Jim wrote:
>
>    "requiring betas as low as 10(!!) or 50 "
>
> Huh?
> Do you mean to say that you were required to
> provide additional "base drive current" in
> order to achive the desired Vcesat (volts collector
> to emitter at saturation) you were looking for?
>
> I'm sorry, but I have to address this issue -
> 'beta' values for a transistor are measured at
> *specified* collector currents and is a parameter
> that varies *greatly* over the range


Exactly my point. The beta specified in the
catalogue as 160, quite reasonable for a low sat
transistor in its happy range.

What annoyed me was the (hidden) fact that YES
the transistor will do 0.3v sat at 3A, but only
at a very poor beta of 10.

Zetex (or Farnell) seem to have deliberately
chosen to show a beta of 160, at a totally
unreasonable current for a 3A transistor. When
operated as a low-sat transistor the beta is
VERY POOR.

Over 20 years experience of having to substitute
hard to get semis in repairing appliances I ALWAYS
test semis. I have many low-sat transistors here,
which WILL give betas of 50 to 100 with high currents
and low sats. A beta of 10 makes the low sat feature
worthless to me.

My gripe is that the Farnell catalogue shows the
Zetex parts as "high gain super low sat" which is
downright misleading when you find that they don't
do either thing *that* well. I don't consider these
transistors to be high gain, and if advertised as
low sat at 3A a more realistic beta should have been
shown, as based on their figures I expected the
Zetex parts to perform similar to the other brands
I had here, with betas around 100 at 1A and maybe 80
at 3A. The Zetex parts have betas of 150 at 200mA
and 10(!) at 3A, gripe gripe gripe.

But they are small.

I also sent back a batch of 1N5819 and 1N5822 schottky
diodes, when I tested them they were the ST brand and
had sat voltages 40% higher(!) than the ones I had in
stock, which were motorola/ON brand. I hate getting ripped
off with semis, and suppliers constantly source cheaper
parts with the same part number, meaning you end up
getting crappier and crappier performance from a part
number you expect to perform as advertised. Grrr.
-Roman

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