Re: SSTC - Self-Resonant Systems with Audio Modulation

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Original poster: "Robert Jones" <alwynj48-at-earthlink-dot-net> 

Hi,

IMHO most feedback systems monitor the zero crossings i.e. frequency not
peak power, peak voltage  or peak current.

It may be possible to provide an additional feedback loop that compared the
average peak output voltage (possibly average peak secondary current) with
the modulation input and vie a compensation circuit derive a drive signal to
pulse width modulate the power drive. This may be more linear (than direct
modulation of the pulse width) as at least the TL494 produces phase shift
when you pulse width modulate it which translates to frequency change and
then to amplitude change via the resonance (or is it magnification) curve of
the secondary. Trying to get both loops to work in harmony may be a little
tricky.

Bob

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, January 11, 2004 7:25 PM
Subject: Re: SSTC - Self-Resonant Systems with Audio Modulation


 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 > The problem is that most self-resonant systems either monitor the current
 > going into the driver or use an antenna (such as Justin's circuit) to
 > monitor output power of
 > the resonator.  In either case, the circuit is a simple feedback circuit
 > that adjusts the driver frequency so that maximum current or maximum power
 > is detected at the
 > current sense or antenna.
 >
 > In an audio modulated circuit, this will not work.  Since the circuit is
 > being power modulated by audio, the input current and output power of the
 > resonator will vary
 > according to the audio being fed into the SSTC.   You can then right away
 > see the problems the existing type of feedback circuits will have.
 >
 > Perhaps the antenna feedback circuit could be modified to monitor only a
 > very narrow band of the SSTC output frequencies and then averaged over a
 > relatively long time.
 > This averaged signal could then be compared to some reference and small
 > frequency changes could be made to maximize power output.
 >
 > Would be a challenge though.
 >
 > Dan
 >
 >
 >
 >  > Steve, why wouldn't a "self-resonant" system work for a audio modulated
 >  > SSTC? I think that a resonance "correction" circuit could be quite
 >  > useful. But I am not sure how to do it. The TL494 seems to be a less
 >  > then perfect IC for modulation, but Dan has proven it to be more than
 >  > capable! I wonder if it would be possible to do modulation with the
 >  > IR2153D IC that Dave Sharpe has been looking into? BTW, where to find
 >  > this IC? I have checked the usual suspects, but haven't found... What
 >  > are folk using to design their boards, Eagle? But finding the right
 >  > component list is troublesome! Arggh! I wish I actually had some time
to
 >  > spend on this. My desire is to make my own board, starting with a vary
 >  > simple "half-bridge" circuit. The challenge of solid state is a very
 >  > luring one that makes VTTC look like child's play! Absolutely no room
 >  > quick lash-up's Those IC's are truly infant weak!
 >  >
 >  > Regards,
 >  >
 >  > David Trimmell
 >
 >