Signal isolation for DC-coupled circuits
The onsemi MCT5211M is a single-channel optoisolator in a 6-DIP through-hole package, designed to pass DC-level signals across a 4170Vrms isolation barrier. The output is a phototransistor with the base brought out to a separate pin, which gives the designer the option to bias the base for faster switching or to connect a base-emitter resistor for noise immunity in high-impedance circuits. With a minimum current transfer ratio of 150% at a forward current of 1.6 mA, this part drives a logic-level load from a low-power microcontroller pin without an external buffer. The 150 mA continuous output current and 30 V output rating cover most PLC digital input modules and industrial sensor interfaces.
Switching speed and saturation margin
Typical turn-on time is 14 µs and turn-off is 2.5 µs, which suits 10 kHz to 50 kHz switching applications like relay drivers, solenoid valves, and motor contactor feedback. The forward voltage is 1.25 V typical at the LED, and the absolute maximum DC forward current is 50 mA — a 330 Ω series resistor from a 5 V supply limits the LED current to about 11 mA, well within the safe operating area while still achieving the 150% CTR minimum.