WESTCODE An IXYS Company

Medium Voltage Thyristor Types K0682LC360 to K0682LC420

9.3 Calculating VT using ABCD Coefficients

The on-state characteristic IT vs. VT, on page 6 is represented in two ways;

(i) the well established VT0 and rT 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:

VT = A + B ⋅ ln(IT ) + C ⋅ IT + D ⋅ IT

The constants, derived by curve fitting software, are given below for the hot and cold characteristics. The

resulting values for VT agree with the true device characteristic over a current range, which is limited to

that plotted.

25°C Coefficients

A 0.363236737

B 0.1892467

C 8.56181×10-4

D -0.013117

125°C Coefficients

A -0.622257363

B 0.4120567

C 1.382919×10-3

D -0.03801195

10.0 Snubber Components

When selecting snubber components, care must be taken not to use excessively large values of snubber

capacitor or excessively small values of snubber resistor. Such excessive component values may lead to

device damage due to the large resultant values of snubber discharge current. If required, please consult

the factory for assistance.

11.0 Reverse recovery ratings

(i) Qra is based on 50% Irm chord as shown in Fig. 1

(ii) Qrr is based on a 150µs integration time i.e.

150 µs

∫Qrr = irr .dt

0

(iii)

K

Factor

=

t1

t2

Fig. 1

12.0 Duty cycle lines

The 100% duty cycle is represented on the frequency ratings by a straight line. Other duties can be

included as parallel to the first.

Provisional Data Sheet. Types K0682LC360 to K0682LC420 Issue 1

Page 5 of 11

March, 2007