STMicroelectronics AN3011 In certain applications such as lcd or plasma tv Datasheet

AN3011
Application note
Wide range input (90 - 265), single output (5 V-11 W)
EVLVIP27H-12SB, VIPer27 demonstration board
Introduction
In certain applications such as LCD or plasma TVs, desk top computers, etc., the power
supply that converts the energy from the mains often includes two modules: the main power
supply that provides most of the power which is off when the application is off or in standby
mode, and the auxiliary power supply that only provides energy to specific parts of the
equipment, like the USB ports, remote receivers, or modems, but stays on when the
application is in standby mode.
In standby mode it is often required that the equipment input power is as low as possible,
which means reducing the input power of the auxiliary power supply, in no-load or light-load
conditions, as low as possible. This demonstration board meets the specifications of a wide
range of auxiliary power supplies for the above mentioned applications. Furthermore, it is
optimized for very low standby consumption which helps to meet the most stringent energy
saving requirements. Using the VIPer27, which has a switching frequency of 115 kHz, helps
to reduce the transformer size.
Figure 1.
Demonstration board image
!-V
January 2011
Doc ID 16043 Rev 1
1/37
www.st.com
Contents
AN3011
Contents
1
2
3
Board descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2
Schematic and bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3
Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1
Typical board waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2
Precision of the regulation and output voltage ripple . . . . . . . . . . . . . . . . 11
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1
3.2
Light load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.1
No-load condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.2
Low-load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Test equipment and measurement of efficiency and input power . . . . . . 23
3.2.1
Measuring input power notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3
Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4
Secondary winding short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . 27
3.5
Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.6
Brown-out protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2/37
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AN3011
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Table 16.
Table 17.
Table 18.
Table 19.
Table 20.
Table 21.
Table 22.
Electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
BOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Output voltage and VDD line-load regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Active-mode efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Line voltage average efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Energy efficiency criteria for standard models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Energy efficiency criteria for low voltage models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
No-load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Energy consumption criteria for no-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Low-load performance. POUT = 30 mW (brown-out disabled) . . . . . . . . . . . . . . . . . . . . . . 19
Low-load performance. POUT = 30 mW (brown-out enabled) . . . . . . . . . . . . . . . . . . . . . . . 19
Low-load performance. POUT = 50 mW (brown-out disabled) . . . . . . . . . . . . . . . . . . . . . . 19
Low-load performance. POUT = 50 mW (brown-out enabled) . . . . . . . . . . . . . . . . . . . . . . . 20
Low-load performance. POUT = 100 mW (brown-out disabled) . . . . . . . . . . . . . . . . . . . . . 20
Low-load performance. POUT = 100 mW (brown-out enabled) . . . . . . . . . . . . . . . . . . . . . . 20
Low-load performance. POUT = 200 mW (brown-out disabled) . . . . . . . . . . . . . . . . . . . . . 21
Output power when the input power is 1 W (BR disabled) . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output power when the input power is 1 W (BR enabled) . . . . . . . . . . . . . . . . . . . . . . . . . 22
Overvoltage protection activation level test results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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List of figures
AN3011
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
4/37
Demonstration board image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Transformer size - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transformer size - side view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pin placement diagram - bottom view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pin placement diagram - electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Drain current and voltage at full-load 115 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Drain current and voltage at full-load 230 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Drain current and voltage at full-load 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Drain current and voltage at full-load 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Output voltage ripple 115 VINAC full-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output voltage ripple 230 VINAC full-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output voltage ripple 115 VINAC no-load (burst mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output voltage ripple 230 VINAC 50 mA load (burst mode). . . . . . . . . . . . . . . . . . . . . . . . . 13
Efficiency vs VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Active mode efficiency vs VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Input voltage average efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ENERGY STAR efficiency criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Converter input power vs Vin_ac in light-load condition . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Converter efficiency vs Vin_ac in light-load condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Efficiency vs AC input voltage when the input power is 1 W . . . . . . . . . . . . . . . . . . . . . . . 23
Wattmeter possible connections with the U.U.T. (unit under test) . . . . . . . . . . . . . . . . . . . 24
Wattmeter connection scheme for low input current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Wattmeter connection scheme for high input current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Output short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Operation with output shorted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Converter power capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Second overcurrent protection - protection tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Operating with the secondary winding shorted. Restart mode . . . . . . . . . . . . . . . . . . . . . . 28
OVP circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
OVP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
OVP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
J7 jumper setting. Brown-out disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
J7 jumper setting. Brown-out enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Brown-out protection, internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Input AC voltage steps from 90 VAC to 65 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Input voltage steps from 90 VAC to 0 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Doc ID 16043 Rev 1
AN3011
Board descriptions
1
Board descriptions
1.1
Electrical specifications
The electrical specifications of the demonstration board are listed in Table 1.
Table 1.
