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Hello,
We bought the TI-PMLK BUCK EVM (https://university.ti.com/en/faculty/teaching-materials-and-classroom-resources/ti-based-teaching-kits-for-analog-and-power-design/power-management-lab-kit-series).
I was doing the experiment 1 of the book in order to show this example in our lab class students (www.ti.com/.../ssqu007b.pdf).
However, I have problems when I try to calculate the the theoretical losses of the power converter. I followed the recommended the "Loss Formulae" of the page 27 and some wrong appears in the inductor core losses:
D=Vout/Vin --> D=6/3.3=0.55
Ipp_ripple=Vout*D'/(fs*L) -->Ipp_ripple=3.3*0.45/(2,50kHz*18uH)=0,33A
P_lc=K1*fs^x(K2*Ipp_ripple)^y where experiments 1 says K1=0.261 K2=0.92 x=1.21 and y=2.01.
The result is P_lc=80830W
I suppose that some value of the inductor characteristics are wrong and I tried find them in internet. The manufacturer doesn't specify this values.
I searched information about similar parameters for other inductors and I can see that the values normally are so different and have wide variability.
Someone can I help my, please? I would like to have the right values or understand how calculate correctly.
These is an really interesting book and board to share with my students and learn about this!
Thanks in advance
Robert
Robert,
Interesting coincidence to see your post as we have just procured that EVM for introductory training. I agree there is something wrong with that equation. I am not sure exactly how that was derived, but it is obvious that the term fs (=250000) is the source of the error. I used Coilcraft online estimator. the total losses at 1 A output, ILp-p = .33 and Fsw = 250 kHz are 84 mW:
Let me see if I can track down the correct equation. It may take a day or two.
