What is Optocoupler?

If you’ve ever taken apart any phone charger or a switching power supply, you’ll find some tiny black IC packages with an unusual number of pins, mostly four or six, both in SMD and through-hole variants. What is more unusual is that these parts are generally found over isolation slots and gaps, which makes their purpose more cryptic.

These components are called optocouplers or optoisolators or simply optos, and they perform the crucial function of passing signals between isolated sections of circuitry. They use light to pass signals between circuits.

MID400 AC Line Logic Optocoupler

The #MID400 is a AC line to logic Power Line Monitor Optocoupler. Meaning, the output of the IC goes low whenever it detects an AC voltage and goes high when no AC voltage is present. This feature can be used to monitor the AC line which will be useful for AC to DC control applications or #Relay/solenoid latching applications.

March 4, 2026 /SemiMedia/ — Vishay Intertechnology has released its VOx619A series of phototransistor optocouplers, designed to keep a stable and linear current transfer ratio (CTR) across temperature while requiring only 0.5 mA of forward current. The new devices support operation up to +125 °C and come in four package options: DIL-4, long-creepage LSOP-4, compact SOP-4, and half-pitch SSOP-4.…