NCP1351PRINTGEVB
http://onsemi.com
4
Figure 4. A Simple Arrangement Provides an Adjustable Overpower Power Compensation
1
2
3
4
5
8
6
7
NCP1351
Vaux
+
+
V
CC
−
N.Vin
R26
2.2 k
Rcomp
470 k
OPP Adjust
C9
220 p
D14
1N4148
Rcs
Rsense
A simple resistor connected between the auxiliary
winding (that swings negative during the ON time) and the
CT capacitor ensure a stable operation in CCM despite the
duty cycle above 50% at very low line, due to the ripple on
the bulk capacitor. The unique features of NCP1351C allow
using a 100
m
F bulk capacitor while delivering the transient
peak power and ensuring the output is still regulated during
line drop-outs.
Finally, the clamping network maintains the drain voltage
below 520 V at high-line (375 Vdc) which provides 85%
derating for the 600 V BVdss device.
Measurements
Once assembled, the board has been operated during
15 min at full power to allow some warm-up time. We used
a WT210A from Yokogawa to perform all power related
measurements coupled to an electronic ac source.
Table 1. EFFICIENCY
V
IN
(P
OUT
)
120 Vac
230 Vac
40 W
84.4%
85.4%
25 W
85.9%
85.9%
10 W
86.0%
85.1%
5 W
85.5%
83.2%
2 W
83.4%
79.5%
1 W
77.7%
73.3%
0.5 W
70.0%
66.3%
Table 2. NO-LOAD POWER
V
IN
(P
OUT
)
120 Vac
230 Vac
No-load
75 mW
140 mW
Overpower Protection Level:
The power supply is able to deliver a peak power of 85 W
during 500 ms from 85 Vac to 270 Vac.
It can deliver a constant output power of more than 40 W,
but less than 80 W over the same input voltage range.
Table 3. START-UP TIME
V
IN
(P
OUT
= 40 W)
85 Vac
230 Vac
Start-up Duration
2.7 s
0.5 s
In the above tables, we can see the excellent efficiency,
especially at light load conditions thanks to the natural
frequency foldback of the NCP1351.
The no-load standby power stays below 150 mW at high
line, a good performance for a dual output power supply able
to deliver 80 W. Please note that the high-voltage probe
observing the drain was removed and the load totally
disconnected to avoid leakage.
Despite operation in the audible range, we did not notice
any noise problems coming from either the transformer or
the RCD clamp capacitor.
V
in(min)
V
in(max)
0
20
40
60
80
100
120
0
20
60
40
80
100
120
140
Figure 5. Switching Freq. Variations vs. Output Load
P
out
F
SW
CCM Transition
