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Resonant charging and quench time
I am designing a DC tank supply employing resonant charging. My target is
to have a bang power (primary capacitor charging voltage) stable and
repetible from bang to bang.
Playing with a MicroSim model of it I bumped into a sad thing: when the
spark gap OPENS there is, of course, some power still left in the primary
capacitor/coil circuit. The current left in the primary coil will make up a
high voltage spike that, in turn, will charge back the primary capacitor to
a certain potential.
The polarity and magnitude of this voltage DEPENDS ON THE QUENCH TIME, i.e.
on the exact moment in time the spark gap opens!
If this voltage is positive, the following resonant charging cycle will not
charge anymore the primary capacitor to a voltage equal to about twice the
tank supply voltage, but to a lower value. Sad thing, because the next bang
will have thus LOWER energy.
If this voltage is negative, the following resonant charging cycle will not
charge anymore the primary capacitor to a voltage equal to about twice the
tank supply voltage, but to a HIGHER value. Again, bad news because you'll
possibly break the capacitor or, at least, trigger the safety gap, if you
are lucky to have one.
This voltage left on the primary capacitor when the spark gap opens is
almost random, as it is random the exact value of the quench time from bang
to bang. Also those not using resonant charging will have their
calculations and setups messed up by this factor.
Has anybody noticed this effect? Any comments about this? Am I wrong ?
For those of you lucky to have MicroSim (evaluation or real version), my
source file can be downloaded from:
http://www.saunalahti.fi/dncmrc/complete4.sch
Try reducing L2 to 0.01 uH and check how the circuit works fine (ideal
condition, only primary capacitor).
Then go for L2 = 30 uH and play with the quench time: try values between 50
and 80 us. You'll notice how the bang voltage varies widely!
Your help is really welcome...