Application Note 12 V/40 W Demonstrator

AND8486/D
A 12 V / 40 W AC-DC
Demonstrator with
NCP1250
Prepared by: Christophe Basso
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
Introduction
The controller drives a 4 A/600 V power MOSFET whose
turn-off is accelerated by the addition of a small PNP
transistor, Q1. A 100 pF capacitor smoothes the drain-source
signal at the switch opening and helps to soften the EMI
signature. The transformer is built in a RM10 ferrite shape
made of 3C90 material. The primary inductance is 700 mH
and the turns ratio between the power secondary and the
primary side is 1:0.15. This number is slightly increased to
1:0.17 on the auxiliary winding to maintain Vcc in no-load
situations.
The secondary side implements a classical TL431 whose
bias current is automatically disconnected in a no-load
situation through C5D7. This proprietary technique reduces
the bias voltage applied to R19 left terminal when the
converter enters standby mode. As this 1 mA burden
disappears from the 19 V output in a no-load configuration,
the input power greatly benefits from the situation.
Furthermore, this architecture does not impact the transient
response of the converter when transitioning from no-load
to full-load.
The converter has been laid out in a compact style as
shown in Figure 2. The board can deliver a continuous
current up to 3.5 A when operated in a 50°C ambient
temperature. The overpower protection trips for a maximum
current of 4.2 A. This value slightly varies between the
boards and the line level but stays typically within a short
range thanks to the proprietary non−dissipative OPP
implemented in the NCP1250. Please see below the board
performance in terms of efficiency in various loading
conditions.
The NCP1250 is implemented in a 40-W ac-dc adapter
delivering a dc voltage of 12 V. The converter takes
advantage of the NCP1250 high integration level to offer a
very good performance in standby power and Over Power
Protection.
The Adapter Schematic
The adopted schematic appears in Figure 1. You can see
the NCP1250B (auto-recovery short-circuit protection,
65 kHz) driving a power MOSFET in a flyback
current-mode configuration. The mains is applied on the
rectifying diodes bridge through an EMI filter made of a
10-mH common-mode choke. Its leakage inductance is used
together with C11 to form a differential mode filter. To
further save power in standby mode (Pout = 0 W), we have
combined the need to discharge the 0.47 mF X2 capacitor
using resistors that will also be used to crank the controller
at start-up. This is achieved by the set of four resistors (R15,
R27, R17 and R20) that ensure the discharge of the capacitor
when the power cord is un-plugged. For a 0.47 mF capacitor,
a total of 2 MW is necessary to make the time constant less
than 1 s, as recommended by the safety document IEC-950.
As these resistors join at the NCP1250 Vcc pin where a
4.7 mF capacitor is connected, it offers a cheap charging
means for the capacitor connected there. Experiments show
that this solution supplies enough current to start the
converter in less than 3 s at an input voltage of 85 V rms.
Over Power Protection, Over Temperature Protection and
Over Voltage Protection are implemented around pin 3.
Please refer to the available application notes for design
details regarding these parts.
© Semiconductor Components Industries, LLC, 2011
February, 2011 − Rev. 0
1
Publication Order Number:
AND8486/D
+
L1
R15
510k
http://onsemi.com
2
250 V
F1
2AT
IN
−
R17
510k
R20
510k
85−265 V rms
C11
470n X2
2 x 10mH
Wurth 744822120
IC4
KBU4K
R27
510k
400 V
C12
82uF
R7
330k
Vbulk
C10 R5
22pF 1.8k
C8
1nF
D1
1N964
R3
330k
R22
470k
1N4148
D10
C9
330pF
C15
220p
4
5
2
3
6
1
NCP1250
R14
NTC
R2 option
220k
22
1
C3
4.7uF
C17
100uF
R23
1k
3
T1
.
2
Np
11
R6a R6b R6c
1.3 1.3 1.3
R18
22k
M1
D4
1N4937
10
Bridge
Naux 12
.
