FA5640 Datasheet, PDF (31/35 Pages) Fuji Electric – Fuji Switching Power Supply Control IC

FA5640/41/42
Advice for designing
(1) Connection of the bypass capacitor
Since large current is fed to the VCC pin when the
MOSFET is driven, relatively large noise tends to be
generated. In addition, noise is also generated from the
current supplied by the auxiliary winding. If this noise is
large, malfunction of the IC may result. To minimize the
noise that is generated at the VCC pin, add a bypass
capacitor C2 (0.1 F or higher) adjacent to the VCC pin of
the IC, between VCC and the GND, as shown in Fig. 29, in
addition to the electrolytic capacitor.
• Operation
This IC, which integrates a startup circuit having withstand
voltage of 500 V, achieves low power consumption.
Figure 30 presents a typical connection method, in which
the VH pin is connected to the half-wave rectification
waveform of the AC line voltage. With this method, the
startup time is the longest of the three connection methods.
In addition, since current supply from the VH pin is
interrupted if the AC line voltage is interrupted after the IC
enters the latch-off mode, the latch-off mode can be reset in
a period of time as short as several seconds.
(2) Adjustment of power supply voltage input range
The recommended supplied voltage range is 11 V to 26 V.
When the load is light, the VCC pin voltage decreases,
whereas when the load is heavy, the voltage increases,
thus deviating from the power supply voltage range. In such
cases, change the resistor between the VCC pin and the
diode to adjust the voltage. Also, by adding beads core at
the foot of the resistor, voltage fluctuation may be
suppressed.
If the above methods do not work, it is recommended to
change the secondary winding and the auxiliary winding of
the transformer to bifilar winding.
(3) When power is supplied directly to the VCC pin
When directly supplying power to the VCC pin without using
VH pin, short-circuit the VH pin and the VCC pin for use.
If the VH pin is connected to the GND, or used in open state,
leakage current may be generated.
(7) Pin No. 7 (N.C.)
Since this pin is placed adjacent to the high-voltage pin, it is
not connected to inside the IC.
Startup circuit
on/off s起ig動na回l 路
on/off信号
VH ₈
start
VCC
6
Fig.30 VH pin circuit (1)
With the connection shown in Fig. 31, the VH pin is
connected to the full wave rectification waveform of the AC
line voltage. The startup time of this method is
approximately half of that of the half-wave rectification
shown in Fig. 30. In addition, by interrupting the AC line
voltage, the time required for resetting the latch mode is as
short as the case shown in Fig. 30. But this connection
method may malfunction when the model which is
integrated line voltage compensation is used, so FA5642
only is recommended this connection.
(8) Pin No. 8 (VH pin)
Function
(ⅰ) Supplies startup current.
(ⅱ) Detects and compensates by the high-line voltage.
How to use
(ⅰ) Supply startup current.
• Connection method
Connect the pin to the high-voltage line. In this case, if
connection is to be made after rectification, connect it via a
resistor of several k (Fig. 32). On the other hand, if
connection is to be made before rectification, connect it to
the high-voltage line via a resistor of several k and a
diode (Figs. 30 and 31).
Startup circuit
on/off s起ig動na回l 路
on/off信号
VH ₈
start
VCC
6
Fig.31 VH pin circuit (2)
Fuji Electric Co., Ltd.
AN-064E Rev.1.1
April 2011
31
http://www.fujielectric.co.jp/products/semiconductor/