Regarding optocouplers..?

[ramanv.india]

I was reading ur posts on 2 ground issues.

Have observed optocoupler circuits wherein the gnds of both the input and o/p ports are isolated. Is this done to reduce noise propating on the ground line.

What will happen if both the grounds are shorted?
:?:

 

[cameo_2007]

I was reading ur posts on 2 ground issues.

Have observed optocoupler circuits wherein the gnds of both the input and o/p ports are isolated. Is this done to reduce noise propating on the ground line.

What will happen if both the grounds are shorted?
:?:

whose posts :?:

If shorted then there is no isolation. Probably it can be used as a voltage level converter in that case.

 

[WimRFP]

Hello,

Photo-couplers are mostly used for (data) communication where grounds may not be connected.

High side driver in a power application (mostly functional insulation), this is a form of level shift: connecting ground together will results in short circuit (blown fuse, blown traces, etc).

Safety insulation barrier (safety insulation) between low voltage and circuits with hazardous voltage: connecting ground together may put the user of the equipment into real danger.

Insulation barrier (functional insulation) to reduce effect of common mode interference: shorting the grounds of the LED and phototransistor may result in more interference. Depending on the margin you have, system performance may degrade.

Besides the closed varieties, there are varieties where the light beam travels partly through air (optical detectors, encoders, etc). Here grounds are connected together frequently.