Hello everyone,
Thank you so much for your replies!
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It is very kind if you to want to help me out.
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Where are those big caps on 15V rail someone recommended earlier?
They are between the inductor, and R5 on the schematic. I cannot place them closer to the transformer than this because of the physical location of the transformer in the application.
Your diagram shows the secondary circuit as going through the primary in order for the output to circuit to complete, can you not tie the lower end to ground and have the spark gap fed from the top of the coil.
I am afraid not. It will be impossible to rewire the transformer, you see, I want to use an automotive coil
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Alternatively, I have to use a different transformer, but for a number of reasons, I would very much like to use an automotive coil as transformer, and all the cheap ones are wired this way.
The problem with sparks is the risetime is extremely fast (typically sub nS), which means that you have very high frequency components, so even a small amount of inductance in ground paths becomes very significant - a piece of wire acts more like a resistor. You will also get capacitive coupling betteen adjacent parts.
I thought so too. So it should be possible to isolate the high frequency component on the 15V rail from the 3v3 rail (which is derived from the 15V rail) using inductors, right? I tried this, it helped. After the inductors, the 15V rail only rings about 4V
PP. Unfortunaltly, my 3V3 rail dips all the way to zero volts. How come my regulator, which is a LDO type drop to zero volts, when the 15 rail only drops to about 11 volts? Should be enough headroom, right? If I could prevent my 3v3 dripping, my problem would be solved, I dont care about noise on the 15 volt rail, as it is used for nothing else but powering the voltage regulators. Does it exist any LDOs which don't dip to 0V like the one I am using?
Looking again at the curcuit, you are injecting the spark current directly into the power supply - the gap should be across the output coil.
I tried this. I drove the coil using a battery, and the circuit using my PSU.
However, they were ground coupled. I got similar problems when I did this. In the actual application, the whole thing has to run from a single 15V rail.
This must be pretty similar to what happens in an automobile, right? How do automotive manufacturers manage to clamp the voltage from the spark plugs? The MCUs in my car seems to have no problem with 4 spark plugs firing tens of times each second.
What are your thoughts?
Thank you for your time.
Kind regards,
Marius