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Re: Solid-state tesla circuit

Greeting all,

>> uc3825 driving a pair of 4422 buffers to 3 * irf740 on each side.
>> Current limiting monitored across a 0.05 ohm resistor -
>> this creates weird feedbacks - I work around it but its something I must
>> sort out in the Mark 2.

>Define wierd. Perhaps transformer is getting into some nasty resonances
>becouse of parasitics? I have had a lot problems with that! Especially
>at high turns ratio (say 15:1 :) when trying to also keep the power
>factor good.

I'm using a pot to apply a varying voltage to the 3825, controling the
pulse width - what I find is that instead of getting a nice increase in
output power I get two distinct peaks one at about 1/2 way and the other
at about 80%. Needs a bit of twiddling. This happens regardless of which
output transformer I'm using.

In the Mark 2, I was going to use a resistor on the high side for current
sensing, with a 1:1 transformer and a bridge rectifier (as in Rob's circuit)
to monitor the current and use current feedback. Or I may use an opto-coupler.

Or I may dispense with the 3825 and use a handful of logic to give a square wave
and an over current limitter.

>Perhaps transformer is getting into some nasty resonances
>because of parasitics? I have had a lot problems with that!

My main problem with the transformers was internal arcing and saturation.
Bathroom sealent (clear silicone) between windings (as well as tape) has solved
the arcing, careful calculation and more primary turns has solved the
saturation.
The next output transformer will use 3 of the present E cores side by side. And
it will
be right next to the driver board, reducing wiring length.

I did consider getting a bunch of ferrite radio rods - say 7 in a hexagon, or
more -
make up a 2" diameter core and winding on that:

For very cheap - hard to saturate - lots of inductance per turn - should be
OK at the higher frequency (made for the medium wave) - Coils on the outside of 
the core for easy cooling - infinite winding window - easy winding

Against - power losses (must be better than an air core say 70% efficent) -
rf transmission - screened box.

Is this worth trying?

I gather from your comments Hari that I can anticipate more problems 
at higher powers :(

>HI
>Coyld you please tell me where the ftp site is ,or could you email the
>circuits etc
>thanking you in advance 
>Wayne Pettett NZ

>[ There is a/the tesla coil ftp site at ftp.funet.fi in
>/pub/sci/electrical/tesla (Maintained by Kristian Ukkonen) -- Chip]

yes thats the one its in the miscellaneos folder Driver.gif, + driver.doc

Alan Sharp (UK)