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Title
Engineering Prototype Report for EP48 - 1.4 W Non-Isolated Buck Converter Using LNK304P (LinkSwitch(R)-TN)
Specification 85-265 VAC Input, 12 V, 120 mA, 1.44 W Output Applications Author Document Number Date Revision
Room Air Conditioners, White Goods, LED Lighting, and Other Applications Requiring a NonIsolated Supply Power Integrations Applications Department
EPR-48
02-May-2005 1.1
Summary and Features * * * * * * * * Low cost, low component count solution (only 16 components) No optocoupler required Much higher output current than "reactive dropper" type power supplies High efficiency (>69% over full input voltage range) Less than 1 W input power with 0.5 W load Low no-load consumption (<0.2 W at 265 VAC) Fully protected against open-loop faults, output overload, short circuit and thermal overload Low-cost input stage meets EMI and surge requirements
The products and applications illustrated herein (including circuits external to the products and transformer construction) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com.
Power Integrations 5245 Hellyer Avenue, San Jose, CA 95138 USA. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
Table Of Contents
1 2 3 4 Introduction.................................................................................................................3 Power Supply Specification ........................................................................................4 Schematic...................................................................................................................5 Circuit Description ......................................................................................................5 4.1 Input Stage and EMI Filtering ..............................................................................5 4.2 LinkSwitch-TN .....................................................................................................5 4.3 Output Rectification .............................................................................................6 4.4 Output Feedback.................................................................................................6 4.5 Operation Below Minimum Drain Voltage Specification ......................................7 5 PCB Layout ................................................................................................................7 6 Bill Of Materials ..........................................................................................................8 7 Performance Data ......................................................................................................9 7.1 Efficiency .............................................................................................................9 7.2 No-load Input Power............................................................................................9 7.3 Regulation .........................................................................................................10 7.3.1 Load ...........................................................................................................10 7.3.2 Line ............................................................................................................10 8 Thermal Performance...............................................................................................11 9 Waveforms ...............................................................................................................12 9.1 Drain Voltage and Current, Normal Operation...................................................12 9.2 Drain Voltage and Current Start-up Profile ........................................................12 9.3 Output Voltage Start-up Profile..........................................................................13 9.4 Load Transient Response (75% to 100% Load Step) .......................................13 9.5 Output Ripple Measurements............................................................................14 9.5.1 Ripple Measurement Technique ................................................................14 9.5.2 Measurement Results ................................................................................15 10 Conducted EMI .....................................................................................................16 11 Revision History ....................................................................................................18 Important Note: Although this board is designed to satisfy safety requirements, the engineering prototype has not been agency approved. In addition, as the output is not electrically isolated from the input, all testing should be performed using an isolation transformer to provide the AC line input to the prototype board.
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
1 Introduction
This document is an engineering report describing a non-isolated 12 V, 120 mA power supply utilizing a LNK304. This power supply is intended as a general purpose evaluation platform for LinkSwitch-TN in a buck converter configuration. The document contains the power supply specification, schematic, bill of materials, printed circuit layout, and performance data.
Figure 1 - EP48 Populated Circuit Board Photograph.
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
2 Power Supply Specification
Description Input Voltage Frequency No-load Input Power (230 VAC) Output Output Voltage 1 Output Ripple Voltage 1 Output Current 1 Total Output Power Continuous Output Power Standby Input Power Efficiency Environmental Conducted EMI Surge
Meets CISPR22B / EN55022B > 6 dB Margin 1.2/50 s surge, IEC 1000-4-5, Series Impedance: Differential Mode 2 Common Mode: 12 Free convection, sea level. For operation at >70 C substitute D1 for a diode with trr 35 ns
Symbol VIN fLINE
Min 85 47
Typ
Max 265 64 0.3 13.2 120 120
Units VAC Hz W V mV mA W W %
Comment
2 Wire - No Protective Earth
50/60
VOUT VRIPPLE1 IOUT POUT PIN (S/B)
10.8 0
12.0
10% 20 MHz Bandwidth 3.5 mA pre-load fitted on board
1.44 1 70
0.5 W output load Measured at 85 VAC, 25 C
o
4
kV
o
Ambient Temperature
TAMB
-20
50/85
C
Table 1 - EP48 Specifications
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
3 Schematic
Figure 2 - EP48 Schematic.