1.2
Electrical specifications
Parameter
Symbol
Value
Input voltage range
VIN
[90 VRMS; 265 VRMS]
Nameplate output voltage
VOUTn
5V
Max output current
IOUT
2.2 A
Precision of output regulation
VOUT − VOUTn
VOUTn
±5 %
High frequency output voltage ripple
ΔVOUT_HF
50 mV
Max ambient operating temperature
TA
60 °C
Schematic and bill of materials
The schematic of the board is shown in Figure 2, and the bill of materials is shown in
Table 2.
Doc ID 16043 Rev 1
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+6 Schematic
AN3011
Figure 2.
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Board descriptions
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AN3011
Table 2.
Board descriptions
BOM
Part
reference
Description
Part name
Manufacturer
BR1
Bridge diodes
DF06M
Fairchild/ Vishay
C1,C13
100 nF X2 capacitor
C3
33 µF 450 V electrolytic cap.
C4
22 µF 35 V electrolytic cap.
C5
N.M
C6
1.8 nF ceramic cap
C7
15 nF
C8
2.2 nF Y1 capacitor
C9, C14
ZL 1000 µF 16 V electrolytic cap.
C10
YXF 47 µF 25 V electrolytic cap.
YXF 47 µF 25 V
C11
22 nF ceramic cap
22 nF
C12
10 nF ceramic cap
10 nF
D1
100 V small signal Schottky diode
BAT46
D2
100 V small signal fast diode
1N4148
D3
600 V 1 A ultra-fast diode
STTH1L06
STMicroelectronics
D4
Power Schottky diode
STPS745
STMicroelectronics
D5
250 V Transil
1.5KE250
STMicroelectronics
D6
18 V Zener
F1
1 A Fuse
HS1
Heat sink
J7
Selector
L1
3.3 µH 3 A inductor
NTC1
15 Ω
OPTO1
Opto-coupler
R1
3.3 Ω resistor
R3
33 kΩ 1% precision resistor
R6
1 2kΩ 1% precision resistor
R8
120 kΩ 1% precision resistor
R9
39 kΩ 1% precision resistor
R10
270 kΩ
R12
47 kΩ
R13
1.5 kΩ
R14
180 kΩ 1% precision resistor
R15
3.3 Meg 1% precision resistor
RUBYCON
RUBYCON
STMicroelectronics
EPCOS
PC817
Doc ID 16043 Rev 1
SHARP
7/37
Board descriptions
Table 2.
AN3011
BOM (continued)
Part
reference
Description
R16, R17
2.7 Meg 1% precision resistor
R18
47 kΩ 1% precision resistor
R19
220 Ω
T1
Part name
Manufacturer
Switch mode transformer
WE - 750871012
Würth Elektronik
T2
Common mode line filter
BU15-4530R4BL
Coilcraft
U1
Offline switching regulator
VIPER27HN
STMicroelectronics
VR1
Voltage reference
TS431
STMicroelectronics
1.3
Transformer
Transformer characteristics are listed in Table 3:
Table 3.
Transformer characteristics
Properties
Value
Test condition
Manufacturer
Würth Elektronik
Part number
750871012
Primary inductance
900 µH ±10 %
Measured at 10 kHz 0.1 V
Leakage inductance
25 µH max
Measured at 100 kHz 0.1 V (primary
and secondary windings shorted)
Primary to secondary turn ratio
(4 - 5) / (6, 7 – 8, 9)
14.75 ±1 %
Measured at 10 kHz 0.1 V
Primary to auxiliary turn ratio (6 - 4) /
(3 - 1)
5.36 ±1 %
Measured at 10 kHz 0.1 V
Insulation
4 kV
Primary to secondary
Figure 3, 4, 5, and 6 show the size and pin distances (inches and [mm]) of the transformer.
8/37
Doc ID 16043 Rev 1
AN3011
Figure 3.
Board descriptions
Transformer size - top view
Figure 4.
Transformer size - side view
!-V
Figure 5.
Pin placement diagram - bottom
view
!-V
Figure 6.
Pin placement diagram - electrical
diagram
!-V
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!-V
9/37
Testing the board
AN3011
2
Testing the board
2.1
Typical board waveforms
Figure 7 and 8 show the drain current and the drain voltage waveforms at the nominal input
voltages, which are 115 VAC and 230 VAC when at maximum load (2.2 A). Figure 9 and 10
show the same waveforms for the same load condition, but with the input voltages at the
minimum 90 VAC and the maximum 265 VAC.
The converter is designed to operate in continuous conduction mode (in full-load condition)
at low-line. CCM (continuous conduction mode) allows the reducing of the root mean square
currents value, at the primary side, in the power switch inside the VIPer, and in the primary
winding of the transformer; at the secondary side in the output diode (D4) and in the output
capacitors (C9 and C14). Reducing RMS currents means reducing the power dissipation
(mainly in the VIPer) and the stress on the above mentioned components.
Figure 7.
