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Application Note, V1.0, 7 September 2011
Application Note
AN- EVAL-2QR0680Z-40W
40W20V Evaluation Board with QuasiResonant CoolSET® ICE2QR0680Z
Power Management & Supply
N e v e r
s t o p
t h i n k i n g .
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2011 Infineon Technologies AG
All Rights Reserved.
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including without limitation, warranties of non-infringement of intellectual property rights
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EVAL-2QR0680Z-40W
Title
Revision History:
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7 September 2011
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Subjects (major changes since last revision)
40W20V Evaluation Board with Quasi-Resonant CooLSET® ICE2QR0680Z
License to Infineon Technologies Asia Pacific Pte Ltd
V1.0
AN-PS0066
Wong Siew Teng Winson
[email protected]
Eric Kok Siu Kam
[email protected]
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Application Note
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EVAL-2QR0680Z-40W
Table of Contents
1 2 3 4 5 Content ............................................................................................................... 6 Evaluation Board ............................................................................................... 6 List of Features .................................................................................................. 6 Technical Specifications ................................................................................... 7 Circuit Description............................................................................................. 7 5.1 5.2 5.3 5.4 Mains Input and Rectification ...................................................................................................... 7 Integrated MOSFET and PWM Control........................................................................................ 7 Output Stage .................................................................................................................................. 7 Feedback Loop .............................................................................................................................. 7 6 Circuit Operation ............................................................................................... 7 6.1 6.2 6.3 6.4 6.5 Startup Operation.......................................................................................................................... 7 Normal Mode Operation ............................................................................................................... 8 Primary side peak current control............................................................................................... 8 Digital Frequency Reduction ....................................................................................................... 8 Burst Mode Operation .................................................................................................................. 8 7 Protection Features ........................................................................................... 8 7.1 7.2 7.3 7.4 7.5 7.6 Vcc under voltage and over voltage protection ......................................................................... 8 Foldback point protection ............................................................................................................ 8 Open loop/over load protection ................................................................................................... 9 Adjustable output overvoltage protection.................................................................................. 9 Short winding protection.............................................................................................................. 9 Auto restart for over temperature protection ............................................................................. 9 8 Circuit diagram ................................................................................................ 10 8.1 8.2 PCB Top overlayer ...................................................................................................................... 11 PCB Bottom Layer ...................................................................................................................... 11 9 10 11 Component List ............................................................................................... 12 Transformer Construction .............................................................................. 13 Test Results ..................................................................................................... 14 11.1 Efficiency and standby performance ........................................................................................ 14 12 References ....................................................................................................... 16 Application Note
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1
Content
This application note is a description of 40W switching mode power supply evaluation board designed in a
quasi resonant flyback converter topology using ICE2QR0680Z Quasi-resonant CoolSET®.The target
application of ICE2QR0680Z are for set-top box, portable game controller, DVD player, netbook adapter and
auxiliary power supply for LCD TV, etc. With the CoolMOS® integrated in this IC, it greatly simplifies the
design and layout of the PCB. Due to valley switching, the turn on voltage is reduced and this offers higher
conversion efficiency comparing to hard-switching flyback converter. With the DCM mode control, the
reverse recovery problem of secondary rectify diode is relieved. And for its natural frequency jittering with
line voltage, the EMI performance is better. Infineon’s digital frequency reduction technology enables a
quasi-resonant operation till very low load. As a result, the system efficiency, over the entire load range, is
significantly improved compared to conventional free running quasi resonant converter implemented with
only maximum switching frequency limitation at light load. In addition, numerous adjustable protection
functions have been implemented in ICE2QR0680Z to protect the system and customize the IC for the
chosen application. In case of failure modes, like open control-loop/over load, output overvoltage, and
transformer short winding, the device switches into Auto Restart Mode or Latch-off Mode. By means of the
cycle-by-cycle peak current limitation plus foldback point correction, the dimension of the transformer and
current rating of the secondary diode can both be optimized.Thus, a cost effective solution can be easily
achieved.