4 Circuit Description
4.1 Input Stage and EMI Filtering The input stage is comprised of fusible resistor RF1, diodes D3 and D4, capacitors C4 and C5, and inductor L2. Two diodes are used to both increase the surge withstand to 2 kV and provide EMI gating (noise current only flows when the diodes conduct). Placing D3 and D4 directly in series would meet the surge requirements, but without EMI gating, conducted EMI on the neutral line would be higher. Resistor RF1 is a flameproof, fusible, wire wound resistor. It accomplishes several functions: (a) limits inrush current to safe levels for rectifiers D3 and D4, (b) provides differential mode noise attenuation and (c) acts as an input fuse in the event any other component fails short circuit. As this component is used as a fuse, it should fail safely open circuit without emitting smoke, fire or incandescent material to meet typical safety requirements. To withstand the instantaneous inrush power dissipation, wire wound types are recommended. Metal film resistors are not recommended. 4.2 LinkSwitch-TN LinkSwitch-TN integrates a 700 V power MOSFET and control circuitry into a single low cost IC. The internal fixed switching frequency of 66 kHz was selected to allow up to 120 mA of output current using a standard 1 mH inductor. Lower frequencies require higher value, more costly inductors while higher frequencies increase EMI and cause undesirable high di/dt values as the inductor value reduces. The device is completely self-powered from the DRAIN pin with local supply decoupling provided by a small 100 nF capacitor connected to the BYPASS pin.
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
Here, the device is configured in a buck converter. The supply is designed to operate in mostly discontinuous conduction mode (MDCM), with the peak L1 inductor current set by the LNK304P internal current limit. The control scheme used is similar to the ON/OFF control used in TinySwitch(R). The on-time for each switching cycle is set by the inductance value of L1, LinkSwitch-TN current limit and the high voltage DC input bus across C5. Output regulation is accomplished by skipping switching cycles in response to an ON/OFF feedback signal applied to the FEEDBACK (FB) pin. This differs significantly from traditional PWM schemes that control the duty factor (duty cycle) of each switching cycle. Unlike TinySwitch, the logic of the FB pin has been inverted in LinkSwitch-TN. This allows a very simple feedback scheme to be used when the device is used in the buck converter configuration. Current into the FB pin greater than 49 A will inhibit the switching of the internal MOSFET, while current below this allows switching cycles to occur. In the event of a fault condition such as output overload, output short circuit, or an open loop condition, LinkSwitch-TN enters into auto-restart operation. If no feedback is received for >50 ms, the internal MOSFET is disabled for 800 ms and auto-restart alternately enables and disables the switching of the power MOSFET until the fault condition is removed and feedback is received. 4.3 Output Rectification During the ON time of U1, current ramps in L1 and is simultaneously delivered to the load. During the OFF time the inductor current ramps down via free-wheeling diode D1 into C2 and is delivered to the load. Diode D1 should be selected as an ultra-fast diode (trr 50 ns) with a voltage rating greater than the maximum DC voltage across C5, 600 V in this case. In designs that operate in continuous conduction mode, trr of 35 ns is recommended. Capacitor C2 should be selected to have an adequate ripple current rating (low ESR type). 4.4 Output Feedback The voltage across L1 is rectified and smoothed by D1 and C2 during the off-time of U1. To a first order, the forward voltage drops of D1 and D2 are identical and therefore, the voltage across C3 tracks the output voltage. To provide a feedback signal, the voltage developed across C3 is divided by R1 and R3 and connected to U1's FB pin. The values of R1 and R3 are selected such that at the nominal output voltage, the voltage on the FB pin is 1.65 V. This voltage is specified for U1 at an FB current of 49 A with a tolerance of +/-7% over a temperature range of -40 to 125 oC. This allows this simple feedback to meet the required overall output tolerance of +/-10% at rated output current. Operation down to 0 mA output current can be accomplished while still meeting +/-10% by increasing the size of the preload from 3.5 mA to 5 mA.
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
4.5 Operation Below Minimum Drain Voltage Specification In certain abnormal conditions, the drain voltage can drop below the minimum drain voltage specification of 50 V. If these conditions exist in combination with very light output loading (<5 mA), it is possible for the output voltage to go out of regulation. These abnormal conditions can exist, for example, during a brownout condition when the input voltage can drop to <30 VAC. To avoid the output voltage exceeding acceptable levels under these conditions, the output of the power supply has to either be pre-loaded with 5 mA or the output has to be clamped with an appropriate Zener diode (e.g. 15 V, 1.3 W device).
