From: "Jan Wagner"
Subject: gapped core design
Date: Wed, 1 Jan 2003 22:30:31 +0200
Organization: Helsinki Television
NNTP-Posting-Date: 1 Jan 2003 20:28:55 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2720.3000
about to make a gapped ferrite core transformer for a 4 kW resonant
converter for welding, but I'm worried about xfmr saturation (despite the
It's a LLC style resonant converter, and it resonates with the leakage
inductance (80..120 kHz). For this welding inverter, I'd need a magnetizing
inductance of 10uH and leakage inductance of 8uH. The E core is 3C85
material and 65mm x 65mm x 27mm, ~4cm^2 center pole cross section, so it is
quite large and "probably ok" for 4 kW even without a gap.
1) Trial-and-error designing probably goes this way: remove the ferrite E
core halves, wind the primary on the bobbin until it reaches 8uH, then
insert the E core halves slowly until you measure a total inductance of
(8+10)uH. Is that the correct approach??
2) Having 8uH leakage inductance shouldn't mean that the primary and
secondaries could not be well/tightly coupled... right?
3) The main question though is if the gapped E core can still saturate? I.e.
because the number of pri turns is of course much less than the minimum # of
turns of the same core non-gapped, and the voltage seen by the pri can be
400Vac 120kHz. The air gap won't saturate, but the ferrite would easily go
over B_sat (+-420mT for 3C85) and saturate. Or that a real problem at all?
Comments would be very much welcome!