FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 29

• Manufacturer Part Number: FA5527
• Description: Fuji Switching Power Control IC
• Manufacturer: FUJI [Fuji Electric]

(7) Improvement of input power at light load
frequency at light load in order to reduce power dissipation.
However, depending on the circuit used, switching
frequency cannot be sufficiently reduced, leading to
insufficient reduction of power dissipation at light load.
In such a case, connect R6 between the auxiliary winding
and the IS pin as shown in Fig.36. When R4 is 1k ohm, R6
is several hundreds of k ohm to 1Meg ohm. The smaller the
R6 is, the lower the switching frequency at light load.
R6 for some time while MOSFET is ON. Be aware that the
negative voltage shall not be lower than absolute maximum
rationg,-0.3V.
light load, transformer or other apparatus may produce
noise.
(8) Prevention of malfunction caused by noise
the pins may cause malfunction. If malfunction is detected,
use the IC through referring to the following description and
fully checking a power supply unit.
close to the IC as possible and take great care of wiring, for
effective noise suppression.
(8-1) FB pin
comparator. Any noise applied to the FB pin may disturb
output pulses. Usually the capacitor C5 is connected as
shown in Fig.37 to suppress noise.
(8-2) IS pin
function, and malfunction caused by a surge current
produced at turn-on of the MOSFET is hard to occur.
is excessively large or when any noise is externally applied
at other than turn-off.
Fig.38.
(8-3) VCC pin
a large current flows from the VCC pin at the instant of
driving the MOSFET. If noise is excessively large, a
malfunction may occur of the IC. Pay full attention to
capacitance and characteristics of the capacitor between
the VCC pin and GND to reduce noise as much as possible.
AN-087E Rev.1.0
April-2011
This IC is provided with a function to lower switching
However, negative voltage is applied to the IS pin due to
In addition, when switching frequency is set too low at
This IC is an analog IC, and noise applied to anyone of
In addition, arrange the capacitors connected to pins as
The FB pin sets the threshold voltage of the current
As described in “9.-(4) Blanking,” this IC has a blanking
A malfunction, however, may occur when a surge current
In such a case, add a CR filter to the IS pin as shown in
Relatively large noise may occur at the VCC pin because
Fuji Electric Co., Ltd.
FA5526/5527/5528/5536/5537/5538
Fig.36 Input power improvement circuit at light load
Fig.37 Prevention of malfunction caused by noise
Fig.38 Prevention of malfunction caused by noise
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http://www.fujielectric.co.jp/products/semiconductor/
(IS pin)
(FB pin)