Chapter 02 : Power Semiconductor Diodes and Transistors

Example 2.1, Page No 21

In [5]:
import math
#initialisation of variables
B=40.0
R_c=10                    #ohm
V_cc=130.0                #V
V_B=10.0                  #V
V_CES=1.0                 #V
V_BES=1.5                 #V

#Calculations
I_CS=(V_cc-V_CES)/R_c     #A
I_BS=I_CS/B                #A
R_B1=(V_B-V_BES)/I_BS
P_T1=V_BES*I_BS+V_CES*I_CS
ODF=5
I_B=ODF*I_BS
R_B2=(V_B-V_BES)/I_B
P_T2=V_BES*I_B+V_CES*I_CS
B_f=I_CS/I_B

#Results
print("value of R_B in saturated state= %.2f ohm" %R_B1)
print("Power loss in transistor=%.2f W" %P_T1)
print("Value of R_B for an overdrive factor 5 = %.2f ohm" %R_B2)
print("Power loss in transistor = %.2f W" %P_T2)
print("Forced current gain=%.0f" %B_f)

value of R_B in saturated state= 26.36 ohm
Power loss in transistor=13.38 W
Value of R_B for an overdrive factor 5 = 5.27 ohm
Power loss in transistor = 15.32 W
Forced current gain=8

Example 2.2, Page No 24

In [7]:
import math

#initialisation of variables
I_CEO=2*10**-3            #A
V_CC=220.0                #V
P_dt=I_CEO*V_CC           #instant. power loss during delay time
t_d=.4*10**-6            #s
f=5000
P_d=f*I_CEO*V_CC*t_d      #avg power loss during delay time
V_CES=2                     #V
t_r=1*10**-6               #s
I_CS=80                    #A

#Calculations
P_r=f*I_CS*t_r*(V_CC/2-(V_CC-V_CES)/3)            #avg power loss during rise time
t_m=V_CC*t_r/(2*(V_CC-V_CES))
P_rm=I_CS*V_CC**2/(4*(V_CC-V_CES))           #instant. power loss during rise time

#Results
P_on=P_d+P_r                
print("Avg power loss during turn on = %.2f W" %P_on)
P_nt=I_CS*V_CES 
print("Instantaneous power loss during turn on = %.0f W" %P_nt)
t_n=50*10**-6
P_n=f*I_CS*V_CES*t_n
print("Avg power loss during conduction period = %.0f W" %P_n)

Avg power loss during turn on = 14.93 W
Instantaneous power loss during turn on = 160 W
Avg power loss during conduction period = 40 W

Example 2.3 Page No 26

In [8]:
import math

#initialisation of variables
I_CEO=2*10**-3         #A
V_CC=220          #V
t_d=.4*10**-6   #s
f=5000
V_CES=2         #V
t_r=1*10**-6    #s
I_CS=80         #A
t_n=50*10**-6   #s
t_0=40*10**-6   #s
t_f=3*10**-6    #s

#Calculations
P_st=I_CS*V_CES  # instant. power loss during t_s
P_s=f*I_CS*V_CES*t_f   #avg power loss during t_s
P_f=f*t_f*(I_CS/6)*(V_CC-V_CES)        #avg power loss during fall time
P_fm=(I_CS/4)*(V_CC-V_CES)          #peak instant power dissipation
P_off=P_s+P_f

#Results
print("Total avg power loss during turn off = %.2f W" %P_off)
P_0t=I_CEO*V_CC
print("Instantaneous power loss during t_0 = %.2f W" %P_0t)
P_0=f*I_CEO*V_CC*t_0              #avg power loss during t_s
P_on=14.9339              #W    from previous eg
P_n=40                    #W    from previous eg
P_T=P_on+P_n+P_off+P_0     
print("Total power loss = %.2f W" %P_T)

Total avg power loss during turn off = 44.91 W
Instantaneous power loss during t_0 = 0.44 W
Total power loss = 99.93 W

Example 2.4, Page No 28

In [10]:
import math
#initialisation of variables
I_CS=100.0 
V_CC=200.0 
t_on=40*10**-6

#Calculations
P_on=(I_CS/50)*10**6*t_on*(V_CC*t_on/2-(V_CC*10**6*t_on**2/(40*3)))       #energy during turn on
t_off=60*10**-6
P_off=(I_CS*t_off/2-(I_CS/60)*10**6*(t_off**2)/3)*((V_CC/75)*10**6*t_off)  #energy during turn off
P_t=P_on+P_off           #total energy
P_avg=300.0
f=P_avg/P_t

#Results
print("Allowable switching frequency = %.2f Hz" %f)
#in book ans is: f=1123.6 Hz. The difference in results due to difference in rounding of of digits

Allowable switching frequency = 1125.00 Hz