L6563ATR datasheet(27/39 Pages) STMICROELECTRONICS

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L6563 - L6563A

Application information

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6.6

Inductor saturation detection (L6563 only)

Boost inductor's hard saturation may be a fatal event for a PFC pre-regulator: the current

upslope becomes so large (50-100 times steeper, see Figure 42) that during the current

sense propagation delay the current may reach abnormally high values. The voltage drop

caused by this abnormal current on the sense resistor reduces the gate-to-source voltage,

so that the MOSFET may work in the active region and dissipate a huge amount of power,

which leads to a catastrophic failure after few switching cycles.

However, in some applications such as ac-dc adapters, where the PFC pre-regulator is

turned off at light load for energy saving reasons, even a well-designed boost inductor may

occasionally slightly saturate when the PFC stage is restarted because of a larger load

demand. This happens when the restart occurs at an unfavorable line voltage phase, so that

the output voltage may drop significantly below the rectified peak voltage. As a result, in the

Figure 40. 80W, wide-range-mains PFC pre-regulator with tracking boost function active

BRIDGE

4 x 1N4007

0.22 µF

400V

22m F

25V

FUSE

4A/250V

68 k

Ω

L6563

C6 100 nF

Ω

MOS

STP8NM50

56 µF

400V

Vo=200 to 385 V

Po=80W

Vac

(88V to 264V)

R7a,b

0.68

Ω

1/4 W

47.5 k

Ω

2.2nF

STTH1L06

NTC

62 k

Ω

1 µF

470 nF

21 k

Ω

R8b

1 M

Ω

Supply Voltage

10.3 to 22V

R8a

1 M

Ω

10 nF

R10b

3.3 M

Ω

R10a

3.3 M

Ω

R11

34.8 k

Ω

R1b

3.3 M

Ω

R1a

3.3 M

Ω

51.1 k

Ω

R10

390 k

Ω

Figure 41. Tracking boost and voltage feedforward blocks

L6563

L6563A

INV

Vout

TBO

1:1 CURRENT

MIRROR

2.5V

E/A

COMP

ITBO

IR1

MULT

Rectified mains

"ideal"

diode

MULTIPLIER

1/V

current

reference

IR2

ITBO

9.5V

VFF

CFF

RFF

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