2
Evaluation Board
Figure 1-EVALQR-40W-ICE2QR0680Z
3
List of Features
800V avalanche rugged CoolMOS® with built in depletion startup cell
Quasi-resonant operation
Digital frequency reduction with decreasing load
Cycle-by-cycle peak current limitation with foldback point correction
Built-in digital soft-start
Direct current sensing with internal Leading Edge Blanking Time
VCC under voltage protection: IC stop operation, recover with softstart
VCC over voltage protection: IC stop operation, recover with softstart
Openloop/Overload protection: Auto Restart
Output overvoltage protection: Latch-off with adjustable threshold
Short-winding protection: Latch-off
Over temperature protection: Autorestart
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4
Technical Specifications
Input voltage
Input frequency
Output voltage and current
Output power
Average Efficiency
Standby power
Minimum switching frequency at full load,
minimum input voltage
5
85Vac~282Vac
50Hz, 60Hz
20V 2.0A
40W
>85% at full load
<[email protected] load
65kHz
Circuit Description
5.1
Mains Input and Rectification
The AC line input side comprises the input fuse F1 as overcurrent protection. The X2 Capacitors C1 and
Choke L1 form a main filter to minimize the feedback of RFI into the main supply. After the bridge rectifier
BR1, together with a smoothing capacitor C2, provide a voltage of 70VDC to 380 VDC depending on mains
input voltage.
5.2
Integrated MOSFET and PWM Control
ICE2QR0680Z is comprised of a power MOSFET and the quasi-resonant controller; this integrated solution
greatly simplifies the circuit layout and reduces the cost of PCB manufacturing. The PWM switch-on is
determined by the zero-crossing input signal and the value of the up/down counter. The PWM switch-off is
determined by the feedback signal VFB and the current sensing signal VCS. ICE2QR0680Z also performs all
necessary protection functions in flyback converters. Details about the information mentioned above are
illustrated in the product datasheet.
5.3
Output Stage
On the secondary side, 5V output, the power is coupled out via a schottky diode D21. The capacitors C21
provides energy buffering followed by the L-C filters L21 and C22 to reduce the output ripple and prevent
interference between SMPS switching frequency and line frequency considerably. Storage capacitor C21 is
designed to have an internal resistance (ESR) as small as possible. This is to minimize the output voltage
ripple caused by the triangular current.
5.4
Feedback Loop
For feedback, the output is sensed by the voltage divider of Rc1 and Rc3 and compared to TL431 internal
reference voltage. Cc1, Cc2 and Rc4 comprise the compensation network. The output voltage of TL431 is
converted to the current signal via optocoupler IC2 and two resistors Rc5 and Rc6 for regulation control.
6
Circuit Operation
6.1
Startup Operation
Since there is a built-in startup cell in the ICE2QR0680Z, there is no need for external start up resistor, which
can improve standby performance significantly.
When VCC reaches the turn on voltage threshold 18V, the IC begins with a soft start. The soft-start
implemented in ICE2QR0680Z is a digital time-based function. The preset soft-start time is 12ms with 4
steps. If not limited by other functions, the peak voltageon CS pin will increase step by step from 0.32V to 1V
finally. After IC turns on, the Vcc voltage is supplied by auxiliary windings of the transformer.
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EVAL-2QR0680Z-40W
6.2
Normal Mode Operation
The secondary output voltage is built up after startup. The secondary regulation control is adopted with
TL431 and optocoupler. The compensation network Cc1, Cc2 and Rc4 constitute the external circuitry of the
error amplifier of TL431. This circuitry allows the feedback to be precisely controlled with respect to
dynamically varying load conditions, therefore providing stable control.
6.3
Primary side peak current control
The MOSFET drain source current is sensed via external resistor R4 and R4A. Since ICE2QR0680Z is a
current mode controller, it would have a cycle-by-cycle primary current and feedback voltage control which
can make sure the maximum power of the converter is controlled in every switching cycle.
6.4
Digital Frequency Reduction
During normal operation, the switching frequency for ICE2QR0680Z is digitally reduced with decreasing load.
At light load, the MOSFET will be turned on not at the first minimum drain-source voltage time, but on the nth.
The counter is in range of 1 to 7, which depends on feedback voltage in a time-base. The feedback voltage
decreases when the output power requirement decreases, and vice versa. Therefore, the counter is set by
monitoring voltage VFB. The counter will be increased with low VFB and decreased with high VFB. The
thresholds are preset inside the IC.
6.5
Burst Mode Operation
At light load condition, the SMPS enters into Active Burst Mode. At this stage, the controller is always active
but the Vcc must be kept above the switch off threshold. During active burst mode, the efficiency increase
significantly and at the same time it supports low ripple on Vout and fast response on load jump.
For determination of entering Active Burst Mode operation, three conditions apply:
1. the feedback voltage is lower than the threshold of VFBEB(1.25V). Accordingly, the peak current sense
voltage across the shunt resistor is 0.18;
2. the up/down counter is 7;
3. and a certain blanking time, 24ms (tBEB).