Drain current and voltage at fullload 115 VAC
Figure 8.
!-V
Figure 9.
Drain current and voltage at fullload 90 VAC
!-V
Figure 10. Drain current and voltage at fullload 265 VAC
!-V
10/37
Drain current and voltage at fullload 230 VAC
Doc ID 16043 Rev 1
!-V
AN3011
2.2
Testing the board
Precision of the regulation and output voltage ripple
The output voltage of the board was measured in different line and load conditions. The
results are given in Table 4. The output voltage is practically not affected by the line
condition and only slightly affected by load condition (a difference of 10 mV between max
and minimum VOUT, see Table 4). The VDD voltage was also measured.
Table 4.
Output voltage and VDD line-load regulation
Full load
Half load
No load
VINAC (V)
VOUT (V)
VDD (v)
VOUT (V)
VDD (V)
VOUT (V)
VDD (V)
90
5.073
21.1
5.078
20.00
5.083
9.98
115
5.073
20.98
5.078
20.02
5.083
9.83
230
5.073
20.94
5.077
20.08
5.083
9.30
265
5.073
20.98
5.077
20.04
5.083
9.17
In a two-output flyback converter, when just one output is regulated, the unregulated output
does not rigorously respect the turn ratio. The unregulated output voltage value depends not
only by the turn ratio but also, approximately, from the output currents ratio (output current at
the regulated output divided by output current of the unregulated output).
As confirmed from the results reported in Table 4, the VDD voltage (unregulated auxiliary
output) increases as the load on the regulated output increases. In order to avoid the VDD
voltage exceeding the VIPer27 operating range, an external clamp was used (D6, R19, see
schematic).
The ripple at the switching frequency superimposed at the output voltage was also
measured. The board is provided with an LC filter for cleaner output voltage. The high
frequency voltage ripple across capacitors C9 and C14 (VOUT_FLY), that is the output
capacitors of the flyback converter before the LC filter (see schematic in Figure 2), was also
measured to verify the effectiveness of the LC filter.
The waveforms of the two voltages (VOUT and VOUT_FLY) are reported in Figure 11 and
12. The output voltage ripple when the converter input voltage is 115 VAC is shown in
Figure 11, and the output voltage ripple when the converter input voltage is 230 VAC is
shown in Figure 12.
Doc ID 16043 Rev 1
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Testing the board
AN3011
Figure 11. Output voltage ripple 115 VINAC full-load
#H 6/54?&,9
#H 6/54
#H 6$2!).
!-V
The measured output voltage ripple is around 20 mV, well below the maximum admitted
value (50 mV, see electrical specification in Table 1).
Figure 12. Output voltage ripple 230 VINAC full-load
#H 6/54?&,9
#H 6/54
#H 6$2!).
!-V
When the device is working in burst mode, a lower frequency ripple is present. In this
operation mode the converter does not supply continuous power to its output. It alternates
periods when the power MOSFET is kept off, and no power is processed by the converter,
and periods when the power MOSFET is switching and power flows towards the converter
output. Even no-load is present at the output of the converter, during no switching periods
the output capacitors are discharged by their leakage currents and by the currents needed
to supply the circuitry of the feedback loop present at the secondary side. During the
switching period the output capacitance is recharged. Figure 13 and 14 show the output
voltage and the feedback voltage when the converter is no-loaded. In Figure 13 the
converter is supplied with 115 VAC, and with 230 VAC in Figure 14.
12/37
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AN3011
Testing the board
Figure 13. Output voltage ripple 115 VINAC no-load (burst mode)
#H 6 /54
#H ) $2!).
!-V
Figure 14. Output voltage ripple 230 VINAC 50 mA load (burst mode)
#H 6 /54
#H ) $2!).
!-V
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Efficiency
3
AN3011
Efficiency
The efficiency of the converter was measured in different load and line voltage conditions. In
accordance with the ENERGY STAR® active mode testing efficiency method, the
measurements are done with different load values (full-load, 75%, 50%, and 25% of the fullload) for different input voltages. The results are given in Table 5 below.
Table 5.
Efficiency
Efficiency (%)
VINAC
(VRMS)
Full load (2.2 A)
75 % load (1.65
A)
50 % load (1.1 A)
25 % load (0.55
A)
90
73.0
75.1
76.9
77.9
115
75.3
76.5
77.9
78.1
132
75.9
76.9
77.8
77.7
175
76.8
77.3
77.6
76.4
230
77.4
77.6
77.3
75.4
265
76.8
76.9
76.3
74.2
For better visibility the results are plotted in the diagrams below. In Figure 15, efficiency
versus converter AC input voltage (VIN), for four different load values, is plotted. In
Figure 16, the value of efficiency versus load for different input voltages is plotted.
