What the 4N28SM does in your circuit
The 4N28SM is a single-channel optoisolator from onsemi that couples a DC input LED to a phototransistor with a base terminal, providing 4170 Vrms of galvanic isolation between input and output sides. The base pin gives the designer the option to bias the transistor for faster switching or to use it as a photodarlington by connecting an external transistor. Typical turn-on and turn-off times of 2 µs each suit low-speed signal isolation, such as PLC digital inputs or motor drive feedback.
Package and mounting — 6-SMD gull wing
The 6-SMD gull wing package is surface-mount compatible with standard reflow soldering profiles.
The 60 mA maximum forward current and 30 V output voltage provide headroom for common logic rails, with 500 mV Vce saturation limiting voltage drop.
Sourcing and lifecycle — active production
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