Every once in a while Voltage Multipliers Inc. receives an inquiry about parts being sensitive to ambient light.
One question recently was about one of the high voltage optocouplers – the OC150 family. The OC150 family uses two LED to illuminate light-sensitive silicon junctions in high voltage diode (the photo diode).
Glass encapsulated diodes can be sensitive to ambient light. Just how sensitive depends on many factors – the wavelength of the light, temperature, orientation of the diode junctions, distance from the light source, thickness of the glass, and so on.
Normally it’s not an issue, but when you’re dealing with very low levels of leakage current, light sensitivity can be a problem.
For that reason, many VMI customers take steps to protect their optocouplers from ambient light by over potting them with an optically opaque material. Another strategy is to coat the optocoupler with a non-conductive coating, making sure that you’re not creating a leakage path that might allow the optocoupler to arc.