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<DIV><FONT face=Arial size=2>This would be "diffusion" current. Carriers
injected into the base region from</FONT></DIV>
<DIV><FONT face=Arial size=2>the emitter will diffuse to the depletion region of
the base-collector reverse biased </FONT></DIV>
<DIV><FONT face=Arial size=2>pn junction, where they are then swept
across.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Diffusion occurs merely because of the tendency for
an imbalance in the concentration</FONT></DIV>
<DIV><FONT face=Arial size=2>of carriers to even out due to random thermal
motions. The net motion (and hence</FONT></DIV>
<DIV><FONT face=Arial size=2>current) is in the direction of decreasing
concentration (and thus from emitter to</FONT></DIV>
<DIV><FONT face=Arial size=2>collector).</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Jim</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A href="mailto:h.j.vanderlinden@el.utwente.nl"
title=h.j.vanderlinden@el.utwente.nl>Heiko van der Linden</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
href="mailto:synth-diy@node12b53.a2000.nl"
title=synth-diy@node12b53.a2000.nl>synth-diy@node12b53.a2000.nl</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, October 19, 2000 3:39
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Conduction current in a bipolar
transistor</DIV>
<DIV><BR></DIV>
<DIV><FONT size=2>Hi All,</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>This may sound like a stupid question but I would really
like to know the answer.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>I was talking with a friend about bipolar transistors and
how they work. This went ok for a while but</FONT></DIV>
<DIV><FONT size=2>after some talking we got into </FONT><FONT size=2>a
problem: what kind of current flows through the collector </FONT><FONT
size=2>during normal</FONT></DIV>
<DIV><FONT size=2>operation ?</FONT></DIV>
<DIV><FONT size=2>I</FONT><FONT size=2> understand that the majority carriers
come from the emitter </FONT><FONT size=2>into the base. And t</FONT><FONT
size=2>hen they </FONT><FONT size=2>feel the electric</FONT></DIV>
<DIV><FONT size=2>field coming from the collector and are swept over the
</FONT><FONT size=2>reverse biased base </FONT><FONT size=2>collector
junction.</FONT></DIV>
<DIV><FONT size=2>This sounds all very intuitive (the charge carriers are
attracted by the oppositely charged collector)</FONT></DIV>
<DIV><FONT size=2>but the </FONT><FONT size=2>base collector junction
is reverse biased. So the current that flows is not a "normal"
current.</FONT></DIV>
<DIV><FONT size=2>What I would like to know is: what's the conduction
mechanism of this current ? </FONT><FONT size=2>Is it an avalanche type
</FONT></DIV>
<DIV><FONT size=2>of conduction or something else ? And what's this type
</FONT><FONT size=2>of conduction called ?</FONT></DIV>
<DIV><FONT size=2>I couldn't find a website that explained this aspect of
transistors. Some of them say it's a transistor</FONT></DIV>
<DIV><FONT size=2>current etc. So that's not much use either when you want to
understand what is really happening in</FONT></DIV>
<DIV><FONT size=2>those little black and silver cans....</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Thanks,</FONT></DIV>
<DIV><FONT size=2>Heiko</FONT></DIV></BLOCKQUOTE></BODY></HTML>