Roman Black wrote:
[snip]
> I did the calcs on paralleling two or more BC327
> transistors, with a track width of 10 thou and 600mA
> the track gets 22mV drop at 1.5 inches. This is about
> 5% of Vbe, which is enough to make effective emitter
> resistors and balance current acceptably. As a minimum
> cost solution 2x $0.06 is a much cheaper transistor than
> 1x $0.50 for the special transistor. :o)
>
>> Thanks again for sharing!
>
> You're welcome. :o)
> -Roman

... paralleling is good, but never forget that paralleling has a weak
chain link too.  Not two transistors are made exactly the same, they
will have little different VCEs, for small that this difference can be
the smaller VCE transistor will drain more current than the other(s),
until it heats enough (by excess current) and increases its VCE, then
current start to be proportionally shared again with other(s).  If
this excess current and temperature is supported by the transistor,
then everything is ok, but if is not, then it will blows up, leaving
the problem for the other(s) transistor(s), and the cycle will repeat.
Of course, you already said - current limiting / balancing emitter
resistors will always help, but try that in SMD configuration, mostly
with SMD resistores with values less than one Ohm, and you'll see the
price going sky high.

/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Wagner Lipnharski - UST Research Inc
Orlando FLorida - USA - www.ustr.net
/_/_/_/ Atmel AVR Consultant /_/_/_/

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