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high voltage analog optocoupler
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hussamaldean:
I am just looking for linear optocoupler for feedback purpose
what type shall I use ?
TL431 is enough ?
Doctorandus_P:

--- Quote from: hussamaldean on January 25, 2019, 12:38:59 pm ---... which shall boost the input voltage from 12V to about 200V.

--- End quote ---

How accurate woul you want thet "about 200V" to be?

TL431 has a pretty sharp "Knee" between of and on and with that it delivers a very small window in which there is some analog amplification.
TL431 is also the defacto standard for these kind of applications, and very many are being used in PC power supplies and most wallwarts of better quality than the lowliest crap.

Do you have some wallwarts lying around?
If you crack them open you are likely to find most of the components you need.
You can exchange the primary and secondary of the transformer.
Adjes the circuit around the TL431 to limit at a higher voltage.
But directly powering the optocoupler LED from 200VDC is a problem.

A nice approach is to have an extra transformer winding with a 1:40 ratio to the 200V winding.
Then you have an auxillary 5V to power the opto coupler.

And Again:
Houw much current do you need @ 200V?
It has been asked before, but I missed the response.



T3sl4co1l:
Also, TLV431 may be better, because it needs less current.

Any phototransistor opto will do, 4N35, FOD817, etc.

Tim
TimNJ:

--- Quote from: hussamaldean on January 26, 2019, 03:25:00 am ---I am just looking for linear optocoupler for feedback purpose
what type shall I use ?
TL431 is enough ?

--- End quote ---

Just a reminder that the TL431 is not an opto-coupler. It is an error amplifier with an open-collector output. The TL431 is connected to an optocoupler to control/modulate the signal fed back to the primary-side.

When you hook up the open-collector output of a TL431 to the cathode of an opto-coupler's LED, the TL431 can adjust how much current it pulls through the LED by turning on or shutting off its output transistor.

Typical opto-coupler part number is LTV-817.
Zero999:
Another possibility is an isolation amplifier, such as the ACPL-7900-300E, to monitor the voltage using a potential divider, but it will be more expensive than the TL431 and an opto-isolator and will require a 5V  axillary power supply on the secondary side.
https://docs-emea.rs-online.com/webdocs/133c/0900766b8133c16e.pdf
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