Design Note 12 V/ 30 W, Off-Line Mini Forward Converter

DN05029/D
Design Note – DN05029/D
A 12 Volt, 30 Watt, Off-line Mini-Forward Converter
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP1251B
NCP431
NDD04N60
White Goods, Small
Instruments, EMeters, Industrial
Equipment
90 – 267 Vac
30 Watts
RCD Reset
Forward
Converter
3 kV
Other Specification
Output Voltage
Ripple
Nominal Current
Max Current
Min Current
Output 1
Output 2
Output 3
Output 4
12 Vdc
< 1%
2.5 Amps
3 Amp surge
zero
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PFC (Yes/No)
Efficiency
Inrush Limiting / Fuse
Operating Temp. Range
Cooling Method /
Supply Orientation
Signal Level Control
No
84% at full load
Yes
0 to 50C
Convection
NA
No
Others Input EMI filter
Circuit Description
This Design Note describes a simple, low cost,
high performance, off-line forward converter
power supply using ON Semiconductor’s
NCP1251B flyback controller (TSOP6 package),
NDD04N60 D-Pak Mosfet, and the NCP431
programmable zener (SOT23 package). This
design is an extension of the “mini-forward”
converter design described in ON
Semiconductor’s Application Note AND8489 in
which the NCP1028 monolithic switcher was
used as the main controller.
topology. This design is particularly useful in Emeter and white goods applications where a
higher output power is required but low
ripple/noise and high efficiency are imperative.
In addition, all of the various features of the
NCP1251current mode controller can be utilized
as needed.
The output inductor is an off-the-shelf part
(Coilcraft) and the transformer is the same as
that used in AND8489 and is available from
Wurth Electronics (see drawing below).
Key Features
The use of an RCD snubber reset type of
forward converter allows the extension of the
useful duty cycle to over 50% without excessive
voltage excursions across the MOSFET. The
topology provides lower output ripple and noise,
lower EMI generation, and slightly higher
efficiency than an equivalent 12V/2.5A flyback
Rev 0, May, 2012
 Input EMI filter for conducted EMI compliance
 Low Vf Schottky rectifier for high efficiency
 Low standby (no load) power
 Current mode control with adjustable output
voltage and current limit setpoints
 5V/6A version also designed and tested.
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1
DN05029/D
Forward Converter Schematic 1
J1
R1
L1
3.9 mH
4.3, 5W
D1-D4
MRA4007
C2
C1
90 - 265Vac
100nF
Input
"x"
F1
L2
470 uH
R2 2.2M
0.5W
100nF
"x"
T1
C3
C4
10 uF,
400Vdc
1.5 A,
250 Vac
47K,
1W
47uF
400V
2.2nF
2 kV
NDD04N60
Q1
R8
470K
R9
470K
10K
D6
1N4937
3
1
9
2
+
C7
10nF
R11
1K
C14 12V,
2.5A
0.1
_
10
5
1nF
"Y1"
6
4
R10
D7
2.2K
MMSD
4148A
R14
1K
R15
10K
2
MMSZ
5252B
1000uF
16V
+
C11
U1
Z1
C13
R13
43
7
3
4
U2
3
opto
1
R12
C8
4.7uF
35V
D8
4
1.0
0.5W
NCP1251B1
5
390pF
100uH
NTSB2011CT
R6
R7
J2
C12
R4
C5
D5
MRA4007
L3
1
R3
10
C9
1nF
1K
+
C10
220pF
C6
1 uF,
100V
2
U3
R16
C15
47K
0.1
NCP431A
R17
20K
R18
5.1K
NOTES:
1. L1 is Coilcraft E3491-AL common mode EMI inductor ( 3.9mH)
2. L2 is Wurth 744772471 (470 uH) or similar
3. L3 is Coilcraft PCH-45X-104LT (100uH, 2.8A) inductor
4. R10 sets slope compensation.
5. R12 value dependent on Vout and Vcc winding turns.
6. R17 sets Vout (R17/18 node is set to 2.5V)
7. R6 sets current limit level.
8. R1 is optional inrush limiter.
9. U1 optocoupler is Vishay SFH6156A-4 or similar.
10. Crossed schematic lines are not connected.
11. Heavy schematic lines are recommended ground plane areas.
30 Watt, 12 Volt Output NCP1251
Single Switch Forward Converter
1
© 2012 ON Semiconductor.
Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor
does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to
assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated
with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its
products at any time, without notice.
Design note created by Frank Cathell, e-mail: [email protected]
Rev 0, May, 2012
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2
DN05029/D
MAGNETICS DESIGN DATA SHEET
Project / Customer: ON Semiconductor - 30 watt, 12 vout NCP1251 Fwd Conv
Part Description: 30 watt resonant reset forward conv. xfmr (Rev 1)
Schematic ID: T1
Core Type: EF25 (E25/13/7); 3C90 material or similar
Core Gap: No gap
Inductance: (Primary) 12 mH minimum
Bobbin Type: 10 pin horizontal mount for EF25
Windings (in order):
Winding # / type
Turns / Material / Gauge / Insulation Data
Primary A (1 - 2)
50T of #28HN over 2 layers (25 TPL). Insulate for
1 kV to next winding. Self leads to pins.
Vcc (4 - 5)
14 turns of #28 HN over 1 layer, close wound
and centered in window. Self leads to pins.
Insulate to 3 kV to next winding
12V Secondary (9 - 7)
20 turns of #24 triple insulated wire over one layer.
Self leads to pins.
Primary B (2 - 3)
Same as Primary A. Insulate with tape and selfleads to pins.
Hipot: 3 kV from primaries & Vcc to secondary for 1 minute.
Lead Breakout / Pinout
Schematic
1
(Top View of Bobbin)
Pri A
2
10 9 8 7 6
9
12V sec
Pri B
0.20" pin
separation
(8 places)
0.80"
7
3
4
1 2 3 4 5
Vcc
5
Transformer is available from Wurth Electronics as part number 750312228 Rev 0.
Rev 0, May, 2012
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3
DN05029/D
Efficiency Plots
References:
ON Semiconductor Data Sheet for NCP1251 controller.
ON Semiconductor Application Note AND8489/D
ON Semiconductor Design Notes DN05012 and DN05028
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