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BJT bias point - RF Cafe Forums
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Post subject: BJT bias point Posted: Sun Jan 07, 2007 7:47
am
Captain
Joined: Tue May 02, 2006 4:59 am
Posts:
15
Can anyone explain how the Emitter resistance RE stablize the
DC bias Point ? ( commom emitter ).
Something about negetive
feedback ?
Is this stabilization is instead active bias ?
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IR
Post subject: Posted: Sun Jan 07, 2007 2:20
pm
Site Admin
Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
RE is used as a negative feedback.
The current gain of Beta increases with the operating temperature
of the BJT. Therefore Ic (Collector current) raises. This current flows
through RE and as a result the voltage drop on RE increases - Ve becomes
higher. Vb is usually kept constant in common emitter topology (By means
of a voltage divider), hence Vbe decreases, which turns the BJT more
to off state and reduces the Ic.
This mechanism can be used instead
of active bias.
Posted 11/12/2012 |
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