Chapter 5: Discrete Linear Power Amplifier

Example 5.1,Page 215

In [1]:
#finding Id vs Vgs

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
Vth=3.6;
Vgs=4;#voltage
#volt change beyond 3.6 causes a major increase in Id as it is cut off voltage

#result
print('Id=0 from 0 to 2 so not shown in the graph')
x=np.linspace(2,3.6,300);
y=(-2.5*(x-3.6))**.5;
plt.plot(x,y)
plt.xlabel('Vgs(volts)');
plt.ylabel('Id(amps)');
plt.title('Id vs Vgs');

Id=0 from 0 to 2 so not shown in the graph

Example 5.2,Page 217

In [1]:
#finding drain current

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
V=4.5;#voltage
T=25;#degreeC
Id=3.8;

#result
print "drain current is",round(Id,2), "A"
print('Vth=4V is assumed')

drain current is 3.8 A
Vth=4V is assumed

Example 5.3,Page 219

In [2]:
#finding drain current of IRF530N

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
Vgs=-5;#voltage
Vthl=-4;
Vthu=-2;
Id=2.3;#current

#result
print('MOSFET is IRF530N')
print "lower limit of Vth is",round(Vthl,2), "V"
print "upper limit of Vth is",round(Vthu,2), "V"
print "current is",round(Id,2), "A"

MOSFET is IRF530N
lower limit of Vth is -4.0 V
upper limit of Vth is -2.0 V
current is 2.3 A

Example5.5,Page 225

In [3]:
#finding Pq,Pl,Ps,resistance,load voltage

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
R1=22.0;#resistance
Vg=3.6;#voltage
Vd=56.0;
G=.98;#gain
Vi=40.0;
Rl=8.0;#load resistance
Vp=36.5;

#calculation
Vr=Vd-Vg;
Ir=Vr/R1;
R2=Vg/Ir;
Va=(R1/(R1+R2))*Vi;
Vl=G*Va;
Il=Vp/Rl;
Pl=Vp*4.6/4;
Ps=Vd*4.6/pi;
Pq=Ps-Pl;

#result
print "resistance is",round(R2,2), "kohm"
print "load voltage is",round(Vl,2), "V"
print "Pq is",round(Pq,2), "watt"
print "Ps is",round(Ps,2), "watt"
print "Pl is",round(Pl,2), "watt"

resistance is 1.51 kohm
load voltage is 36.68 V
Pq is 40.02 watt
Ps is 82.0 watt
Pl is 41.97 watt

Example 5.6,Page 232

In [4]:
#finding resistance and current 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
R1=22.0;#resistance
V1=56.0;#voltage
V2=2.0;#voltage

#calculation
I=(V1-V2)/R1;
R2=V2/I;

#result
print "current is",round(I,2), "mA"
print "resistance2 is",round(R2*1000,3), "ohm"
print('pick R2=R3=820ohm R1=R4=22 kohm')

current is 2.45 mA
resistance2 is 814.815 ohm
pick R2=R3=820ohm R1=R4=22 kohm

Example 5.7,Page 234

In [5]:
#finding load voltage 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
Vi=350.0;#voltage
f=100.0;#frequency
Rf=10000.0;#resistance
Ri=520.0;

#calculation
Vp=(1+(Rf/Ri))*Vi*2**.5;

#result
print "load voltage is",round(Vp/1000,2), "V"

load voltage is 10.01 V

Example 5.8,Page 238

In [6]:
#designing amplifier

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
P=50.0;#power
Z=4.7#impedence
R=4.0;#resistance
Ta=40.0;#degreeC
Tj=140.0;#degreeC
Vd=28.0;
R2=22.0;

#calculation
Vr=(P*R)**.5;
Vp=Vr*2**.5;
Av=-Vr/1.23;
Rf=-Av*Z;
I=(Vd-2)/R2;
Vm=.63*Vd;
Ip=Vm/R;
Ps=Vd*Ip/pi;
Pl=Ip**2/2*R;
Pq=round(Ps)-Pl/2;
Qs=(Tj-Ta)/Pq-2.1;

