Hi Alan,
On the cores:
> Yes but Farnell (the only suppliers I've found for these) only stock
> little dinky ones in 3F3.
That'd be the EFD (extra flat design) cores yes? Ungapped, they
have quite a high initial permeability so you don't need a huge
number of turns to generate switchmode type inductances. I wound
a pushpull transformer on one of those which consisted of a 3+3 turn
bifilar strap primary (one strap on top of the other with insulation
between the straps and co-wound) and about 120 turns of Litz
for the secondary. I think that was using a EFD25 core from memory.
> By the way Malcolm that was an excellent article in Wireless World -
> you really crammed a lot in.
Thank you. I'd actually written it in two parts as I couldn't see how
to make it one and keep within the magazine's criteria. They did a
nice job of reducing it down. For the benefit of anyone reading it,
I'll give a short list of errata (it was written before I'd joined
any lists) :
(1) The equations I gave for terminal capacitances are incorrect (as
I've learned from Bert, Ed Harris and others).
(2) The output voltage equation was a synthesis I attempted and
should have left out (invalid for limited energy Cap discharge)
(3) I forgot to mention grounding the secondary for the coupling check
(4) Some of the construction techniques I included are rather
primitive compared to the excellent information posted by Richard
Quick and there are obvious defficiencies in the simple gap design
I wasn't aware of at the time of writing.
I think otherwise it's stood the test of time reasonably well.
Regards all,
Malcolm