Why such tight linearity?

Charging a battery. For example, this TI charger chip has 0.5% voltage precision.

Charge accuracy: ±0.5% charge voltage regulation
https://www.ti.com/lit/ds/symlink/bq25300.pdf

This balancer claims 1 mV precision, which, if true, is 0.025% (if my math is correct).
https://www.amazon.com/Equalizer-Precision-Lifepo4-Capacitor-Balancer/dp/B0BNDXLBCN

Power supplies I build with opto isolators do not require linearity. When the supply is in regulation the isolator current is at a constant current. Changing load does not change current in the isolator. With reason, the CTR does not effect the current in the output of the isolator.

At the moment, i happen to be looking for a very simple, low-cost current-mode converter, but separate question.

look for CTR that is high enough that it can do the job

"High" enough. I have to contemplate that means. I'm guessing in a voltage-mode SMPS, you want a 1:1 relationship, no?

normal way is to pass value in digital form (on/off) rather than analog. and that is exactly what takes place in SMPS.

I happen to be looking for an SMPS with on/off feedback, tho' if i'm comprehending correctly, others here seem to disagree with you about TL431 feedback:

No, the output from the TL431 to the opto is a DC current as determined by the output voltage, and the output of opto is the DC feedback voltage to the converter chip..

Go back and read #3. It answered this question very clearly.

I was responding to #9, which replied "no" to a multiple-choice question.

it does not mean less drift or more linearity.

got it -- it means tolerances -- without binning for best parts, opto's off the production line can vary from 100% to 200%.

the TS suffers from selective comprehension

I was responding to #9, which replied "no" to a multiple-choice question. You might have missed that if you comprehend selectively. We all do that from time to time

 

There may be a lack of communication here. In opto-isolators it seems to me that "linear" means "Not Digital", and probably "ANALOG" would be a better term. And in real world devices things do change with temperature and so a valid specification also states the temperature range for the numbers to be true.

 

multiple-choice question. You might have missed that if you comprehend selectively. We all do that from time to time

The question you asked was fully and clearly answered in post #3.

 

The question you asked was fully and clearly answered in post #3.

Happens all the time. People ask for my advice, then ignore it and go do precisely what they want to do.

 

Happens all the time. People ask for my advice, then ignore it and go do precisely what they want to do.

I hear you.

 

Happens all the time. People ask for my advice, then ignore it and go do precisely what they want to do.

i was responding to a someone else's answer. Try not to take it personally.

I guess you're saying "When Papabravo speaks, ignore all others. They are wrong."