AN4314 Application note 25 W wide-range high power factor buck-boost converter demonstration board using the L6564H Introduction This application note describes a wide-range non-isolated 25 W regulated LED driver with high power factor. The EVL6564H-25W-BB demonstration board is well-suited to the Japanese market due to the broad use of standard 100 Vac lighting applications and also 200 Vac tubes in building automation systems. The EVL6564H-25W-BB demonstration board has been designed in order to obtain the highest possible power factor over the entire input mains voltage, remaining compliant to EN55022 Class-B and keeping the average output current in a tight band with different LED characteristics. The board is based on ST's L6564H power factor controller and the SEA05L CC-CV controller for LED current regulation in a non-isolated flyback configuration. The form factor has been designed to fit into a standard LED driver case, facilitating the replacement of the incandescent flood lamps up to 80-100 W power. Figure 1. EVL6564H-25W-BB demonstration board using the L6564H July 2013 DocID024821 Rev 2 1/31 www.st.com Contents AN4314 Contents 1 Main characteristics and circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 LED current ripple definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Electrical diagram and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4 Performance and considerations with LED Loads . . . . . . . . . . . . . . . 12 5 PFC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.1 Input and output current and voltage waveforms . . . . . . . . . . . . . . . . . . . 16 5.2 Transition mode operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.3 Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.4 Line sags and fast on-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.5 Load disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.6 Short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.7 Feedback failure protection (open loop) . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6 Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 7 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 8 Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 27 9 PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2/31 DocID024821 Rev 2 AN4314 List of tables List of tables Table 1. Table 2. Table 3. Table 4. Main characteristics and circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Measured temperature at 100 Vac/50 Hz and 230 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . 26 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 DocID024821 Rev 2 3/31 31 List of figures AN4314 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. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38. Figure 39. 4/31 EVL6564H-25W-BB demonstration board using the L6564H. . . . . . . . . . . . . . . . . . . . . . . . 1 EVL6564H-25W-BB demonstration board: electrical schematic. . . . . . . . . . . . . . . . . . . . . . 8 LED string voltage vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 LED current vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Power factor vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 THD vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Efficiency vs. line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Input current waveform at 100 Vac -50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 input current waveform at 230 Vac -50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 TM operation at 100 Vac - 0.35 A - fsw =35 kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 TM operation at 230 Vac - 0.35 A- fsw = 50 kHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Start-up at 100 Vac - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Start-up at 230 Vac - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 TOFF = 40 ms at 100 Vac / 50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 TOFF = 40 ms at 230 Vac / 50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 TOFF = 500 ms at 100 Vac/50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 TOFF = 500 ms at 230 Vac/50 Hz - 0.35 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Load disconnection transition at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 