5 PCB Layout
Figure 3 - EP48 Printed Circuit Layout (Dimension 0.001 Inches).
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
6 Bill Of Materials
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Qty 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 Reference C4, C5 C1 C3 C2 D3, D4 D1 D2 L1 L2 R3 R1 R4 RF1 U1 J1 J2 Description 4.7 F, 400 V, 8mm x 11 mm 0.1 F, 50 V, ceramic 10 F, 35 V general purpose 180 F, 16 V, low ESR 250 m, 400 mA 1 A, 1000 V, plastic rectifier 1 A, 600 V, Ultra Fast (trr 50 ns) 1A, 600 V, glass passivated rectifier (trr = 2 s) 1 mH inductor 0.28 A 1 mH inductor 0.21 A 2.05 k, 0.25 W, 1% 13.0 k, 0.25 W, 1% 3.3 k, 0.25 W, 5% 8.2 wire wound fusible, 2 W LinkSwitch-TN 3-pin connector (center pin removed) 2-pin connector P/N 380VB4R7M8X11LL ECU-S1H104KBB ECA-1VM100 EEU-FC1C181 1N4007 UF4005 1N4005GP SBC3-102-281 SBC1-102-211 MFR-25FBF-2K05 MFR-25FBF-13K CFR-25JB-3K3 CRF0414-253-4 8R2 LNK304P 26-48-1031 26-48-1021 Manufacturer UCC Panasonic Panasonic Panasonic Diodes Inc (or Generic) General Semiconductor (or Generic) General Semiconductor (or Generic) Tokin Tokin Yageo (or generic) Yageo (or generic) Yageo (or generic) VTM Power Integrations Molex Molex
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
7
7.1
Performance Data
Efficiency
100% 90% 80% 70%
85 VAC 115 VAC 265 VAC
All measurements performed at room temperature, 60 Hz input frequency.
Efficiency
60% 50% 40% 30% 20% 10% 0% 0 20 40 60 80 100 120 140
Output Current (mA)
Figure 4 - Efficiency vs. Output Current, Room Temperature, 60 Hz.
7.2
No-load Input Power
200 180 160
Input Power (mW)
140 120 100 80 60 40 20 0 80 100 120 140 160 180 200 220 240 260 280
Input Voltage (VAC)
Figure 5 - Zero Load Input Power vs. Input Line Voltage, Room Temperature, 60 Hz.
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter 7.3 Regulation
02-May-2005
7.3.1 Load
13 12.8 12.6
Output Voltage (V)
12.4 12.2 12 11.8 11.6 11.4 11.2 11 0 10 20 30 40 50 60 70 80 90 100 110 120 130
Output Load (mA)
Figure 6 - Load Regulation, Room Temperature.
7.3.2 Line
13 12.8 12.6
Output Voltage (V)
12.4 12.2 12 11.8 11.6 11.4 11.2 11 80 100 120 140 160 180 200 220 240 260 280
Input Voltage (VAC)
Figure 7 - Line Regulation, Room Temperature, Full Load.
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Page 10 of 20
02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
7.4 Thermal Performance To verify acceptable thermal performance, thermocouples were placed on key components on the board and the unit was placed into a thermal chamber. The ambient was raised to 85 C with no air flow over the board. The unit was fully loaded and allowed to stabilize at three different line voltages, at which point temperature measurements were recorded. In addition, a thermal image was taken of a unit painted matte black, operating at full load, 85 VAC and an ambient temperature of 23 C. These results show very acceptable temperature rise figures and show that the unit can operate in a very high ambient with sufficient margin to thermal shutdown.
Figure 8 - Infrared Thermograph of EP48, 85 VAC Input, Full Load and 23 C Ambient.
Temperature (C) Item Ambient LinkSwitch-TN (U1) Output Inductor (L1) Freewheeling Diode (D1) Input Capacitor (C5) Output Capacitor (C2) 90 VAC 85 112 102 103 95 90 115 VAC 240 VAC 85 112 103 103 92 90 85 106 105 107 90 91
Table 2 - Temperature of Key Components, 85 VAC, Full Load, 85 C Ambient.
