FA5540 Fuji Electric holdings CO.,Ltd, FA5540 Datasheet - Page 31

• Manufacturer Part Number: FA5540
• Description: Fuji Switching Power Supply Control Ic
• Manufacturer: Fuji Electric holdings CO.,Ltd

Rev.0 July-2007
(7) No.7 pin (N.C.)
(8) No.8 pin (VH pin)
・Connection
・Operation
・Compliment
Function
Usage
As this pin is next to a high voltage pin, this pin is
not yet connected to IC inside.
Provides startup current.
this is connected after the current is rectified,
this should be connected through a resistor of
several kΩ (Fig.22). On the other hand, if
connected before the current is rectified, this
should be connected to a high voltage line
through a resistor of several kΩand a diode
(Fig.23, Fig.24).
This pin is connected to a high voltage line. If
If VH pin is connected to high voltage, current
flows out from Vcc pin through the startup
circuit in the IC. This current charges the
capacitor between Vcc and GND, and Vcc
voltage rises. When Vcc exceeds 10.2V (typ),
IC is activated and begins to operate.
If Vcc is provided by an auxiliary winding, a
startup circuit goes into shutdown state. On
the other hand, if no power is supplied from
the auxiliary winding, IC operates normally
with a current provided by the startup circuit.
If Vcc is provided not by an auxiliary winding
In addition, much attention is required in
selecting MOSFET to drive, because there is
a limit to the current to be provided when IC
is driven only by a startup circuit.
but only by a startup circuit, standby power
requirement
dissipation increases. Therefore it is better to
provide Vcc by an auxiliary winding for low
standby power dissipation requirement.
becomes
larger
and
FA5540/5541/5542
heat
31
Starting circuit
Starting circuit
Starting circuit
On/off signal
On/off signal
On/off signal
on/off 信号
on/off 信号
on/off 信
起動回路
Fig.22 VH pin circuit (1)
起動回路
Fig.23 VH pin circuit (2)
Fig.24 VH pin circuit (3)
起動回路
Fuji Electric Device Technology
号
VH
VH
VH
start
start
start
8
8
8
6
6
6
VCC
VCC
VCC