Post subject: BJT bias point Posted: Sun Jan 07, 2007 7:47
Joined: Tue May 02, 2006 4:59 am
Can anyone explain how the Emitter resistance RE stablize the
DC bias Point ? ( commom emitter ).
Something about negetive
Is this stabilization is instead active bias ?
Post subject: Posted: Sun Jan 07, 2007 2:20
Joined: Mon Jun 27, 2005 2:02 pm
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.