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Re: Hash through chassis ground

Triode Kingdom asks:

"Even if the tube is removed, each SS diode will be reverse biased to nearly the full voltage of the transformer once each cycle. Won't that create reverse current?"

The reverse leakage caused by the reverse bias is not the issue.

The real issue happens at the point where the SS diode is conducting the full load current then is asked to switch off. Their is a finite time it takes to sweep the minority cariers out the PN junction. What this means is when the diode is reverse biased at switch off, current starts flowing backwards through the SS diode. When the diode finally does switch off there is some current flowing backwards into the secondary of the output transformer. Just like in your car's ignition system, when this current is interupted a narrow high voltage spike is generated. This is the issue that all the snubbers and other tricks to get SS diodes to sound good tries to address.

Shottky diodes, Vacuum diodes, and the new sillicon carbide high voltage diodes don't have minority cariers like PN junction diodes do. This is why they don't generate the reverse recovery spike.

Gary



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