> SINGLE DIVIDER?
>
> Blame Jinx for the inspiration.
>
> Assume inputs are 0/+50V wrt aq common ground.
> Other polarities and relationships can be dealt with similarly.
>
> 90 optocouplers.
> PIC drives optos in row/column arrays.
> Opto collector per input.
> Combine emitters
> Monitor emitters as optos are turned on either one at a time or in groups.

Answering myself.

My previously mentioned "reverse biased CE junction concern matters as
a reversed biased transistor will break down (Veco) at a much lower
voltage than it will withstand when normally biased (VCEO). Veco is
usually in the 5 to 10 volt range.

With the above assumptions, if the opto couplers use  PNP transistors,
apply Vin x 90 to separate emitters and combine all collectors the
transistors will always be correctly biased..

Transistors are now "happy" with bias conditions under all circumstances.

If swing is 0/-50V wrt ground then use NPN optos for same result.

I'm not aware of PNP optocouplers - they may exist.

IF this is a relphone line sampling situation, as it may be, then th
ability to use NPN optos in this manner is 'fortunate.'

_________________

A special case may exist if input s are say [+50 V | float]  rather
than +50/ground. In such a case if inputs are taken to emitters of NPN
optos and collectors all joined, then a sense resistor from the
combined collectors to a voltage > 50V (say 60V) will cause all
combined collectors to be at 60 V (transistor off OR inout float) and
50V (transistor on and input = +50V.

Whether it is acceptable for a floating input to have 60V applied in
this was is moot in the absence of a proper problem definition.



   Russell
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