Once all of these conditions are fulfilled, the Active Burst Mode flip-flop is set and the controller enters Active
Burst Mode operation. This multi-condition determination for entering Active Burst Mode operation prevents
mistriggering of entering Active Burst Mode operation, so that the controller enters Active Burst Mode
operation only when the output power is really low during the preset blanking time.
During active burst mode, the maximum current sense voltage is reduced from 1V to 0.34V so as to reduce
the conduction loss and the audible noise. At the burst mode, the FB voltage is changing like a sawtooth
between 3.0 and 3.6V. The switching frequency is set to a fix frequency of 52kHz.
The feedback voltage immediately increases if there is a high load jump. This is observed by one comparator.
As the current limit is 34% during Active Burst Mode a certain load is needed so that feedback voltage can
exceed VLB (4.5V). After leaving active busrt mode, maximum current can now be provided to stabilize VO.
In addition, the up/down counter will be set to 1 immediately after leaving Active Burst Mode. This is helpful
to decrease the output voltage undershoot
7
Protection Features
7.1
Vcc under voltage and over voltage protection
During normal operation, the VCC voltage is continuously monitored. When the Vcc voltage falls below the
under voltage lock out level (VCCoff) or the Vcc voltage increases up to VCCovp, the IC will enter into
autorestart mode.
7.2
Foldback point protection
Application Note
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EVAL-2QR0680Z-40W
For a quasi-resonant flyback converter, the maximum possible output power is increased when a constant current
limit value is used for all the mains input voltage range. This is usually not desired as this will increase additional
cost on transformer and output diode in case of output over power conditions.
The internal fold back protection is implemented to adjust the VCS voltage limit according to the bus voltage. Here,
the input line voltage is sensed using the current flowing out of ZC pin, during the MOSFET on-time. As the result,
the maximum current limit will be lower at high input voltage and the maximum output power can be well limited
versus the input voltage.
7.3
Open loop/over load protection
In case of open control loop, feedback voltage is pulled up with internally block. After a fixed blanking time
30ms, the IC enters into auto restart mode. In case of secondary short-circuit or overload, regulation voltage
VFB will also be pulled up, same protection is applied and IC will auto restart.
7.4
Adjustable output overvoltage protection
During off-time of the power switch, the voltage at the zero-crossing pin ZC is monitored for output
overvoltage detection. If the voltage is higher than the preset threshold 3.7V for a preset period 100μs, the
IC is latched off.
7.5
Short winding protection
The source current of the MOSFET is sensed via two shunt resistors R4 and R4A in parallel. If the voltage at
the current sensing pin is higher than the preset threshold VCSSW of 1.68V during the on-time of the power
switch, the IC is latched off. This constitutes a short winding protection. To avoid an accidental latch off, a
spike blanking time of 190ns is integrated in the output of internal comparator.
7.6
Auto restart for over temperature protection
The IC has a built-in over temperature protection function. When the controller’s temperature reaches 140 °C,
the IC will shut down switch and enters into autorestart. This can protect power MOSFET from overheated.
Application Note
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EVAL-2QR0680Z-40W
8
Circuit diagram
40W 20V SMPS Demoboard with ICE2QR0680Z
Figure 2 – Schematics
Application Note
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EVAL-2QR0680Z-40W
8.1
PCB Top overlayer
Figure 3 –Component Legend – View from topside
8.2
PCB Bottom Layer
Figure 4 Solder side copper – View from bottom side
Application Note
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EVAL-2QR0680Z-40W
9
Component List
Items
1 2 Designator
F1 Part type
1.0A/250Vac Part No.
