Original question:
UCC28700: Loss calculation of the MOSFET during valley switching
Tool/software:
Hello Mike,
In that case why the MOSFET turn-off current was taken as I_pri_peak?
As per my understanding I_pri_peak is the peak primary current at V_bulk_min.
According to you it should be the current at V_bulk_max right? Since the Vds voltage is taken as V_bulk_max + V_flyback.
Hello Ning,
I was referring to the document https://www.ti.com/seclit/ml/slup302/slup302.pdf (Exposing the Inner Behavior of a
Quasi-Resonant Flyback Converter).
where the switching loss is given by
The question is:
Here it is mentioned the Coss loss and the overlap loss during turn-off, and the MOSFET current mentioned is Primary peak current at Vmin(Minimum input voltage),
whereas the MOSFET voltage mentioned is V_bulkmax + V_flyback.
Why are we considering the current for V_bulkmin and Vds for V_bulkmax?
Hello Ning...Thanks for your response.
Referring to the above image,
The frequency modulation occurs in region 4, where the primary peak current remains the same.
But here we have considered the max switching frequency in the loss calculation which can happen at minimum input voltage and maximum load.
