AN3276 datasheet(18/22 Pages) STMICROELECTRONICS

18 / 22 page

BC2 design in 450 W PFC

AN3276

18/22

Doc ID 17975 Rev 1

3.4

Thermal measurement

The soft current switching method allows the power dissipation in the switch transistor to be

reduced. Figure 18 shows that a high thermal temperature difference (18 °C) occurs

between the BC2 and the SiC diode in the PFC application. For the same working junction

temperature in the power transistor, the size of the thermal heatsink could be reduced. In

this way, the space saving balances out the space from the small L inductor required by the

BC2 circuit. Therefore, the BC2 circuit can have the same power density as the SiC diode

solution. Nevertheless, the BC2efficiency decreases due to the power MOSFET RDS(on)

thermal rising. Figure 18 shows that 0.75 W should be removed from the 5.4 W measured in

the efficiency comparison at 90 V rms. Even in this configuration, the BC2 circuit has a

better efficiency than the SiC diode. The BC2 circuit has a better power density and

efficiency criteria than the SiC diode.

Another consideration is that, for the same thermal heatsink, the Power MOSFET size could

be reduced to further reduce the PFC cost.

Figure 18.

Thermal measurement comparison

STP20NM50

STTH8BC065DI

STTH8BC065 diode in the BC² circuit

Power MOS thermal junction measurement

BC² circuit

Tj(avg)= 72 °C

Rdson STP20NM50

Rdson= 0.26

TR Cond. losses

(0.26/2)x4.28² =2.38W

Power MOS thermal junction measurement

SiC diode

Tj(avg)= 90 °C

Rdson STP20NM50

Rdson= 0.34

TR Cond. losses

(0.34/2)x4.28² = 3.12W

+0.75W

STP20NM50

STPSC806D

STPSC806D diode in the Boost circuit

PFC : V

= 90 V

mains

RMS ,

Fs = 140 kHz , P

= 450 W ,

OUT

= 4.28 A , Rg = 47

TRRMS

AN3276 bảng dữ liệu(PDF) 18 Page - STMicroelectronics

AN3276 bảng dữ liệu(HTML) 18 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

bảng dữ liệu tải về

Link URL