Figure 15. Efficiency vs VIN
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Efficiency
Figure 16. Efficiency vs load
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The active mode efficiency is defined as the average of the efficiencies measured at 25%,
50%, and 75% of maximum load and the maximum load itself. Table 6 shows the active
mode efficiency calculated from the measured value of Table 5. The values in Table 6 are
plotted in Figure 17. In Figure 18 the average value of the efficiency versus load is shown
(the average was obtained considering efficiency at different input voltages).
Table 6.
Active-mode efficiency
Active mode efficiency
VINAC (VRMS)
Efficiency (%)
90
75.8
115
77.0
230
76.9
265
76.1
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Efficiency
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Figure 17. Active mode efficiency vs VIN
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Figure 18. Input voltage average efficiency vs load
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Table 7.
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Line voltage average efficiency vs load
Load (% of full load)
Efficiency (%)
100
75.7
75
76.5
50
77.1
25
76.4
In version 2.0 of the ENERGY STAR® program requirement for single voltage external
AC/DC power supplies (see References 2), the power supplies are divided into two
categories: low voltage power supplies and standard power supply, with respect to the
nameplate output voltage and current. An external power supply, in order to be considered a
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Efficiency
low voltage power supply, must have a nameplate output voltage lower than 6 V and a
nameplate output current greater than or equal to 550 mA.
Table 8 and 9 show the EPA energy efficiency criteria for AC/DC power supplies in active
mode for standard models and for low voltage models respectively.
Table 8.
Energy efficiency criteria for standard models
Nameplate output power (Pno)
Minimum average efficiency in active mode (expressed as
a decimal)
0 to = 1 W
= 0.48 *Pno+0.140
> 1 to = 49 W
= [0.0626 * In (Pno)] + 0.622
> 49 W
= 0.870
Table 9.
Energy efficiency criteria for low voltage models
Nameplate output power (Pno)
Minimum average efficiency in active mode (expressed as
a decimal)
0 to = 1 W
= 0.497 *Pno+0.067
> 1 to = 49 W
= [0.075 * In (Pno)] + 0.561
> 49 W
= 0.860
Figure 19. ENERGY STAR efficiency criteria
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The criteria are plotted in Figure 19 above where the red line is the criteria for the standard
model and the blue line is the criteria for the low voltage model. The PNO axe is in the
logarithmic scale.
The presented power supply belongs to the low voltage power supply category and, in order
to be compliant with ENERGY STAR requirements, must have an efficiency higher than 74.1
% when the converter input voltage is at the nominal value (115 VAC or 230 VAC in this
case). For all the considered input voltages the efficiency (see Table 6) results are higher
than the required value.
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3.1
Light load performance
3.1.1
No-load condition
The input power of the converter was measured in no-load condition, with brown-out
protection disabled (see relevant section) and brown-out protection enabled for different
applied input voltages (see Table 10). The converter in no-load condition always works in
burst mode so that the average switching frequency is strongly reduced. The average
switching frequency values were also measured. The presence of the resistor dividers (R16,
R17 and R18, see schematic of Figure 2) to sense the flyback input voltage, when brownout protection is enabled, does not affect the average switching frequency, but obviously
affects the input power due to the power dissipated in the resistor divider itself.
Table 10.
No-load input power
Pin (mW)
Pin (mW)
(BR enabled)
(No BR)
90
19.20
16.80
1.0816
115
22.90
17.50
0.9706
132
25.00
18.60
0.9139
175
33.00
23.00
0.7552
230
48.00
29.00
0.6923
265
62.00
37.00
0.6561
Vin AC (VRMS)
fSW_AVG (kHz)
In the ENERGY STAR program version, the power consumption of the power supply when it
is no-loaded is also considered. The compliance criteria is shown in Table 11:
Table 11.
Energy consumption criteria for no-load
Nameplate output power (Pno)
Maximum power in no-load for AC/DC
EPS
0 to = 50 W
< 0.3 W
> 50 watts < 250 W
< 0.5 W
The performance of the demonstration board is far better then required, but it is worth noting
that often the AC/DC adapter or battery charger manufacturer have stricter requirements
regarding no-load consumption, compared to ENERGY STAR requirements, due also to
other standards or recommendations which they want to be compliant with. In cases where
the converter is used as the standby power supply for LCD TVs, PDPs or other applications,
the line filter is often the big line filter of the main power supply which heavily contributes to
the standby consumption, even though the power needed to the auxiliary power supply is
very low.
The ENERGY STAR program does not have other requirements regarding light-load
performance, however the input power and efficiency of the demonstration board, also in
other low load cases, is given in order to supply more complete information.
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3.1.2
Efficiency
Low-load performance
The demonstration board was tested not only in no-load condition but also with a low-load
applied. The tests were performed with 30 mW, 50 mW, 100 mW and 200 mW with brownout protection enabled and with brown-out protection disabled
●
POUT = 30 mW
Table 12.
