STMicroelectronics L78L05ACD

Overview

L78L05ACD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 5 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components and is used for local on-card regulation in microcontroller power rails, sensor interfaces, and low-power logic circuits.

For engineers reviewing the L78L05ACD datasheet, L78L05ACD pinout, L78L05ACD application, or L78L05ACD equivalent, this device is selected for cost-sensitive, space-constrained 5 V supply domains where dropout voltage (1.7 V), quiescent current (6 mA at 25 °C), noise performance (40 µV RMS), and ±4% output tolerance are critical design parameters.

Technical Context

The L78L05ACD implements a monolithic silicon-based series pass transistor architecture with built-in thermal shutdown and foldback current limiting. Its regulation loop maintains output stability across input voltages from 7 V to 20 V and load currents from 1 mA to 100 mA at junction temperatures from 0 °C to 125 °C.

It operates as a fixed-output, non-adjustable regulator with a typical dropout voltage of 1.7 V and achieves 41–49 dB supply voltage rejection at 120 Hz under 40 mA load. Output noise is specified at 40 µV RMS over 10 Hz–100 kHz bandwidth.

Key Specifications

Pinout & Package

Supplied in TO-92 package (3-pin plastic case) with standard through-hole mounting. Pin 1 = V_OUT, Pin 2 = GND, Pin 3 = V_IN. Thermal resistance junction-to-ambient is 200 °C/W (no heatsink), enabling 100 mA operation with adequate PCB copper area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L05ACZ and MC78L05ACP, the L78L05ACD offers superior output accuracy (±4% vs. ±5%), lower noise (40 µV vs. ≥65 µV), and better SVR (41–49 dB), making it optimal for noise-sensitive embedded control and sensor systems.

Availability

L78L05ACD is available at Aetrix Electronics and suitable for microcontroller power supply, sensor interface regulation, USB peripheral power, and legacy logic board regulation requiring stable component supply across industrial, automotive, and IoT production cycles.

Supply support for L78L05ACD 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 industrial, automotive, and consumer markets.

The L78L series is part of ST's legacy linear regulator portfolio, engineered for simplicity, robustness, and cost-effective local regulation in space-constrained PCBs where external components must be minimized.

FAQ

What is the minimum input voltage required for L78L05ACD to maintain regulation?

The L78L05ACD requires a minimum input voltage of 6.7 V to sustain 5 V output at full 100 mA load, based on its 1.7 V typical dropout voltage. At lighter loads (e.g., 10 mA), regulation holds down to ~5.5 V input. Operation below the dropout threshold results in unregulated, input-following output behavior.

Can L78L05ACD be used in surface-mount designs?

No - the L78L05ACD variant is specified only in TO-92 through-hole packaging per ST's ordering matrix. Surface-mount alternatives include L78L05ACZ-TR (SO-8) and L78L05ACDT-TR (SOT-89), which share identical electrical specs but differ in thermal performance and footprint.

Does L78L05ACD require input and output capacitors?

Yes - a 0.33 µF ceramic capacitor is required at the input pin and a 0.1 µF ceramic capacitor at the output pin, placed as close as possible to the device. These stabilize the internal control loop and prevent oscillation; omitting them risks instability or excessive noise under dynamic load conditions.

How does thermal performance differ between TO-92 and SO-8 packages of L78L05AC?

TO-92 has R_thJA = 200 °C/W (no heatsink), limiting continuous 100 mA operation without PCB copper; SO-8 (L78L05ACZ-TR) achieves R_thJA = 55 °C/W with 6 cm² copper, enabling higher ambient temperature operation. Junction temperature must stay ≤125 °C for reliable long-term use in both packages.