DocID027309 Rev 1

21/23

AN4638

Topology equations and device selection

23

Setting the following electrical conditions at maximum input power operation for the 6 kW

welder:

Therefore, from the previous formulas, the maximum collector current is:

The last result is valid for a single IGBT device mounted in a two-switch forward

configuration, while for two devices connected in parallel, the value for each IGBT is:

which is the maximum operating collector current for a single IGBT device connected in a

paralleled configuration for a 6 kW welder.

Figure 13. Two switch forward topology

Figure 14. IGBT Collector current in CCM

P

IN

P

OUT

η

--------------

=

6000 W;

=

V

IN max

,

220

2;

⋅

=

I

∆

C max

,

25% I

C max

,

⋅

=

D

MAX

T

ONmax

T

---------------------

=

31%;

=

I

C ave on

,

,

P

OUT

η V

IN min

,

D

MAX

⋅

⋅

-----------------------------------------------

6000

220

2 0.31

⋅

⋅

--------------------------------------

62.2 A

=

=

=

I

C max

,

I

C ave on

,

,

I

∆

C

2

--------

I

C ave on

,

,

0.25 I

C max

,

⋅

2

--------------------------------

+

=

+

≥

I

C max

,

2 I

C ave on

,

,

⋅

1.75

-----------------------------

72 A

∼

≥

I

C max

,

72

2

------

36 A

=

≥