regulator, using an internal bandgap reference (1.25 V) between output and adjustment terminals to set output voltage via external resistive divider. Its feedback loop maintains constant current through R1, enabling precise VO = 1.25 V × (1 + R2/R1) + I_ADJR2.

It features internal safe-area compensation, eliminating need for external SOA protection circuitry, and supports programmable current regulation when configured with fixed resistor between ADJ and OUT. Junction temperature monitoring ensures thermal shutdown activation before damage occurs at T_J ≥ 150 °C.

Key Specifications

Pinout & Package

LM317MT is housed in a standard TO-220-3 package with vertical mounting orientation, metal tab electrically connected to the output terminal, and RoHS-compliant ECOPACK® construction.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317T, LM317MT offers identical functionality with ST's ECOPACK® compliance and tighter thermal resistance (3 °C/W vs. typical 4.5 °C/W). Versus TL783CP, it trades off high-voltage capability for superior thermal efficiency and compact TO-220 packaging-making it optimal for general-purpose 5–37 V regulated supplies.

Availability

LM317MT is available at Aetrix Electronics and suitable for lab power supplies, industrial sensor bias rails, LED drivers, and programmable current sources requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for LM317MT 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 management ICs, analog chips, and MEMS sensors for industrial, automotive, and consumer markets.

The LM317 series belongs to ST's legacy linear regulator product line, engineered for robustness, ease of use, and compatibility with decades-old designs-targeting cost-sensitive, reliability-critical analog power applications where simplicity and field-proven behavior outweigh switching efficiency.

FAQ

What is the minimum load current required for stable regulation with LM317MT?

The LM317MT requires a minimum load current of 3.5–10 mA depending on operating conditions, primarily to ensure the adjustment pin current (50–100 µA) flows through the external resistor network and prevents output voltage drift. This is typically satisfied by the R1 resistor in the voltage divider or an explicit bleeder resistor across the output.

Can LM317MT be used in a floating configuration for negative output voltages?

No-LM317MT is a positive adjustable regulator only and cannot generate negative outputs. For negative regulation, the complementary LM337M must be used. However, LM317MT can float above ground (e.g., regulating +40 V relative to a +30 V rail) as long as the input-to-output differential remains ≤40 V and the metal tab is properly insulated.

Is an input bypass capacitor mandatory for LM317MT stability?

An input bypass capacitor is not mandatory for basic stability but is strongly recommended when the regulator is located >6 inches from bulk input capacitance. A 0.1 µF ceramic or 1 µF tantalum capacitor placed close to the input pin reduces sensitivity to source impedance and suppresses high-frequency noise that could modulate the reference node.

How does the LM317MT handle thermal overload during continuous 500 mA operation?

At 500 mA and 10 V dropout, LM317MT dissipates 5 W, raising junction temperature rapidly without heatsinking. With its 3 °C/W junction-to-case thermal resistance and typical 50 °C/W junction-to-ambient (TO-220, 1 in² copper), it reaches thermal shutdown (~150 °C) within seconds. A 2°C/W heatsink extends safe continuous operation to >400 mA at 10 V dropout.