Efficiency measurement

AN4242

22/26

DocID024196 Rev 1

4.1

dI/dt optimization

The contribution of the SiC diode in the switching cell is essential. Its switching performance

leads to new optimizations that can help to go a step forward in increasing the efficiency. It is

well known that the MOSFET switching speed (dI/dt) is an important parameter to optimize

the efficiency. The dI/dt slope (when the transistor turns on and when the diode turns off)

Figure 19 shows, the efficiency drop between SiC diodes and silicon diodes for different

dI/dt slopes. This efficiency drop is defined by the total power losses due to the diode

account.

With silicon bipolar rectifiers, there is an optimized dI/dt slope to reduce the power losses.

When the slope increases, the switching time decreases but the reverse recovery current

increases. For low dI/dt values, the impact of the switching time dominates, and for higher

also be made taking into account electromagnetic considerations (EMC) which sometimes

impose a limitation of that slope.

With SiC diodes, the power losses continue to decrease whenever dI/dt increases. Being

naturally soft (due to capacitive nature of the recovery current), they offer the possibility to

switch the transistor more quickly and thus increase the efficiency of the converter.

8A Tandem G2

8A Tandem G1

8A Ultrafast diode

6A SiC G1

6A SiC G2

Efficiency (%)

dI/dt (A/µs)

0

100

200

300

400

500

600

700

800

900

1000

1100

6

5

4

3

2

1

0