Re: TSG instability

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
> 
> It appears that this is not as mysterious as I had feared.  Dragging out
> the digital scope, I observed the 556 timer output that triggers the SCR
> that fires the trigger xfmr.  When the Variac is less than ~75%, the pulse
> train is as expected - one pulse every 8.33 msec.  But when the Variac is
> cranked up, there are often two pulses per half-cycle, the second one
> coming maybe 1 msec after the gap fires.  And on cycles where when the gap
> misfires, the first pulse is missing.
> 
> Some further circuit design work is going to be needed to curb spurious
> pulses and stabilize things.

I once tried to make an ignition coil driver controlled by a monostable
circuit, so that I could produce just one spark, at a time controlled
by an external signal. This is the same case of a TSG.
I observed that the spark of the ignition coil (not to mention the spark
of a triggered Tesla coil soon after) was causing strong interference, 
that could easily trigger again the monostable. The result was a series 
of sparks instead of just one.
The solution was to add another monostable, triggered by the fall of the
first one, and wired so that during its pulse the first monostable could
not be triggered in any way. With the pulse of this second monostable
lasting for more time than the operation cycle of the ignition coil, and
of the triggered circuit, the driver was kept inactive and insensitive
to interference.
I didn't use ICs in the circuit, but I'm sure that two 555s can be wired
in the same way.

Antonio Carlos M. de Queiroz