STMicroelectronics L78L18ACD

Overview

L78L18ACD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 18 V output at up to 100 mA, featuring thermal overload protection, short-circuit protection, and ±4% output voltage tolerance (A-grade). It requires no external components and operates with a 1.7 V dropout voltage, making it suitable for local on-card regulation in industrial control modules and embedded sensor interfaces.

For engineers reviewing the L78L18ACD datasheet, L78L18ACD pinout, L78L18ACD application, or L78L18ACD equivalent, this page provides verified electrical characteristics, TO-92 package details, real-world use cases, and validated alternative parts for low-power fixed-voltage regulation design.

Technical Context

The L78L18ACD implements internal current limiting and thermal shutdown circuitry, enabling robust operation without external protection components. Its architecture supports stable DC output under load transients from 1 mA to 100 mA across input voltages of 22–33 V.

It delivers 18 V ±4% over temperature (0–125 °C) and input line variations, with 85 mV load regulation (1–40 mA) and 270 mV line regulation (22–33 V), while maintaining 120 µV RMS output noise (10 Hz–100 kHz) and 33–38 dB supply voltage rejection at 120 Hz.

Key Specifications

Pinout & Package

Supplied in TO-92 package (JEDEC TO-226AA), with 3.3 mm body height, axial leads, and through-hole mounting. Thermal resistance junction-to-ambient is 200 °C/W (no heatsink), reduced significantly with ≥6 cm² PCB copper pour.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed positive voltage regulation applications.

Compared with LM78L18ACZ and MC78L18ACP, the L78L18ACD offers superior supply rejection (33–38 dB), lower noise (120 µV), tighter tolerance (±4%), and guaranteed thermal shutdown-making it optimal for new designs demanding reliability and signal integrity.

Availability

L78L18ACD is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller power rails, legacy equipment retrofit, and test & measurement front-end designs requiring stable component supply and long-term manufacturability.

Supply support for L78L18ACD 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 sensing solutions for industrial, automotive, and consumer markets.

The L78L series targets cost-effective, robust local regulation in space-constrained embedded systems-designed specifically to replace Zener/resistor networks with integrated protection and tighter DC accuracy.

FAQ

What is the minimum input voltage required for L78L18ACD to maintain regulation?

The L78L18ACD requires a minimum input voltage of 19.7 V to sustain 18 V output under full 100 mA load, based on its 1.7 V dropout specification. At lighter loads (e.g., 40 mA), regulation holds down to ~19.3 V. Input below 19.3 V risks output collapse, especially at elevated temperatures.

Can L78L18ACD be used in parallel to increase output current?

No-L78L18ACD is not designed for parallel operation. Its output voltage tolerance (±4%) and lack of current-sharing features cause unequal load distribution, risking thermal runaway in one device. For >100 mA, use a single higher-current regulator (e.g., L7818CD) or external pass transistor topology.

Is a heat sink required for continuous 100 mA operation?

A heat sink is not required for 100 mA operation at ambient ≤50 °C with ≥6 cm² of 2 oz copper on the PCB connected to Pin 2 (GND). Without copper pour, junction temperature exceeds 125 °C above 40 mA at 25 °C ambient-verify thermal performance using R_thJA = 200 °C/W and power dissipation P_D = (V_IN − 18 V) × I_OUT.

Does L78L18ACD support reverse-polarity input protection?

No-the L78L18ACD lacks built-in reverse-voltage protection. Applying negative voltage to VIN relative to GND can damage the IC. External protection (e.g., series Schottky diode or polarity-reversal MOSFET circuit) is required in environments prone to incorrect connector insertion or battery reversal.