Circuit Operation Theory
API Confidential
No Copy/Reproduction Allowed
2-9
2.2.3.3 Switching Element and Isolation Transformer
B61
C53
C51
C50
*
13
12
11
10
8
1
6
16
15
18
9
D613
ZD601
FR702
FR704
FR701
T601
Q602
L608
L606
L607
C613
C624
C614
D610
D608
D614
R607
R608
R611
R604
R619
C608
(OPEN)
(OPEN)
(SHORT)
(SHORT)
(SHORT)
FS14SM-12
(BEAD)
(BEAD)
(BEAD)
(D)
1KV
0.01U
(D)
1KV
220P
(OPEN)
EGP30B
UF4007
RGP10D
UF4007
2W
0.15
20K
1K
2W
82K
2W
470
25V
47U
(EL)
In a flyback converter operated in the discontinuous mode, the energy stored in the flyback
transformer (actually an inductor) must be zero at the beginning and end of each switching period.
During the "ON" time, energy taken from the input is stored in the transformer when the switching
transistor turn-off, this stored energy is all delivered to the output.
2.2.3.4 Output Rectifier and Filter
The structure of each output is illustrated as below
T601
+
C1
+
C2
D1
L1
Since the transformer T601 acts as a storing energy inductance, diode D1 and capacitor C1 are to
produce a dc output and additional L1, C2 to suppress high-frequency switching spikes.
2.2.3.5 Control Circuit
*
*
4
1
VCC
OUT
ISSEN
GND
FB
COMP
R/C
VREF
7
6
4
3
5
2
1
8
G
K
A
+
+
IC601
IC603
ZD602
ZD603
M603
M604
C619
C620
C618
C625
D611
D612
R620
R613
R607
R611
R615
R614
R612
R738
R616
R622
C627
C617
C615
C616
UC3842
MCR100-3
24V
5.1V
(D)
50V
0.022U
(D)
50V
820P
(D)
50V
0.01U
(OPEN)
1N4148
1N4148
1N4004
10K
36K
2W
0.15
1K
51K
100K
47
1/2W
82
10K
510
50V
10U
(EL)
50V
4.7U
(EL)
50V
2200P
(PE)
100V
0.01U
(PE)
+6.5VA