written 6.5 years ago by |
The specifications of transistor 2N525 are
PD(max)=225mW
hfe=45(typ)
hc=1.4KΩ hre=3.2×10−4, hoe=25μmho
i)Calculation of RC
The voltage gain is given as
Av=hfeRchfe+ΔhRc
and Δh=hiehoe−hfehre
=(1.4k×25μ=mho)−(45×3.2×10−4)
Δh=0.0206
40=45×Rc1.4k+0.0206×RC
RC=1.25KΩ
select RC=1.3kΩ
ii)Selection of Q-point
VCEQ≥Vp+VCE(gat)
≥4V+0.3V
≥4.3V
Select VCEQ=6V,VRC−7.5V,VRE=1.5VandVCC=15V
Ic=VRcRC=7.5V1.3kΩ
=5.77mA(Select I_{C}=6mA)
Q-point will be (6V.6mA) .........(ii)
iii)Calcualtion of RE
As IE=IC=6mA
RE=VREIC=1.5V6mA=250Ω
Select RE=270Ω ........(iii)
iv)Selection of R1andR2
If S=10 then
RB=9RE=9×2700=2430Ω
VB=VE+VBE=1.5+0.7=2.2V
Ri=RBVCCVB2430×15V2.2V=16.6kΩ
and RB=R1||R2 substituting values of R_{B} and R_{1} in this equation we get R2=2.874kΩ
Select R1=16kΩ and R2=3kΩ .......(iv)
v)Calculation of by-pass capacitor CE
The XCE should be very much less than RE so as to bypass the dc signal to the ground
XCE=RE10=270Ω10=27Ω
CE=12πfXCE
As lower cutoff frequency is not given let us take f=20HZ
=12π20Hz27Ω=295μF
Select CE=330μF .........(v)
vi) Calculation of coupling capacitor, Cc
The coupling capacitor is used to allow only ac signal to go to next stage and to block all dc
The output impedance of first stage is
R01=RL=RC=1.3kΩ
and the input impedance of second stage
Rin1=RB||Rin2=0.888kΩ
The capacitace reactance
XCC=R01+Rin2
=1.3k+0.888k=2.188kΩ
CC=12πfXCC=12π×20Hz×2.188kΩ=3.63μF
Select CC=10μF ........(vi)