FA5502PM Fuji Electric holdings CO.,Ltd, FA5502PM Datasheet - Page 18

• Manufacturer Part Number: FA5502PM
• Description: Power Factor Correction
• Manufacturer: Fuji Electric holdings CO.,Ltd

9. Design advice
(1) Vcc circuit
FA5502P/M
Vac
UVLO
UVLO
winding of the inductor. An example circuit is shown in
Fig.15.
resistor R8 should be satisfied the following formula in
order to supply with at least 30µA of IC start up
current.
starting the IC. Practically, determine the value upon
taking into account the start up time required for
converter. The start up time must be determined upon
measurement at actual circuit operation.
winding (sub) of inductor. When the IC is just starting
up, however, it takes time for the voltage from auxiliary
winding to rise enough. The value of capacitor C5
connected to Vcc pin should be determined to prevent
Vcc from falling below the OFF threshold voltage of
UVLO during this period. The capacity of C5 should be
determined by evaluation in the actual circuit because
the time lag is different in each circuit.
OFF
ON
Vcc
Vcc voltage can be supplied from an auxiliary
In this circuit, R8 is a start up resistor. The start up
Note that this formula is a minimum condition for
In steady state, Vcc is supplied from the auxiliary
R
8
FA5502
Fig.16 Vcc voltage at start up
2
Rs
VCC
R8
Vac
Fig.15 Vcc circuit (1)
30
10
(min)
10
GND
6
(sub)
L
7
17
D3
5 .
Auxiliary winding voltage
• • • • • (11)
C5
Vcc must not drop
below UVLO OFF.
Q1
D1
Co
t
(2) Supplying Vcc from external power supply
18
changes of the load or inputs. To prevent the IC from
stopping in those cases, the circuit shown in Fig.17 is
effective to prolong the hold time of the Vcc voltage.
After the PFC converter starts up, Vcc is supplied
through C6. Therefore, you can prolong the hold time
of Vcc by using a large capacity for C6.
enough in light load condition. In this case, the circuit
shown in Fig.18 may be effective to improve the Vcc.
The appropriate value of C7 and R9 should be
determined by evaluation in actual circuit because
they depend on each circuit.
inductor but from an external power supply, pay
attention to the followings.
• In order to start up the IC, Vcc must be above the ON
• If a noise is applied to Vcc pin, it may cause
Even after PFC starts up, Vcc may fall due to step
In some case, the Vcc voltage cannot be supplied
If Vcc is not supplied from the auxiliary winding of
threshold voltage VTHUON (17.5V (max.)) of
undervoltage lockout circuit (UVLO). When starting
up, apply at least this VTHUON. After starting up,
the operation is available within the recommended
range of 10 to 28V.
malfunction. To avoid a noise, connect a capacitor
near VCC pin even when Vcc is supplied from an
external power supply. To prevent a malfunction,
suppress the noise below about ±0.6V. And, make
sure there is no malfunction attributable to noise.
VCC
Quality is our message
Quality is our message
Quality is our message
Quality is our message
VCC
Fig.17 Vcc circuit (2)
Fig.18 Vcc circuit (3)
C5
R8
C5
R8
D3
D3
D5
C7
C6
D4
R9
sub
sub