Re: Optocoupler datasheets

On 5/29/2024 8:53 AM, bitrex wrote:

Situations where they're just left on for DC most of the time and trying to get minimal forward current by optimizing a resistor value seem hopeless.

Exactly.  You can "play games" with how hard you "overdrive" the emitter as
well as add current gain on the isolated side to store enough charge to carry
over long enough for the longest off period (duty cycle and frequency related)
that you want to tolerate.
We use this technique for driving outputs that need to be self-reseting
in the event that the processor "dies" (you have to make sure you design
your code so the processor can't crash in a loop that keeps pulsing the
output(s) -- I've seen more than one fool make that mistake!)

Could wrap a DC feedback loop around it which would only make sense in the situations where you have a lot more power available on the secondary side for some reason, hard to think of a use case.

<frown>  Unless you're looking for a linear transfer function, feedback
(except as a diagnostic) is usually not appropriate.

Logic-output couplers seem somewhat better specified in the sense they explicit state the relatively high minimum forward currents or all bets are off.