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Old 17th June 2015, 10:01 AM   #1
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Location: Amsterdam, Netherlands
Default Coil for Active PFC stage

I'd like an active PFC stage for a SMPS half bridge but most designs are either low power or have parts I cannot find. It seems the coil is the limiting factor so I would like to wind one myself. I've done coil winding before in a low power application with a custom produced core and that was off by orders of magnitude. So I'm curious if there's any rule of thumb calculation to get the right inductance with a specific commercially available core or maybe a software tool like the ExcellentIT tool for transformers that will spare me that process of numerous winding iterations.

I'm considering this schematic as a reference design for the PFC stage.
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Old 28th July 2015, 02:12 AM   #2
FQR is offline FQR  Germany
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Join Date: Nov 2012
Location: Bad Birnbach, Bavaria
Default Some questions...

Hey man!

You had a "custom produced core" - but you wound it by yourself... hmmm. Is it my weak english? Please tell a little more about, right now i canīt understand...

The right way to build a switcher is to begin somewhere, right? Youīll have to know, what you... : 1. ...want (at least to some extent). 2. ...have to know about. 3. ...have to do for it. Are these 3 compadres complete?

Most Important: For a topology, power and frequency one could choose the right core size, shape and material. Thatīs not too hard, i could help you there. But one extremely important point, if you went so far, is, that all cores have a so-called "AL-Value", measured in "NanoHenries per squared winding count". And this value leads to a fitting winding count for the converter.

Ok, until a few years there were (on the whole) 2 main choices (and for the first PFC stage one wishes to build i think itīs still the best way to do...): Lo Power with "Transition Mode" topology (what your schematic is like, itīs also called boundary conduction mode, or constant-on-time, or...), and Hi(er) Power with "Continuous Conduction Mode".

CCM has fixed freq. operation, TM has not, but with TM the coil/inductance can be smaller, cause the current is allowed to go to zero each switching cycle. This is also the reason that for TM one can use slower diodes with higher reverse recovery time - for CCM youīd need faster ones, or, much better, SiliconCarbide- ("SiC"-) diodes instead of the cheaper silicon ones. With TM the diode can recover "naturally" while the current goes to zero, and the switch can turn on at least under zero current condition also, really fine against losses... but at the price of higher current ripple (and lower power factor) than at CCM. The bigger inductance at CCM carries a more constant current than at TM.

If you know, what topology and controller IC you want to choose (what is also related to the required power - i could help you with the decision, if you tell me), then you`d find all necessary formulae, for the switch, the diode, and the coil, at the IC-related Application Notes.

Maybe somewhere thereīs software for calculation of TM PFC, i donīt know. But for CCM thereīs at least one website, that you could visit: Schmidt-Walter SMPS dimensioning. The design there is conservative, and the choice of topologies not complete (like said, no TM PFC, and no resonant converters, no 3-Level-architecture etc.). Itīs a german site, but wit option to change language to english.

Right now i donīt wanna speak bout interleaving etc. If you want more (real) help, from me or others, then please write some facts, what exactly youīd need, ok? Because thereīs so much important information bout this theme, but nearly all different, relating at the exact demands and topology.

Good luck...


Greets, Fred

Last edited by FQR; 28th July 2015 at 02:36 AM.
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Old 30th July 2015, 12:19 AM   #3
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Join Date: Jun 2009
PIXIs Designer includes a detailed set of PFC inductor calculations as part of the Hiper PFS and PFS-II designer which would likely suit your purposes.
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