STMicroelectronics LM317BT

Overview

LM317BT from STMicroelectronics is a monolithic adjustable positive voltage regulator in TO-220 single-gauge package, delivering 1.5 A output current with 1.2 V to 37 V adjustable output range, 0.1% line and load regulation, and integrated thermal shutdown, current limiting, and safe operating area (SOA) protection. It serves as a floating regulator in power supply rails for industrial instrumentation, lab bench supplies, and battery chargers where precise, stable DC voltage is required.

For engineers reviewing the LM317BT datasheet, LM317BT pinout, LM317BT application, or LM317BT equivalent, this page provides verified technical context, validated pin functions, confirmed thermal resistance values (R_thJC = 5 °C/W), real-world load regulation performance (≤25 mV for V_O ≤ 5 V), and design-meaningful alternatives for adjustable linear regulation.

Technical Context

The LM317BT implements a bandgap-referenced error amplifier driving a series pass transistor, with internal 1.25 V reference voltage between output and adjust pins. Its floating architecture allows operation with input-to-ground potentials far exceeding 37 V, provided input-output differential remains ≤40 V.

It uses external resistive feedback (R1–R2 divider) to set output voltage per V_O = 1.25 V × (1 + R2/R1) + I_ADJ×R2, where I_ADJ is tightly controlled at 50–100 µA. Protection circuitry actively limits current, disables conduction during overtemperature, and enforces SOA compliance under high V_IN–V_OUT stress.

Key Specifications

Pinout & Package

LM317BT is supplied in TO-220 single-gauge package (ECOPACK® compliant), featuring three leads: Input (pin 1), Output (pin 2), and Adjust (pin 3). The metal tab is electrically connected to the output pin and serves as thermal path to heatsink.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317T, the LM317BT offers wider industrial temperature qualification; compared with TLV1117-33CDCY, it delivers full adjustability, higher current, and higher input-output differential capability-but requires external resistors and lacks LDO efficiency.

Availability

LM317BT is available at Aetrix Electronics and suitable for industrial power supplies, laboratory test equipment, battery charging systems, and precision analog current sources requiring stable component supply across long production lifecycles.

Supply support for LM317BT 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 sensing solutions for industrial, automotive, and consumer markets.

The LM317 series belongs to ST's legacy linear regulator product line, engineered specifically for robust, low-noise, adjustable DC voltage regulation in cost-sensitive and thermally demanding applications where simplicity and reliability outweigh switching efficiency requirements.

FAQ

What is the minimum load current required for stable regulation with LM317BT?

The LM317BT requires a minimum load current of 3.5–10 mA (depending on V_IN–V_OUT) to maintain regulation. This is due to its internal quiescent current returning to the output pin. If load current falls below this threshold-such as in standby or light-load conditions-the output voltage may rise uncontrollably. A 240 Ω resistor from output to adjust pin typically satisfies this requirement while contributing negligibly to total output error.

Can LM317BT be used in parallel for higher current output?

No-LM317BT is not designed for direct parallel operation. Its output voltage tolerance (±1%) and load regulation characteristics prevent natural current sharing, leading to thermal runaway in one device. For >1.5 A, use a single higher-current regulator (e.g., LM338), or implement active current-sharing circuitry with external op-amps and sense resistors, which adds complexity and reduces reliability.

Does LM317BT require an input bypass capacitor?

Yes-a 0.1 µF ceramic capacitor placed within 2 cm of the input pin is mandatory for high-frequency stability and to suppress ringing caused by PCB trace inductance. Without it, the regulator may oscillate under dynamic load changes or fast input transients, especially when fed from long cables or switch-mode supplies. Larger electrolytic bulk capacitors (e.g., 10–100 µF) are recommended upstream but do not replace the local ceramic cap.

How does the adjust pin capacitor (CADJ) improve performance?

A 10 µF capacitor from adjust pin to ground (CADJ) improves ripple rejection by ~15 dB at 120 Hz and enhances transient response by stabilizing the internal reference node. It reduces output noise contribution from the adjust pin's 50–100 µA current and minimizes sensitivity to PCB layout parasitics. This capacitor must be low-ESR (tantalum or polymer) and placed directly at the pin-long traces degrade its effectiveness.