Type 3 compensation in SMPS with opto

[eem2am]

type 3 compensation

hello

does anybody know how i can model a 4N35 opto coupler for use in an offline SMPS feedback control circuit ?

it is a one transistor forward converter and i need to use Type 3 compensation.

4N35 datasheet:-
http://www.datasheetcatalog.org/datasheet2/1/03tgz200g5x4946jka7isojyj5wy.pdf

Page 2 (top) of this shows type 3 compensation but without an opto-coupler, i am wondering how too do this but with an opto.

http://www.exar.com/Files/Documents/sipex/ApplicationNotes/ANP-18_SelectTypeIIorTypeIII_120506.pdf

 

[max0412]

compensation of tl431

Basso's book has an example of type3 comp tl431-opto if I remember correctly.

The authors page.

https://pagesperso-orange.fr/cbasso/Spice.htm

It used to be posted here in the forum but no more ,if you know how to search google you should be able to find a copy on one of the file hosting sites without to much difficulty.You want the second edition.

Or just buy it you seem to be interested in SMPS. So it might be a worthwhile investment.

 

[eem2am]

tl431 model compensation page

max0412

Thankyou very very much for that.......i looked in the online chapter review and it does indeed have type 3 and TL431, so i have ordered this book.

more than 50 pounds UK so it was expensive but the chapters do look excellent, and its the only thing ive ever seen with TL431 and type 3,

so thankyou for your help,

all the best.

 

[eem2am]

type 3 compensator with optocoupler

hi

i now have the book by Basso, its excellent, but its going to take a few reads to get into it here, and i've read the chapter twice so far.

does any reader know of any other article on type 3 compensation with TL431 and opto?

I am unclear as to how the use of a fixed voltage providing the LED current affects it. Also, on the interplay between R(LED) and R(pull-up). Also, on what happens if R(led) and R(upper) connect to the same node, as well as how to find the opto-coupler pole, and whether or not the bode plot looks just the same as a normal type 3..(i.e. one without the TL431)

Type 3 compensation is easy with non-isolation, but when TL431/OPTO isolation is used, a whole can of wrigglers opens up.