Original question:
Using UCC28951 Excel calculation sheet, I arrived at an Lmag value of 7mH.
I Went ahead with Planar transformer Vendor for the design of Transformer. He has manufactured a transformer with lesser Winding inductance of around 1mH.
FYI, i did read through Peak current mode control sub harmonic oscillations, etc. Its a lot to grasp.
What is the criticality in choosing Lesser winding inductance. please explain in detail On your analysis.
Hello,
The excel design tool was based on application note slua560. The link to the application note is below.
https://www.ti.com/lit/pdf/slua560
So if chose a magnetizing inductance that is 1/7th of what what was recommended. The magnetizing current will 3.5 times greater than the reflected output inductor ripple current.
The output inductor ripple current based on the application note was 20% of the load.
So the magnetizing current + reflected inductor ripple current with be equal to the reflected DC output current. This is 4 times larger than what is recommended and the design will most likely operate in voltage control instead of peak current mode control at loads of 50% or less. This could lead to loop compensation issues and instability.
Also if the design operates in voltage mode control to avoid transformer saturation you will need a DC blocking capacitor.
Regards,