No load at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Load disconnection transition at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 No load at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Short circuit at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Short circuit at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Overload behavior after a short circuit at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Overload behavior after a short circuit at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Short circuit removal at 100 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Short circuit removal at 230 Vac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Feedback failure protection at 100 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Feedback failure protection at 230 Vac/50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 EVL6564H-25W-BB at 100 Vac/50 Hz compliance with JEIDA-MITI class-C limits at PF = 0.9801 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 EVL6564H-25W-BB at 230 Vac/50 Hz compliance with EN61000-3-2 class-C limits at PF = 0.9180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Thermal map at 100 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Thermal map at 230 Vac/50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 100 Vac/50 Hz - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 100 Vac/50 Hz - neutral. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 230 Vac/50Hz - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 230 Vac/50Hz - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 DocID024821 Rev 2 AN4314 1 Main characteristics and circuit Main characteristics and circuit The main characteristics of this single-stage LED driver demonstration board are given in the table below. Table 1. Main characteristics and circuit Parameter Value Line voltage range 85 to 265 VAC Line frequency (fL) 47-63 Hz LED string voltage drop 70 V ±10 % (23-LED p.n. X42182) [6] LED nominal current 350 mA ±3 % LED current ripple pk-pk 100 mA Rated output power 25 W Power factor > 0.9 Efficiency > 89 @ 230 V Maximum ambient temperature 50 °C Conducted EMI In accordance with EN55022 Class-B Protections Preventing overvoltage, load disconnection and short-circuit The main feature of the converter is that the input current is almost in phase with the mains voltage; therefore the power factor is close to unity. This is achieved by the L6564H controller, which shapes the input current as a sine wave in phase with the mains voltage. An external high-voltage startup circuitry is not needed because it is already embedded in the IC. The power supply utilizes a typical non-isolated buck-boost converter topology with a simple inductor to transfer energy to the LED load. The converter is connected after the mains rectifier and the capacitor filter, which in this case is quite small, to avoid damage to the shape of the input current. The buck-boost switch is represented by the power MOSFET Q3 and driven by the L6564H. At startup, a 0.85 mA internal current source of the L6564H charges the VCC capacitor (C8), until the voltage on the Vcc pin reaches the startup threshold, then it is shut down. The T1 auxiliary winding (pins 6-7), the charge pump (C14, R16, D4) and the BJT voltage regulator (Q2, DZ2, R3) generate a constant VCC voltage that powers the L6564H during normal TM operation. R37 is also connected to the auxiliary winding to provide the transformer demagnetization signal to the L6564H ZCD pin, turning on the MOSFET at any switching cycle. The MOSFET used is the STI8N65M5, a new MDmesh™ V, low-cost, low on-resistance, 710 V device housed in an I2PAK package [5], and without any heatsink. The multilayer inductor, using a standard ferrite size EF-25, is manufactured by Magnetica. DocID024821 Rev 2 5/31 31 Main characteristics and circuit AN4314 The resistors R27 and R26 sense the current flowing into the inductor primary side. Once the signal at the current sense pin has reached the level programmed by the internal multiplier of the L6564H, the MOSFET turns off. The divider R13, R14, R15 and R30 provides the L6564H multiplier pin with instantaneous voltage information which is used to modulate the current flowing into the inductor. To