NCP1055: 7 W, non-isolated buck ac-dc converter

DN06028/D
Design Note – DN06028/D
7 W, Non-Isolated Buck AC-DC Converter
Device
NCP1055
Application
Input Voltage
1 Output AC to DC
converter
108-132 Vac
Output Power
Topology
I/O Isolation
7 Watts
Non-Isolated
Buck
Converter
No
Other Specifications
Output
91 V
3V
75 mA
100 mA
8 mA
Output Voltage
Ripple
Nominal Current
Max Current
Min Current
PFC (Yes/No)
No
Inrush Limiting / Fuse
Cooling Method/Supply
Orientation
None
Convection
Circuit Description
This design note explains the changes required to modify
the NCP1052 Buck Demo Board’s (AND8098/D) output
from 12V/100mA into 91V/75mA. Please read the original
NCP1052 evaluation board manual for reference 1 .
Design Considerations
NCP105X and Inductor
The first step in the design process is determining which
version of the NCP105x to use. Refer to the “NCP105x
Discontinuous Mode Flyback Design Worksheet” 2 . The
desired input voltages of this particular board range from
108 to 132 Vac (about 150 Vdc to 190 Vdc). The inductor
is chosen to be around 390 μH, a slightly reduced value
compared to the original NCP1052 circuit. The result from
table 1 of the Worksheet indicates that the NCP1055 at 136
kHz can be used for the desired output power of 7 W. A
different version NCP105X may be suggested by the
Worksheet by simply changing the inductor value. The
NCP1055 136 kHz version is used in this design.
Zener Diodes
The output voltage of the converter is set by the breakdown
voltage of Z1. The breakdown voltage of the diode is
calculated using the equation below:
VZ 1 = Vout − 5V
Capacitors
Since the output voltage is increased to 91V, the output
capacitor (C5) must be changed. An electrolytic capacitor
is used as they are more readily available at this voltage
level. The value of C5 is reduced to reduce cost. The
value of the bulk input capacitor (C3) is increased from 10
μF to 33 μF to reduce the input voltage ripple to 3 V. C3
and C5 can be increased to reduce the output voltage
ripple, or they may be reduced to reduce cost. Capacitor
C2 is increased to increase the startup time. Finally, a
filtering capacitor (C4) is added between the feedback pin
and source pin to reduce noise into the feedback pin; this
is a very important addition to the board.
Unchanged Components
Diodes D1, D2, D3, D4 and Capacitor C1 remain the same
as the original NCP1052 board.
1
Available at http://www.onsemi.com/pub/Collateral/NCP1052EVB_MANUAL.PDF.
2
Available at http://www.onsemi.com/pub/Collateral/NCP105X_WORKSHEET.XLS
June 2007, Rev. 0
This equation comes from application note AND8098/D. A
91 V output is achieved using an 86 V Zener. The
breakdown of zener diodes can be added in series to
obtain the desired breakdown voltage. In this design two
43 V Zeners in series are used for Z1. Zener diode Z1 is
used in the original NCP1052 board to clamp the voltage
down at light or no load. However, the higher voltage of
this design requires a higher power dummy load (R2) to
maintain the output in regulation when no load is present.
It may be possible to use a lower frequency version of the
NCP1055 and reduce the power rating of R2.
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DN06028/D
Key Features
y Low-cost, simple design
y Relatively few changes for output voltage change
y Self-powered from high input voltage
y Frequency jittering for low electromagnetic
interference(EMI)
y Thermal and short circuit fault protection
Schematic
Figure 1: Circuit Schematic
Bill of Materials
Designator
Quantity
Description
Value
Tolerance
Manufacturer
Manufacturer
Part Number
U1
D1, D4
D2
D3
Z1a, Z1b
R1
R2
C1
C2
C3
C4
C5
L1
1
2
1
1
2
1
1
1
1
1
1
1
1
Switching Regulator
Ultrafast Diode
Switching Diode
General Diode
Zener Diode
Chip Resistor
Axial Resistor
Ceramic Capacitor
Tantalum Capacitor
Electrolytic Capacitor
Ceramic Capacitor
Electrolytic Capacitor
Inductor
680 mA / 136 kHz
1 A / 600 V
200 mA / 100 V
1 A / 600 V
43 V
2 kΩ / 250 mW
12 kΩ / 1 W
0.22 µF / 50 V
10 µF / 25 V
33 µF / 450 V
1000 pF / 50 V
10 µF / 250 V
390 µH / 450 mA
N/A
N/A
N/A
N/A
5%
5%
10%
10%
10%
20%
10%
20%
20%
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
Vishay
Ohmite
Vishay
Vishay
Panasonic
Vishay
Panasonic
Coilcraft
NCP1055ST136G
MURS160T3
MMSD914T1
MRA4006T1
MMSZ5260BT1G
CRCW12062K00JNEA
OX123KE
VJ1206Y224KXXA
595D106X9025B2T
ECA-2WM330
VJ1206Y102KXXA
ECA-2EM100
RFB0807-391L
June 2007, Rev. 0
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DN06028/D
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Output Waveforms*
Figure 2: 89V Output at Full Load
(Left: Vin=108Vac, Right: Vin=132Vac)
Figure 3: 89V Output 3V Ripple
(Left: Vin=108Vac, Right: Vin=132Vac)
Figure 4: 89V Output at Startup
(Left: Vin=108Vac, Right: Vin=132Vac)
*Note: output waveforms in Figures 2 through 4 were taken using an 89 V version of the board. The only difference being the breakdown voltage of the Zener diodes.
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© 2007 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 David Berdy, e-mail: [email protected]
June 2007, Rev. 0
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