H - 6

© 2000 IXYS All rights reserved

Application

Protection of thyristors against overvoltages in forward

direction.

V

D

i

BOD

Thyristor

V

a. The maximum junction temperature shall be

calculated for a module IXBOD 1 -30R at an

ambient temperature T

decaying current I

an operating frequency f = 50 Hz and natural

convection. From the diagram Fig. 6 the energy per

pulse is obtained:

E

-3

Ws

For a module IXBOD1-30R the number of single

IXBOD elements is:

n = 3

At natural air cooling the thermal resistance junction

to ambient amounts to (Fig.8):

R

and the unknown temperature can be calculated as:

T

VJmax1

= T

T

= 82.2°C

b. If following these steady-state conditions an

overload for 1 minute occurs with I

pulse-width tp = 4

µs at the same operating

frequency f = 50 Hz, then the resulting maximum

junction temperature is calculating as follows:

T

The diagrams Fig. 11 and Fig. 8 show

E

-3

Ws

Z

From what follows:

T

which is allowed because the maximum admissible

junction temperature T

Calculation example