maintain a constant (average) output current, some kind of regulation is required and for this reason, on the output side, an error amplifier (inside the SEA05L) senses the LED current on sense resistors R6, R7, and it drives the input of the internal error amplifier of the L6564H. As a consequence, the PWM comparator is modulated too. The inductor T1 is charged by Q3 when it is turned on, and it discharges into the output capacitor C3 and into the LED load when Q3 turns off. Due to the topology, the LED string load is connected to a floating output so the loop is closed through a current mirror formed by two high-voltage BJTs (Q4, Q5). For the constant current regulation an SEA05L CC-CV has been used. The current loop regulates the LED current at a nominal level of 350 mA, the nominal voltage drop of the LED string is 70 Vdc with a tolerance of 10 %. Normally the voltage loop does not operate in the range 63 V - 77 Vdc, but it works in case the LED string opens to protect the output bulk capacitor C3 from overvoltage. The R8, R9 divider senses the output voltage and regulates the output voltage to around 84 Vdc. In case one of the loops fails and the output voltage is no longer regulated, a protection preventing an open loop is performed using the PFC_OK pin, the L6564H sensing the increase of the auxiliary winding voltage. The board is equipped with an input EMI pi-filter stage (C2-L1-C6) connected after the input connector. An input fuse and a varistor (VR1) are also provided at the input of the board, protecting from short-circuits and improving immunity against input voltage fast transients. In order to prevent a short-circuit of the output stage, an external, low-cost circuit (composed of Q6, Q9, Q8, R23, R24, R32, R20, D3, D8, R40) disables the L6564H using the PFC_OK pin. The circuit is composed of a buffer stage (Q6, R23) connected to the feedback loop. When Q9 is off, a current through the R32 resistor connected to VCC_PROT will charge the C7 capacitor up to a voltage level imposed by the sum of two diode voltage drops (D7 + D3). At that voltage level, the transistor Q8 will switch on and it pulls the PFC_OK pin to ground, disabling the L6564H controller. Removing the short, the C7 capacitor will discharge through R40 connected to the Gate Drive pin during the MOSFET off-time (low state). The time constant R32 with C7 is set in order to mask the transition time during startup. In fact during this time phase, when the loop is still open, the feedback signal is still low and it could activate the protection unnecessarily. The board has been designed using the procedure described in AN1059 [1] used to design a standard high-power factor flyback. This application note has been used as a reference for calculating this demonstration board, since the buck-boost topology can be considered as a simple flyback with a unity transformer turn ratio and with the output voltage corresponding to the reflected voltage of the flyback. A description of the dimensioning of the output capacitor and the LED current ripple definition appears in Section 2 as it is not included in AN1059 [1]. 6/31 DocID024821 Rev 2 AN4314 2 LED current ripple definition LED current ripple definition In a typical LED application the definition of ripple current must be carefully considered. We have defined a current ripple lower than 100 mA pk-pk, corresponding to about 30 % of the average LED current. This parameter depends only on two factors, one is linked to the load and the other to the converter as follows: – the dynamic resistance of the LED string RDtot – the output capacitor value of the converter Co The following formula describes the relation between the current ripple and the previous two factors: Equation 1 I ripple ∝ I OUT 1 + (4 ⋅ π ⋅ f l ⋅ RDtot ⋅ C O ) 2 First, note that the value of the output capacitor will depend on the load so it is important to know the final application of the converter. Second, the form factor of the converter will depend on the output capacitor size and, as a consequence, on the output current ripple specification. In this application a 680 μF capacitor has been selected in order to maintain the current ripple below 100 mA. DocID024821 Rev 2 7/31 31 Electrical diagram and bill of material 3 AN4314 