AN-57

Posted by: mdeluca on 02/19/2013

I am having trouble w. equation 23 which supposedly defines the TL431 transfer function in AN-57; it seems to be missing something.

Comments

Hi.

You are absolutely right. RF3 should be taken into account, and the gain of the opto should be there as well. So where we read K_TL431, we should read K_TL431*K_Opto*(1/RF3). The rest of the equation remains the same.

We are finalizing a reviewed version of AN57.

Thanks for pointing this out

Yes I understand that, but are you sure the s-terms are correct?

(1 + s/(RC)) / (1 + s/ (KRC)) doesn't look right either.

While you are reviewing AN-57 pls also check "Step 8 - selection of CF1".

It states "fzero be set at 50Hz rather than 100Hz" and I believe you mean this for continuous mode (not discontinuous which is stated).

Its correct... It is a mechanism of taking the finite open loop gain of the error amplifier into account. This looks like a pole at a frequency close to 0Hz.