FA5640 Datasheet, PDF (30/35 Pages) Fuji Electric – Fuji Switching Power Supply Control IC

FA5640/41/42
(5) Fine adjustment of overload detection level
The overload detection level is determined by the value of
resistor Rs in principle. To fine-tune the level, add resistor
R6 as shown in Fig. 25 to input the voltage divided by
resistors Ris and R6 into the IS pin.
to achieve low standby power, it is recommended to supply
VCC from the auxiliary winding.
At the same time, if the startup circuit only is used for
startup, the MOSFET to be driven must be selected
carefully because there is a limit in current to be supplied.
(4) Pin No. 4 (GND pin)
Function
Pin No. 4 serves as the basis of the voltage of each part of
the IC.
(5) Pin No. 5 (OUT pin)
Function
Drives the MOSFET
How to use
• Connection method
Connect pin No. 5 to the MOSFET gate (Figs. 26, 27, and
28).
• Operation
While the MOSFET remains ON, it is in high state, and
VCC voltage is output.
While the MOSFET remains OFF, it is in low state, and 0
voltage is output.
Advice for designing
Connect the gate resistor to limit the current fed to the OUT
pin or prevent vibration of gate pin voltage.
Adjust the gate resistor not to exceed the IC output current
rating of 0.25 A (source) and 0.5 A (sink).
Ris
3
IS ^Cis
R6
Rs
Fig.25 Fine adjustment of overload detection level
6
VCC
Driver
OUT
5
GND
4
Fig.26 OUT pin circuit (1)
6
VCC
Driver
OUT
5
GND
4
(6) Pin No. 6 (VCC pin)
Function
Supplies for the IC.
How to use
• Connection method
Generally, the pin is connected the auxiliary winding of the
transformer which is rectified and smoothed (Fig. 29).
The auxiliary winding that can be connected to the ZCD pin
can be shared.
• Operation
Set the voltage to be supplied from the auxiliary winding
within the 11 to 26 V range (recommended operation
condition) in normal operation. Since the startup circuit is
operated when the VCC pin voltage decreases to the
startup current restart voltage, 9 V, or lower, the VCC pin
voltage is recommended to be used by 11 V or higher
because the startup circuit is not operated.
It is also possible to operate the IC not by using the
auxiliary winding but using the current supplied from the
startup circuit. However, standby power increases and
heating of IC also increases in these cases. Consequently,
Fuji Electric Co., Ltd.
AN-064E Rev.1.1
30
April 2011
Fig.27 OUT pin circuit (2)
6
VCC
Driver
OUT
5
GND
4
Fig.28 OUT pin circuit (3)
6
VCC
C2
ZCD
1
R1
C1
Fig.29 VCC circuit
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