Electrical diagram and bill of material Figure 2. EVL6564H-25W-BB demonstration board: electrical schematic 8/31 DocID024821 Rev 2 AN4314 Electrical diagram and bill of material Table 2. Bill of material Ref. Part N. Type Supplier BR1 2KBP08M Bridge rect. 2 A 800 V Conn.1 Line-input Connector MKDS 1.5/3-5.08-PS.5.08 Phoenix contact Conn.2 DC-OUT Connector MKDS 1.5/2-5.08-PS.5.08 Phoenix contact C1 2.2 nF Ceramic capacitor X1/Y2+-20%-P.7,5 mm Murata C2 150 nF Capacitor MKP+-20%-PS15-X2 Epcos C6 150 nF Capacitor MKP+-20%-PS15-X2 Epcos C3 680 uF Electrolytic capacitor V.105 °C-PW-8000h C4 220 nF Capacitor MKP+-5%-200 Vac-PS15 Epcos C5 3.3 uF Ceramic capacitor X7S 10% EIA1210-SMD Kemet C7 22 uF Electrolytic capacitor V.105 °C-2000h-PW Nichicon C8 33 uF Electrolytic capacitor V.105 °C-10000h-YXM Rubycon C9 10 nF N.M. C10 Vishay Nichicon Capacitor X7R 10% EIA0805-SMD Murata 100 nF Ceramic capacitor X7R 10% EIA1206-SMD Yageo C11 100 nF Ceramic capacitor X7R 10% EIA0805-SMD Kemet C23 100 nF Ceramic capacitor X7R 10% EIA0805-SMD Kemet C12 2.2 nF Capacitor X7R 10% EIA0805-SMD Kemet C17 2.2 nF Capacitor X7R 10% EIA0805-SMD Kemet C18 2.2 nF Capacitor X7R 10% EIA0805-SMD Kemet C21 2.2 nF Capacitor X7R 10% EIA0805-SMD Kemet C13 220 nF Ceramic capacitor Y5V -20+80% EIA0805-SMD C14 22 nF Ceramic capacitor X7R 5% EIA1206-SMD Kemet C15 1 μF Ceramic capacitor X7R 10%-EIA0805-SMD Murata C16 1 μF Ceramic capacitor X7R 10%-EIA0805-SMD Murata C19 1 μF Ceramic capacitor X7R 5%-EIA0805-SMD Kemet C20 220 pF N.M. Capacitor HV-U2J-5% EIA1206-SMD Ceramic capacitor C0G 5% EIA0805-SMD AVX Murata C22 220 pF DZ1 BZV55-C24 Zener-diode 5%-Sz 19.6 mV/K-SMD NXP DZ2 BZV55-C15 Zener-diode 5%-Sz 11.4 mV/K-SMD NXP D1 STTH2L06 Ultrafast-diode 85 ns STMicroelectronics D2 LL4148 Fast-diode 4 ns-SMD Vishay D3 LL4148 Fast-diode 4 ns-SMD Vishay D4 LL4148 Fast-diode 4 ns-SMD Vishay D5 LL4148 Fast-diode 4 ns-SMD Vishay D6 LL4148 Fast-diode 4 ns-SMD Vishay D7 LL4148 Fast-diode 4 ns-SMD Vishay DocID024821 Rev 2 Kemet 9/31 31 Electrical diagram and bill of material AN4314 Table 2. Bill of material (continued) Ref. Part N. Type D8 BAT48J Schottky-diode SMD-MK 48 STMicroelectronics D9 STPS3150U Schottky-diode Vf 0, 82 V @ 25 °C 3 A-SMDMKG315 STMicroelectronics F1 2AT Fuse 2 A 250 V 8.5 x 4-392/TE05-TIME-LAG Littelfuse J1 PS10 mm Wire jumper 0 Ω - J2 PS30 mm Wire jumper 0 Ω - J3 PS23 mm Wire jumper 0 Ω - J4 PS20 mm Wire jumper 0 Ω - J5 PS29 mm Wire jumper 0 Ω - J6 PS12 mm Wire jumper 0 Ω - J7 PS24 mm Wire jumper 0 Ω - J8 PS5 mm Wire jumper 0 Ω - L1 62 mH Q1 10/31 Common mode chokes-270 Vac max ZTX560-N.M. BJT.PNP-hfe 50 to 300 BJT.NPN-hfe 40 to 180 Supplier Magnetica Diode Inc. Q2 MJE243G Q3 STI8N65M5 Q4 FZT560 BJT.PNP-SMD-hfe 50 to 300 Diode Inc. Q5 FZT560 BJT.PNP-SMD-hfe 50 to 300 Diode Inc. Q6 BC847C BJT.NPN-hfe 420 to 800-SMD-MK1G NXP Q8 BC847C BJT.NPN-hfe 420 to 800-SMD-MK1G NXP Q9 BC847C BJT.NPN-hfe 420 to 800-SMD-MK1G NXP Q7 STN715N.M. BJT.NPN-SMD-hfe80-MK N715 R1 8.2 K Resistor 1% TE-LR1F8K2 R2 N.M. Resistor 1% TE-LR1F8K2 R3 20 K Resistor 1% TE-LR1F20K R4 N.M. Resistor 1%-150Vac/dc -EIA0805-SMD Vishay R5 1K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R6 0.15 Resistor 1%-200 Vac/dc -EIA1206-SMD IRC-LRC R7 3.3 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R8 330 K Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R9 10 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R10 270 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R11 62 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R12 10 K Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay MOSFET-N-0.6 Ω-tr/tf 14/11 ns-trr 200 ns DocID024821 Rev 2 ON STMicroelectronics STMicroelectronics AN4314 Electrical diagram and bill of material Table 2. Bill of material (continued) Ref. Part N. R13 2.2 M Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R14 2M Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R15 2M Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R16 12 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R17 0 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R18 0 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R31 0 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R19 750 Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R20 47 