4N26S

Overview

The Fairchild Semiconductor 4N26S is a single-channel optoisolator featuring a phototransistor output with a base connection. It provides electrical isolation between input and output circuits using an infrared LED coupled to a silicon NPN phototransistor. The device is housed in a 6-SMD package, designed for surface-mount applications requiring reliable signal transmission across isolated domains while maintaining high voltage separation standards.

Feature Summary

• Integrates an infrared emitting diode and a silicon NPN phototransistor within a single compact package for efficient electro-optical conversion.
• Includes a dedicated base terminal on the phototransistor to allow for external biasing or sensitivity adjustment capabilities.
• Provides robust galvanic isolation between input and output sections to protect sensitive control circuitry from high-voltage transients.

Applications

• Digital logic signal transmission and level shifting between isolated domains
• Power supply control and switching circuit interfaces
• Electrical insulation isolation between distinct system grounds

Procurement Notes

Verify manufacturer authenticity as the component is marked obsolete by Fairchild. Confirm if the specific suffix matches Everlight equivalents like 4N26S(TB)-V when sourcing replacements. Check datasheet revisions for pinout consistency across different manufacturers offering similar form factors.

Selection Notes

Select this component for applications requiring a standard transistor-output optocoupler with base access. Consider the 5300Vrms isolation rating for high-noise environments. Evaluate the turn-on and turn-off times against system speed requirements before finalizing the design integration.

Part Context

This part belongs to the family of general-purpose phototransistor optoisolators. It shares functional similarities with other industry-standard models but is distinguished by its specific packaging and base-terminal configuration. The device serves as a fundamental building block for basic isolation tasks in industrial and consumer electronics.

Replacement Considerations

The 4N26SM is identified as an official direct active migration path from onsemi. Verify pin compatibility and electrical specifications against the original datasheet before substituting with equivalent parts from other manufacturers such as Everlight.

FAQ

What is the maximum isolation voltage rating?

The device supports an isolation voltage of 5300Vrms.

Does the phototransistor have a base connection?

Yes, the internal phototransistor includes a base terminal for potential external control or sensitivity tuning.