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
8 Waveforms
8.1 Source Voltage and Current, Normal Operation
Figure 9 - 85 VAC, Full Load. Upper: IDRAIN, 0.1 A / div Lower: VSOURCE, 100 V, 2 s / div
Figure 10 - 265 VAC, Full Load. Upper: IDRAIN, 0.1 A / div Lower: VSOURCE, 100 V / div
8.2
Source Voltage and Current Start-up Profile
Figure 11 - 85 VAC Input and Maximum Load. Upper: IDRAIN, 0.1 A / div Lower: VSOURCE, 100 V & 1 ms / div
Figure 12 - 265 VAC Input and Maximum Load. Upper: IDRAIN, 0.1 A / div Lower: VSOURCE, 100 V & 1 ms / div
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Page 12 of 20
02-May-2005 8.3
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
Output Voltage Start-up Profile
Figure 13 - 85 VAC Input and Maximum Load. 2 V / div, 10 ms
Figure 14 - 265 VAC Input and Maximum Load. 2 V / div, 10 ms
8.4 Load Transient Response (75% to 100% Load Step) The oscilloscope was triggered using the load current step as a trigger source.
Figure 15 - 85 VAC Input and Maximum Load. Upper: 100 mA / div Lower: 50 mV / div, 5 ms / div
Figure 16 - 265 VAC Input and Maximum Load. Upper: 100 mA / div Lower: 50 mV / div, 5 ms / div
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
8.5
Output Ripple Measurements
8.5.1 Ripple Measurement Technique For DC output ripple measurements, a modified oscilloscope test probe must be utilized in order to reduce spurious signals due to pickup. Details of the probe modification are provided in Figure 17 and Figure 18. The 5125BA probe adapter is affixed with two capacitors tied in parallel across the probe tip. The capacitors include one (1) 0.1 F/50 V ceramic type and one (1) 1.0 F/50 V aluminum electrolytic. The aluminum electrolytic type capacitor is polarized, so proper polarity across DC outputs must be maintained (see below).
Probe Ground
Probe Tip
Figure 17 - Oscilloscope Probe Prepared for Ripple Measurement. (End Cap and Ground Lead Removed).
Figure 18 - Oscilloscope Probe with Probe Master 5125BA BNC Adapter (Modified with Wires for Probe Ground for Ripple Measurement and Two Parallel Decoupling Capacitors Added).
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
8.5.2 Measurement Results
Figure 19 - Ripple, 85 VAC, Full Load. 2 ms, 50 mV / div
Figure 20 - 5 V Ripple, 115 VAC, Full Load. 2 ms, 50 mV / div
Page 15 of 20
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
9
Conducted EMI
Figure 21 - Conducted EMI, 12 V Out, 120 mA, 115 VAC, 60 Hz, EN55022 B Limits, Neutral.
Figure 22 - Conducted EMI, 12 V Out, 120 mA, 115 VAC, 60 Hz, EN55022 B Limits, Line.
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
Figure 23 - Conducted EMI, 12 V Out, 120 mA, 230 VAC, 60 Hz, EN55022 B Limits, Neutral.
Figure 24 - Conducted EMI, 12 V Out, 120 mA, 230 VAC, 60 Hz, EN55022 B Limits, Line.
Page 17 of 20
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
10 Revision History
Date 16-Sept-03 17-Sept-03 22-Sept-03 20-Nov-03 22-Dec-03 02-May-05 Author AO PV PV AO PV SK Revision 0.1 0.2 0.3 0.4 1.0 1.1 Description & changes First Draft 2nd Draft 3rd Draft 4thDraft 5th Draft Corrected scales in Figures 10 and 12
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02-May-2005
EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
NOTES
Page 19 of 20
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EP48 - 12 V, 1.44 W, Non-Isolated Buck Converter
02-May-2005
For the latest updates, visit our website: www.powerint.com Power Integrations may make changes to its products at any time. Power Integrations has no liability arising from your use of any information, device or circuit described herein nor does it convey any license under its patent rights or the rights of others. POWER INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. PATENT INFORMATION The products and applications illustrated herein (including circuits external to the products and transformer construction) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. The PI Logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch and EcoSmart are registered trademarks of Power Integrations. PI Expert and PI FACTS are trademarks of Power Integrations. (c) Copyright 2005 Power Integrations.
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