TOPswitch-HX Flyback Feedback Loop?

[cupoftea]

Hi,
We have just done this 20W Offline Flyback. (90VAC input, 24vout and 0.8A out)
Transformer is np/ns = 84/19 and Lp = 1.07mH
Its in CCM at 90VAC.
TOPswitch-HX is voltage mode controller.
We used AN57 to give the Bode plots.
But they come out "nonsense" as the attached excel shows.
Do you think AN57 is incorrect?

We calculated Q as 1/R * SQRT(L/C)
where Cout = 1mF
L = sec coil L

AN57
Its in the top post here.,...

What is open loop gain of TL431

Hi, In the attached AN-57, do you know what is the "K(TL431)" value? (page 14).....the open loop gain of the TL431. We are trying to stabilise a 20W TOP256GN Flyback, and need to know the K(TL431) so we can calculate the feedback bodes. TL431...

www.edaboard.com

 

[Easy peasy]

step load testing is a great way to verify stability, and should always be done as it is a very large signal system test

whereas loop measurement is small signal.

 

[cupoftea]

Thanks, the situation is that this is a voltage mode Flyback in ccm too.
And as the following demo's, its not safe to just rely on step load testing...