# Chapter 3:Transistor Amplifiers¶

## example 3.1, page No.117¶

In [1]:
#Gain Impedence and ac load
import math
#Variable declaration
ib=10.0                   #in uA
ic=1.0                    #in mA
ic=ic*10**3               #in uA
vi=0.02                   #in Volt
RC=5.0                    #in kohm
RL=10.0                   #in kohm

#Calculations

#Part (i)
Ai=-ic/ib                 #unitless
Beta=Ai                   #unitless

#Part (ii)
Rie=vi/(ib*10**-6)        #in Ohm

#Part (iii)
Rac=RC*RL/(RC+RL)         #in kohm

#Part (iv)
Av=-Rac*10**3*Beta/Rie    #unitless

#Part (v)
PowerGain=Av*Ai           #unitless

#Result
print("(i)\tCurrent gain : %.2f"%Ai)
print("(ii)\tInput impedence in kohm :%.0f"%(Rie*10**-3))
print("(iii)\tAC load in kohm : %.1f"%Rac)
print("(iv)\tVoltage gain :%.3f"%Av)
print("(v)\tPower Gain is : %.3f"%PowerGain)
#Note : Ans of Av and Power gain is wrong in the book.

(i)	Current gain : -100.00
(ii)	Input impedence in kohm :2
(iii)	AC load in kohm : 3.3
(iv)	Voltage gain :166.667
(v)	Power Gain is : -16666.667


## example 3.2, page No.125¶

In [16]:
#Gain input and output impedence
import math

#Varible declaration
RL=10.0                    #in kohm
RS=1.0                     #in kohm
hie=1.1                    #in kOhm
hre=2.5*10**-4             #unitless
hfe=50.0                   #unitless
hoe=25.0                   #in u mho

#Calculations
Aie=-hfe/(1+hoe*10**-6*RL*10**3)#unitless
Zie=hie+hre*Aie*RL              #in kOhm
Zie=math.ceil(Zie)
Ave=Aie*RL/Zie                  #unitless
Avs_e=Ave*Zie/(Zie+RS)
deltah=hoe*10**-6*hie*10**3-hfe*hre
Zoe=(hie*10**3+RS*10**3)/(hoe*10**-6*RS*10**3+deltah)
Ais_e=Aie*RS/(Zie+RS)
Ape=Ave*Aie
Aps_e=Avs_e*Ais_e

#Result
print("Current gain :%.0f "%Aie)
print("\nCurrent gain with source resistance : %.0f"%Ais_e)
print("\nVoltage gain : %.0f"%Ave)
print("\nVoltage gain with source resistance : %.0f"%Avs_e)
print("\nPower gain :%.0f "%Ape)
print("\nPower gain with source resistance :%.0f "%Aps_e)
print("\nInput impedence in kohm :%.1f"%Zie)
print("\nOutput impedence in kohm :%.1f"%(Zoe/10**3))

Current gain :-40

Current gain with source resistance : -20

Voltage gain : -400

Voltage gain with source resistance : -200

Power gain :16000

Power gain with source resistance :4000

Input impedence in kohm :1.0

Output impedence in kohm :52.5


## example 3.3, Page No. 126¶

In [2]:
#Input Output impedence and output voltage
import math
#Variable declaration
InputVoltage=1.0                     #in mV
RL=5.6                               #in kohm
RS=600.0                             #in ohm
hre=6.5*10**-4                       #unitless
hie=1.7                              #in kOhm
hfe=125.0                            #unitless
hoe=80.0                             #in uA/V

#Calculations
deltah=hoe*10**-6*hie*10**3-hfe*hre
Zie=(hie*10**3+RL*10**3*deltah)/(1+hoe*10**-6*RL*10**3)
Zoe=(hie*10**3+RS)/(hoe*10**-6*RS+deltah)
Ave=-(hfe*RL*10**3)/(hie*10**3+RL*10**3*deltah)
Avs_e=Ave*Zie/(Zie+RS)
OutputVoltage=Avs_e*InputVoltage

#Result
print("Input impedence in kohm :%.3f"%(Zie/1000))
print("Output impedence in kohm :%.3f"%(Zoe/10**3))
print("Voltage gain : %.3f"%Ave)
print("Voltage gain with source resistance : %.3f"%Avs_e)
print("Output Voltage in mV :%.3f "%OutputVoltage)
#Note : Answers are wrong in the book.

