FAN7930C Fairchild Semiconductor, FAN7930C Datasheet - Page 16

• Manufacturer Part Number: FAN7930C
• Description: The FAN7930C is an active power factor correction (PFC) controller for boost PFC applications that operate in critical conduction mode (CRM)
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN7930C • Rev. 1.0.1
By THD optimizer, turn-on time over one AC line period
is proportionally changed, depending on input voltage.
Near zero cross, lengthened turn-on time improves THD
performance.
9. V
input voltage sensing resistors and to optimize THD, the
FAN7930C omits AC input voltage detection. Therefore,
no information about AC input is available from the
internal controller. In many cases, the V
controller is supplied by a independent power source,
like standby power. In this scheme, some mismatch
may exist. For example, when the electric power is
Figure 42.
IN
Absent Detection: To save power loss caused by
Figure 41.
Operation without V
Effect of THD Optimizer
IN
Absent Circuit
CC
of PFC
16
V
V
MOSFET gate
NewV
V
OUT
AUX
I
suddenly interrupted during two or three AC line
periods; V
voltage drops because there is no input power source.
Consequently, the control loop tries to compensate for
the output voltage drop and V
maximum. This lasts until AC input voltage is live again.
When AC input voltage is live again, high V
high switching current and more stress is put on the
MOSFET and diode. To protect against this, FAN7930C
checks if the input AC voltage exists. If input does not
exist, soft-start is reset and waits until AC input is live
again. Soft-start manages the turn-on time for smooth
operation when it detects AC input is applied again and
applies less voltage and current stress on startup.
10. Current Sense: The MOSFET current is sensed
using an external sensing resistor for over-current
protection. If the CS pin voltage is higher than 0.8V, the
over-current
protection signal. An internal RC filter of 40kΩ and 8pF
is included to filter switching noise.
11. Gate Driver Output: FAN7930C contains a single
totem-pole output stage designed for a direct drive of
the power MOSFET. The drive output is capable of up
to +500/-800mA peak current with a typical rise and fall
time of 50ns with 1nF load. The output voltage is
clamped to 13V to protect the MOSFET gate even if the
V
DS
IN
FAN7930 Rev.00
CC
Figure 43.
COMP
voltage is higher than 13V.
CC
is still live during that time, but output
eliminated, operation of
controller is normal due
protection
f
MIN
D
Operation with V
to the large bypass
MAX
Though V
capacitor.
V
f
MIN
IN
comparator
IN
Absence Detected
is
D
MIN
IN
Absent Circuit
COMP
generates
Soft-Start
Smooth
reaches its
www.fairchildsemi.com
COMP
allows
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