"Trevor Wilson"
"Phil Allison"
** You have shown no such thing with a meaningless test with that
unsuitable " Peak " meter - which is clearly intended for small signal
devices.
The Hfe of high power BJTs typically falls off sharply below 100mA Ic.
The very same group of MJ15003s will likely test very close in Hfe at an
Ic of 250mA or more.
**Indeed. I made that very point earlier. For matching output devices in
an
output stage, it is important to match at suitably high currents. I am
still
waiting to find out if that is how Mouser match their devices. Here are
some
more results form my own stock. The first column are some devices
(MJ15004)
tested at 1 Amp (by Peter Stein). The second column at around 4ma (the
Peak
tester):
81 79
89 85
80 77
74 71
81 77
85 81
From the above, we can see that you are correct. The gain is lower at
lower
currents. Importantly, however, the gain difference appears to be similar
across all the devices. IOW: Although not an accurate indicator of Hfe at
high currents, a low current measurement may provide a rough
approximation.
Which is what I was attempting to demonstrate.
** Completely **False ** demonstration - the fallacy of picking your
examples
to suit your claim.
OK:
That Peak tester you use tests Hfe at 2.5 mA (according to the published
specs) and at around 2.5 volt Vce - so is easily duplicated .
http://www.peakelec.co.uk/acatalog/jz_dca55.html (See note 2. )
OTOH - my "Simple Power Transistor Tester" operates at 500mA and 6 volt
Vce.
I picked 3 x TO3 NPNs at random:
Hfe test: SPTT Peak
MJ15003#1 89 13
MJ15003#2 92 9
MJ802 175 39
So, low current testing of high power BJTs gives grossly WRONG answers.
It is complete ******** !!
Get yourself a proper power BJT tester - anytime.
....... Phil