Input impedence in kohm :1.386
Output impedence in kohm :22.384
Voltage gain : -348.849
Voltage gain with source resistance : -243.444
Output Voltage in mV :-243.444


## example 3.4, Page no.129¶

In [3]:
#Net voltage gain in dB
import math
#variable declaration
A1=100.0                            #unitless
A2=200.0                            #unitless
A3=400.0                            #unitless

#calculations
A1=20*math.log10(A1)                #in dB
A2=20*math.log10(A2)                #in dB
A3=20*math.log10(A3)                #in dB
NetVoltageGain=A1+A2+A3             #in dB

#Result
print("Net Voltage Gain in decibels :%.3f"%NetVoltageGain)
#Note : Answer in the book is wrong.

Net Voltage Gain in decibels :138.062


## example 3.5, Page No.129¶

In [22]:
#Bandwidth and cut off frequencies
import math
#Variable declaration
MaxGain=1000.0                    #unitless(at 2kHz)
f1=50.0                           #in Hz
f2=10.0                           #in KHz

#Result
print("Bandwidth is from %.0f Hz to %.0f kHz"%(f1,f2))
print("Lower cutoff frequency %.0f Hz"%f1)
print("Upper cutoff frequency %.0f kHz"%f2)

Bandwidth is from 50 Hz to 10 kHz
Lower cutoff frequency 50 Hz
Upper cutoff frequency 10 kHz


## example 3.6, Page No.137¶

In [27]:
#Overall voltage gain
import math
#Variable declaration
RC=10.0                       #in kohm
hfe=330.0                     #unitless
hie=4.5                       #in kOhm

#Calculation
#RS<<hie
AVM=hfe*RC*10**3/(hie*10**3+RC*10**3)
AVM1=AVM                      #Gain of 1st stage
AVM2=AVM                      #Gain of 2nd stage
AVM3=hfe*RC*10**3/(hie*10**3) #unitless(//Gain of 3rd stage)
OverallGain=AVM1*AVM2*AVM3    #unitless

#Result
print("Gain in mid frequeny range : %.1f"%AVM)
print("This is the gain of 1st and 2nd stage.")
print("Overall Voltage gain for mid frequency range : %.1f * 10^7"%(OverallGain/10**7))

Gain in mid frequeny range : 227.6
This is the gain of 1st and 2nd stage.
Overall Voltage gain for mid frequency range : 3.8 * 10^7


## example 3.7, Page No.138¶

In [29]:
#Couopling capacitor
import math
#variable declaration
RC=5.5                 #in kohm
hfe=330.0              #unitless
hie=4.5                #in kohm
f1=30.0                #in Hz

#Calculation
#Formula : f1=1/(2*%pi*C*(hie+RC))
C=1/(2*math.pi*f1*(hie*10**3+RC*10**3))

#Result
print("Value of coupling capacitor in micro farad : %.2f"%(C*10**6))

Value of coupling capacitor in micro farad : 0.53


## example 3.8, Page No.142¶

In [31]:
#Voltage gain
import math
#Variable declaration
RC=10.0                    #in kohm
Rin=1.0                    #in kohm
Beta=100.0                 #unitless
RL=100.0                   #in ohm

#Calculation
RCdash=RC*10**3*RL/(RC*10**3+RL)
VoltageGain=Beta*RCdash/(Rin*10**3)

#Result
print("Voltage Gain :%.2f "%VoltageGain)

Voltage Gain :9.90


## example 3.9, Page No. 142¶

In [33]:
#Inductance of primary and secondary
import math

#variable declaration
Rout=10.0                   #in kohm
Rin=2.5                     #in kohm
f=200.0                     #in Hz

#Calculations

#Formula : Rout=omega*Lp=2*%pi*f*Lp
Lp=Rout*10**3/(2*math.pi*f) #in H
#Formula : Rin=omega*Ls=2*%pi*f*Ls
Ls=Rin*10**3/(2*math.pi*f)  #in H

#Result
print("Inductance of primary in Henry : %.0f"%Lp)
print("Inductance of seondary in Henry : %.0f"%Ls)

Inductance of primary in Henry : 8
Inductance of seondary in Henry : 2


## example 3.10, Page No.142¶

In [38]:
#Turn ratio of transformer
import math
#variable declaration
ZL=10.0                #in ohm
ZP=1000.0              #in ohm

