Topswitch Flyback...spiral the last turn back across the bobbin?.....why not done as standard?
Hi,
A contractor has given us a transformer manufacture spec for a 70W Offline Topswitch Flyback.
For the secondary, he has 11 turns of 3 strands of TEX-FS 0.7mm triple insulated wire.
This 11 turn secondary has a total width of 29.7mm, when the bobbin width is only 27.7mm.
Would you presume that this means he has wound ten turns and then the eleventh turn is spiral wound evenly back round and across the bobbin to be terminated?
This method of spiralling the final turn back and then terminating it, sounds like a great idea....why is it not done as a standard technique? After all, with offline SMPS transformers, one usually terminates all primary side windings to the same side of the bobbin (for isolation reasons)...which means having to bring the coil_end back across the bobbin.....if you've gotta do that, then why not spiral the final turn back as described. Why is this technique not standard?
(The bobbin is a 12 pin E42/21/15)
E42/21/15 former
https://en.aet.com.pl/Portals/en/Katalogi_pdf/Kat_rdz_i_korp/Kat_korp/korp_e/korpus%20EE42_15%20POZ%201SEK%2012PIN%20HY4214.pdf?ver=2015-06-11-…
Tex FS 0.7mm triple insulated wire:
http://www.pacecomponents.co.uk/pace-components/triple-insulated-wire/tex-fs-wire/tex-fs-0-7mm-furukawa-triple-insulated-wire
评论
Thanks, but dont you think that doing all turns on the same layer, and that trying to put a right angle bend in the three_strands_of_0.7mm_TIW may be difficult to do physically?.....and spiral winding it back may be easier?
Regarding coupling...surely if its only the last turn of an 11 turn winding thats spiralled back, then coupling variation will be insignificant?
Hi, treez
Your question was 'Why is this technique not standard?'
Standard means has to to work with 11 turns and with 3 turns, for example.
My answer is pointing the issues preventing this particular technique to become 'standard'
Strictly speaking, there is hardly any universal solutions in transformers. Most of the approaches are tradeoffs and a fine balance between wanted and un-wanted effects in the limited space of the restrictions.
Best regards,
Hi treez,
There two points where the described technique about the last transformer turn could be problematic.
First, it will close to double the layer height (for the layer in question) all around the circular perimeter of the transformer.
Most transformers are designed to be 'copper full' and simply does not have the stack height for sticking another nearly complete layer of the winding.
Second, the coupling of such transformer will be worse than the one wound with all turns in place.
Best regards,