AN3112

Designing a fixed-off-time PFC

Doc ID 16820 Rev 3

19/36

this circuit operates in the continuous current mode, the MOSFET has to recover the boost

diode minority carrier charge at turn-on. Therefore, an ultrafast or a SiC rectifier must be

selected.

In this 400 W application an STTH8R06 (600 V, 8 A) can be selected. The STTH8R06 offers

the best solution for the continuous current mode operation due to its very fast reverse

recovery time, typically 25 ns. This part has a breakdown voltage rating (Vrrm) of 600 V,

average forward current rating (Ifave) of 8 A and reverse recovery time (trr) of 25 ns. The

rectifier AVG (

Equation 8) and RMS (Equation 17) current values and the parameter Vth

(rectifier threshold voltage) and Rd (dynamic resistance) given in the datasheet allow the

calculation of the rectifier losses.

From the STTH8R06 datasheet, Vth is 1.16 V, Rd is 0.08

Ω, neglecting the recovery losses:

Equation 37

From

(13) and Equation 37 the maximum thermal resistance to keep the junction

temperature below 125°C is then:

Equation 38

4.3.7

L6564 biasing circuitry

Following the dimensioning of the power components, the biasing circuitry for the L6564 is

also described here. For reference, the internal schematic of the L6564 is represented in

Figure 11. For more detail on the internal functions please refer to the datasheet.

Figure 11.

L6564 internal schematic

rms

2

d

out

th

diode

ID

R

I

V

P

⋅

+

⋅

=

()

W

69

.

1

A

56

.

2

08

.

0

A

0

.

1

V

16

.

1

P

2

diode

=

⋅

Ω

+

⋅

=

diode

ambx

th

P

T

C

125

R

−

°

=

W

C

45

.

44

W

69

.

1

C

50

C

125

R

th

°

=

°

−

°

=