Hacker News Reader

Delightfully cursed.

I wonder how consistent the breakdown voltages are between manufacturers? I mean, I am sure there is some spec, but is it not just a minimum in this case?

View on HN

While the breakdown voltage of the base-collector junction varies wildly even between transistors of the same type, the breakdown voltage of the base-emitter junction varies very little between planar-epitaxial transistors, because in all such transistors the emitter has the maximum possible doping, which is limited by the solubility in silicon, and the base must also be much more strongly doped than the collector, but much less doped than the emitter, which limits the range of possible dopings. Because in this case the breakdown voltage of the base-emitter junction is determined mainly by the doping of the base, there is little variance between transistor types and between manufacturers.

Typical breakdown voltages for base-emitter junctions are e.g. around 10 volt, while the manufacturers specify breakdown voltages like 7 volt, to have a safety margin.

It's one of those characteristics you can't rely on unless you select / bin parts. Also depends on temperature. Which is why no one does this in a production design - it's expensive and unreliable.

Reply on news.ycombinator.com