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT
(mW)
fSW_AVG (kHz)
90
29.48
51.60
57.13
22.12
3.731
115
29.48
54.40
54.19
24.92
3.375
132
29.48
55.00
53.60
25.52
3.155
175
29.48
59.60
49.47
30.12
2.814
230
29.48
69.00
42.73
39.52
2.876
265
29.48
74.00
39.84
44.52
2.534
Table 13.
●
Low-load performance. POUT = 30 mW (brown-out disabled)
Low-load performance. POUT = 30 mW (brown-out enabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT (mW)
90
29.48
54.80
53.80
25.32
115
29.48
57.90
50.92
28.42
132
29.48
62.30
47.32
32.82
175
29.48
69.80
42.24
40.32
230
29.48
87.00
33.89
57.52
265
29.48
101.00
29.19
71.52
POUT = 50 mW
Table 14.
Low-load performance. POUT = 50 mW (brown-out disabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT (mW)
fSW_AVG (kHz)
90
54.39
85.90
63.32
31.51
6.248
115
54.39
87.40
62.23
33.01
5.663
132
54.39
88.20
61.66
33.81
5.314
175
54.39
94.80
57.37
40.41
5.259
230
54.39
104.00
52.30
49.61
4.845
265
54.39
111.00
49.00
56.61
4.299
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Table 15.
●
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT (mW)
90
54.39
87.20
62.37
32.81
115
54.39
93.80
57.98
39.41
132
54.39
94.00
57.86
39.61
175
54.39
104.20
52.20
49.81
230
54.39
125.00
43.51
70.61
265
54.39
139.00
39.13
84.61
POUT = 100 mW
Table 16.
Low-load performance. POUT = 100 mW (brown-out disabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT
(mW)
fSW_AVG (kHz)
90
106
152
69.5
46
11.3
115
106
157
67.3
51
10.2
132
106
157
67.3
51
9.6
175
106
162
65.3
56
8.5
230
106
177
59.7
71
8.7
265
106
181
58.4
75
7.8
Table 17.
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Low-load performance. POUT = 50 mW (brown-out enabled)
Low-load performance. POUT = 100 mW (brown-out enabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT (mW)
90
106
155
68.2
49
115
106
159
66.5
53
132
106
166
63.7
60
175
106
174
60.8
68
230
106
195
54.2
89
265
106
206
51.3
100
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Efficiency
●
POUT = 200 mW
Table 18.
Low-load performance. POUT = 200 mW (brown-out disabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT
(mW)
fSW_AVG (kHz)
90
208.403
286
72.87
77.597
21.3115
115
208.403
293
71.13
84.597
19.2462
132
208.403
294
70.89
85.597
18.1681
175
208.403
296
70.41
87.597
16.0584
230
208.403
313
66.58
104.597
16.4671
265
208.403
328
63.54
119.597
14.7167
Low-load performance. POUT = 200 mW (brown-out enabled)
VIN_AC
POUT (mW)
PIN (mW)
Eff. (%)
PIN-POUT (mW)
90
208.403
289
72.11
80.60
115
208.403
296
70.41
87.60
132
208.403
299
69.70
90.60
175
208.403
313
66.58
104.60
230
208.403
336
62.02
127.60
265
208.403
349
59.71
140.60
Figure 20. Converter input power vs Vin_ac in light-load condition
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Efficiency
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Figure 21. Converter efficiency vs Vin_ac in light-load condition
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Depending on the equipment supplied, it’s possible to have several criteria to measure the
standby or light-load performance of a converter. One of these is the measurement of the
output power when the input power is equal to 1 watt. In Table 19 and 20, the output power
needed to have 1 W of input power in different line conditions is shown, with BR disabled
and with BR enabled respectively. Figure 22 shows the diagram of the efficiency
(proportional to the output power) versus the input voltage when the input power is 1 W.
Table 19.
Output power when the input power is 1 W (BR disabled)
VIN (VRMS)
PIN (mW)
POUT (mW)
Efficiency (%)
Pin-Pout (mW)
90
1000
737
73.70
263
115
1000
752
75.23
248
132
1000
757
74.74
243
175
1000
717
71.67
283
230
1000
686
68.62
314
265
1000
666
66.59
334
Table 20.
Output power when the input power is 1 W (BR enabled)
PIN
POUT
Efficiency
Pin-Pout
(mW)
(mW)
(%)
(mW)
90
1000
737
73.70
263
115
1000
752
75.23
248
132
1000
742
74.21
258
175
1000
712
71.16
288
230
1000
676
67.60
324
265
1000
656
65.57
344
VIN (VRMS)
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Figure 22. Efficiency vs AC input voltage when the input power is 1 W
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Test equipment and measurement of efficiency and input
power
The converter input power was measured using a wattmeter. The wattmeter
contemporaneously measures converted input current (using its internal ammeter) and
voltage (using its internal voltmeter). The wattmeter is a digital instrument, therefore, it
samples the current and voltage and converts them into digital form. The digital samples are
then multiplied giving the instantaneous measured power. The sampling frequency is in the
range of 20 kHz (or higher depending on the instrument used). The display provides the
average measured power, averaging the instantaneous measured power.
