I'm working on a PSFB converter design.
Calculate magnetic inductance for PSFB. Formula (30) have a (1-D) in UCC28950 datasheet. Formula (30) ： Lmag≥（Vin*(1-D)）/{(ΔI*0.5/a1)*2*Fsw}
I think that Out inductor current downslope happens during the Toff, when the transformer voltage is 0 volt. The formula should replace (1-D) with (D)?
I have seen the related answer https://e2e.ti.com/support/power-management/f/196/t/783125
I would like help.
Thanks
Dear user,
I am so pleased hear from you. It is a interest question. I understand you why think the 1-D should be replaced by D. because you think min Lmag should be defined by Peak primary magnetizing current (Imag) .
But in fact, in the equation 30 in UCC28950 datasheet, The key thing is we want the slope of the primary magnetizing current to be 50% of the downslope of the output inductor current. The output inductor current downslope dI_Lout/dt = (dI_Lout/(1-D))*2*fsw. The last thing we need to do is to take the 50% output inductor downslope and transfer it into the primary side by multiplying it by 0.5 *(1/a1 ). We can put this into eq A above to get eq30.
Thanks
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