What is the internal structure of a photocoupler?

For photocouplers, the structure inside the package also varies depending on the condition such as the required isolation performance, package size, and internal chip size.

1. Face-to-face type in single mold

The LED-mounted frame and the photodetector-mounted frame face each other (transmissive) and are molded. Silicone resin is used for the optical transmission part between the LED and the photodetector.

2. Face-to-face type in single mold (with a polyimide film)

To increase an isolation voltage between an input and an output, a polyimide film is inserted between the LED and the photodetector.

3. Face-to-face type in double mold

This photocoupler adopts a face-to-face type structure, and is white-molded inside and black-molded outside. Resin with high infrared light transmittance is used for the white mold of the optical transmission part.

4. Reflective type

This photocoupler adopts a structure that has the LED-mounted frame and the photodetector-mounted frame on the same plane. It is called "reflective type" because LED light reflected inside silicone resin reaches the photodetector.