Figure 23 shows how the wattmeter is connected to the UUT (unit under test) and to the AC
source and the wattmeter internal block diagram.
An electronic load was connected to the output of the power converter (UUT) sinking the
load current. The electronic load also measures the load current. A voltmeter was used in
order to measure the output voltage of the power converter.
Once the input power and the output power can be measured, the efficiency in different
operating conditions can be calculated by properly setting the AC source output voltage and
the current sourced by the electronic load.
3.2.1
Measuring input power notes
With reference to Figure 23, the UUT input current causes a voltage drop across the
ammeter internal shunt resistance (the ammeter is not ideal so it has an internal resistance
higher than zero) and across the cables that connect the wattmeter to the UUT.
If the switch of Figure 23 is in position 1 (see also the simplified scheme of Figure 24) this
voltage drop causes an input measured voltage higher than the input voltage at the UUT
input which, of course, affects the measured power. The voltage drop is generally negligible
if the UUT input current is low (for example, when measuring the input power of UUT in lowload condition). In the case of high UUT input current the voltage drop can be relevant
(compared to the UUT real input voltage) and therefore, if this is the case, the switch in
Figure 23 can be changed to position 2 (see simplified scheme of Figure 25) where the UUT
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AN3011
input voltage is measured directly to the UUT input terminal, and the input current does not
affect the measured input voltage.
The voltage across the voltmeter causes a leakage current inside the voltmeter itself (which
is not ideal and which doesn't have infinite input resistance). If the switch in Figure 23 is in
position 2 (see simplified scheme of Figure 25) the voltmeter leakage current is measured
by the ammeter, together with the UUT input current, causing a measurement error. The
error is negligible in a case where the UUT input current is much higher than the voltmeter
leakage. If the UUT input current is low, and not much higher than the voltmeter leakage
current, it is probably better to set the switch (in Figure 23) to position 1.
In a case where it is not certain which measurement scheme least affects the results, it is
possible to try with both and register the input power lower value.
Figure 23. Wattmeter possible connections with the U.U.T. (unit under test)
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Figure 24. Wattmeter connection scheme for low input current
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Efficiency
Figure 25. Wattmeter connection scheme for high input current
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As noted in IEC 62301, instantaneous measurements are appropriate when power readings
are stable. The UUT is to be operated at 100% of the nameplate output current for at least
30 minutes (warm-up period) immediately prior to conducting efficiency measurements.
After this warm-up period, the AC input power is monitored for a period of 5 minutes, to
assess the stability of the UUT. If the power level does not drift by more than 5% from the
maximum value observed, the UUT can be considered stable and the measurements can
be recorded at the end of the 5 minute period.
If the AC input power is not stable over a 5 minute period, the average power or
accumulated energy is measured over time for both AC input and DC output.
Some wattmeter models allow the integration of the measured input power in a time range,
and then measures the energy absorbed by the UUT during the integration time. Dividing
this by the integration time itself gives the average input power.
3.3
Overload protection
VIPer27 is protected against overload or output short-circuit. If the load power demand
increases the output voltage decreases and the feedback loop reacts by increasing the
voltage on the feedback pin. The PWM current set point is increased, leading to higher
power delivered to the output until this power equals the load power demands. If the load
power demand exceeds the converter power capability (fixed by the RLIM value) the voltage
on the feedback pin continuously rises, but the power delivered does not rise further. When
the feedback pin voltage exceeds VFB_lin (3.3 V typ), VIPer27 logic assumes it is a warning
for an overload event. Before shutting-down the system, the device waits for a period, fixed
by the capacitor present on the feedback pin. In fact, if the voltage on the feedback pin
exceeds VFB_lin, the internal pull-up is disconnected and the pin starts sourcing a 3 µA
current that charges the capacitor connected to it. As the voltage on the feedback pin
reaches the VFB_olp threshold (4.8 V typ.), VIPer27 stops switching and is not allowed to
switch again until the VDD voltage goes below VDD_RESTART (4.5 V typ.) and rises again up
to VDD_ON (14 V typ.).
The following waveforms show the behavior of the converter when the output is shorted.
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Efficiency
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Figure 26. Output short-circuit
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If the short-circuit is not removed the system starts to work in auto-restart mode. The
behavior, when a short-circuit is permanently applied on the output, is a short period of time
where the MOSFET is switching and the converter tries to deliver as much power as it can to
the output, and a longer period where the device is not switching and no power is
processed.
The duty cycle of power delivery is very low (around 1 %), therefore, the average power
throughput is then very low (seeFigure 27).
Figure 27. Operation with output shorted
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The power capability of the converter was also tested, verifying the minimum value of the
output current needed to activate the overload protection (IOL) and the maximum value of
the output current that allows the system to restart (I_REST). Results are given in Figure 28.
