FL7930C(2013) 查看數據表（PDF） - Fairchild Semiconductor

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FL7930C
(Rev.:2013)

Single-Stage Flyback and Boundary-Mode PFC Controller for Lighting

Fairchild Semiconductor 

VCC

VSTART

VSTOP

5V

VINV(=VPFCOUT)

2.500V

2.240V

2.051V

PFC operation

VRDY

VCC

VSTART

VSTOP

5V

VINV(=VPFCOUT)

2.500V

2.240V

2.051V

FL7930C Rev0.0

t

PFC operation

VRDY

FL7930C Rev0.0

t

Figure 25. Two Cases of RDY Triggered HIGH

VCC

VSTART

VSTOP

5V PFC operation

VINV(=VPFCOUT)

2.500V

2.240V

2.051V

VRDY

VCC

VSTART

VSTOP

5V PFC operation

VINV(=VPFCOUT)

2.500V

2.240V

2.051V

FL7930C Rev0.0

t

VRDY

Figure 26.

FL7930C Rev0.0

t

Two Cases of RDY Triggered LOW

© 2011 Fairchild Semiconductor Corporation

FL7930C • Rev. 1.0.2

4. Zero-Current Detection: Zero-current detection

(ZCD) generates the turn-on signal of the MOSFET

when the boost inductor current reaches zero using an

auxiliary winding coupled with the inductor. When the

power switch turns on, negative voltage is induced at the

auxiliary winding due to the opposite winding direction

(see Equation 1). Positive voltage is induced (see

Equation 2) when the power switch turns off.

VAUX





TAUX

TIND



VAC

(1)

  VAUX



TAUX

TIND



VPFCOUT

 VAC

(2)

where:

VAUX is the auxiliary winding voltage;

TIND is boost inductor turns;

TIND auxiliary winding turns;

VAC is input voltage for PFC converter; and

VOUT_PFC is output voltage from the PFC converter.

VINPFC

PFC inductor

VOUTPFC

RZCD

Aux winding

VCC

Negative Clamp

circuit

FL7930 Rev.00

CZCD

ZCD

5

optional

-

Positive Clamp

circuit

+

VTH(ZCD)

THD optimized

saw-tooth

generator

restart

timer

SQ

fMAX

limit

RQ

gate

driver

Figure 27. Circuit Near ZCD

Because auxiliary winding voltage can swing from

negative to positive voltage, the internal block in ZCD

pin has both positive and negative voltage clamping

circuits. When the auxiliary voltage is negative, an

internal circuit clamps the negative voltage at the ZCD

pin around 0.65 V by sourcing current to the serial

resistor between the ZCD pin and the auxiliary

winding. When the auxiliary voltage is higher than

6.5 V, current is sinked through a resistor from the

auxiliary winding to the ZCD pin.

ISW

IMOSFET

IDIODE

VACIN

FL7930 Rev.00

VAUX & VZCD

VAUX

VZCD

6.2V

0.65V

t

Figure 28. Auxiliary Voltage Depends on

MOSFET Switching

www.fairchildsemi.com

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