ncp1651 ON Semiconductor, ncp1651 Datasheet - Page 14

• Manufacturer Part Number: ncp1651
• Description: Single Stage Power Factor Controller
• Manufacturer: ON Semiconductor

P
Vin = 85−265 V
Efficiency = 80%
P
V
Freq = 100 kHz
Transformer turns ration N = 4
Continuous Mode (CCM)
majority of the input voltage range (85−265 Vac), L
to be at least 1 mH. Figure 26 shows the typical current
through the windings of the flyback transformer. During
switch on period, this current flows in the primary and
during the switch off time it flows in the secondary.
I
where I
T
T
I
= 3.35 A
Discontinuous Mode (DCM)
current falls to zero prior to the end of the switching period
as shown in Figure 27.
To ensure DCM, LP needs to be reduced to approximately
100 mH.
I
I
converter operating in the Continuous Conduction Mode is
PK
PK
PK
PK
O
in
on
on
O
If we look at a single application and compare the results.
To force the inductor current to be continuous over the
The peak current is:
In the discontinuous mode of operation, the inductor
The results show that the peak current for a flyback
= 90 watts
= 108 W
= 48 Vdc
= I
= (1.414 113)/85 sin q + (1.414 85 6.15 ms 2) /1 mH
= (V
= 1.414 85 sin 90 5.18 ms/100 mH = 6.23 A
= T/((N
= 6.19 ms
avg
avg
in
+ ((1.414 V
sin q 1.414 t
= 1.414 P
S
/N
P
rms
1.414 V
(analyzed at 85 V
in
I
in
PK
Figure 26.
/V
Figure 27.
I
PK
sin q t
on
in
TIME
TIME
I
in
avg
)/L
sin q
I
avg
sin q /V
P
on
2)/L
rms
O
) +1)
input)
P
)
P
http://onsemi.com
needs
NCP1651
14
one half the peak current of a flyback converter operating in
the Discontinuous Conduction Mode.
Continuous Conduction Mode
current distortion, EMI, and a lower Power Factor, in
comparison to CCM. While the higher peak current can be
filtered to produce the same performance result, it will
require a larger filter.
to provide a comparison between the harmonic current
levels for CCM and DCM. The harmonic current levels will
affect the size of the input EMI filter which in some
applications are required to meet the levels of C.I.S.P.R. In
the SPICE FFT model we did not add any front end filtering
so the result of the analysis could be compared directly.
the FFT is 260 mA, and the 2nd harmonic (200 kHz) is
55 mA rms.
2nd harmonic (200 kHz) is 500 mA rms.
A second result of running in DCM can be higher input
A simple Fast Fourier Transform (FFT) was run in Spice
At the 100 kHz switching frequency, the rms value from
At 100 kHz the rms value from the FFT are 2.8 A, and the
300
250
200
150
100
2.8
2.4
2.0
1.6
1.2
0.8
0.4
50
0
0
Figure 29. Discontinuous Conduction Mode
Figure 28. Continuous Conduction Mode
0.2
0.2
0.4
0.4
0.6
0.6
FREQUENCY (MHz)
FREQUENCY (MHz)
0.8
0.8
1.0
1.0
1.2
1.2
1.4
1.4
1.6
1.6
1.8
1.8
2.0
2.0