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Photocouplers have various types of internal package structure because of various restrictions such as required insulation performance, package size, and size of internal chip.
Transmissive type in single mold:
Frame-mounted LED and frame-mounted photodetector face each other in the same molded package. Silicon resin is used for the optical transmission part between LED and photodetector.
Transmissive type in single mold with film:
To raise isolation voltage, polyimide film is inserted between LED and photodetector.
Transmissive type in double mold:
In this transmissive structure, inner mold is white, and outer mold is black. Resin with high infrared light transmittance is used for white mold of the optical transmission part.
Frame-mounted LED and frame-mounted photodetector are on the same plane. LED light reflected in silicon resin reaches the photodetector. Thus, it is called reflective type.