Design a DC circuit that will give a DC output V0 of 8 V It

Design a DC circuit that will give a DC output V_0 of 8 V. It is desired for R_B to have the largest possible value while the circuit operates in the active mode. Find the value for current I_c Find the value of R_B for the case of beta = 100 Find the value of R_B for the case of beta = 200

Solution

Apply KVL in collector to emitter loop

Vcc=IcRc+V0+IcRe (in active region Ie=Ic)

Ic=(Vcc-V0)/(Rc+Re)

Ic=(15-8)/(2+0.5)k=2.8mA

Ic=2.8mA

b)

B=100

Ib=Ic/B=2.8m/100=28uA

Apply KVL in base emitter loop

5V=IbRb+Vbe+IcRe

Rb=(5-0.7-(2.8m*0.5k))/28u=103.5Kohm

Rb=103.5Kohm

c) when

B=200

Ib=Ic/B=2.8m/200=14uA

Apply KVL in base emitter loop

5V=IbRb+Vbe+IcRe

Rb=(5-0.7-(2.8m*0.5k))/14u=103.5Kohm

Rb=207.1Kohm