26/37
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Figure 28. Converter power capability
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3.4
Secondary winding short-circuit protection
VIPer27 is provided with an adjustable first level of primary overcurrent limitation that
switches off the power MOSFET if this level is exceeded. This limitation acts cycle by cycle
and its main purpose is to limit the maximum deliverable output power. A second level of
primary overcurrent protection is also present but in this case it is not adjustable, it is fixed to
1 A (typical value). If the drain current exceeds this second overcurrent protection threshold,
the device enters a warning state. In the next cycle the MOSFET is switched on, and if the
second level of overcurrent protection is exceeded again, the device assumes that a
secondary winding short-circuit or a hard saturation of the transformer is happening and
stops the operation. In order to re-enable the operation, VDD voltage must be recycled, that
means: VDD must go down, up to VDD_RESTART, then rise up to VDD_ON. When the VIPer27
is switched on again (VDD equals VDD_ON), the MOSFET can start to switch again. If the
cause of the second overcurrent protection activation is not removed, the device goes into
auto-restart mode.
This protection was tested on the demonstration board. The secondary winding of the
transformer was shorted, in different operating conditions. Figure 29 and 30 show the
behavior of the system during these tests.
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Efficiency
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Figure 29. Second overcurrent protection - protection tripping
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In Figure 29, when the board is working in full-load condition with an input voltage of 115
VAC, the secondary winding is shorted. If the converter runs with the secondary winding
shorted, there is a very high current flowing through the transformer windings, the
secondary diode, and the VIPer power section. The second over-current protection, which
stops the converter operation after two switching cycles, prevents the flow of these high
currents. Figure 30 shows the situation when a permanent short-circuit is applied on the
secondary winding. Most of the time the power section of the VIPer is off, eliminating any
risk of overheating.
Figure 30. Operating with the secondary winding shorted. Restart mode
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Output overvoltage protection
Output overvoltage protection is implemented, monitoring the voltage across the auxiliary
winding during the MOSFET off time, through the D2 diode and the R3 and R14 resistor
dividers (see schematic of Figure 31) connected to the CONT pin of the VIPer27. If the
voltage on the CONT pin exceeds the VOVP thresholds (3 V typ.), VIPer assumes an
overvoltage event and the power section is no longer allowed to be switched-on. To reenable operation, the VDD voltage has to be recycled. In order to provide high noise
immunity and avoid spikes erroneously tripping the protection, a digital filter was
implemented so the CONT pin must sense a voltage higher than VOVP for four consecutive
cycles before it stops operation (see device datasheet for details).
Figure 31. OVP circuit
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The value of the output voltage when the protection must be tripped can be properly fixed by
selecting the R3 and R14 resistor dividers. When R3 is selected, considering the maximum
power that the converter must manage, R14 output must be selected, according to the
formula:
Equation 1
ROVP _(R14 ) =
RLIM _(R2) ⎛ NAUX
⎞
⋅ ⎜⎜
⋅ VOUT _ OVP − Vdrop _ Dovp _(D 2 ) − 3V ⎟⎟
3V
⎝ Ns
⎠
The protection was tested by shorting the voltage reference pin of the TS431 device (pin 3
of VR1 in the schematic) with pin 2 of the same device during converter operation. In this
way the converter operates in open loop and delivers the maximum power possible to
output. The excess of power, in respect to the maximum load, charges the output
capacitance increasing the output voltage, as the OVP is tripped and the converter stops
working.
In Figure 32 it is possible to see that the output voltage increases, and as it reaches the
value of 5.58 V the converter stops switching. In the same figure the CONT pin voltage
(Ch3, fuchsia waveform) and the drain current (Ch4 green waveform) are shown (see
Figure 32 and 33). The crest value of the CONT pin voltage tracks the output voltage.
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Figure 32. OVP protection
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Figure 33. OVP protection
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The test was performed in different line and load conditions to check the dependence of the
output voltage value, when protection is activated, from the converter input voltage and load.
Results are shown in Table 21.
Table 21.
Overvoltage protection activation level test results
VOUT_OVP (V)
Load
VIN
30/37
(VRMS)
No-load
25% of load
Half-load (1.1 A)
Full-load
90
7.019
6.754
6.749
6.731
115
7.022
6.722
6.754
6.740
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Efficiency
Table 21.
Overvoltage protection activation level test results (continued)
VOUT_OVP (V)
Load
VIN
(VRMS)
No-load
25% of load
Half-load (1.1 A)
Full-load
230
7.029
6.735
6.760
6.752
265
7.035
6.786
6.765
6.762
Except for the no-load condition, the variation with load and line is very low ([6.731 V; 6.786
V], ΔVOUT_OVP = 55 mV less then 1% of variation); including the values in the no-load
condition ([6.731 V; 7.035 V], ΔVOUT_OVP = 304 mV less then 5% of variation).
