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Old 3rd Aug 2020, 12:09 pm   #91
dave cox
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Join Date: Jan 2009
Location: Bristol, UK.
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Default Re: High voltage regulator circuit.

The reduced power at higher voltage is due to 'secondary breakthrough'. This was the PLAGUE of early power transistors and gave them a reputation of going up in smoke! Things are much better now but at HV it is poking its head up!

I've read that its due to 'defects' in the semiconductor crystal causing a slight current hot-spot. As the resistance drops with increasing temperature you get even more current in a runaway effect. The quality of crystals has improved over the years and thermal conductivity irons this out, somewhat, but not entirely MOSFETS tend to increase resistance with temperature so don't suffer, AFAIK.

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