Turns ratio for LLC resonant converter?

[grizedale]

Hello,

In the following article , do you agree that the "n" value in Equation 6 , page 2 SHOULD BE "NS/NP"?


https://www.fairchildsemi.com/an/AN/AN-4151.pdf


In figure 6, it says "n = NP/NS".......but this is surely wrong?


"n" is in the numerator of equation 6, page 2, and so it ABSOLUTELY MUST be "NS/NP"....do you agree?


...otherwise , gain increases with increasing primary:secondary turns ratio...which would be nonsense?


.....

 

[FvM]

Gain is not the primary to secondary voltage ratio of the transformer, it's the peak voltage ratio. As far as I see, all formulas in the AN are consistently using n:1 = np:ns

 

[grizedale]

i see, the thing is, i am abiding by the equations of this app note (for NON-integrated transformer) and the results are not coming out right.

When at maximum load of 80V & 4A , The Gain vs frequency curve re-shapes such that the "f0" resonant frequency corresponds to the peak of the curve........this is bad news as it means with a little bit of tolerance in the frequency , then it will be operating in the capacitive region, to the left-hand-side of the curve peak.

So something is wrong here, do you know what?