Electronic – Detecting sparks at the output of a high voltage flyback transformer

555flybackhigh voltagespark

I was trying to generate plasma inside a cylinder for a hobby project, so I decided to use a flyback transformer from an old TV and drive it with a 555 timer as shown in the schematics.
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It solves my problem and the plasma looks something like this. Almost evenly distributed across the cylinder.

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But, sometimes due to foreign objects like metal pieces or mosquitoes inside the cylinder the entire discharge happens through a single spark (which is obvious). But that's not what I want; I want an even distribution of the plasma. I want to detect these sparks and shutdown the flyback for say 1 sec and then start it again(like in a hiccup mode) or report a fault with an LED.

I tried measuring the current via the R10 shunt resistor to find a change in current waveform during normal operation and during a spark, but I couldn't see much difference between the both. Is there a way to find the high voltage sparks and shutdown the circuit?

PS: I have limited knowledge of electrical engineering.

Best Answer

Do you have 300MHz BW on your scope? That's what you will need I suspect. See my other answer on what to expect. Parasitic Capacitor current of an inductor Put one or more turns around the secondary into high quality coax ( not RG58) or SAT. coax and terminate with 50 or 75 Ohms to match the coax. This is a 1:1 CT.

The energy stored into the falling dielectric starts as a rising voltage relative to the kV/mm in the plasma , then it breaks down and explodes inspite of the low capacitance but large V^2. The plasma waves are semi-conductive ( negative resistance ) rather than insulative air dielectric.

Then use a peak detector that has 300MHz BW (CML comparator) to amplify and peak detect the pulse with a low pF high speed diode to small cap to stretch it but not current limited then out to trigger a lower (20MHz) BW 1-shot to 1 second.

There may be a PD pulse before a full breakdown arc and if you are fast enough you can divert the energy, somehow.

For commercial and researcher solutions, use google scholar on "PD detector" which tend to cover a wide range in costs. You just want to detect the secondary stored energy pulse which does not show up on primary.

My signal came from an invisible contaminant in a jar of oil at about 20kV with a 1mm gap.