CHAPTER 12 POWER AMPLIFIERS

Example 12-1, Page 384

In [13]:
import math   # This will import math module

VCC=30                #collector voltage(V)
RE=20                 #Emitter resistance(Ohm)
R1=490.0              #Base resistance1 (Ohm)
R2=68.0               #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=180                #Load Resistance(Ohm)
RC=120                #Collector resistance(Ohm)

VB=VCC*(R2/(R1+R2))    #Base voltage(V)
VE=math.ceil(VB-VBE)   #Emitter voltage(V)
IE=VE/RE               #Emitter current(A)
ICQ=IE                 #collector current (A)
VC=VCC-(ICQ*RC)        #collector voltage(V)
VCEQ=VC-VE             #collector-emitter voltage (V) 
rc=RC*RL/(RC+RL)       #ac collector resistance(Ohm)

print 'Collector current ICQ = ',ICQ*1000,'mA'
print 'collector-emitter voltage VCEQ = ',VCEQ,'V'
print 'ac collector resistance rc = ',rc,'Ohm'

Collector current ICQ =  150.0 mA
collector-emitter voltage VCEQ =  9.0 V
ac collector resistance rc =  72 Ohm

Example 12-2, Page 385

In [18]:
VCC=30                #collector voltage(V)
RE=20                 #Emitter resistance(Ohm)
R1=490.0              #Base resistance1 (Ohm)
R2=68.0               #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=180                #Load Resistance(Ohm)
RC=120                #Collector resistance(Ohm)

ICQ=150                 #collector current (mA)
VCEQ=9                  #collector-emitter voltage (V) 
rc=72.0                 #ac collector resistance(Ohm)

ic_sat=ICQ+(VCEQ/rc)*1000      #ic(sarturation) (mA)
VCE_cut=VCEQ+((ICQ*rc)/1000)   #VCE(cut-off)  (V)
MP1=ICQ*RC
MP2=VCEQ
MPP=2*(min(MP1,MP2))           #maximum peak-to-peak voltage (V)

print 'ic(sarturation) = ',ic_sat,'mA'
print 'VCE(cut-off) = ',VCE_cut,'V'
print 'maximum peak-to-peak voltage MPP = ',MPP,'V'

ic(sarturation) =  275.0 mA
VCE(cut-off) =  19.8 V
maximum peak-to-peak voltage MPP =  18 V

Example 12-3, Page 387

In [28]:
import math   # This will import math module

VCC=30                #collector voltage(V)
RE=20                 #Emitter resistance(Ohm)
R1=490.0              #Base resistance1 (Ohm)
R2=68.0               #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=180.0              #Load Resistance(Ohm)
RC=120                #Collector resistance(Ohm)
vin=200               #input voltage(mV)
zin=100               #input impedance of base(Ohm)
MPP=18                #peak-to-peak voltage (V)

Zin_stage=((zin**-1)+(R1**-1)+(R2**-1))**-1      #input impedance of stage(KOhm)
Pin=vin**2/(Zin_stage*8)/1000                    #ac input power (mW)
Pout=1000*MPP**2/(RL*8)                          #ac output power (mW)
Ap=Pout/Pin                                      #power gain

print 'Power gain Ap = ',math.ceil(Ap)

Power gain Ap =  1683.0

Example 12-4, Page 388

In [8]:
import math   # This will import math module

VCC=30                #collector voltage(V)
RE=20                 #Emitter resistance(Ohm)
R1=490.0              #Base resistance1 (Ohm)
R2=68.0               #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=180                #Load Resistance(Ohm)
RC=120                #Collector resistance(Ohm)

VB=VCC*(R2/(R1+R2))    #Base voltage(V)
VE=math.ceil(VB-VBE)   #Emitter voltage(V)
IE=VE/RE               #Emitter current(A)
ICQ=IE                 #collector current (A)
VC=VCC-(ICQ*RC)        #collector voltage(V)
VCEQ=VC-VE             #collector-emitter voltage (V) 
PDQ=VCEQ*ICQ           #power dissipation(W)
I_bias=VCC/(R1+R2)     #bias current(mA)
Idc=I_bias+ICQ         #dc current(mA)
Pdc=VCC*Idc            #dc input power to stage(W)
Pout=0.225             #Output power as per example 12-3 (W)
n=(Pout/Pdc)*100       #efficiency of stage

print 'Power dissipation PDQ = ',PDQ,'W'
print 'efficiency of stage n = ',round(n,2),'%'

Power dissipation PDQ =  1.35 W
efficiency of stage n =  3.68 %

Example 12-6, Page 391

In [89]:
VCC=12               #collector voltage(V)
RE=16                #Emitter resistance(Ohm)
R1=50.0              #Base resistance1 (Ohm)
R2=100.0             #Base resistance2 (Ohm)
VBE=0.7              #Base-emitter voltage drop(V)
RL=16                #Load Resistance(Ohm)

VB=VCC*(R2/(R1+R2))    #Base voltage(V)
VE=(VB-VBE)            #Emitter voltage(V)
IE=VE/RE               #Emitter current(A)
ICQ=IE                 #collector current (A)
VCEQ=VCC-VE            #collector-emitter voltage (V) 
re=RE*RL/(RE+RL)       #ac emitter resistance(Ohm)

print 'Collector current ICQ = ',ICQ*1000,'mA'
print 'collector-emitter voltage VCEQ = ',VCEQ,'V'
print 'ac collector resistance re = ',re,'Ohm'

Collector current ICQ =  456.25 mA
collector-emitter voltage VCEQ =  4.7 V
ac collector resistance re =  8 Ohm

