FA5626 FUJI [Fuji Electric], FA5626 Datasheet - Page 15

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

8. Operation of each block
(1)Startup circuit
The IC integrates a startup circuit having withstood voltage
of 750V to achieve low power consumption.
Fig.1 to Fig.3 shows connections.
Turning on the power, capacitor C2 connected to the VCC
pin is charged and the voltage increases due to the current
fed from the startup circuit to the VCC pin. If the ON
threshold voltage (Vcc = 18V typ.) of the under-voltage
lockout circuit (UVLO) is exceeded, the power for internal
operation is turned on, and the IC starts operating.
If the VCC pin voltage exceeds the ON threshold
voltage(VCCon=18V (typ)) and the IC starts operating, the
startup circuit is shut down and the VH pin current
decreases to several 10 to several 100uA.
RVH is connected in series to the VH pin to prevent the IC
from being damaged by the surge voltage of the AC line.
Fig.1 shows a typical connection where the VH pin is
connected to the half-wave rectifier circuit of AC input
voltage.
The startup time of this connection is the longest in 3 types
of connection.
Fig.2 shows the connection where the VH pin is connected
to the full-wave rectifier circuit of AC input voltage. The
startup time of this connection is approximately half of the
connection shown in Fig.1.
Fig.3 shows the connection where the VH pin is connected
to the back of rectification and smoothing of AC input
voltage. The startup time of this connection is the shortest
in 3 types. In this connection, however, even if the AC input
voltage is shut down after the IC enters the latch mode, the
voltage charged in C1 is kept impressed to the VH pin,
requiring much time for the latch mode to be reset. It takes
approximately several minutes to reset the latch mode,
although the time varies depending on conditions.
If the overvoltage protection is actuated, causing the IC to
enter the latch mode, then the startup circuit is subjected to
ON/OFF control to maintain the VCC voltage within the 12V
to 13V (typ) range.
(P.19 8-(7) over voltage protection)
AN-071E Rev.1.2
April-2011
Fuji Electric Co., Ltd.
FA5626
15
Fig.3 Startup circuit 3 (Rectification)
Fig.1 Startup circuit 1 (Half-wave)
Fig.2 Startup circuit 2 (Full-wave)
Startup
current
circuit
Startup
control
circuit
signal
http://www.fujielectric.co.jp/products/semiconductor/
R
VH
VH
C1
start
8
6
VCC C2