2-Level turn-off

AN2123

10/15

Maximum voltage reached on the IGBT collector and commutation losses are shown in the charts of

Figure 15. The influence of the LVoff value is studied both for nominal rated current at 25°C (75 A) and

over current (300 A) conditions.

It can be noted that in over-current conditions (see Figure 15, left graph) the 2-level turn-off can bring a

significant reduction of Vcemax during turn-off. With LVoff values from 8 to 11 V, Vcemax is reduced from

1000 V to less than 750 V. The price to pay is an increase of the switching losses Eoff that are shifted

from 20 mJ to 30~40 mJ.

In normal conditions (see Figure 15, right graph) there is no noticeable difference to be seen regardless

wheter the 2-level turn-off feature is used or not, as long as LVoff is greater than 8.5 V.

These results suggest that it is useful to set the LVoff value from 9 to 10 V.

Tip:

How does one disable the 2-level turn-off feature?

4.7 k

Ω to 10 kΩ resistor.

Figure 15. Influence of LVoff value on Vcemax and turn-off energy (IGBT Fuji 6MBI50S120L)

over-current conditions: 400V/300A

0

200

400

600

800

1000

1200

7

8

9

101112

Lvoff (V)

0

10

20

30

40

50

60

Vce max 2-level

Vce max standard

Eoff 2-level

Eoff standard

normal conditions: 400V/75A

0

200

400

600

800

7

8

9

10

11

12

Lvoff (V)

0.00

2.00

4.00

6.00

8.00

Vce max 2-level

Vce max standard

Eoff 2-level

Eoff standard