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay C//R20 10 nF Ceramic capacitor X7R 10% EIA0805-SMD Kemet R21 5.6 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R22 390 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R23 12 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R24 470 Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R25 20 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R26 0.82 Resistor 1% EIA1210-SMD Rohm R27 0.82 Resistor 1% EIA1210-SMD Rohm R28 51 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R29 1M Resistor 1%-50 Vac/dc -EIA0805-SMD Vishay R30 51 K Resistor 1%-50 Vac/dc -EIA0805-SMD Vishay R32 330 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R33 680 K Resistor 1%-200 Vac/dc -EIA1206-SMD Vishay R34 56 K Resistor 5% -150 Vac/dc -EIA0805-SMD Vishay R35 0 Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R36 220 Resistor 5%-200 Vac/dc -EIA1206-SMD Vishay R37 36 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay R38 100 K Resistor 5%-150 Vac/dc -EIA0805-SMD Vishay R39 27 Resistor 5%-200 Vac/dc -EIA1206-SMD Vishay R40 510 K Resistor 1%-150 Vac/dc -EIA0805-SMD Vishay T1 680 uH Lighting buck/boost inductor 40 kHz U1 SEA05L I.C.-CC/CV controller 3.5 to 36 V-Vac 0.5%Iacc 4%-MK S5L-SMD STMicroelectronics U2 L6564H I.C.-PFC controller HVS-TM-SMD STMicroelectronics VR1 300 Vac VDR-300 Vac-385 Vdc-47J-D12 mm (1) Type Supplier Magnetica Epcos 1. Add a 10 nF capacitor in parallel to R20 (0805). DocID024821 Rev 2 11/31 31 Performance and considerations with LED loads 4 AN4314 Performance and considerations with LED loads The board has been designed to source 350 mA nominal value into a string of 23 LEDs of about 1 W power and a forward drop of 3.2 V typical at ambient temperature. The LEDS used to test the demonstration board have been furnished by Seoul Semiconductor (part number X42182) [6]. In order to reproduce the possible LED string drop variation due to thermal heating of a single LED, measurements have been done first by loading the SMPS with a string of 23 LEDs having a voltage drop of 71 Vdc, then loading 22 LEDs (68 Vdc) and finally 24 (75 Vdc). The behavior of the board has been checked also at the limit of the LED tolerance of the voltage drop, at -10 %, that is, 63 Vdc and +10 %, that is, 77 Vdc by using an active load. Figure 3 represents the different load voltage drops of the LEDs, applied to the converter, at each point of the wide-range mains. This figure is necessary to understand the following Figure 4, 5, 6 and 7. Figure 3. LED string voltage vs. line voltage /('6WULQJYROWDJH>9@ 9GF /(' /(' /(' 9GF 9LQ>9DF@ $09 Figure 4 shows the LED string current versus the mains input voltage according to the load. The LED current has been set at 350 mA nominal, using Equation 2 and considering the internal Vcsth of SEA05L (see datasheet): Equation 2 RS _ SEA05 L = 50mV = 0.14Ω 350mA The SEA05L perfectly regulates the current loop over the entire mains voltage and load range [-10 %, +10 %]. 12/31 DocID024821 Rev 2 AN4314 Performance and considerations with LED loads Figure 4. LED current vs. line voltage /('FXUUHQW>$@ 9GF /(' /(' /(' 9GF 9LQ>9DF@ $09 Unlike boost topology, the buck-boost topology does not permit unity power factor even in an ideal case. From AN1059 [1], the ratio is defined as: Equation 3 KV = V PK Vout The power factor is a function of Kv where Vpk is the input peak mains voltage and Vout is the nominal 70 Vdc LED voltage drop. The current would normally be sinusoidal for Kv = 0 but will be distorted from an ideal sinusoid in proportion to the increase of KV. Since Kv in this application varies according to the mains [85-265] Vac in the range [1.7-5.3], a different PF versus input line voltage has been measured. The PF is then affected by the current phase shift caused by the CX capacitor of the input EMI. A common-mode choke with high leakage value has been selected in order to increase the power of the EMI filter but at the same time reducing the two CX capacitors. The test results of the following Figure 5 and Figure 6 show the PF and THD versus line voltage. The power factor remains above 0.9 up to the European range even considering the minimum tolerance value of the LED voltage drop (-10 %). Considering the LED voltage drop variation, the