Chapter3 Fabrication and Thermal characteristics

Example 3.1, Pg.no 10

In [6]:
import math 
Xa=50    #Ambient temperature
P=150     #on state power loss in Watts
Rjc=0.02   #junction case thermal resistance
Rcs=0.05   #case sink thermal resistance
Rsa=0.08   #sink atmosphere thermal resistance
Xj=Xa+P*(Rjc+Rcs+Rsa)   #junction temperature 
Xj=round(Xj,1)
print 'value of junction temperature=',Xj,'c'

value of junction temperature= 72.5 c

Example 3.2,Pg.no 10

In [7]:
import math
from math import exp
Xa=50      #Ambient temperature
P20=25      #on state power loss at 20%load in Watts
P200=350    #on state power loss at 200%load in Watts
Rjc=0.02    #junction case thermal resistance
Rcs=0.05    #case sink thermal resistance
Rsa=0.12    #sink atmosphere thermal resistance at 20% load cycle
T1=60       #time period for the supply of 200% load
T=((200**2-202)*T1)/(100**2-20**2)    #time period of one cycle
print 'value of time period of one cycle=',T,'s'
Ts=140    #thermal time constant for heat sink
Xj20=Xa+P20*(Rjc+Rcs+Rsa)      #junction temperature
print 'value of junction temperature=',Xj20,'c'
P=P200 -P20     #power required to cool down from 200 %load cycle to 20% load cycle
print 'power required to cool down=',P,'watts'
Rsa200=((Rsa)*(1-exp(-T1/Ts)))/(1-exp(-T/Ts))    #sink atmosphere thermal resistance at 200% load cycle
Xj200=Xj20+(P*(Rjc+Rcs+Rsa200))     #maximum junction temperature
Xj200=round(Xj200,2)
print 'value of maximum junction temperature=',Xj200,'c'

value of time period of one cycle= 248 s
value of junction temperature= 54.75 c
power required to cool down= 325 watts
value of maximum junction temperature= 106.01 c

Example 3.3 ,Pg.no11

In [8]:
import math 
Xa=35    #Ambient temperature
P=150    #on state power loss in Watts
Rjc=0.01  #junction case thermal resistance
Rcs=0.08   #case sink thermal resistance
Rsa=0.09   #sink atmosphere thermal resistance
Xj=Xa+P*(Rjc+Rcs+Rsa)   #junction temperature
print 'value of junction temperature=',Xj,'c'

value of junction temperature= 62.0 c

Example 3.4,Pg.no 12

In [9]:
import math
Xa=45     #Ambient temperature 
Rjs=0.1    #junction sink thermal resistance 
Rsa=0.08   #sink atmosphere thermal resistance 
Xj=120      #junction temperature
P=(Xj-Xa)/(Rjs+Rsa)      #on state power loss
P=round(P,2)
print 'value of on state power loss=',P,'watts'

value of on state power loss= 416.67 watts

Example 3.5,Pg.no 12

In [10]:
import math
Xa=40        #Ambient temperature
P=300        #on state power loss in Watts
Rjc=0.015    #junction case thermal resistance
Rsa=0.1      #sink atmosphere thermal resistance
Xj=105       #junction temperature
Rcs=((Xj-Xa)/(P))-(Rjc+Rsa)   #case sink thermal resistance
print  'value of case sink thermal resistance=',Rcs,'c/w'

value of case sink thermal resistance= -0.115 c/w