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AP3703 Datasheet(PDF) 7 Page - BCD Semiconductor Manufacturing Limited

Part # AP3703
Description  LOW-POWER OFF-LINE PRIMARY SIDE REGULATION CONTROLLER
PDF  11 Pages
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Manufacturer  BCDSEMI [BCD Semiconductor Manufacturing Limited]
Direct Link  http://www.bcdsemi.com
Logo BCDSEMI - BCD Semiconductor Manufacturing Limited

AP3703 Datasheet(HTML) 7 Page - BCD Semiconductor Manufacturing Limited

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LOW-POWER OFF-LINE PRIMARY SIDE REGULATION CONTROLLER
AP3703
7
BCD Semiconductor Manufacturing Limited
Feb. 2009 Rev. 1.0
Preliminary Datasheet
Operation Description
Figure 7 illustrates a simplified flyback converter
controlled by AP3703.
Constant Primary Peak Current
The primary current ip(t) is sensed by a current sense
resistor RCS as shown in Figure 7.
The current rises up linearly at a rate of:
As illustrated in Figure 8, when the current ip(t) rises
up to Ipk, the switch Q1 turns off. The constant peak
current is given by:
The energy stored in the magnetizing inductance LM
each cycle is therefore:
So the power transferring from the input to the output
is given by:
Where the fsw is the switching frequency. When the
peak current Ipk is constant, the output power depends
on the switching frequency fsw.
Constant Voltage Operation
The AP3703 captures the auxiliary winding feedback
voltage at FB pin and operates in constant-voltage
(CV) mode to regulate the output voltage. Assuming
the secondary winding is master, the auxiliary winding
is slave during the D1 on-time and the auxiliary
voltage is given by:
Figure 7. Simplified Flyback Converter Controlled by AP3703
M
L
t
vg
dt
t
dip
)
(
)
( =
......(1)
Ip
0A
See equation 2
Figure 8. Primary Current Waveform
Rcs
Vcs
Ipk
=
......(2)
2
2
1
Ipk
L
Eg
M ⋅
×
=
SW
M
f
Ipk
L
P
×
×
×
=
2
2
1
......(4)
()
Vd
Vo
N
N
V
S
AUX
AUX
+
×
=
......(5)
......(3)
+
Bridge
C1
+C
O
V
O
D1
Q1
V
S
OUT
FB
CS
GND
AP3703
N
S
N
P
L
M
I
S
V
AUX
N
AUX
I
P
V
IN
I
O
R
CS
Vg



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