#result
print "load rms voltage is",round(Vp,2), "V"
print "resistance is",round(Rf,2), "kohm"
print "current is",round(I,2), "mA"
print "load current is",round(Ip,2), "A"
print "supply power is",round(Ps,2), "watt"
print "load power is",round(Pl,2), "W"
print "power is",round(Pq,3), "W"
print "thermal resistance is",round(Qs,2), "degreC/W"

load rms voltage is 20.0 V
resistance is 54.04 kohm
current is 1.18 mA
load current is 4.41 A
supply power is 39.3 watt
load power is 38.9 W
power is 19.552 W
thermal resistance is 3.01 degreC/W

Example 5.9,Page 243

In [7]:
#finding load current,output voltage 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
Vi=7.5e-3;#voltage
Ib=800e-9;#current
R=53.9e3;#resistance

#calculation
Vo=11.5*Vi+Ib*R;
Id=Vo/4;

#result
print "output voltage is",round(Vo*1000,2), "mV"
print "load current is",round(Id*1000,2), "mA"

output voltage is 129.37 mV
load current is 32.34 mA

Example 5.10,Page 249

In [8]:
#finding resistance,voltage,power 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
G=6.4;#A/V
I=5.0;#current
Pq=9.8;#W
Tj=140.0;
Ta=40.0;
R1=.33;

#calculation
R=2/G;
Im=I/3;
Vr=Im*R1;
P=Vr*Im/4;
Qs=(Tj-Ta)/Pq-2.1;

#result
print "resistance is",round(R,2), "ohm"
print('thus pick a .33ohm rsistance')
print "voltage is",round(Vr,2), "V"
print "power is",round(P,2), "W"
print "thermal resistance is",round(Qs,2), "degreeC/W"

resistance is 0.31 ohm
thus pick a .33ohm rsistance
voltage is 0.55 V
power is 0.23 W
thermal resistance is 8.1 degreeC/W

Example 5.11,Page 251

In [9]:
#finding limit current 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
P=200;#power
R=8;#ohm

#calculation
Il=(P/R)**.5*2**.5;
Ilm=1.2*Il;

#result
print "limit level current is",round(Ilm,2), "A"

limit level current is 8.49 A

Example 5.12,Page 253

In [10]:
#finding resistance,power,temperature 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
I=6;#current
V=.6;#voltage
D=.5;#duty cycle
T=40;#temperature

#calculation
Rs=V/I;
Pr=D*V*I;
Vp=28;
Pm=D*Vp*I;
Tj=T+Pm*5.1;

#result
print "resistance is",round(Rs,2), "ohm"
print "power is",round(Pr,2), "W"
print "MOSFET power is",round(Pm,2), "W"
print "temperature is",round(Tj,2), "degreeC"

resistance is 0.1 ohm
power is 1.8 W
MOSFET power is 84.0 W
temperature is 468.4 degreeC

Example 5.13,Page 255

In [11]:
#finding maximum safe temperature 

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
T=130;#temperature
P=19.5;#power

#calculation
Ts=T-P*2.1;

#result
print "maximum safe temperature is",round(Ts,2), "degreeC"

maximum safe temperature is 89.05 degreeC

Example 5.14,Page 257

In [12]:
#finding 3 powers and current across resistance

#initialisation of variable
from math import pi,tan,sqrt,sin,cos,acos,atan
V=15.0;#voltage
f=300.0;#frequency
L=4.7;#inductance
Vdc=28;#V
Pr=12.5;

#calculation
Xl=2*pi*f*L;
Zload=sqrt(8**2+8.9**2);#magnitude of Zload
Vload=15.0;#msgnitude of Vload
Vr=Vload*8/Zload;
I=Vr/8*sqrt(2);
Psupply=Vdc*I/pi;
Pq=Psupply-Pr/2;

#result
print "reactance is",round(Xl/1000,2), "ohm"
print "voltage across resistor is",round(Vr,2), "V"
print "-48 is the angle of the voltage in degrees";
print "power dissipated by load is",round(Pr,2), "watts"
print "current across the resistance is",round(I,2), "A"
print "power supply is",round(Psupply,2), "W"
print "power dissipated by transistor is",round(Pq,2), "watts"

reactance is 8.86 ohm
voltage across resistor is 10.03 V
-48 is the angle of the voltage in degrees
power dissipated by load is 12.5 watts
current across the resistance is 1.77 A
power supply is 15.8 W
power dissipated by transistor is 9.55 watts