PF remains above 0.9 until 250 Vac. DocID024821 Rev 2 13/31 31 Performance and considerations with LED loads AN4314 Figure 5. Power factor vs. line voltage 9GF /(' /(' /(' 9GF 3RZHU)DFWRU 9LQ>9DF@ $09 Figure 6. THD vs. line voltage 7+'> @ 9GF /(' /(' /(' 9GF 9LQ>9DF@ $09 14/31 DocID024821 Rev 2 AN4314 Performance and considerations with LED loads Finally the efficiency of the converter has been measured showing a curve varying between 89 % and 90 %. Figure 7. Efficiency vs. line voltage (IILFLHQF\> @ 9GF /(' /(' /(' 9GF 9LQ>9DF@ $09 The voltage drop between the emitter and collector of the Vcc voltage regulator Q2 of the self-supply network increases with the input line voltage. The power losses on this BJT can be calculated as: Equation 4 Plosses = Vce ⋅ I pump The current consumption of the L6564H and driving circuitry is 5 mA and the Q2 voltage drop can reach 70 V at high mains, so the power losses are around 350 mW, that is, 1.5 % of the total output power. We can note that the losses at an input voltage above 200 Vac become significant, causing a slight decrease of efficiency as visible in the diagram. DocID024821 Rev 2 15/31 31 PFC waveforms AN4314 5 PFC waveforms 5.1 Input and output current and voltage waveforms The waveforms of the input current and drain voltage at the nominal input voltage mains (100 Vac/50 Hz or 230 Vac/50 Hz) and 23-LED load condition are illustrated in Figure 8 and Figure 9. . Figure 8. Input current waveform at 100 Vac 50 Hz CH1: DRAIN CH2: Input PFC Current CH3: LED current CH4: LED voltage drop AM13768V1 Figure 9. input current waveform at 230 Vac 50 Hz CH1: DRAIN CH2: Input PFC Current CH3: LED current CH4: LED voltage drop AM13769V1 Note that the regulated LED current remains constant over the entire input mains voltage and with the variation of the LED voltage drop. Drain voltage is modulated by the sinusoidal shape of the input rectified mains voltage. It increases with the input line voltage. As described in Section 4, the PFC input current has more distortion at high mains, but it remains well below the harmonic limits of the international regulations. The LED current ripple amplitude (CH3) is below 100 mA pk-pk according to the calculation and the LED current is at the same level at both input voltages. 16/31 DocID024821 Rev 2 AN4314 5.2 PFC waveforms Transition mode operation The ZCD pin, GD and CS pin have also been checked in order to show transition mode operation Figure 10 and Figure 11. Figure 10. TM operation at 100 Vac - 0.35 A fsw = 35 kHz CH1: DRAIN CH2: GD CH3: ZCD CH4: CS AM13770V1 Figure 11. TM operation at 230 Vac - 0.35 Afsw = 50 kHz CH1: DRAIN CH2: GD CH3: ZCD CH4: CS AM13771V1 An inductor value of 680 μH has been selected in order to get the converter to operate at very low frequency (35 kHz at 100 Vac), minimizing the EMI filter and optimizing the power factor. Turn-on of the MOSFET depends on the ZCD triggering signal during its falling edge, turnoff depends on the CS signal and its comparison with the internal feedback signal (MULT x COMP). 5.3 Startup With a 33 μF capacitor on the VCC pin, the L6564H turns on typically in less than 600 ms and the LED light appears 100 ms later. The turn-on time of the device depends on the value of the VCC capacitor and the charging current of the HVS, according to the following equation (L6564H datasheet [3]): Equation 5 Tstart −up = CVCC ⋅ DocID024821 Rev 2 Vturn−on I ch arg e 17/31 31 PFC waveforms AN4314 After turn-on the L6564H starts switching, absorbing energy from the VCC capacitor. During normal operation the external charge pump provides energy to supply the IC. The power delivered by the charge pump depends on the input mains voltage, the LED voltage drop and on the primary-to-auxiliary turn ratio (n = 4.34): Equation 6 V AUX _ TON = − VAC IN n V AUX _ TOFF = VOUT n The self-supplied circuitry has two worst-case conditions, one is when the circuit is operating at minimum input mains voltage (85 Vac), and the second one is a lower voltage drop tolerance (63 Vdc) of the LEDs. Design has to take into account both worst case conditions contemporaneously. The voltage regulator (Q2, DZ2, R3) regulates the VCC voltage at about 14 Vdc. After the L6564H starts switching, the output capacitor voltage rises