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From: Mike Poulton
Subject: Re: Problems with MOSFET drivers
Date: 17 Nov 2002 23:55:52 GMT
Organization: MTP Technologies
On 17 Nov 2002, analog said:
> Closed loop frequency control would be nice, wouldn't it? To that end
> it is necessary to know the phase relationship between the feedback
> signal and the waveform on the driven primary winding. I would
> imagine that this would depend somewhat upon its physical location
> within the tesla coil's field. If it located where it is
> predominately sensing the field emanating from the resonant solenoid
> of the tesla coil and not the non-linked field from the primary
> winding, I would expect that it's phase would lag the primary voltage
> by 90 degrees right at resonance (it should be in phase well below
> resonance and lag by 180 degrees well above resonance).
Unfortunately, the feedback winding seems to be better coupled to the
primary than the secondary. This is unavoidable, I think. The bottom
of the secondary is the only suitable location for either winding when
it is running in 1/4 wave resonance. Each winding is only marginally
coupled to the secondary (K~0.25). However, they are well coupled to
one another since they are very close together. Some other type of
feedback may be more appropriate. I know others have successfully used
a wire near the output terminal to pick up the electrostatic field, but
that seems a bit unscientific. I wonder about a resistor in the
secondary's ground connection to sense current flow in the LC circuit.
I'm still leaning towards a VCO that is adjusted to maximize primary
current draw, though.
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