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Electronics => Projects, Designs, and Technical Stuff => Topic started by: ocset on November 17, 2017, 02:00:42 pm

Title: PFC inductor as several offtheshelf series inductors
Post by: ocset on November 17, 2017, 02:00:42 pm

Hello,
Do you now why people don’t just use a series chain  of offtheshelf inductors  as a power inductor when they design low power (<150W) critical mode boost PFC  stage?
Why do people always  do  a single custom-wound inductor? (its more expensive)
 8)

Title: Re: PFC inductor as several offtheshelf series inductors
Post by: dmills on November 17, 2017, 02:21:07 pm

In reasonable volumes, it really is not usually any more expensive by the time you pay for assembly.

PFC inductors are usually a gapped core operating at very high flux, not that common to find an off the shelf part that has low core losses when operated in this mode. Also compare copper losses for your series chain with the copper losses for a single inductor of equivalent volume, I think you will find the single part to have a useful efficiency advantage.

I have had custom magnetic components done in the hundred units range for not outrageous money, by the time you are ordering 10k units at a time it is very, very affordable, any you get exactly what you design.

Regards, Dan.

Title: Re: PFC inductor as several offtheshelf series inductors
Post by: Kleinstein on November 17, 2017, 04:21:07 pm

With magnetic parts like transformers and inductors the quality usually get better when they are larger. If you look at transformers, the usual 1 VA type is well below 50% efficiency, while a 100 kVA unit is more like 98 %.

As a crude approximation the weight of a transformer and likely also Inductor goes up like the power rating to a power of about 0.6 to 0.8. So it is also more economic to use one large part than 2 smaller ones.

Title: Re: PFC inductor as several offtheshelf series inductors
Post by: ocset on November 18, 2017, 01:01:31 am

Thanks, we have a 10mm height restriction, and the PCB is 150mm * 66.5mm only. As such, since the off the shelf formers are too high, we have to use offtheshelf indductors instead...and they must only be SMD.
We are thinkin gof the wurth 7447709221

http://www.farnell.com/datasheets/1920198.pdf?_ga=2.213410839.2064163281.1510966879-287702491.1506211291 (http://www.farnell.com/datasheets/1920198.pdf?_ga=2.213410839.2064163281.1510966879-287702491.1506211291)

Do you think we need to have RC dampers across each inductor in order to damp ringing, since the middle of the three inductors is "seeing" high Z in either direction?