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January 2014 DocID15099 Rev 2 1/23

AN2838

Application note

35 W wide-range high power factor flyback converter evaluation

board using the L6562A

Introduction

This application note describes a product evaluation board based on the transition-mode

PFC controller L6562A, and presents the results of its bench demonstration. The board is a

35 W, wide-range mains input, power factor corrected SMPS (switched mode power supply)

suitable for all low power applications requiring a high PF (power factor), such as lighting

applications and power supplies for LEDs. The low-cost L6562A and the simple flyback

topology combine to provide a very competitive PFC controller solution.

Figure 1. EVL6562A-35WFLB evaluation board using the L6562A

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Summary of content (23 pages)

PAGE 1
AN2838 Application note 35 W wide-range high power factor flyback converter evaluation board using the L6562A Introduction This application note describes a product evaluation board based on the transition-mode PFC controller L6562A, and presents the results of its bench demonstration.
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Contents AN2838 Contents 1 Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 4 2 Electrical diagram and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Test results and significant waveforms . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1 Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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AN2838 List of figures 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. EVL6562A-35WFLB evaluation board using the L6562A . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 EVL6562A-35WFLB evaluation board: electrical schematic . . . . .
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Main characteristics and circuit description 1 AN2838 Main characteristics and circuit description The main characteristics of the SMPS evaluation board are: • Line voltage range: 90 to 265 VAC • Minimum line frequency (fL): 47-63 Hz • Regulated output voltage: 48 V • Rated output power: 35 W • Power factor (load = 50 %): 0.9 minimum • Minimum efficiency: 85 % at full load • Maximum 2 fL output voltage ripple: 1.5 V pk-pk / 0.
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AN2838 Main characteristics and circuit description isolated voltage loop by the optocoupler U2, and using an inexpensive TL431 (U3) to drive the optocoupler. The opto-transistor modulates the input voltage of the L6562A internal amplifier, thus closing the voltage loop. The output rectifier is a fast recovery type, selected according to its maximum reverse voltage, forward voltage drop and power dissipation. A small LC filter is added on the output, filtering the high frequency ripple.
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Electrical diagram and bill of material 2 AN2838 Electrical diagram and bill of material Figure 2.
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AN2838 Electrical diagram and bill of material Table 1. Bill of material Reference Part value Type/description Supplier C1 2.2 nF Ceramic Y2 Murata C2 2.2 nF Ceramic Y2 Murata C3 0.22 µF R.46 275 VAC Arcotronics C4 0.1 µF R.41 MKP Y2/X1 300 VAC n.d. C5 220 nF MKT X2 275 VAC n.d. C6 47 µF 35 V n.d. C7 100 nF Ceramic n.d. C8 2.2 nF Ceramic n.d. C9 2.2 nF Ceramic n.d.
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Electrical diagram and bill of material AN2838 Table 1. Bill of material (continued) 8/23 Reference Part value Type/description Supplier L1 4135 Filter inductor 15 µH/3 A Magnetica Q1 STP5NK80ZFP Power MOSFET, TO-220FP w/heatsink STMicroelectronics R1 150 kΩ Axial n.d. R2 150 kΩ Axial n.d. R3 68 kΩ Axial n.d. R4 10 R Axial n.d. R5 680 kΩ Axial n.d. R6 20 kΩ Axial n.d. R7 1 MΩ Axial n.d. R8 1 MΩ Axial n.d. R9 1 MΩ Axial n.d. R10 0R shorted n.d.
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AN2838 Test results and significant waveforms 3 Test results and significant waveforms 3.1 Harmonic content measurement One of the main purposes of this converter is the correction of input current distortion, decreasing the harmonic contents below the limits of the actual regulation. Therefore, the board has been tested according to the European standard EN61000-3-2 Class-C and Japanese standard JEIDA-MITI Class-C, at full load and both nominal input voltage mains.
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Test results and significant waveforms AN2838 Figure 6. EVL6562A-35WFLB input current waveform @100 V-50 Hz - 35 W load Figure 7. EVL6562A-35WFLB input current waveform @230 V-50 Hz - 35 W load The converter’s efficiency has been measured and it is significantly high in all load and line conditions (see Figure 8). At full load, the efficiency is higher than 85% at any input voltage, making this design suitable for high efficiency power supplies.
