80W SMPS evaluation board using ICE2QS02G

Application Note, V1.0, 25 JUNE 2008
Application Note
AN- EVALQRS-ICE2QS02G-80W
80W Evaluation Board with Quasi-Resonant
PWM Controller ICE2QS02G
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
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Title
Revision History:
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25 JUNE 2008
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Subjects (major changes since last revision)
80W Evaluation Board with Quasi-Resonant PWM Controller ICE2QS02G
License to Infineon Technologies Asia Pacific Pte Ltd
Mao Mingping
[email protected]
He Yi
[email protected]
Jeoh Meng kiat
[email protected]
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V1.0
AN-PS0018
EVALQRS-ICE2QS02G-80W
Table of Contents
1
Content ............................................................................................................... 5
2
Evaluation Board ............................................................................................... 5
3
List of Features .................................................................................................. 6
4
Technical Specifications ................................................................................... 6
5
Circuit Description............................................................................................. 6
5.1
Mains Input and Rectification ......................................................................................................6
5.2
PWM Control..................................................................................................................................6
5.3
Snubber Network ..........................................................................................................................6
5.4
Output Stage..................................................................................................................................6
5.5
Feedback Loop..............................................................................................................................6
6
Circuit Operation ............................................................................................... 7
6.1
Startup Operation..........................................................................................................................7
6.2
Normal Mode Operation ...............................................................................................................7
6.3
Digital Frequency Reduction .......................................................................................................7
7
Protection Features ........................................................................................... 7
7.1
Vcc under voltage protection ......................................................................................................7
7.2
Foldback point protection ............................................................................................................7
7.3
Open loop/over load protection...................................................................................................7
7.4
Adjustable output overvoltage protection..................................................................................8
7.5
Short winding protection..............................................................................................................8
7.6
Mains undervoltage protection....................................................................................................8
8
Circuit diagram .................................................................................................. 9
8.1
PCB Topover layer ......................................................................................................................10
8.2
PCB Bottom Layer ......................................................................................................................11
9
Component List ............................................................................................... 12
10
Transformer Construction .............................................................................. 13
11
Test Results ..................................................................................................... 14
11.1
Efficiency .....................................................................................................................................14
12
References ....................................................................................................... 16
Application Note
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EVALQRS-ICE2QS02G-80W
1
Content
The demo-board described here is an 80W power supply using quasi-resonant flyback converter topology.
The PWM controller ICE2QS02G is a second generation quasi-resonant controller IC developed by Infineon
Technologies. Its application is mainly focused on power supplies which has auxiliary converter working
during standby mode, such as power supplies used in LCD TV, home audio or printer applications. The
required VCC voltage for the IC is here drawn from the additional auxiliary power supply. In normal operation,
the digital frequency reduction with decreasing load 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. In
addition, numerous asjustable protection functions have been implemented in ICE2QS02G 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 the secondary diode can be lower which leads to more cost effective
design.
2
Evaluation Board
Figure 1-EVALSQ-80W-ICE2QS02G
Application Note
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EVALQRS-ICE2QS02G-80W
3
List of Features
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 undervoltage protection: IC stop operation, recover with softstart
Main undervoltage protection: Block gate and recover with soft start
Openloop/Overload protection: Auto Restart with adjustable blanking time and adjustable restart time
Output overvoltage protection: Latch-off with adjustable threshold
Short-winding protection: Latch-off
4
Technical Specifications
Input voltage
Input frequency
Output voltage and current
Output power
Efficiency
Minimum switching frequency at full load,
minimum input voltage
5
85VAC~265VAC
50Hz, 60Hz
20V 4A
80W
>86% at full load
65kHz
Circuit Description
5.1
Mains Input and Rectification
The AC line input side comprises the input fuse FUSE1 as overcurrent protection. The X2 Capacitors CX1,
CX2 and Choke L1 and Y1 capacitors CY1 and CY2 forms a main filter to minimize the feedback of RFI into
the main supply. After the bridge rectifier BR1, together with a smoothing capacitor C1, provide a voltage of
80VDC to 380 VDC depending on mains input voltage. RT1 is placed in series with input to limit the initial
peak inrush current whenever the power supply is switched on when C1 is fully discharged.
5.2
PWM Control
The PWM pulse is generated by the 8-pin Quasi Resonant PWM curremt-mode Controller ICE2QS02G. It
comprises the complete control for quasi-resonant flyback switch mode power supply especially in LCD TV,
home audio and Printer applications. 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. ICE2QS02G also performs all necessary protection functions in flyback converters. Details
about the information mentioned above are illustrated in the product datasheet.
