12W 5V evaluation board using ICE2QR4780Z

Application Note, V1.0, 24 March 2011
A p p l i ca t i o n N o t e
AN- EVAL-2QR4780Z-12W
12W5V Evaluation Board with QuasiResonant CoolSET® ICE2QR4780Z
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
© 2007 Infineon Technologies AG
All Rights Reserved.
Legal Disclaimer
The information given in this document shall in no event be regarded as a guarantee of
conditions or characteristics. With respect to any examples or hints given herein, any typical
values stated herein and/or any information regarding the application of the device,
Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind,
including without limitation, warranties of non-infringement of intellectual property rights
of any third party.
Information
For further information on technology, delivery terms and conditions and prices, please
contact the nearest Infineon Technologies Office (www.infineon.com).
Warnings
Due to technical requirements, components may contain dangerous substances. For information
on the types in question, please contact the nearest Infineon Technologies Office.
Infineon Technologies components may be used in life-support devices or systems only with
the express written approval of Infineon Technologies, if a failure of such components can
reasonably be expected to cause the failure of that life-support device or system or to affect
the safety or effectiveness of that device or system. Life support devices or systems are
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Title
Revision History:
24 March 2011
Previous Version:
none
Page
V1.0
Subjects (major changes since last revision)
®
12W5V Evaluation Board with Quasi-Resonant CooLSET ICE2QR4780Z
License to Infineon Technologies Asia Pacific Pte Ltd
Wong Siew Teng Winson
[email protected]
Eric Kok
[email protected]
Jeoh Meng kiat
[email protected]
We Listen to Your Comments
Any information within this document that you feel is wrong, unclear or missing at all?
Your feedback will help us to continuously improve the quality of this document.
Please send your proposal (including a reference to this document) to:
[email protected]
AN-PS0039
EVAL-2QR4780Z-12W
Table of Contents
1
Content ............................................................................................................... 5
2
Evaluation Board ............................................................................................... 5
3
List of Features .................................................................................................. 5
4
Technical Specifications ................................................................................... 6
5
Circuit Description............................................................................................. 6
5.1
Mains Input and Rectification ...................................................................................................... 6
5.2
Integrated MOSFET and PWM Control........................................................................................ 6
5.3
Output Stage .................................................................................................................................. 6
5.4
Feedback Loop .............................................................................................................................. 6
6
Circuit Operation ............................................................................................... 6
6.1
Startup Operation.......................................................................................................................... 6
6.2
Normal Mode Operation ............................................................................................................... 6
6.3
Primary side peak current control............................................................................................... 7
6.4
Digital Frequency Reduction ....................................................................................................... 7
6.5
Burst Mode Operation .................................................................................................................. 7
7
Protection Features ........................................................................................... 7
7.1
Vcc under voltage and over voltage protection ......................................................................... 7
7.2
Foldback point protection ............................................................................................................ 7
7.3
Open loop/over load protection ................................................................................................... 8
7.4
Adjustable output overvoltage protection.................................................................................. 8
7.5
Short winding protection.............................................................................................................. 8
7.6
Auto restart for over temperature protection ............................................................................. 8
8
Circuit diagram .................................................................................................. 9
8.1
PCB Top overlayer ...................................................................................................................... 10
8.2
PCB Bottom Layer ...................................................................................................................... 11
9
Component List ............................................................................................... 12
10
Transformer Construction .............................................................................. 12
11
Test Results ..................................................................................................... 14
11.1
Efficiency and standby performance ........................................................................................ 14
12
Waveforms and Scope Plots........................................................................... 17
12.1
Startup at Full Load .................................................................................................................... 17
12.2
Zero Crossing Point During Normal Operation ....................................................................... 17
12.3
Load Transient Response .......................................................................................................... 18
12.4
Burst Mode Operation ................................................................................................................ 18
12.5
Protection Mode .......................................................................................................................... 19
13
References ....................................................................................................... 19
Application Note
4
24 March 2011
EVAL-2QR4780Z-12W
1
Content
This application note is a description of 12W switching mode power supply evaluation board designed in a
®
quasi resonant flyback converter topology using ICE2QR4780Z Quasi-resonant CoolSET .The target
application of ICE2QR4780Z 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 ICE2QR4780Z 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-12W-ICE2QR4780Z
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
Application Note
5
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EVAL-2QR4780Z-12W
4
Technical Specifications
Input voltage
Input frequency
Output voltage and current
Output power
Efficiency
Standby power
Minimum switching frequency at full load,
minimum input voltage
5
85Vac~282Vac
50Hz, 60Hz
5V 2.4A
12W
>80% 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
ICE2QR4780Z 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. ICE2QR4780Z 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 ICE2QR4780Z, 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 ICE2QR4780Z 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.
