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Re: Optimal Quenching



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Hi all,
         Having done experiments with a MOSFET "gap" system last 
year, I'd like to make a few comments on John Freau's post and ask a 
few questions.
     First, why do sidebands occur (and increase as quench time is 
increased)? If you look at a quarter cycle of ring, it has a well 
defined amplitude, right? No change in amplitude = no sideband 
production. If you look at a half cycle, you now see a change in 
amplitude. Spectrally decomposing this there are now several 
frequencies present, the centre frequency and two sidebands of rather
low amplitude. As the time over which you examine the 
amplitude-changing-waveform increases, the sideband amplitudes 
increase at the expense of centre frequency amplitude until you 
decompose a complete beat envelope at which point, the centre 
frequency is entirely suppressed and the sideband amplitude hits a 
maximum. This spectrum is not intuitively obvious when you look at 
the waveform in the time domain. What you see there is the centre 
frequency whose amplitude is changing.

    I did exactly what John did and increased the dwell time 
progessively. What I saw was the secondary amplitude increase in 
proportion to the dwell until the point (1/2kF approx) at which no 
energy remained in the primary to be transferred. At no stage did I 
see the secondary reach that amplitude when cutting the dwell time 
shorter. I didn't expect to because loose coupling kept a high 
proportion of the primary energy more closely coupled to the primary
than the secondary. On cutting dwell time to that of a quarter cycle, 
I got enormous spikes across the parasitic primary capacitances as 
the energy still coupled to the primary coil dumped itself into those 
strays when the cutoff gap disconnected Cp from the primary coil. It 
never coupled into the secondary for the most part. Cutting 
conduction time off at half a cycle left a reversal on the 
cap as I described in the SCR post.

    Question: Did you (John) manage to get all primary energy into 
the secondary in just 1/4 cycle of oscillation despite the loose 
coupling? I would love to know how this is possible.
    I think I'll repeat those expts over the Easter break when I'll 
have time.

Malcolm






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