5.3
Snubber Network
A snubber network R1, C2 and D1 dissipate the energy of the leakage Inductance and to suppress ringing
on the SMPS transformer.
5.4
Output Stage
On the secondary side, 20V output, the power is coupled out via a dual schottky diode D2. The capacitors
C4, C5 and C6 provide energy buffering followed by the L-C filters to reduce the output ripple and prevent
interference between SMPS switching frequency and line frequency considerably. Storage capacitors C4, C5
and C6 are designed to have an internal resistance as small as possible (ESR). This is to minimize the
output voltage ripple caused by the triangular current.
5.5
Feedback Loop
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EVALQRS-ICE2QS02G-80W
For feedback, the output is sensed by the voltage divider of R15, R16 and R17 and compared to TL431
internal reference voltage. C15, C16 and R14 comprise the compensation network. The output voltage of
TL431 is converted to the current signal via Optocoupler and two resistors R12 and R13 for regulation
control.
6
Circuit Operation
6.1
Startup Operation
When VCC reaches the turn on voltage threshold 12V, the IC begins with a soft start which is realized
internally with a built-in digital block. The maximum soft start time is 20ms. During this period, feedback
voltage will be generated internally, which is 1.8V at the first step and increases step by step with preset
voltage at a time interval of 4ms. In such a way, the primary peak current and the gate drive pulse width are
both gradually increased during the soft start.
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 C15, C16 and R14 constitutes the external circuitry of
the error amplifier of TL431. This circuitry allows the feedback to be precisely controlled to dynamically
varying load conditions, therefore providing stable control.
6.3
Digital Frequency Reduction
During normal operation, the switching frequency for ICE2QS02G 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.
7
Protection Features
7.1
Vcc under voltage protection
During normal operation, the VCC voltage is continuously monitored. When the Vcc voltage falls below the
under voltage lock out level (VCCoff), the IC is off and gate signal is disabled.
7.2
Foldback point protection
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 incase 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 an adjustable blanking
time, the IC enters Auto restart mode. In case of secondary short-circuit or overload, regulation voltage VFB
will also be pulled up, same protection will be applied and IC will enters Auto restart mode.
The charging time and the discharging time of the capacitor C8, determines respectively the openloop/overload
protection blanking time and the restart time of the IC. This allows the system to face a sudden power surge for a
Application Note
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25 June 2008
EVALQRS-ICE2QS02G-80W
short period of time fixed by the charging time of C8 without triggering the overload protection. Once the protection
triggered, the IC will restart using the internal soft-start circuit, after a period of time fixed by the discharging time of
C8.
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 for a preset period, the IC is latched
off.
7.5
Short winding protection
The source current of the MOSFET is sensed via two shunt resistors R11 and R19 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
Mains undervoltage protection
Finally, this IC has an adjustable main undervoltage detection system. Once the Voltage at pin VINS drops
below 1.25V, the protection is triggered. For a stable operation, a hysteresis operation is ensured using an
internal current source. When the VINS exceeds the hysteresis point, the system resumes its operation with
a soft-start.
