Flyback core gap is too big?

[Orson Cart]

Either voltage controlled PWM (normal) or peak current mode (better response to input variations), contrary to your comments, we have found in our high power flybacks, DCM or boundary mode is far better than CCM as you have much reduced FET switching losses and easier EMC compliance. I would be interested to hear from anyone else who, like us, has built flybacks in the 300-1kW region, Regards, Orson Cart.

 

[mtwieg]

Either voltage controlled PWM (normal) or peak current mode (better response to input variations), contrary to your comments

That's not contrary at all. The modulation scheme (constant frequency, constant off time, etc) is completely independent of the control scheme (current mode, voltage mode, etc). Here's a tech paper from Venable on CMC, with a section near the end about the benefits of fixed off time modulation:
https://www.venable.biz/tp-05.pdf
Every single tech paper from venable is fantastic, by the way.

 

[Orson Cart]

I see the point you are trying to make, however, most engineers would agree that the modulation scheme is the control scheme (or at least a major part of it), constant off time is fine if the EMC compliance will allow variable freq and low freqs at full power, by far the best in practice is peak current mode operating in boundary mode (always just DCM) and hence variable freq (but with lowest RFI), I note the paper you mention, the best effect of constant off time is to shift the right hand plane zero out in freq - which is always useful, Regards, Orson Cart.