Arfa Daily wrote:

"Eeyore" wrote

The test is done with a current limited supply and the test is for a given
leakage current.

Due to necessity (the situation was forced on me) I've had both bipolar
and
mosfet devices selected very successfully for breakdown voltage.

By these guys in fact.
http://www.semelab.co.uk/


Ah, ok. I can see how that would work. Do manufacturers ( rather than
distributors like SEME) really still do this ?

Absolutely they do ! Semelab manufactures transistors too btw. They and Zetex
probably represent the entire UK semiconductor manufacturing sector.


Seems like a lot of trouble
to go to. There are so many (hundreds of thousands ??) of transistor types
available now, I would have thought that it was possible to select one for
whatever breakdown voltages, gain, and whatever other parameters you might
require, without difficulty ? Maybe not. Thanks for the info.

The Semi makers have to test the devices for function and things like gain, so
they test for loads of stuff at the same time. It's all automated.

Here's an example of what sometimes goes on with device selection.

Decades ago we were using a Motorola part, an MJ410 in a high power audio
amplifiers as a driver. The purchasing dept found the RCA410 'equivalent' at a
lower price and initial samples worked fine so we used them.

Some months later we started getting stability problems with *some* of the
RCA410s. An alert test engineer noticed that the problem parts had a specific
code stamped into the TO-3 header. It turned out that were 3 such codes in
total; C, CN, and CNX.

I sawed the lid off one of each and even a quick inspection by eye showed that
each one had a different die fitted.

RCA initially denied everything but I eventually got an admission form their
Belgian European Headquarters.

Motorola's spec on the MJ410 was quite minimal. It didn't matter to them because
they made the part all from the same line. RCA however looked at the skimpy spec
and reckoned they could fit lots of devices that failed to meet better and more
financailly worthwhile specs into their eqivalent RCA410 device spec. So they
made RCA410s from the fall-outs from 3 other product lines with widely varying
other specs (that weren't on the data sheet). Those varying 'other specs' were
what was giving us trouble.

Graham