Application Note
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EVALQRS-ICE2QS02G-80W
8
Circuit diagram
Figure 2 – Schematics
Application Note
9
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EVALQRS-ICE2QS02G-80W
8.1
PCB Topover layer
Figure 3 – Component side Component Legend – View from Component Side
Application Note
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EVALQRS-ICE2QS02G-80W
8.2
PCB Bottom Layer
Figure 1 Solder side copper – View from component side
Application Note
11
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EVALQRS-ICE2QS02G-80W
9
Component List
Table 1– Component List
Items
Part
Type
Quantity
1
BR1
KBU6G,4A/400V
1
2
C1
330uF/400V
1
3
C2
15nF/630V
1
4
C3
47pF/1kV
1
5
C4
1000uF/35V
1
6
C5
1000uF/35V
1
7
C6
1000uF/35V
1
8
C7
470uF/35V
1
9
C8
1uF/50V
1
10
C9
100pF/50V
1
11
C10
100nF/50V
1
12
C11
47uF/50V
1
13
C12
1.5nF/50V
1
14
C13
100pF/50V
1
15
C14
47pF/1kV
1
16
C15
22pF/50V
1
17
C16
0.1uF/50V
1
18
C17
470pF/1kV
1
19
CX1
0.33uF/275VAC
1
20
CX2
0.33uF/275VAC
1
21
CY1
2.2nF/250VAC
1
22
CY2
2.2nF/250VAC
1
23
CY3
2.2nF/250VAC
1
24
D1
UF4006
1
25
D2
MBR20100
1
26
D3
IN4148
1
27
FUSE1
4A
1
28
IC1
ICE2QS02
1
29
IC2
SFH617-3
1
30
IC2
TL431
1
31
L1
2*3.3mH/4.6A
1
32
L2
1.5uH
1
33
Q1
IPA60R199CP
1
34
R1
33k/2W
1
Application Note
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EVALQRS-ICE2QS02G-80W
10
35
R2
62k
1
36
R3
1.0M
1
37
R4
1.0M
1
38
R5
1.0M
1
39
R6
620k
1
40
R7
10k
1
41
R8
24k
1
42
R9
110
1
43
R10
27
1
44
R11
0.47/1W
1
45
R12
680
1
46
R13
1.1k
1
47
R14
22k
1
48
R15
120k,1%
1
49
R16
20k, 1%
1
50
R17
20k, 1%
1
51
R18
200k
1
52
R19
0.47/1W
1
53
RT1
S237/5
1
54
VR1
S10K275
1
55
TR1
E36/18/11_N87
1
Transformer Construction
Core and material: E 36/18/11, N87
Bobbin: Horizontal Version
Primary Inductance, Lp=220uH, measured between pin 1 and pin 4 (Gapped to Inductance)
Figure 5 – Transformer structure
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EVALQRS-ICE2QS02G-80W
Pin 16
Pin 15
Pin 14
Pin 13
Pin 12
Pin 11
Pin 10
Pin 9
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
Figure 6 – Transformer complete – top view
11
Test Results
11.1
Efficiency
Table 2 – Load condition
Full load
20V/4A
Med load
20V/2A
Light load
20V/0.4A
Table 3 – Efficiency vs. AC line voltage
Vin(AC)
85
110
220
265
Application Note
Pin(W)
Vout(V)
Iout(A)
Pout(W)
Efficiency
Full load
92.20
20.01
3.985
79.73
86.48%
Med load
46.10
20.01
1.993
39.880
86.50%
Light load
9.40
20.01
0.388
7.764
82.59%
Full load
90.32
20.01
3.985
79.740
88.28%
Med load
44.96
20.01
1.993
39.880
88.70%
Light load
9.18
20.01
0.390
7.804
85.00%
Full load
89.50
19.99
3.985
79.660
89.00%
Med load
44.88
19.99
1.993
39.840
88.77%
Light load
9.74
20.01
0.390
7.804
80.12%
Full load
90.10
20.00
3.986
79.720
88.47%
Med load
45.15
20.01
1.993
39.880
88.32%
Light load
10.13
20.01
0.390
7.804
77.03%
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EVALQRS-ICE2QS02G-80W
Figure 7 – Efficiency vs. AC line voltage
Table 4 – Efficiency vs. output power at 220Vac line voltage
Pin(W)
Vout(V)
Iout(A)
Pout(W)
Efficiency
9.74
20.01
0.390
7.804
80.12%
18.51
20.00
0.795
15.900
85.89%
27.35
20.01
1.198
23.972
87.64%
35.91
19.99
1.589
31.764
88.45%
44.88
19.99
1.993
39.840
88.77%
53.81
19.99
2.398
47.936
89.08%
62.45
19.99
2.787
55.712
89.21%
71.40
19.98
3.193
63.796
89.35%
80.90
19.99
3.596
71.884
88.85%
89.50
19.99
3.985
79.660
89.00%
Figure 8 – Efficiency vs. output power at 220Vac line voltage
Application Note
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EVALQRS-ICE2QS02G-80W
12
References
[1]
ICE2QS01 datasheet, Infineon Technologies AG, 2006
[2]
ICE2QS02G datasheet, Infineon Technologies AG, 2008
[3]
AN-ICE2QS01, 25W Evaluation Board with Quasi –Resonant PWM Controller ICE2QS01, Infineon
Technologies AG, 2006
[4]
CoolMOS® IPA60R199CP datasheet Rev 1.3, Infineon Technologies AG, 2007
[5]
Converter Design Using the Quasi-Resonant PWM Controller ICE2QS01, Infineon Technologies AG,
2006
Application Note
16
25 June 2008
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