Manufacturer
C1 220nF/275Vac X2 224K/275VAC15MM 3 L1 2 x 27mH, 0.9A B82732R2901B30 Epcos 4 BR1 DB107, 1000V 5 C3 68uF/450V 6 R1 150k/2W 7 D1 UF4007 8 C4 2.2nF/400V 9 TR1 750uH 10 C8 100pF 11 R14 47k 12 R15 8.2K 13 R5 1.8R 14 R5A 0.75R 15 C10 47pF/1kV 16 C9 1nF 17 C7 0.1uF 18 R4 0R 19 R3 0R 20 R2 0R 21 ZD1 22V zener 22 D2 1nN4148 23 IC1 2QR0680Z IFX 24 IC2 EL817 25 D3 STPS20H100CFP 26 C11 1000uF/25V 27 C16 1000uF/25V 28 L2 1.5uH 29 C12 220uF/25V 30 C17 0.1uF/50V 31 R6 680R 32 R7 1.2k 33 C14 100pF 34 R8 22k 35 IC3 TL431 36 R13 510k 37 R12 10k 38 R11 27k 39 R10 43k 40 C15 100nF 41 C5 2.2nF/250V Table 1– Component List
Application Note
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EVAL-2QR0680Z-40W
10
Transformer Construction
Core and material : PQ2620, PC40
Bobbin: Vertical Version
Primary Inductance, Lp=750μH±10%, measured between pin 4 and pin 5 (Gapped to Inductance)
Air Gap in center leg
Figure 5 – Transformer structure
Figure 6 – Transformer complete – top view
Start
Stop
No. of turns
Wire Size
Layer
4
3
19
2UEW,φ0.40mm *1p
½ primary
8
10
5
Triple insulatedφ0.55mm *2p
Secondary
3
5
18
2UEW,φ0.37mm *1p
½ primary
1
2
4
2UEW,φ0.40mm *1p
Auxiliary
Table 2 wire gauge used of the transformer windings
Application Note
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EVAL-2QR0680Z-40W
11
Test Results
11.1
Efficiency and standby performance
Voltage (Vac) 85 85 85 85 115 115 115 115 150 150 150 150 180 180 180 180 230 230 230 230 282 282 282 282 Input Power (W) 11.68 23.46 35.15 47.67 11.56 23.45 34.37 45.93 11.533 22.9 34.01 45.15 11.567 22.83 33.79 45.05 11.67 22.85 33.8 44.87 11.82 22.92 33.89 44.85 Output Voltage (V) 20.26 20.26 20.27 20.27 20.26 20.26 20.27 20.27 20.26 20.26 20.27 20.27 20.26 20.26 20.27 20.27 20.26 20.26 20.27 20.27 20.26 20.26 20.27 20.27 Output Current Output Power (A) (W) 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 0.5062 10.255612 1.0143 20.549718 1.5075 30.557025 2.0025 40.590675 Efficiency (%) 87.80 87.59 86.93 85.15 88.72 87.63 88.91 88.38 88.92 89.74 89.85 89.90 88.66 90.01 90.43 90.10 87.88 89.93 90.41 90.46 86.76 89.66 90.17 90.50 Table 3 – Efficiency vs. Load
Application Note
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EVAL-2QR0680Z-40W
Efficiency vs. Load
91.00
90.17
90.00
90.50
89.66
Efficiency %
89.00
88.00
87.80
87.00
87.59
85Vac
86.93
86.76
282Vac
86.00
85.15
85.00
84.00
25%
50%
75%
100%
Load
Efficiency vs. Load
91.00
90.50
90.41
Efficiency %
90.00
90.46
89.93
89.50
89.00
88.91
88.72
88.50
115Vac
88.38
88.00
230Vac
87.88
87.63
87.50
87.00
25%
50%
75%
100%
Load
Figure 7 – Efficiency vs. Output Load
Application Note
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EVAL-2QR0680Z-40W
Efficiency vs. AC Line Voltage
91.00
90.00
89.90
89.60
90.50
90.46
90.10
89.80
89.67
89.27
Efficiency %
89.00
88.41
88.38
88.00
87.00
Full Load
86.87
Average Eff
86.00
85.15
85.00
84.00
85Vac
115Vac
150Vac
180Vac
230Vac
282Vac
AC Line Voltage (Vac)
Figure 8 Efficiency vs AC line voltage
Standby Power
90.0
83.0
80.0
Power (mW)
70.0
66.0
60.0
55.0
50.0
40.0
42.5
44.0
47.0
No Load
30.0
20.0
10.0
0.0
85Vac
115Vac
150Vac
180Vac
230Vac
282Vac
AC Line Voltage (Vac)
Figure 9 Standby input power vs AC line voltage
12
[1]
[2]
References
ICE2QR0680Z datasheet, Infineon Technologies AG, 2011
ICE2QS03G Design Guide Infineon Technologies AG,2010
Application Note
16
7 September 2011
EVAL-2QR0680Z-40W
[3]
[4]
[5]
Design Tips for flyback converters using the Quasi-Resonant (ANPS0005), Infineon Technologies
AG, 2006
Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01 (ANPS0003), Infineon
Technologies AG, 2006
Determine the Switching Frequency of Quasi-Resonant Flyback Converters Designed with
ICE2QS01 (ANPS0004), Infineon Technologies AG, 2006
Application Note
17
7 September 2011
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