Example 12-7, Page 393

In [56]:
VCC=12               #collector voltage(V)
RE=16                #Emitter resistance(Ohm)
R1=50.0              #Base resistance1 (Ohm)
R2=100.0             #Base resistance2 (Ohm)
VBE=0.7              #Base-emitter voltage drop(V)
RL=16                #Load Resistance(Ohm)

ICQ=456                 #collector current (mA)
VCEQ=4.7                #collector-emitter voltage (V) 
re=8.0                  #ac emitter resistance(Ohm)

ic_sat=(1000*(VCEQ/re))+ICQ    #ic(sarturation) (mA)
VCE_cut=VCEQ+(ICQ*re)/1000   #VCE(cut-off)  (V)
MP1=ICQ*re/1000
MP2=VCEQ
MPP=2*(min(MP1,MP2))           #maximum peak-to-peak voltage (V)

print 'ic(sarturation) = ',ic_sat/1000,'A'
print 'VCE(cut-off) = ',VCE_cut,'V'
print 'maximum peak-to-peak voltage MPP = ',MPP,'V'

ic(sarturation) =  1.0435 A
VCE(cut-off) =  8.348 V
maximum peak-to-peak voltage MPP =  7.296 V

Example 12-8, Page 397

In [58]:
VCC=20                #collector voltage(V)
R1=100.0              #Base resistance1 (Ohm)
R2=100.0              #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=8.0                #Load Resistance(Ohm)

MPP=VCC                #maximum peak-to-peak voltage (V)
PD_max=MPP**2/(40*RL)  #Maximum power dissipation(W)
Pout_max=MPP**2/(8*RL) #Maximum output power(W)

print 'Maximum power dissipation PD_max = ',PD_max,'W'
print 'Maximum output power Pout_max = ',Pout_max,'W'

Maximum power dissipation PD_max =  1.25 W
Maximum output power Pout_max =  6.25 W

Example 12-9, Page 398

In [7]:
import math

VCC=20                #collector voltage(V)
R1=100.0              #Base resistance1 (Ohm)
R2=100.0              #Base resistance2 (Ohm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=8.0                #Load Resistance(Ohm)
Ra=15                 #adjustable resistor(Ohm)

VCEQ=VCC/2            #collector-emitter voltage (V) 
I_bias=VCC/(R1+R2+Ra) #bias current(mA)
Ic_sat=VCEQ/RL        #ic(sarturation) (mA)
Iav=Ic_sat/math.pi    #average current (A)
Idc=I_bias+Iav        #dc current(mA)
Pdc=VCC*Idc           #dc input power to stage(W)
Pout=6.25             #Output power as per example 12-8 (W)
n=(Pout/Pdc)*100      #efficiency of stage


print 'efficiency of stage n = ',round(n,2),'%'

efficiency of stage n =  63.66 %

Example 12-10, Page 400

In [6]:
VCC=20                #collector voltage(V)
R1=3.9                #Base resistance1 (KOhm)
R2=3.9                #Base resistance2 (KOhm)
VBE=0.7               #Base-emitter voltage drop(V)
RL=10.0               #Load Resistance(Ohm)

VCEQ=VCC/2                   #collector-emitter voltage (V) 
I_bias=(VCC-(2*VBE))/(R1+R2) #bias current(mA)
Ic_sat=VCEQ/RL               #ic(sarturation) (mA)
Iav=Ic_sat/math.pi           #average current (A)
Idc=(I_bias/1000)+Iav        #dc current(mA)
Pdc=VCC*Idc                  #dc input power to stage(W)
Pout=VCC**2/(8*RL)           #Output power (W)
n=(Pout/Pdc)*100             #efficiency of stage

print 'efficiency of stage n = ',round(n,2),'%'

efficiency of stage n =  77.96 %

Example 12-11, Page 405

In [9]:
import math

L=2*10**-6           #inductance (H)
C=470*10**-12        #capacitance(F)

fr=((2*math.pi)*((L*C)**0.5))**-1

print 'Resonant frequency fr = ',round((fr*10**-6),2),'MHz'

Resonant frequency fr =  5.19 MHz

Example 12-12, Page 410

In [10]:
import math

fr=5.19*10**6        #frequency as per previous example(Hz)
L=2*10**-6           #inductance (H)
C=470*10**-12        #capacitance(F)
QL=100               #quality factor of coil
RL=1                 #Load resistance(KOhm)

XL=2*math.pi*fr*L                     #inductive impedance(Ohm)
Rp=QL*XL/1000                        #Eq. parallel resistance of coil(KOhm)
rc=1000*Rp*RL/(Rp+RL)                #ac collector resistance(Ohm)
Q=rc/XL                              #Q of overall circuit
BW=(fr/Q/1000)                       #band width of amplifier(KHz)

print 'band width of amplifier BW = ',round(BW,2),'KHz'

band width of amplifier BW =  390.39 KHz

Example 12-13, Page 411

In [91]:
import math   # This will import math module

VCC=15                #collector voltage(V)
rc=867.0              #ac collector resistance as per preceding example (Ohm)

MPP=2*VCC                  #Maximum peak-to-peak voltage(V)
PD=1000*MPP**2/(40*rc)     #worst-case power dissipation(mW)

print 'Worst-case power dissipation PD = ',math.ceil(PD),'mW'

Worst-case power dissipation PD =  26.0 mW

Example 12-14, Page 414

In [94]:
PD=625                #maximum power rating at 25 deg C(mW)
D=5                   #Derating factor(mW/deg C)
TA=50                 #ambient temperature(deg C)

DP=D*(TA-25)            #difference in power(mW)  
PD_max=PD-DP            #maximum power rating(mW)

print 'Maximum power rating PD_max = ',PD_max,'mW'

Maximum power rating PD_max =  500 mW