40W power design review

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Hello Sir,


based on RDR-257, I'm designing a Bulk topology 40W power supply.  The pixls file is attached.


I would kindly request you to review it.   Your thoughts are welcome.



1- For the inductor L3 (as in schematic at page 8), I'm considering to use 2 inductors in parallel  to meet 500uH and Irms;Ip rated currents with KP=0.73, instead of building a transformer with RM8 core as in the design sheet :

( 1.0mH; IR=0.56; ISAT=1.1A; DCR=1.37Ohms,CODE 7445830, WURTH WE-PD4 TYPE X)

datasheet: http://katalog.we-online.de/pbs/datasheet/7445830.pdf


(1.0mH; IR=0.75 ;ISAT=1.0A; DCR=0.82OHMS; COILCRAFT MSS1210-105KE) 

datasheet : http://www.coilcraft.com/mss1210.cfm

 Is this approach a good option ? I'm willing to use inductor ready from manufacturers as those stated above.


2- How can I simulate the harmonics for this design using PI's spreadsheets ? is it possible ?


Thanks for your attention.

Best regards,



I dont see any obvious problem on the design. Just make sure the operating IFB will be below IFBSKIP on the entire line range.


Regarding the inductor, using off the shelf usually will give you a lower efficiency if the off the shelf has more ac and dc resistance compared to the design using RM core. If you parallel inductors, you need to ensure that they share the same current to avoid saturation.


Unfortunately on the buck spreadsheet for LinkSwitch-PH, the harmonic simulation is not included yet. We'll try to incorporate this on next revisions.