6.2
Normal Mode Operation
Application Note
6
24 March 2011
EVAL-2QR4780Z-12W
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 ICE2QR4780Z 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 ICE2QR4780Z 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 (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 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
7
24 March 2011
EVAL-2QR4780Z-12W
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-2QR4780Z-12W
8
Circuit diagram
Figure 2 – Schematics
Application Note
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EVAL-2QR4780Z-12W
8.1
PCB Top overlayer
Figure 3 –Component Legend – View from topside
Application Note
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EVAL-2QR4780Z-12W
8.2
PCB Bottom Layer
Figure 4 Solder side copper – View from bottom side
Application Note
11
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EVAL-2QR4780Z-12W
9
Component List
Items
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Designator
BR1
F1
L21
R11
R13
R15
R16
R110
R111
R21
R22
R23
R24
R26
C11
C13
C14
C15
C16
C17
C18
C19
C21
C22
C23
C26
C27
L11 EMI
TR1
IC12
IC21
D11
D12
ZD11
D21
IC11
Table 1– Component List
36
37
10
Part Type
Part No.
Bridge 800V 1.5A
1.0A/250Vac
1.5uH
330K, 2W
20R, SMD 0806
1.5R, 0.5W
20R, SMD 0806
8.2k, SMD 0806
33K 0.5W
68R, SMD 0806
1.1k, SMD 0806
1.0k, SMD 0806
10k
10k
0.22uF/305V
47uF/500V
2.2nF/400V
2.2nF/250V, Y1
33uF
0.1uF
47pF
1nF
1000uF/35V
1000uF/35V
220uF/25V
680nF
820pF,SMD 0806
2 x 27mH, 0.9A
1000uH (80:5:14)
SFH617A-3
TL431
UF4006
1N485B
22V zener diode
DF08M
STPS30L45CT
ICE2QR4780Z
Manufacturer
NEC
B32922X2MKP/2H
B43501A6476M000
MKPS5 2n2M630
DE1E3KX222MA4BL01
B41851A7336M
Epcos
Epcos
Murata
Epcos
KZE
KZE
KZE
B82732R2901B30
Epcos
UF4006
Vishay
ICE2QR4780Z
Infineon
Transformer Construction
Core and material :EPCOS(N87), E20/10/6
Bobbin: Horizontal Version
Primary Inductance, Lp=1000µH(±3%), measured between pin 4 and pin 5 (Gapped to Inductance)
Air Gap in center leg
Application Note
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EVAL-2QR4780Z-12W
Figure 5 – Transformer structure
Figure 6 – Transformer complete – top view
Start
2
Stop
1
No. of turns
14
Wire size
1XAWG#30
Layer
Auxiliary
3
7
4
6
40
5
1XAWG#30
3XAWG#27
/2 Primary
Secondary
5
3
40
1XAWG#30
1
1
/2 Primary
Table 2 wire gauge used of the transformer windings
Application Note
13
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EVAL-2QR4780Z-12W
11
Test Results
11.1
Efficiency and standby performance
Table 3 – Efficiency vs. Load
Application Note
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EVAL-2QR4780Z-12W
Efficiency vs Output Load
90.0000
88.0000
86.0000
Efficiency (%)
84.0000
82.7220
82.7368
82.4441
83.0153
82.0000
82.1556
80.0000
80.9329
82.5677
85Vac
282Vac
79.0534
78.0000
76.0000
74.0000
72.0000
70.0000
25
50
75
100
Load (%)
Efficiency vs Output Load
90.0000
88.0000
86.0000
Efficiency (%)
84.0000
83.3742
84.1352
83.7612
83.8315
83.1309
82.0000
81.0244
83.2312
83.4911
115Vac
80.0000
230Vac
78.0000
76.0000
74.0000
72.0000
70.0000
25
50
75
100
Load (%)
Figure 7a & 7b – Efficiency vs. Output Load
Application Note
