STMicroelectronics L78L33ACD

Overview

L78L33ACD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 3.3 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components, operates with a 1.7 V dropout voltage, and maintains ±4% output tolerance over 0–125 °C junction temperature for local on-card regulation in microcontroller power domains.

For engineers reviewing the L78L33ACD datasheet, L78L33ACD pinout, L78L33ACD application, or L78L33ACD equivalent, this part serves as a drop-in replacement for Zener/resistor regulators in low-noise, low-quiescent-current (6 mA typ.) embedded power rails where stable 3.3 V supply and robust fault protection are required.

Technical Context

The L78L33ACD implements a monolithic bipolar linear regulator architecture with built-in thermal shutdown and foldback current limiting. Its internal reference and error amplifier maintain output regulation across input voltages from 5.3 V to 20 V, with line regulation of ≤100 mV and load regulation of ≤30 mV under specified conditions.

It achieves 41–49 dB supply voltage rejection at 120 Hz and delivers 40 µV RMS output noise (10 Hz–100 kHz), making it suitable for noise-sensitive analog and digital logic supplies. The device is rated for operation from 0 °C to +125 °C junction temperature and supports TO-92, SO-8, and SOT-89 packages.

Key Specifications

Pinout & Package

Available in TO-92, SO-8, and SOT-89 packages. The L78L33ACD variant referenced here uses the TO-92 package (standard plastic through-hole), with pin 1 = V_OUT, pin 2 = GND, pin 3 = V_IN.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L33ACZ, the L78L33ACD offers superior PSRR and tighter thermal protection; versus MCP1700-3302E/TO, it trades ultra-low IQ for proven fault resilience in industrial environments with variable loads and ambient temperatures.

Availability

L78L33ACD is available at Aetrix Electronics and suitable for industrial control panels, IoT edge nodes, and medical diagnostic devices requiring stable component supply, long-term lifecycle support, and RoHS-compliant through-hole packaging.

Supply support for L78L33ACD 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, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

The L78L series belongs to ST's legacy linear regulator product line, engineered specifically for cost-effective, robust, and easy-to-use local voltage regulation in space-constrained PCB layouts where simplicity and reliability outweigh ultra-low IQ requirements.

FAQ

What is the minimum input voltage required for the L78L33ACD to maintain regulation?

The L78L33ACD requires a minimum input voltage of 5.3 V to sustain 3.3 V output under full 100 mA load, based on its 1.7 V dropout voltage specification. At lighter loads (e.g., 40 mA), regulation holds down to ~5.0 V input. Input below 5.3 V risks output collapse, especially at high temperature or maximum load.

Can the L78L33ACD be used in surface-mount designs?

Yes-the L78L33ACD designation refers to the TO-92 package, but ST also manufactures the same electrical specification in SO-8 and SOT-89 surface-mount packages (e.g., L78L33ACZ-TR for SO-8, L78L33ACDT-TR for SOT-89). Pinout remains identical: pin 1 = V_OUT, pin 2 = GND, pin 3 = V_IN.

Does the L78L33ACD require input and output capacitors?

Yes-ST specifies a 0.33 µF ceramic capacitor (CI) on the input and a 0.1 µF ceramic capacitor (CO) on the output, placed as close as possible to the device pins. These stabilize the regulator, suppress high-frequency noise, and prevent oscillation; omitting them may cause instability or excessive ripple.

How does the L78L33ACD handle thermal stress during continuous 100 mA operation?

In TO-92 package, continuous 100 mA operation at 20 V input generates ~1.6 W dissipation. Without heatsinking, junction temperature rises rapidly beyond 125 °C, triggering thermal shutdown. ST recommends using copper pour or external heatsink for sustained >50 mA loads at high VI–VO differentials.