Hello all,
I noticed that people are using much more turns than me in the output
transformer, so I would appreciate any help in calculating the correct
number of turns for the cores I am using here. Messing around the trafo
would probably allow me to achieve more power than now (450W). Trying to
go higher causes heavy ringing + FET heating. I've tried almost
everything to reduce this (different combinations of Zobel network,
decoupling, inductances in series with gates, screening, grounding
etc.). In every case around 400W things start to go bad, 450W is a
border of manageable heat and ringing. I am thinking about making a new
FET driver in a way that allows regulation of the time of the FET
on-state, leaving some rest period in-between.
Here are some details about my configuration: the power supply is 45V,
dropping to 38-39V at around 12A (depending on the 230V mains voltage).
I am using two R40/24/16 rings made of K2006 material, stuck together,
for detailed info see
http://www.kaschke.de/english/framesets/frame_ringkerne.html . After
experimenting with different configurations, currently there's 2+2 turns
in the primary winding, 5 or 6 turns in the secondary winding. I
remember that 4+4 primary didn't work good, but this was just a short
try with low power - maybe there's a way to make this work with that as
well. Cores are slightly warm but never get hot. The power supply is
driven through a coil made of a single core (the same type), consisting
of 5 turns. This one gets hot only when there's too much ringing in the
PA. Adjusting turns in this one does not change a lot.
Thanks in advance for any help, I hope to make the TX again from scratch
this summer: bigger, better & more powerful ;)
73! Marek SQ5BPM
P.S. Don't be surprised seeing another special callsign on LF, these
days we are celebrating 25-th anniversary of the SP5ZCC Scouts Amateur
Radio Club. I am planning some LF operation with this call on April
9-10th. For the time being, I hope to see some of you in the SP DX
Contest CW/SSB on April 2nd-3rd (HF). Check
http://www.contest.spdxc.org.pl/en/index.php for more information.
|
