why we don't bias BJT by a battery connected B and E?

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Osawa_Odessa

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I'd like to ask about BJT biasing. Why we don't bias BJT by using a battery connected Band E that has a constant voltage?
Vbe = Vbattery = constant and its operating point Q is fixed.
 

Usually, you'll also want a signal voltage to be fed to the base, at least if the transistor is working as an amplifier.

Furthermore, Vbe bias must be varied over temperature.

Finally, who replaces all the batteries?
 

Osawa_Odessa said:
I'd like to ask about BJT biasing. Why we don't bias BJT by using a battery connected Band E that has a constant voltage?
Vbe = Vbattery = constant and its operating point Q is fixed.
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1.) The value of Vbe that is necessary for a particular Ic value is not known with sufficient accuracy because of very large tolerances
2.) Q is not "fixed" because of large Ic deviations caused by temperature changes
3.) The input impedance of the amplifier would tend to zero
 

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