up until it reaches the nominal voltage drop of the LEDs. Figure 12 and Figure 13 show the startup phase at the two nominal conditions. Figure 12. Startup at 100 Vac - 0.35 A CH1: PFC_OK CH2: FB (sensed on R17) CH3: C7 voltage CH4: Vcc 18/31 AM13772V1 Figure 13. Startup at 230 Vac - 0.35 A CH1: PFC_OK CH2: FB (sensed on R17) CH3: C7 voltage CH4: Vcc DocID024821 Rev 2 AM13773V1 AN4314 PFC waveforms Note that during startup, the loop is still open and the feedback signal (CH2-sensed on R17) is still low. The time constant - R32 with C7 - (see CH3- voltage on C7 capacitor) is set in order to mask this transition time, preventing the activation of the protection unnecessarily. 5.4 Line sags and fast on-off The circuit behavior during a mains sags sequence has been tested, varying the OFF time period of the line. Figure 14 and Figure 15 show the behavior during two missed cycles of 20 ms each (line is at 50 Hz). Figure 14. TOFF = 40 ms at 100 Vac / 50 Hz 0.35 A &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF Figure 15. TOFF = 40 ms at 230 Vac / 50 Hz 0.35 A &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 $09 If VCC doesn't discharge until its turn-off level during the missed cycles, the converter restarts immediately. During the missed cycles, the protection on the PFC_OK pin is correctly inactivated. DocID024821 Rev 2 19/31 31 PFC waveforms AN4314 Figure 16. TOFF = 500 ms at 100 Vac/50 Hz 0.35 A &+9$& &+&203 &+9RXW &+9FF $09 Figure 17. TOFF = 500 ms at 230 Vac/50 Hz 0.35 A &+9$& &+&203 &+9RXW &+9FF $09 Figure 16 and Figure 17 show the circuit behavior during a mains interruption of 500 ms, as in the case of a fast on-off-on cycle. If the OFF time increases, VCC discharges until turn-off level, the HVS generator shuts down and it is re-enabled only when the VCC voltage reaches the restart threshold. This is the cause of the delay in the appearance of the LED light when the OFF time period of the line is compared to a manual button switch ON and OFF (T > 500 ms). 5.5 Load disconnection During load disconnection, the output voltage is controlled by the voltage loop and the converter works in auto-restart. Figure 18 and Figure 20 represent the load disconnection transition at 100 Vac/50 Hz and 230 Vac/50 Hz. Figure 19 and Figure 21 show the behavior during the no-load condition. 20/31 DocID024821 Rev 2 AN4314 PFC waveforms Figure 18. Load disconnection transition at 100 Vac/50 Hz &+*' &+&203 &+9RXW &+9FF &+*' &+&203 &+9RXW &+9FF $09 Figure 20. Load disconnection transition at 230 Vac/50 Hz &+*' &+&203 &+9RXW &+9FF Figure 19. No load at 100 Vac/50 Hz $09 $09 Figure 21. No load at 230 Vac/50 Hz &+*' &+&203 &+9RXW &+9FF $09 When the load is disconnected, first the current loop tries to compensate the low current sensed on R6 and R7 and increases the output of U1 (pin 5). As a consequence, the COMP pin increases too, but as the output voltage reaches about 85 Vdc, the voltage loop operates, and the output of U1 is forced to decrease. The overlap of these two effects can be seen on the COMP pin (CH2). As this signal falls, it triggers the burst mode. During this operation the output voltage of the converter decreases, VCC voltage reaches its turn-off level and the L6564H shuts down. Only when VCC voltage reaches the VCC-restart threshold does the HVS generator pump current into the VCC capacitor and the L6564H restarts switching. DocID024821 Rev 2 21/31 31 PFC waveforms AN4314 The intervention of the voltage loop can be set using: Equation 7 VOVP = 2.5V ⋅ R8 + R9 R8 considering that the internal reference of the SEA05L is 2.5 V typ. [4]. The speed of the voltage loop can be increased by fine-tuning the C11, R10 network. A high value of C15 slows down the voltage loop reaction, but it filters the output capacitor voltage ripple, affecting the power factor. In this design a compromise has been found. 