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Snubber circuit

NMNeil

Oct 3, 2014
111
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Oct 3, 2014
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111
I'm working on 'improving' the Kettering system on my 1948 tractor. (Max 2000 engine RPM and 3 amps to the coil) Initially I was going to use an ignition IGBT, such as the ISL9V5045S3ST_F085, which has all of the snubber circuitry already built in.
The problem is that the only practical way to switch the ignition coil, which is mounted on top of the distributor and connected directly to the points by a spring contact, is by switching the high side, and no ignition IGBT's are made that will do that.
As the switching speed and current are both low I decided to use a P channel mosfet, many of which now have very low Rds.
I cannot find any information on how you would design a snubber circuit for a P-channel mosfet on the high side, or even if such a circuit was needed.
Can anyone steer me in the right direction?

 

Bluejets

Oct 5, 2014
6,993
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Oct 5, 2014
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6,993
I cannot find any information on how you would design a snubber circuit for a P-channel mosfet on the high side, or even if such a circuit was needed.
Can anyone steer me in the right direction?
Why you need to change the system at all is beyond me, however , look for "transistor assist ignition" if you must.
There were commercial systems introduced as more of a novelty if anything, back in the 60's and 70's era, most came in projects in electronic magazines.
Claim was to save the points. I used vented points in my Celica and new points were fitted every 30,000 miles or so, no intervention in between.
As long as there was a good capacitor on the points, all was well.
There were/are darlington transistors out there especially for switching ignition coils such as the MJE10012.
Snubber circuit. I imagine would be undesirable in a kettering system anyhow.
 

Delta Prime

Jul 29, 2020
2,055
Joined
Jul 29, 2020
Messages
2,055
I cannot find any information on how you would design a snubber circuit for a P-channel mosfet on the high side, or even if such a circuit was needed.
Can anyone steer me in the right direction?
Screenshot_20230630_222910.jpg
 
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