FA5640 Datasheet, PDF (22/35 Pages) Fuji Electric – Fuji Switching Power Supply Control IC

FA5640/41/42
(2) Startup circuit and auxiliary winding voltage
When power is turned on, the current supplied from the startup circuit to the VCC pin through the VH pin charges the
capacitor connected to the VCC pin to increase voltage. If the VCC pin voltage exceeds ON threshold voltage 14 V or 10 V,
the internal operation power is turned on, and the IC is start operating. At this time, if the voltage supplied from the auxiliary
winding is higher than 9 V, the startup circuit is operated at the time of startup only, and after the startup, auxiliary winding
voltage is used as power supply. Meanwhile, if the auxiliary winding voltage is lower than 9V, the IC maintains operation
within the VCC range between 9V and 11V by ON/OFF of startup circuit.
AC SW
Vcc
14V
11V
9V
8V
Startup
circuit
Switching
Fig.8 Startup and shutdown (When auxiliary winding voltage is higher than 9V)
AC SW
Vcc
14V
11V
9V
8V
Startup
circuit
Switching
Fig.9 Startup and shutdown (When auxiliary winding voltage is lower than 9V)
Fuji Electric Co., Ltd.
AN-064E Rev.1.1
April 2011
22
http://www.fujielectric.co.jp/products/semiconductor/