Dual Darlington optoisolator in 8-SOIC
The MOCD223M from onsemi is a dual-channel optoisolator with Darlington transistor outputs, packaged in an 8-SOIC (0.154", 3.90mm width) surface-mount package. It provides 2500Vrms galvanic isolation between a DC input LED and the output Darlington pair, making it suitable for interfacing low-voltage logic to higher-voltage loads up to 30V. A minimum current transfer ratio of 500% at 1 mA forward current means the output can sink 150 mA continuous per channel while the input LED draws only a few milliamps — useful for driving relays, solenoids, or PLC input modules without an external transistor buffer.
Switching speed and drive margin
Typical turn-on time is 10 µs and turn-off time is 125 µs, with rise and fall times of 8 µs and 110 µs respectively. These figures place the MOCD223M in the medium-speed class — adequate for 50/60 Hz line-frequency isolation, relay coil drives, and status feedback loops, but not for high-speed data or PWM above a few kilohertz. The Darlington output saturates to a maximum Vce of 1V at rated current, which keeps power dissipation low in the output stage. The 1.25V typical forward voltage of the input LED is standard for GaAs infrared emitters and compatible with 3.3V or 5V logic outputs through a current-limiting resistor.
Sourcing and compliance status
For BOM resilience, qualifying a pin-compatible alternative from another brand is straightforward — the package and pinout are industry-standard for dual-channel SOIC-8 optoisolators.