L78L18ACD

Overview

The L78L18ACD is a three-terminal positive linear voltage regulator from the STMicroelectronics L78L series, designed for fixed voltage regulation applications. It provides a nominal output voltage of 18 V with an output current capability up to 100 mA. The device features internal current limiting and thermal shutdown protection, ensuring robust operation under overload conditions. It operates within a junction temperature range of 0 °C to 125 °C and accepts input voltages up to 40 V. The component is available in surface-mount packages including SO-8 and SOT-89, requiring no external components for basic functionality.

Feature Summary

• Internal current limiting and thermal shutdown protection prevent damage during overload or short-circuit events.
• Fixed 18 V output voltage with ±4% tolerance (indicated by 'A' suffix) eliminates the need for external adjustment components.
• Designed for local on-card regulation to eliminate noise and distribution problems associated with single-point regulation.

Applications

• Local or on-card voltage regulation for electronic circuits.
• Replacement for Zener diode and resistor combinations offering lower quiescent current and noise.
• Use with power pass elements to construct high-current voltage regulators.

Procurement Notes

Verify the specific package type required for your design, as the L78L18ACD designation may correspond to either SO-8 or SOT-89 depending on the full ordering code suffix. Confirm that the ±4% voltage accuracy meets your system requirements, distinguishing it from the ±8% 'C' variant. Ensure adequate copper area on the PCB is allocated for heat dissipation given the thermal resistance characteristics of the chosen package.

Selection Notes

Select this component when a stable 18 V supply is needed with moderate current demands up to 100 mA. The L78L18ACD is suitable for industrial applications operating between 0 °C and 125 °C. Consider the dropout voltage of approximately 1.7 V when determining the minimum required input voltage. If higher precision or wider temperature ranges are required, evaluate other variants within the L78L family.

Part Context

The L78L18ACD belongs to the L78Lxx series of three-terminal positive regulators manufactured by STMicroelectronics. This series is characterized by its simplicity, reliability, and built-in safety features. The 'AC' designation typically indicates an automotive-grade or enhanced industrial version with tighter voltage tolerances compared to standard commercial parts. The series is widely used in consumer electronics, industrial controls, and telecommunications equipment.

Replacement Considerations

Direct pin-compatible replacements include other L78L18 variants such as L78L18CD (±8% tolerance) or L78L18AB (wider temperature range). Cross-brand equivalents like LM340-18 or MC78L18 should be verified for pinout compatibility and electrical specifications before substitution.