Datasheet

NCP1351
http://onsemi.com
21
Figure 27. The 19 V Adapter Featuring the Elements Calculated Above
T1
R15
3.7k
C8
270pF
U1A
U1B
+
C15
22p
+
C2
10n
400V
R13
47k
C10
0.1
R1
2.2k
C9
100n
R5
2.5k
C4
100n
+ + +
U2
OVP
Option
D6
1N4148
R16
10
R6
0.4
C3
4.7
25V
C1
100nF
R7
1M
R3
47k
D3
1N4937
D2
MUR
160
R4
22
R2
1M
+
C12
100F
400V
HV-Bulk
NCP1351B
1
2
3
4
8
7
6
5
25V
R18
47k
C17
100
6A/600V
M1
L
P
= 500H
N
P
:N
S
= 1:0.25
N
P
:N
aux
= 0.18
D5
MBR20200
L2
2.2
V
OUT
19V/3A
C5b
1.2mF
25V
C5a
1.2mF
25V
C13
2.2nF
Type = Y1
C7
220F
25V
GND
R14
2.2k
R8
1k
R12
4k
R10
62k
R9
10k
GND
C6
100n
IC2
TL431
On this circuit, the V
CC
capacitor is split in two parts, a
low value capacitor (4.7 F) and a bigger one (100 F). The
4.7 F capacitor ensures a low startup time, whereas the
second capacitor keeps the V
CC
alive in standby mode
(where the switching frequency can be low). Due to D
6
, it
does not hamper startup time.
Application Results
We assembled a board with component values close to
what is described on Figure 27. Here are the obtained
results:
P
in
@ no-load = 152 mW, V
in
= 230 Vac
P
in
@ no-load = 164 mW, V
in
= 100 Vac
The efficiency stays flat to above 80%, and keeps good
even at low output levels. It clearly shows the benefit of the
variable frequency implemented in the NCP1351.
Figure 28. Efficiency Measured at Various Operating
Points
72
74
76
78
80
82
84
86
88
0 0.5 1 1.5 2 2.5 3 3.5
EFFICIENCY (%)
I
out
(A)
V
in
= 230 Vac
V
in
= 100 Vac