How to minimize switching losses

AN4671

10/17

DocID027654 Rev 1

SiC reverse recovery characteristics. In the presence of Miller turn-on, however, the

reverse recovery energy can significantly impact the global switching loss.

The Miller effect may occur in a half-bridge converter under one or more of the following

conditions:

•

•

•

•

0 V:

1.

= 4.7 Ω , R

off-HS

= 2.2 Ω (best case for Miller effect)

2.

= 4.7 Ω , R

off-HS

= 15 Ω (worst case for Miller effect)

3.

= 15 Ω (intermediate case)

Do not exceed -6 V in the negative direction so as to maintain a safe margin with respect to

results for the purposes of completeness only).

Figure 9: SCT30N120 Miller turn-on test results

Therefore, at least one of the following rules must be adopted when the SCT30N120

operates in half-bridge derived topologies:

1.

implement separate turn-on and turn-off paths with the correct ratio between turn-on

2.

use a negative off voltage in the -6 V to -4 V range to keep the MOSFET off

A small negative gate-source voltage (-2 V approx.), even if it is not mandatory, can further

reduce losses and increase robustness when condition 1 (which is easier to implement) is

satisfied.