[TCML] my first sstc......and i actually worked!

[Frosty <frosty90@xxxxxxxxx>]

Hi all,

After much procrastination, I finally got around to building my first SSTC,
and amazingly it worked first time, giving 1.5cm corona, and about 2cm
ground arcs. But as you can imagine I have many questions, so please excuse
this long post;

Ok so the specs are:

H-bridge of irf740 with 1.1uf on each opposite 'leg' (ive only gone up to
30v power so far,  to avoid 'fireworks')
my recycled 4" secondary
so far a 7 turn primary
MOSFETS are driven from a 16 turn gate drive transformer via 5ohm ceramic
resistors
The driver circuit is based on 'Steve's' (my apologies if you are reading, i
dont know your full name) 'mini sstc' but with  a couple of changes, mainly
i used the tc4420 fet drivers.

ok so  now for the questions;

while running it from 30v, after about a 4 minute run the MOSFETS are fairly
warm, my next step is to hook it up to the variac and see what happens at
100v. so my actuall question is: i this amount of heating to be expected
after a couple of minutes at 30v, (my heatsinks are fairly small), also one
of the gate driver chips became very hot, the other one only slightly, so
what can i do to try and reduce heating in the FETS and the drivers?

Also at the moment the base of the secondary is grounded to the -ve supply
rail (for the halfbridge), is this likely to be a problem? leaving it
un-grounded resulted in the coil not working at all, so im a bit worried
about what might be happening there.

The gate drivers are connected to the gate drive  transformer via a series
2.2uf cap. Should this actually be larger of smaller? The problem is i dont
have a 'scope so i cant actually see whats going on there. Also when the
driver circuit is running, there is a buzzing sound from around the region
of the gate drive transformer/driver chips. i suspect that there might be
some high voltage kickback from the primary of the GDT. I think this may
also be bad for the driver chips. Would a suitable solution be to add some
fast zenner diodes back to back across the
primary of the GDT?

Finally: I have some fast recovery diodes antiparrallel with the MOSFETS,
but i dont think they are fast enough. the data sheet says 400ns maximum.
what would be some better diodes?

Thanks for any help,

cheers

Jesse Frost
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