biasing of the bjt (part 2)

 We Have discussed two varieties of bias connections.we will consider few more bias connections in this post.
a.emitter bias:


In emitter bias configuration the input is applied across the base and the emitter and the output
is taken across the collector and emitter.
Ib=(vee-0.7)/rb+(h+1) re
Ic=h* Ib
Ie=(h+1) Ib
Vce=vcc-Ic*(rc+re)

B.collector feedback bias:
This configuration employs negative feedback to prevent thermal runaway and stabilize the operating point. In this form of biasing, the base resistor ${\displaystyle R_{\text{B}}}$ is connected to the collector instead of connecting it to the DC source ${\displaystyle V_{\text{cc}}}$. So any thermal runaway will induce a voltage drop across the ${\displaystyle R_{\text{C}}}$ resistor that will throttle the transistor's base current.



Vcc=(Ic+Ib) Rc+Ib*Rb+vbe
Ib=(Vcc-vbe)/Rb+(h+1) Rc
Ic=h*Ib
Vce=Vcc-Ic*Rc

C.emitter feed back bias:

The fixed bias circuit is modified by attaching an external resistor to the emitter. This resistor introduces negative feedback that stabilizes the Q-point.
The way feedback controls the bias point is as follows. If V_be is held constant and temperature increases, emitter current increases. However, a larger I_e increases the emitter voltage V_e = I_eR_e, which in turn reduces the voltage V_Rb across the base resistor. A lower base-resistor voltage drop reduces the base current, which results in less collector current because I_c = β I_B. Collector current and emitter current are related by I_c = α I_e with α ≈ 1, so the increase in emitter current with temperature is opposed, and the operating point is kept stable.


Ib=(Vcc-vbe)/(rb+(h+1) re)
Ic=h*Ib
Ie=(h+1)*Ib
Vce=Vcc-(Ic*Rc)-(Ic*Re)