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AN2838 Test results and significant waveforms Figure 10. EVL6562A-35WFLB output voltage ripple @ 90 VAC - full load Figure 11. EVL6562A-35WFLB output voltage ripple @ 265 VAC - full load In Figure 10 and Figure 11 the output voltage ripple at twice the input mains frequency is measured. As shown it is less than 0.4 V peak-to-peak, which is ideal for LED or lighting applications. High frequency noise, including spikes, is significantly reduced as well.
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Test results and significant waveforms AN2838 Figure 14. EVL6562A-35WFLB VDS and ID Figure 15. EVL6562A-35WFLB VDS and ID @ 265 VAC - full load @ 265 VAC - full load - detail CH1: drain current - 0.5 A/div CH1: drain current - 0.5 A/div CH2: drain voltage - 200 V/div CH2: drain voltage - 200 V/div Figure 14 shows the measurement at the maximum drain voltage of 265 VAC and max load.
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AN2838 Test results and significant waveforms Figure 18. EVL6562A-35WFLB VDS and ID Figure 19. EVL6562A-35WFLB VDS and ID @ 265 VAC - 40 mA @ 265 VAC - 40 mA - detail CH1: drain current - 0.2 A/div CH1: drain current - 0.2 A/div CH2: drain voltage - 200 V/div CH2: drain voltage - 200 V/div The above figures show the MOSFET waveforms at light load. Even in this load condition the waveforms are correct.
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Thermal measurements 4 AN2838 Thermal measurements To check the reliability of the design, thermal mapping by means of an IR camera was carried out. Figure 20 and Figure 21 show thermal measurements on the component side of the board at nominal input voltages and full load. Some pointers visible on the pictures placed across key components show the relevant temperature. Table 1 provides the correlation between the measured points and components, for both thermal maps.
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AN2838 5 Conducted emission pre-compliance test Conducted emission pre-compliance test The following images are the peak measurements of the conducted noise at full load and nominal mains voltages. The limits shown on the diagrams are those of EN55022 Class-B, which is the most popular standard for domestic equipment. As visible in the diagrams, good margins with respect to the limits are present in all test conditions. Figure 22. 115 VAC and full load - phase Figure 23.
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Burst test 6 AN2838 Burst test The board has been tested against burst pulses, with good results. The tests have been carried out using the following equipment and the procedures: • Surge generator: Schaffner NSG 200 E 7 NSG 224 A • Test types: • – SYM = symmetric with respect to earth pole (pulse applied between line and neutral) – ASYM = asymmetric (pulse applied between line and earth and between neutral and earth) Output load 700 mA. Figure 26.
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AN2838 Burst test • Test passed with a total of 200 pulses applied and a medium energy of 80 mJ (when connected to a 50 Ω load).
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Schematic with output voltage and current loop 7 AN2838 Schematic with output voltage and current loop All tests described in this document have been done using the schematic in Figure 1 and using a TL431 for the output voltage feedback. If a secondary current loop is also needed, the schematic below can be implemented on the PCB by making the modifications listed in Table 4. The proposed schematic has been designed to drive LEDs with a current rating of 700 mA.
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AN2838 Schematic with output voltage and current loop Table 4. Modification list for TSM1052 implementation Reference Part value Modification C15 Type/ Description Removed C16 100 nF Changed value Ceramic C25 2.
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Power transformer specification 8 AN2838 Power transformer specification • Transformer type: open – Winding type: layer – Coil former: vertical type, 6 + 6 pins – Mains insulation: 4 kV – Unit finishing: varnished Electrical characteristics (all measurements taken with pins 10 and 11 shorted) • Converter topology: flyback, TM mode • Core type: ETD29 • Min. operating frequency: 36 kHz • Primary inductance: 550 mH 10% @ 1 kHz - 0.25 V (a) • Leakage inductance: 4.5 mH@ 50 kHz - 0.
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AN2838 9 References References • L6562A transition-mode PFC controller datasheet • Application note AN1059: Design equations of high-power-factor flyback converters based on the L6561 • Application note AN1060: Flyback converters with the L6561 PFC controller DocID15099 Rev 2 21/23 23
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Revision history 10 AN2838 Revision history Table 5.
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AN2838 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale.