While designing converter I got to the point of calculating secondary coil. Most guides have these equations for it:
Wait a second, didn't I calculate Nps already at the very beginning? Yes, I did! And I've used it extensively throughout the process.
Nevertheless, I use these formulas and get a different Nps. I thought I am going crazy, until I noticed tiny detail: I did not use (1-Dmax) in the beginning. Instead, I used (0.8-Dmax) to leave 20% dead time before CCM boundary.
Question: Is the above equation for reflected voltage applicable in DCM? Or should I just use the Nps that I already have?
This tiny change unfortunately resolves into 30% in coil turns, the difference that does not fit on the core.
In the equations and text:
Vr - voltage reflected to primary when the switch is off
Vin(min) - minimum input voltage
Vo - output voltage
Vf - forward voltage drop on rectifier
Dmax - maximum duty cycle
Nps - primary-to-secondary turns ratio