AN3276

Existing solutions

Doc ID 17975 Rev 1

3/22

1

Existing solutions

This section describes some existing areas for efficiency improvements in PFC applications.

1.1

Diode switch-on losses

Usually, in mass market applications between 200 W and 2 kW, a power factor corrector

(PFC) working in continuous conduction mode (CCM) is mandatory. To improve the power

converter density, the switching frequency should be increased. Nevertheless, when the

switching frequency increases, power dissipation in the power switch/rectifier commutation

cells leads to the major switching losses in the PFC. The main power losses occur during

turn-on of the power switch due to both the voltage and current crossing area of the

MOSFET and the reverse recovery losses [see Section 5: References, 2.] produced by the

PN diode as shown in Figure 1.

Figure 1.

Switch-on losses in PN diode behavior

To reduce the losses of the PN rectifier, many semiconductor manufacturers have recently

introduced high-voltage Schottky diodes using SiC and GaN technologies. However, it is

impossible to completely remove the voltage and current crossing area during transistor

turn-on by improving component performance only.

t

Losses are due to area

between I +I

and V

0RM

DS

I+I

RM

0

I

0

V

DS

W

ON