STMicroelectronics L78L15ABD

Overview

L78L15ABD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 15 V output at up to 100 mA, with ±4% output voltage tolerance (AB grade), thermal overload protection, short-circuit protection, and 1.7 V dropout voltage. It operates across –40 °C to +125 °C junction temperature and requires no external components for basic regulation-commonly used in local on-board power conditioning for microcontroller peripherals and sensor interfaces.

For engineers reviewing the L78L15ABD datasheet, L78L15ABD pinout, L78L15ABD application, or L78L15ABD equivalent, this page provides verified technical context, package-specific pin roles, real-world use cases, and validated alternative parts for industrial control, embedded instrumentation, and low-power analog subsystems where stable 15 V biasing is required.

Technical Context

The L78L15ABD implements an internally compensated, monolithic bipolar linear regulator architecture with built-in current limiting and thermal shutdown. Its AB-grade specification ensures output voltage stability over –40 °C to +125 °C operating junction temperature, and its 1.7 V dropout enables operation from as low as 16.7 V input when delivering full 100 mA load current.

It achieves 34–39 dB supply voltage rejection at 120 Hz under 40 mA load, and delivers 90 µV RMS output noise (10 Hz–100 kHz), supporting noise-sensitive analog circuits. The device draws only 6.5 mA quiescent current at 25 °C and maintains regulation across input voltages from 17.5 V to 30 V.

Key Specifications

Pinout & Package

Supplied in TO-92 package (standard plastic through-hole), with 3-pin vertical lead configuration and JEDEC-standard pinout: Pin 1 = VOUT, Pin 2 = GND, Pin 3 = VIN. Thermal resistance is 200 °C/W (junction-to-ambient, no heatsink); derating required above 50 °C ambient for sustained 100 mA operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output linear regulator applications.

Compared with LM78L15ACZ and MC78L15ACP, the L78L15ABD offers superior temperature range (–40 °C to +125 °C), tighter output tolerance (±4%), and documented 120 Hz supply rejection-making it the preferred choice for automotive, industrial, and high-reliability embedded systems demanding consistent 15 V regulation under thermal stress.

Availability

L78L15ABD is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller I/O power rails, legacy analog instrumentation, and test equipment auxiliary supplies requiring stable component supply with long-term lifecycle assurance.

Supply support for L78L15ABD 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 silicon solutions for automotive, industrial, and power management applications.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-effective, robust local regulation in space-constrained embedded systems where simplicity, reliability, and wide temperature operation are critical.

FAQ

What is the maximum input voltage for L78L15ABD?

The absolute maximum input voltage is 35 V for 15 V output variants, as specified in Table 1 of the datasheet. For continuous operation, ST recommends limiting input to ≤30 V to ensure safe thermal margin under full 100 mA load and worst-case ambient conditions. Exceeding 30 V increases junction temperature and may trigger thermal shutdown.

Can L78L15ABD be used in parallel to increase current capacity?

No-L78L15ABD is not designed for parallel operation. Its output voltage tolerance (±4%) and lack of current-sharing features mean mismatched units will cause one device to dominate conduction, leading to thermal imbalance and premature failure. For >100 mA, use a single higher-current regulator or add an external pass transistor with proper biasing.

Is a heat sink required for 100 mA operation?

A heat sink is not required for 100 mA operation at ambient temperatures ≤50 °C with the TO-92 package, provided the PCB has ≥1 cm² of 2-oz copper connected to Pin 2 (GND) for thermal spreading. Above 50 °C ambient or with sustained 100 mA load, thermal derating applies: output current must be reduced by ≈0.5 mA/°C above 50 °C to avoid exceeding 125 °C junction temperature.

What capacitor values are mandatory for stable operation?

A 0.33 µF ceramic capacitor (CI) is required between VIN and GND, placed within 5 mm of the TO-92 package, and a 0.1 µF ceramic capacitor (CO) is required between VOUT and GND, also placed within 5 mm. These values are validated for stability across all operating conditions; substituting with larger electrolytics or omitting either capacitor risks oscillation or poor transient response.