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Re: Arnold Toroidal Ferrite?? Cores

Hello Scott,

eh>> I think the real question is:
eh>> How much of the oscillation voltage at 100kHz (or
eh>> whatever) appears across the chokes and how much
eh>> appears across the the supply transformer.

sm>What about the bypass caps?

You're right. I was just trying not to complicate the
issue yet. 


sm>I do have figures on a 12 KV potential 
sm>transformer.  It was about a
sm>4 KVA unit, if memory serves.  It has an inductance 
sm>value of 59 H. With 59 H -at- 100 KHz, we get a 
sm>reactance of 37 MegaOhms.

One small point. I think the 59 H figure is a "quasi"-DC
inductance. Since there is a lot of interturn capacitance,
the effective inductance will be much lower at 100kHz. How
much smaller - I have no idea - since it depends on the
exact way the transformer was manufactured. Anyway, from
an experimental perspective, one could just send a small (1v)
signal into the secondary of the transformer with/without a 
shorted primary. measuring the current and voltage of the
drive signal would allow  one to compute a rough value for
the HF impedance. [Perhaps I'll give it a quick try on a 
60ma 15kV neon I've got on hand]

sm>This is where I don't see the logic of even considering 
sm>the transformer impedance into the picture.  After all, 
sm>there is a capacitor(s) directly after the choke that 
sm>has only several hundred ohms impedance that goes directly 
sm>to a RF ground. 

Right, as before. The caps should be conducting most of the 
RF as long as people are using them. However, as above, I 
doubt that the Rf impedance of the transformer is really
37 Meg. If the internal capacitance of the transformer is
near the value of your shunt capacitors value, the transformer
still MIGHT be absorbing a lot of RF.... only testing
will tell.

sm>are practically a dead short at these RF frequencies, when 
sm>compared to the transformer.  The reactance of a 1 nF cap 
sm>-at- 100 KHz is 1592 Ohms.  The reactance of a 1 nF cap 
sm>-at- 200 Khz is 796 Ohms.  These figures should be much lower
sm> than the reactance of any HV transformer at these frequencies.
Sm>  Please correct me if I am wrong on this point.

Nope, I think you're absolutely right. I'm just suggesting
that we(I) don't know for sure that the 100kHz impedance of
the transformer is much greater than 1500ohms.

sm>I have heard talk of considering the transformer's impedance 
sm>before.  The bypass caps are basically in parallel with each 
sm>leg of the transformer.  Since the bypass cap is there, doesn't 
sm>the impedancevalue at that point fall below that of the cap?  
sm>It seems like a reactances in parallel problem.

Exactly.

-Ed Harris