FA13842 Datasheet, PDF (11/15 Pages) Fuji Electric – CMOS IC(For Switching Power Supply Control)

3-1 The method of detecting an overvoltage (detection
on primary side)
A typical latched shutdown circuit to protect against
overvoltages detected on the primary side is shown in Fig. 11.
When the secondary voltage increases in the flyback circuit,
the voltage of the bias winding also increases in proportion.
When this voltage increase is detected by zener diode ZD1, a
latched shutdown is accomplished. As the secondary voltage
is detected through a transformer, detection accuracy is low.
3-2 The method of detecting an overvoltage (detection
on secondary side)
A typical latched shutdown circuit to protect against
overvoltages detected on the secondary side is shown in
Fig. 12.
The detected voltage accuracy is high compared to
overvoltage detection on the primary side.
3-3 The method of detecting an overcurrent (detection
of primary current)
A typical primary overcurrent detection circuit is shown in
Fig. 13.
3-4 The method of detecting an overcurrent (detection
of secondary current)
A typical secondary overcurrent detection circuit is shown in
Fig. 14.
DB
~+
AC INPUT
~
R1
R6
ZD1
7
FA13842
6
1
T1
+
C1
D1
+
C2
MOSFET
Rs
R4
Tr2
D5
Tr1
R3
C6
Fig. 11
FA13842, 13843, 13844, 13845
AC INPUT
DB
~+
~
T1
+
C1
D6
+
C7
R1
R6
7
FA13842
6
1
D1
+
C2
MOSFET
Rs
R9
ZD2
PC1
R4
Tr2
D5
Tr1
R3
C6
R8
R7
PC1
Fig. 12
AC INPUT
DB
~+
~
T1
+
C1
R1
D1
+
R6
C2
7
FA13842
6
1
3
MOSFET
R12
R4
D5
Tr2
Tr1
R3
C6
Tr3
C8
Fig. 13
Rs
R11
R10
DB
~+
AC INPUT
~
R1
R6
7
FA13842 ₆
1
R4
Tr2 _D5
R7
Tr1
R3
C6
T1 ^D6
R13
+
+
C1
C7 ^Tr4
D1
+
C2
R15
MOSFET
Rs
R16
R8
PC1
Fig. 14
R14
PC1
Tr5
11