Q1
2N2907
1N4148 R16
D6
D3
1N4937
R24
220
R21
22
C2
10n
R11 R13
47k 47k
R25
47
R26
47
C5
10nF
R19
1k
D7
1N4937
L2
2.2uH
IC2
TL431
C6
10nF
R8
1k
C18
22pF
C5a C5b
680uF 680uF
C13
2.2nF
Type = Y1
1 kV
C4
100pF
Ns
5−6
.8−7
D5
NTST30100SG
R9
10k
R10
20k
R12
18k
C7
12
220uF
V / 3.3 A
AND8486/D
Figure 1. The adapter uses all the features brought by the NCP1250 to implement a high-performance 40-W
converter.
AND8486/D
Figure 2. The PCB layout and component arrangement offers a compact size.
Light load efficiency:
Efficiency Performance
The NCP1250 excels in terms of efficiency and standby
power. We have made a series of tests on the proposed
adapter, carried at both high and low lines. The load is
applied directly at the board terminals. The results appear
below.
Output Power
Efficiency - Vin =
115 V rms (%)
Efficiency - Vin =
230 V rms (%)
10.3 W - 25%
87.18
85.1
20.7 W - 50%
88.13
86.9
31.2 W - 75%
88.10
88.2
41.5 W - 100%
87.76
88.5
Average efficiency
87.8
87.2
Output Power
Input power – Vin
= 100 V rms (W)
Input power – Vin
= 230 V rms (W)
0.5 W
0.7
0.76
0.6 W
0.83
0.89
The performance is linked to the combined action of the
frequency foldback and the skip cycle operation at constant
peak current. Please note that the no-load standby power
includes the 2 MW discharge resistors string placed across
the X2 capacitor on the input filter. These numbers are
excellent considering a low-voltage controller featuring a
start-up network.
Conclusion
This application note describes how an ac-dc converter
meeting all new efficiency challenges can be built with the
new NCP1250. Despite a small TSOP-6 package and a
limited amount of pins, the performance of the final board
nicely competes against other more complex circuits by
offering a similar set of options plus some unique features
such as the non-dissipative OPP circuit. This makes the part
the ideal candidate where space constraints, performance
and cost sensitivity have to be combined.
No-load standby power:
Output Power
Input power - Vin
= 100 V rms (mW)
Input power - Vin
= 230 V rms (mW)
0
33
75
http://onsemi.com
3
AND8486/D
Designator Quantity
Description
C2
1
high-voltage capacitor
C3
1
electrolytic capacitor
Manufacturer
Manufacturer
Part Number
Vishay
MKT1822310635
through-hole
Panasonic
ECA1VAD4R7X
100 pF/1000 V through-hole
Value
Footprint
10 nF/630 Vdc through-hole
4.7 uF/35 V
C4
1
ceramic capacitor
Panasonic
ECKA3A101KBP
C5a, C5b
2
electrolytic capacitor
680 uF/35 V
through-hole
Rubycon
35ZL680MEFC12.5X20
C5
1
ceramic capacitor
10 nF
SMD1206
Multicomp
MC1206B103K500CT
C6
1
film capacitor
10 nF
through-hole
Multicomp
MCRR50103X7RK0050
C7
1
electrolytic capacitor
220 uF/25 V
through-hole
Rubycon
25ML220M8X9
C8
1
ceramic capacitor
1 nF
SMD1206
Multicomp
MC1206B102K500CT
C9
1
ceramic capacitor
330 pF
SMD1206
Multicomp
MC1206B220K500CT
C10
1
ceramic capacitor
22 pF
SMD1206
Multicomp
MC1206B331K500CT
C11
1
X2 capacitor
Epcos
B32922C3474M
C12
1
high-voltage electrolytic capacitor
through-hole
Panasonic
EEUED2G820
