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BJT bias point - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


Noise
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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