#For max power : ZP=n^2*ZL
n=math.sqrt(ZP/ZL)      #turn ratio

#Result
print("Turn ratio : %.0f"%n)

Turn ratio : 10


## example 3.11, Page No.149¶

In [42]:
#Collector eficieny and power rating
import math
#Variable declaration
Po_dc=10.0                     #in watt
Po_ac=3.5                      #in watt

#calculation
ETAcollector=Po_ac/Po_dc       #unitless
ETAcollector=ETAcollector*100  #collector efficiency in %

#Result
print("Collector Efficiency : %.0f%%"%ETAcollector)
print("\nZero signal condition represents maximum power loss.")
print("Therefore, all the 10 W power is dissipated by it. Hence Powe Rating of transistor in Watt : %.0f"%Po_dc)

Collector Efficiency : 35%

Zero signal condition represents maximum power loss.
Therefore, all the 10 W power is dissipated by it. Hence Powe Rating of transistor in Watt : 10


## example 3.12, Page No.149¶

In [5]:
#Power and eficiency
import math
#variable declaration
VCC=20.0                      #in volt
RC=20.0                       #in ohm
VCEQ=10.0                     #in volt
ICQ=500.0                     #in mA

#calculations
#part (i) :
Pin_dc=VCC*ICQ*10**-3         #in watt

#part (ii) :
PRc_dc=ICQ**2*10**-6*RC       #in watt

#part (iii) :
Io=250                        #in mA(maximum value of output ac current)
Irms=Io/math.sqrt(2)          #in mA
Po_ac=Irms**2*10**-6*RC       #in watt

#part (iv) :
Ptr_dc=Pin_dc-PRc_dc          #in watt

#part (v) :
PC_dc=Pin_dc-PRc_dc-Po_ac     #in watt

#part (vi) :
ETAoverall=Po_ac*100/Pin_dc   #Overall Efficiency (in %)

#part (vii) :
ETAcollector=Po_ac*100/PRc_dc#Collector Efficiency (in %)

#Result
print("(i)\nTotal dc power taken by the circuit in Watt : %.0f"%Pin_dc)
print("\n(ii)\ndc power dissipated by the collector load in Watt : %.0f"%PRc_dc)
print("\n(iii)\nPower developed across the load in Watt :%.3f "%Po_ac)
print("\n((iv)\ndc power dissipated by the collector load in Watt :%.0f "%Ptr_dc)
print("\n(v)\ndc power dissipated by the collector load in Watt : %.3f"%PC_dc)
print("\n(vi)\nOverall Efficiency :%.3f%%"%ETAoverall)
print("\n(vii)\nCollector Efficiency  :%.2f%%"%ETAcollector)

(i)
Total dc power taken by the circuit in Watt : 10

(ii)
dc power dissipated by the collector load in Watt : 5

(iii)
Power developed across the load in Watt :0.625

((iv)
dc power dissipated by the collector load in Watt :5

(v)
dc power dissipated by the collector load in Watt : 4.375

(vi)
Overall Efficiency :6.250%

(vii)
Collector Efficiency  :12.50%


## example 3.13, Page No.151¶

In [47]:
#Maximum ac power output
import math
#variable declaration
n=10.0                 #turn ratio
RL=100.0               #in ohm
ICQ=100.0              #in mA

#calculations
RLdash=n**2*RL
MaxPowerOut=(ICQ*10**-3)**2*RLdash/2

#result
print("Maximum Power output in watt : %.0f"%MaxPowerOut)

Maximum Power output in watt : 50


## example 3.14, Page No.152¶

In [51]:
#Maximum permissible power dissipation
import math
#Part (i) : without heat sink

#variable declaration
ThetaMax=90.0             #in degree C
Theta_o=30.0              #in degree C
R=300.0                   #in degree C/W

#calculation
Pr=(ThetaMax-Theta_o)/R #in watt

#Result
print("Without heat sink, Maximum permissible power dissipatio in watt :%.1f"%Pr)

#Part (ii) : with heat sink

#variable declaration
ThetaMax=90.0             #in degree C
Theta_o=30.0              #in degree C
R=60.0                    #in degree C/W

#calculation
Pr=(ThetaMax-Theta_o)/R   #in watt

#Result
print("With heat sink, Maximum permissible power dissipatio in watt :%.0f"%Pr)

Without heat sink, Maximum permissible power dissipatio in watt :0.2
With heat sink, Maximum permissible power dissipatio in watt :1