NCP1124, NCP431: Universal AC Input, 5 Volt Output, 10 Watt Power Supply

DN05064/D
Design Note – DN05064/D
Universal AC Input, 5 Volt Output,
10 Watt Power Supply
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP1124
NCP431
Smart Meters,
Electric Meters,
White Goods
85 to 265 Vac
10W
CCM Flyback
Isolated
( 3 kV)
Output Specification
Output Voltage
Ripple
Nominal Current
Max Current
Min Current
5 Vdc nominal
100 mV p/p @ full load
2 Amps continuous
2.2 A maximum
zero
PFC (Yes/No)
Input Protection
Operating Temp. Range
No(Pout ≤ 10 watts)
Fuse
0 to +50°C
Cooling Method
Convection
Standby Power
30 mW at 115 Vac
80 mW at 230 Vac
Circuit Description
This design note describes a simple 10 watt,
universal AC input, constant output voltage
power supply intended for AC adapters,
industrial equipment, or white goods, where
isolation from the AC mains is required, and low
cost, high efficiency, and low standby power are
essential.
Performance characteristics for efficiency,
output ripple, and internal MOSFET drain
switching characteristics (Vds, Id) are shown in
the figures and plots below. Enhanced input
transient protection (lightning, etc.) can be
accomplished with the addition of an
appropriate TVS device across the input of the
diode bridge.
.
The featured power supply is a simple CCM
flyback topology utilizing ON Semiconductor’s
new NCP1124 monolithic with with integral 9ohm, vertical channel MOSFET in a PDIP7
package (U1). This Design Note provides the
complete circuit schematic details and BOM for
5V, 2A power supply. The simple input EMI
filter (C1, L1) is adequate to pass Level B for
FCC conducted EMI compliance. The NCP431
programmable zener is used as an error
amplifier (U3), plus an optocoupler feedback
scheme (U2) provides for excellent line and
load regulation with high input-to-output safety
isolation.
April 2014, Rev. 0
Key Features
 Universal AC input range (85 – 265 Vac).
 Input filter for conducted EMI attenuation.
 650V Avalanche rated MOSFET.
 Input filter for conducted EMI attenuation.
 Very low standby (no load) power consumption.
 Frequency foldback under light load.
 Inherent over-current, over-voltage and over
temperature protection.
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DN05064/D
For optimum thermal characteristics, the printed circuit board should be laid out to include clad “pours”
around pins 5 and 6 of the DIP8 package (MOSFET drain pins). Resistors 9 sets the peak current limit
point for the internal overcurrent protection circuit of U1 and can be adjusted for desired max output
current. For output voltages other than 5 volts, typical circuit changes include the transformer turns ratio
for both the secondary and the primary aux winding, the value of R17 in the output voltage sense divider,
and selecting appropriate voltage ratings for output rectifier D8 and output capacitors C9A, B & C.
Depending on the transformer aux winding characteristics, it may be necessary to change R11 to a
higher value resistance value to adjust the nominal Vcc voltage. Z1 can be added as an option in the
event that the compliance range of the Vcc over the output load range exceeds the OVP trip point on pin
1 of U1 (28 volts). Such a scenario would be the result of a transformer with high leakage inductance.
Circuit Schematic
NCP1124
06
R9
0 6W
10k
NOTES:
1. Crossed lines on schematic are NOT connected.
2. U2 is NEC PS2561L-1 or equivalent optocoupler(CTR>50%).
3. R1 is optional for increased inrush limiting- use wire wound only.
4. L1A/L1B are Wurth #7447728215 inductors (820uH, 500mA).
5. Output caps(C9A/B/C) are radial lead, low impedance types(UCC LXV series or similar).
6. R11 is for Vcc trimming(<28Vmax), typically zero ohms.
7. R9A/B sets max output current.
8. Heavy schematic lines indicate recommended ground plane areas.
10 Watt NCP 1124 Power Supply With Universal AC Input
Circuits Optimized for 650V 9MOSFET (compared to MOSFET NCP1126/NCP1129)
A single 0.6 W, 1.5Ω resistor with 1% tolerance is used to limit the maximum current flowing through the
MOSFET, instead of paralleling two 1.8Ω,1/2W resistors with 5% tolerance.
April 2014, Rev. 0
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DN05064/D
T1 Transformer Designs (Available from ICE Components Inc. and Wurth Electronics)
5V/2A, 65 kHz Version (ICE # TO0915-1, Wurth Electronics #750313860 Rev 01)
Core: E25/10/6 (812E250)
Primary A: 55 turns of 0.25mm mag wire
5V Secondary: 11 turns bifilar of 0.6mm Triple Insulated Wire (2 layers)
Aux/Vcc: 25 turns of 0.15mm mag wire spiral wound over 1 layer
Primary B: 55 turns of 0.25mm mag wire
Primary Inductance (Pri A and B in series): 2 mH +/- 10% (gap in center leg)
Leakage Inductance (5Vsec & Aux shorted): 40 uH max
5 Volt Efficiency vs Output Load Curves
0.81
0.8
0.79
0.78
115Vac
0.77
230Vac
0.76
0.75
0.74
0.73
0.5
1
1.5
2
Board Picture
April 2014, Rev. 0
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Full Load Output Ripple @ 120 Vac Input
10mV/div,
12.5us/div
MOSFET Drain Voltage (120 Vac Input)
Full Load
100V/div,
10us/div
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0.5 Amp Load
100V/div
,10us/div
Mosfet Drain Current (120 Vac Input)
Full Load
600mV/div
,10us/div
0.5 Amp Load
600mV/div
10us/div
April 2014, Rev. 0
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DN05064/D
Conducted EMI Plot
dBuV
80
70
EN 55022; Class B Conducted, Average
EN 55022; Class B Conducted, Quasi-Peak
60
50
40
30
20
10
1124_Demo_N_AVG
0
-10
-20
1
10
1/16/2014 10:43:19 AM
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(Start = 0.15, Stop = 30.00) MHz
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Bill of Materials
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References
ON Semiconductor data sheet for NCP1126, 1129 monolithic switcher.
ON Semiconductor Design Notes DN05012, DN05017, DN05018, DN05028, DN05029, DN05043/D
ON Semiconductor Application Note AND8489
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© 2014 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 Le Du, e-mail: [email protected]
Frank Cathell email: [email protected]
April 2014, Rev. 0
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