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EVAL-2QR4780Z-12W
Efficiency vs AC Line Input Voltage
85.0000
84.2456
84.0084
84.0000
83.7636
83.6004
83.8315
Efficiency (%)
83.7247
83.0000
82.8945
83.1476
83.0153
82.2090
82.0000
Average Efficiency
Full Load Efficiency
81.6980
81.0000
80.9329
80.0000
79.0000
85
115
150
180
230
282
AC Input Voltage (V)
Figure 8 Efficiency vs AC line voltage
Standby Power at No Load versus Input Voltage (AC)
1600
Output Power (mW)
1400
1200
1286
1297
1308
1340
1370
1284
1016
1014
1026
1041
1058
1085
657
658
666
671
681
705
290
292
298
310
322
17.8
18.32
19.08
19.95
23.35
85
115
150
180
230
1000
800
600
400
300
200
0
33.83
282
AC Input Voltage
0W
0.2W
0.5W
0.8w
1W
Figure 9 Standby input power vs AC line voltage
Application Note
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EVAL-2QR4780Z-12W
12
Waveforms and Scope Plots
12.1
Startup at Full Load
Figure 10: Constant Charging VCC at Startup
Figure 11: 4 Steps Softstart
CH1
Supply Voltage, VCC
CH1
Supply Voltage, VCC
CH2
Zero Crossing Voltage, VZC
CH2
Zero Crossing Voltage, VZC
CH3
Current Sense Voltage, VCS
CH3
Current Sense Voltage, VCS
CH4
Feedback Voltage, VFB
CH4
Feedback Voltage, VFB
12.2
Zero Crossing Point During Normal Operation
st
th
Figure 12: Working at 1 ZC
Figure 13: Working at 7 ZC
CH1
Supply Voltage, VCC
CH1
Supply Voltage, VCC
CH2
Zero Crossing Voltage, VZC
CH2
Zero Crossing Voltage, VZC
CH3
Current Sense Voltage, VCS
CH3
Current Sense Voltage, VCS
CH4
Feedback Voltage, VFB
CH4
Feedback Voltage, VFB
Application Note
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EVAL-2QR4780Z-12W
12.3
Load Transient Response
Figure 14: AC Output Ripple undershoot
Figure 15: AC Output Ripple Overshoot
CH1
Output Current, Io
CH1
Output Current, Io
CH4
Output Voltage, Vo
CH4
Output Voltage, Vo
12.4
Burst Mode Operation
Figure 16: Entering Burst Mode
Figure 17: Leaving Burst Mode
CH1
Feedback Voltage, VFB
CH1
Feedback Voltage, VFB
CH2
Zero Crossing Voltage, VZC
CH2
Zero Crossing Voltage, VZC
CH3
Current Sense Voltage, VCS
CH3
Current Sense Voltage, VCS
CH4
Output Voltage, Vo
CH4
Output Voltage, Vo
Condition: ZC=7, FB<1.2V, Blanking time =30ms
Application Note
18
Condition: VFB>4.5V
24 March 2011
EVAL-2QR4780Z-12W
12.5
Protection Mode
Figure 16: Over ZC Latch
Figure 17: Over Load/ Open Loop Protection
CH1
Feedback Voltage, VFB
CH1
Feedback Voltage, VFB
CH2
Zero Crossing Voltage, VZC
CH2
Zero Crossing Voltage, VZC
CH3
Current Sense Voltage, VCS
CH3
Current Sense Voltage, VCS
CH4
Supply Voltage, VCC
CH4
Supply Voltage, VCC
Condition: VZC > 3.7V
13
Condition: VFB > 4.5V for 30ms
References
[1]
ICE2QR4780Z datasheet, Infineon Technologies AG, 2010
[2]
Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01, Infineon Technologies AG,
2006. [ANPS0003]
[3]
Design tips for flyback converters using the Quasi-Resonant PWM controller ICE2QS01, Infineon
Technologies, 2006. [ANPS0005]
[4]
Determine the switching frequency of Quasi-Resonant flybacl converters designed with ICE2QS01,
Infineon Technologies, 2006. [ANPS0004]
[5]
ICE2QRXX65/80X Quasi Resonance Coolset Design Guide. [ANPS0053]
Application Note
19
24 March 2011
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