SMPS opto/TL431 transfer function

[eem2am]

tl431 smps

Hello,

Basso’s book, page 290 gives the transfer function of the TL431/OPTO feedback network in a flyback converter as per the transfer function in the below diagram.

*****Diagram and transfer function of OPTO / TL431 Feedback network.

My question is, supposing that I don’t use the CLC filter on the flyback output as shown above. That is, supposing I omit the output inductor between the C1 and C2……….

….Then does this above given transfer function still hold?



*****UC3845 Datasheet
https://focus.ti.com/lit/ds/symlink/uc3842.pdf

 

[FvM]

smps tl431

If I give the same answer as in reply to your previous copy of this question , and you still don't like it but get no others answers unfortunately, will you re-schedule it a third time next week?

 

[eem2am]

tl431 opto

Sorry....and thanks for the reply.

Before i posted this, i searched this forum with "eem2am" but i did not get this post in the list, in spite of looking for it.....so i am wondering what i did wrong.

 

[wei9321]

smps opto

i have a problem
why the G(s) is negative?

 

[FvM]

uc3842+tl431 smps

why the G(s) is negative

It's a property of the shown circuit. Increasing Vout results in decreasing VFB (within it's linear operation range). Without considering the UC3845 transfer function, the sign of G(s) has no particular meaning. But it should result in an overall negative feedback to make the circuit act as a voltage regulator, and fortunately, it does.

@ eem2am: No problem. Just a confusing déjà vu.