FA5626 FUJI [Fuji Electric], FA5626 Datasheet - Page 24

• Manufacturer Part Number: FA5626
• Description: Fuji Switching Power Supply Control IC
• Manufacturer: FUJI [Fuji Electric]

(7) Reduction of overload detection level on
input voltage
Output current at overload depends on the input voltage
because of propagation delay of current limit by IS pin.
(Fig.26) The dependency will be compensated by
connecting resistor R9 between the auxiliary winding and
IS pin. (Fig. 27)
A negative voltage of the auxiliary winding is proportional to
the input voltage. Current sense of this IC is negative
voltage; therefore line compensation for overload can be
achieved by negative auxiliary voltage.
This design can reduce the power loss of the compensation
resistor. For example, in case of 1kΩ of resistor R7,100 k
to 1 M is recommended for resistor R9.
Line compensation becomes large as R9 is decreased.
AN-071E Rev.1.2
April-2011
(Fig.28)
Fig.27 Input voltage compensation circuit of
Fig.26 Overload detection level of input voltage (1)
Vds
Current
Limit
Fuji Electric Co., Ltd.
Id
overload detection level
tpdls
High Line
voltage
tpdls
Difference of
High Line and Low Line
Low Line
voltage
FA5626
Fig.28 Overload detection level on input voltage (2)
(8) Input power improvement at light load
FA5626 can reduce the standby power by lowering the
oscillation frequency at light load.
However, in some case internal function of IC may not
reduce standby power enough. In such a case, connect
resistor R8 between OUT pin and IS pin.
If resistor R7 is 1 k for example, select resistance R8
between several hundred k and 1 M.
Fig.29 Compensation circuit of
24
Input power improvement at light load
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