
WESTCODE Positive development in power electronics
R500CH20 to R500CH28
Provisional Data Sheet. Types R500CH20 to R500CH28 Issue 1
Page 6 of 13
January, 2000
14.0 Computer Modelling Parameters
14.1 Calculating VT using ABCD Coefficients
The on-state characteristic IT vs VT, on page 11 is represented in two ways; (i) the well established Vo and
rs tangent used for rating purposes and (ii) a set of constants A, B, C, D, forming the coefficients of the
representative equation for VT in terms of IT given below:
() ( )
T
I
D
I
C
I
B
A
V
.
ln
+
+
=
The constants, derived by curve fitting software, are given in this report for hot characteristics where
possible. The resulting values for VT agree with the true device characteristic over a current range which is
limited to that plotted.
25°C Coefficients
125°C Coefficients
A
2.55370235
A
1.91935125
B
9.282949×10
-3
B
-2.537837×10
-3
C
1.261395×10
-4
C
2.602254×10
-4
D
-0.01063571
D
-0.01168784
14.2 D.C. Thermal Impedance Calculation
∑
=
=
n
p
t
p
t
p
e
r
1
τ
Where p = 1 to n, n is the number of terms in the series.
t = Duration of heating pulse in seconds.
r
t = Thermal resistance at time t.
rp = Amplitude of pth term.
τp = Time Constant of rth term.
D.C. Double Side Cooled
Term
12
34
5
rp
3.9923×10
-3
3.78878×10
-3
1.350742×10
-3
1.378728×10
-3
4.276688×10
-4
τp
1.046993
0.3853506
0.1243419
0.01277299
6.863691×10
-3
D.C. Single Side Cooled
Term
1
234
rp
0.01254722
4.466491×10
-3
3.518626×10
-3
1.791548×10
-3
τp
10.41272
1.051407
0.1929561
9.884119×10
-3