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From: Mike Poulton
Subject: Re: Problems with MOSFET drivers
Date: 18 Nov 2002 22:06:50 GMT
Organization: MTP Technologies
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <3DD92019.EAE8BE@ieee.org>
On 18 Nov 2002, analog said:
> This is a very crude control scheme typical of a bit head who is only
> comfortable thinking in ones and zeros. The gain is non proportional,
> slew rate limited, and is zero within the dead zone. It relies on the
> physical inertia of disturbing objects moving about within the tesla
> coil's field to provide the dominant pole to stabilize the system.
> This may more or less work under most conditions - until a pesky arc
> is drawn that breaks into fluctuations at the cycle time of the
> micro's simplistic control loop. Then the control scheme might live
> up to its common name of "bang-bang" control in a most exciting way.
The only consequence of operating off-resonance is reduced power output.
The VCO will be limited in it's range so it can't get to dangerously
low or dangerously high frequencies. It does rely on objects moving
slowly, but that's pretty much guaranteed. Arcs to ground may cause it
to oscillate, but that isn't necessarily a terrible thing and it could
be avoided with good code.
> However, with the right precautions, such as digital or analog low-
> pass filtering of the current signal and some proportional feedback,
> it might just get the job done. Whatever works, eh?
Yep. Besides, it might be the first microprocessor-controlled Tesla
> Doesn't the current signal actually have both a resonance and an anti
> resonance due to the uncoupled primary inductance feeding into the
> stacked resonant tank? Has anyone ever run this experiment on the
> test bench? If this is indeed true then current phase will only be
> monotonic in the very immediate vicinity of the resonance and will
> flop right over through the lower frequency anti resonance. Such
> feedback signal behavior would be nearly as problematic to a control
> circuit as that presented by attempting to use current magnitude.
Couldn't tell you. I'm not an EE, and that's beyond me.
> In my opinion, Mike would do much better to use the integrated signal
> from his sense coil that he wrote about in a prior post. That signal
> should be completely monotonic within the control band and beyond and
> be perfectly suited for automatically tracking tesla coil resonance.
> How about it, Mike, have you yet measured the phase relationship of
> sense coil signal to the tesla coil primary voltage? -- analog
Not yet. It may be awhile. I have way too much work this week to play
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