Considering a 10% precision of the OVP threshold in the CONT pin ([2.7 V; 3.3 V]), using as
ROVP and RLIM 1% precision resistances and with a turn ratio between the secondary and
auxiliary windings which has a precision of 5%, and considering a large production, it is
possible to fix the output overvoltage at 25% over the nominal output voltage, making sure
that the OVP protection is not erroneously activated.
It is possible to not implement this protection, if it is not necessary, by not mounting the D2
diode and the R14 resistor. Therefore if OVP protection is not required, the total number of
components can be reduced.
3.6
Brown-out protection
Brown-out protection is basically an unlatched device shutdown function with a typical use
of sensing mains undervoltage or the main unplug. The VIPer27 has a dedicated pin (BR,
pin 5) for this function, which must be connected to the DC HV bus. If protection is not
required, it can be disabled by connecting the pin to ground. In the converter presented
here, brown-out protection is implemented but can be disabled by changing the J7 jumper
setting (see schematic in Figure 2). The settings of the J7 jumper are shown in Figure 34
and 35. The converter's shutdown is accomplished by means of an internal comparator,
internally referenced to 450 mV (typ, VBRth), which disables the PWM if the voltage applied
at the BR pin is below the internal reference (as shown in Figure 36). PWM operation is reenabled as the BR pin voltage is more than 450 mV plus 50 mV of voltage hysteresis that
ensures noise immunity. The brown-out comparator is also provided with current hysteresis.
An internal 10 µA current generator is ON as long as the voltage applied at the brown-out
pin is below 450 mV and OFF if the voltage exceeds 450 mV plus the voltage hysteresis.
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Efficiency
AN3011
Figure 34. J7 jumper setting. Brown-out
disabled
Figure 35. J7 jumper setting. Brown-out
enabled
!-V
!-V
Figure 36. Brown-out protection, internal block diagram
P97\S
'LVDEOH
9%5K\VW
9$&B2.
9%5WK
,%5K\VW
!-V
The current hysteresis provides an additional degree of freedom. It is possible to set the ON
threshold and the OFF threshold for the flyback input voltage separately by properly
choosing the external divider resistors. The following relationships can be established for the
ON (VIN_ON) and OFF (VIN_OFF) thresholds of the input voltage:
Equation 2
⎛ R + RL
VIN _ OFF = VBRth ⋅ ⎜⎜ H
⎝ RL
⎞
⎟⎟
⎠
Equation 3
⎛ R + RL
VIN _ ON = VBRth + VBRhyst ⋅ ⎜⎜ H
⎝ RL
(
)
⎞
⎟⎟ + RH ⋅ IBRhyst
⎠
Where IBRhyst=10 µA (typ.) is the current hysteresis, VBRhyst=50 mV (typ.) is the voltage
hysteresis and VBRth=450 mV (typ.) is the brown-out comparator internal reference.
One purpose of this protection is to stop operation of the converter when the line voltage is
too low, avoiding too high root mean square current value flowing inside the main switch an
then its overheating. Another purpose is to avoid a false restart of the converter and then
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Efficiency
having a monotonically decay to zero of the output voltage when the converter itself is
unplugged from the mains. A typical situation, in most cases for converters designed for the
European range (230 VAC), could be a converter that when unplugged shuts down due to
the overload protection (due to the low input voltage the converter is not able to supply full
power), but the voltage on the Bulk capacitor is higher than VDRAIN RESTART, so the device
starts again and the output voltage rises again. This situation could be dangerous for some
loads, and in many applications is best avoided.
Figures 37 and 38 show how brown-out protection works in the VIPer27 board when used.
Figure 37 shows the behavior of the board when the input voltage is changed from 90 VAC to
75 VAC with full-load applied. The system stops switching and the output load, no longer
supplied, decays monotonically to zero. Figure 38 shows the system behavior when the
input voltage changes from 75 VAC to 90 VAC.
Figure 37. Input AC voltage steps from 90 VAC to 65 VAC
#H 6 /54
#H 6 $$
#H 6 "5,+
#H ) $2!).
)/54 !
!-V
Figure 38. Input voltage steps from 90 VAC to 0 VAC
#H 6 /54
#H 6 "2
#H 6 "5,+
#H ) $2!).
)/54 !
!-V
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Conclusions
4
AN3011
Conclusions
The flyback converter is suitable for different applications and can be used as an external
adapter or as an auxiliary power supply in consumer equipment. Special focus was put on
low-load performance and the bench results are good with a very low input power in lightload conditions. The efficiency performance was compared with the requirements of the
ENERGY STAR program for external AC/DC adapters with very good results, as the
measured active mode efficiency is always higher with respect to the minimum required.
34/37
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5
References
References
1.
2.
ENERGY STAR® Program requirements for single voltage external AC/DC adapter
(Version 2.0)
VIPER27 datasheets
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Revision history
6
AN3011
Revision history
Table 22.
36/37
Document revision history
Date
Revision
13-Jan-2011
1
Changes
Initial release.
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