C13
1
EMI Y1 capacitor
2.2 nF/ 250 Vac through-hole
CERAMITE
440LD22
C15
1
ceramic capacitor
220 pF
SMD1206
Multicomp
MC1206B221K500CT
C17
1
electrolytic capacitor
100 uF/35 V
through-hole
Panasonic
ECA1VM101
C18
1
ceramic capacitor
22pF
through-hole
Murata
RPE5C2A220J2M1Z03A
D1
1
Zener diode
18 V/ 0.5 W
SOT23
ON Semiconductor
BZX84C18LT3G
D3, D4
2
fast diode
1N4937
D5
1
power diode
NTST30100SG
TO220
ON Semiconductor
NTST30100SG
D6
1
signal diode
1N4148
through-hole
NXP
1N4148
470 nF/275 Vac through-hole
82 uF/400 V
through-hole ON Semiconductor
1N4937G
D7
1
fast diode
MURA160
SMA
ON Semiconductor
MURA160T3G
D10
1
signal diode
1N4148
SOD123
ON Semiconductor
MMSD4148T3G
F1
1
Fuse
250 V / 2 A T
through-hole
Multicomp
MST 2A 250V
HS1, HS2
2
heat sink
IC2
1
shunt regulator
TL431
through-hole ON Semiconductor
IC4
1
diode bridge
KBU4K
through-hole
J1
1
connector
-
through-hole
Multicomp
JR-201S
J2
1
connector
-
through-hole
WEIDMULLER
PM5.08/2/90
L1
1
common mode inductor
2*10 mH/2 A
through-hole
Wurth Elektronik
744823210
L2
1
inductor
2.2 uH/6 A
through-hole
Wurth Elektronik
744772022
M1
1
high-voltage MOSFET
4 A/600 V
TO220
ON Semiconductor
NDF04N60ZG
Q1
1
PNP transistor
BC857
SOT23
ON Semiconductor
BC857ALT1G
Multicomp
TL431CLPG
KBU4K
R5
1
resistor
1.8 k
SMD1206
Vishay
CRCW12061K80FKEA
R6a, R6b,
R6c
3
resistor
1.3
through-hole
Multicomp
MF251R3
R8, R19
2
resistor
1 k / 0.25 W
through-hole
Multicomp
MF251K
R9
1
resistor
10 k
SMD1206
Vishay
CRCW120610K0FKEA
R10
1
resistor
20 k
SMD1206
Vishay
CRCW120620K0FKEA
R11, R13
2
power resistor
47 k / 3 W
through-hole
Vishay
PR03000204702JAC00
R12
1
resistor
18 k
SMD1206
Vishay
CRCW120618K0FKEA
R14
1
NTC thermal sensor
[email protected]°C
through-hole
Vishay
NTCLE100E3104JB0
R15, R17,
R20, R27
4
mains-connected resistor
510k
SMD1206
Vishay
CRCW1206510K00FKEA
http://onsemi.com
4
AND8486/D
Designator Quantity
Description
Value
Footprint
Manufacturer
Manufacturer
Part Number
R16
1
resistor
10
SMD1206
Vishay
CRCW120610R0FKEA
R18
1
resistor
22 k
through-hole
Multicomp
MF2522K
R21
1
power resistor
22 /1 W
through-hole
Vishay
PR01000102209JR500
R22
1
resistor
470 k
SMD1206
Vishay
CRCW1206470KFKEA
R23
1
resistor
1k
SMD1206
Vishay
CRCW12061K00FKEA
R24
1
resistor
220
through-hole
Multicomp
MF25220
R25, R26
2
resistor
47 / 1 W
through-hole
Vishay
PR01000104709JA500
T1
1
RM10 flyback transformer
through-hole
CME France
17452/02
U1
1
optocoupler
SFH615A-2
Vishay
SFH615A-2
U3
1
65 kHz controler
NCP1250B
TSOP6
ON Semiconductor
NCP1250A
V1
1
countersunk head screws + nut
M3x6mm
V2
1
nylon screw + nut
M3x6mm
The transformer has been designed and manufactured by the following French company:
CME transformateurs - 01160 – St Martin du Mont – France – Tel. : +33 (0)4 74 35 55 11 – Fax. : +33 (0)4 74 35 53 97
web: www.cmetransformateur.com
e-mail: [email protected]
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
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AND8486/D
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