The Figure below shows a circuit diagram of common emitter amplifier. Taking Vbe = 0.7 v and Ic = Ie, determine the following bias voltages and currents.

 (I) Base voltage Vb

Soln 

 Base voltage Vb = Voltage drop across resistor R2

 Base voltage Vb = { (R2/(R1+R2)) x Vcc}

                = { ( 4000/(4000+ 40000)) X 22 v}

                 = 2 Volts

(II) Emitter voltage Ve

Emitter voltage Ve = Vb - Vbe

                                  = 2 - 0.7

                                   = 1.3 Volts

(III) Emitter current Ie

        Emitter current Ie = Ve/Re

                                         = 1.3V/ 1500 ohms

                                          = 8.667 x 10^ -4 A

(III) Collector voltage Vc

       Collector voltage Vc = Ic Rc

                         = (8.667 x 10^ -4 x 10000)

                          = 8.667 Volts

(V) Collector emitter voltage Vce

Collector emitter voltage Vce = Vcc -Ic(Rc+Re)

= 22 - 8.667x 10^-4(10000+1500)

= 22- 9.967

= 12 Volts