5.6 Short-circuit During a short of the output connector, all the energy stored in the output electrolytic capacitor C3 is discharged into the output side loop, and no current will flow into the external LEDs, preventing their failure. The SEA05L CC-CV controller is no longer supplied and it cannot regulate the loop. A peak high current of 60 A has been measured during 100 ns flowing from the output capacitor into the output side loop. In order to protect the sense resistor of the cc-cv controller, a Schottky diode D9 of 80 A surge current (see STPS3150U datasheet [7]) has been added in the demonstration board. After this initial transient the short-circuit protection, described above, senses the feedback signal and disables the L6564H from the PFC_OK pin (see disable function of the L6564H [3]). The behavior of the protection has been tested with positive results over the entire input voltage range; only the two nominal conditions at 100 Vac and 230 Vac have been discussed in this application note. Figure 22. Short-circuit at 100 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 23. Short-circuit at 230 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 22 and Figure 23 show that PFC_OK is pulled to GND when the voltage on the C7 capacitor reaches the value of 3 x Vbe (2 x Vf (LL4148) + BC847C Vbe). 22/31 DocID024821 Rev 2 AN4314 PFC waveforms Figure 24 and Figure 25 show the resulting hiccup mode of the converter during shorts, when the protection is tripped. Figure 24. Overload behavior after a shortcircuit at 100 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 26. Short-circuit removal at 100 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 25. Overload behavior after a shortcircuit at 230 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 27. Short-circuit removal at 230 Vac &+3)&B2. &+)%VHQVHGRQ5 &+&YROWDJH &+9FF $09 Figure 26 and Figure 27 show the behavior after the short removal. The startup sequence is activated. DocID024821 Rev 2 23/31 31 PFC waveforms 5.7 AN4314 Feedback failure protection (open loop) A kind of protection that any power supply must have is one which prevents the failure of the feedback circuitry. If a failure occurs, for example degradation of one BJT (Q4 or Q5), the output voltage can increase, damaging the electrolytic capacitor and the LED load. Figure 28 and Figure 29 show the board behavior opening the loop by removing the resistor R17 (0 Ω). Figure 28. Feedback failure protection at 100 Vac/50 Hz &+3)&B2. &+&203 &+9RXW &+9FF $09 Figure 29. Feedback failure protection at 230 Vac/50 Hz &+3)&B2. &+&203 &+9RXW &+9FF $09 The feedback signal on C15 falls, activating the same external protection that pulls down the PFC_OK (CH1) pin below its disable threshold. The delay in triggering is due to the charging time of the capacitor C7 through R32. The output voltage (CH3) is limited. 24/31 DocID024821 Rev 2 AN4314 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 Japanese standard JEIDA-MITI Class-C and European standard EN61000-3-2 Class-C, at full load and both nominal input voltage mains. Figure 30. EVL6564H-25W-BB at 100 Vac/50 Hz compliance with JEIDA-MITI class-C limits at PF = 0.9801 0HDVXUHGYDOXH -(,7$0,7,&ODVV&OLP LWV +DUPRQLF&XUUHQW>$@ +DUPRQLF2UGHU>Q@ $09 Figure 31. EVL6564H-25W-BB at 230 Vac/50 Hz compliance with EN61000-3-2 class-C limits at PF = 0.9180 0HDVXUHGYDOXH (1 &ODVV&OLP LWV +DUPRQLF&XUUHQW>$@ 6 Harmonic content measurement +DUPRQLF2UGHU>Q@ $09 As shown in the figures that follow, the circuit is capable of reducing the harmonics well below the limits of both regulations. DocID024821 Rev 2 25/31 31 Thermal measurements 7 AN4314 Thermal measurements To check the reliability of the design, thermal mapping using an IR camera was carried out. Figure 32 and Figure 33 show thermal measurements on the component side of the board at nominal input voltages and full load. Pointers show the relevant temperature of key components. Table 3 provides the correlation between the measured points and components for both thermal maps. The ambient temperature during both measurements was 25 °C. According to these measurement results, all components on the board function within their temperature limits. Figure 32. Thermal map at 100 Vac/50 Hz Figure 33. Thermal map at 230 Vac/50 Hz $09 $09 Table 3. Measured temperature at 100 Vac/50 Hz and 230 Vac/50 Hz Point 26/31 Component Temp. at 100 Vac (ºC) Temp. at 230 Vac(ºC) A Common-mode choke 46.9 35.5 B Diode bridge 46.9 35.5 C Output diode D1 61.4 63.7 D R1 (SEA05-FB bias) 70.1 71.8 E Q3 inductor choke T1-L 51.4 54.4 F Q3 inductor choke T1-R 48.6 52.7 G BJT voltage regulator 44.4 64.0 H MOSFET 46.3 50.3 DocID024821 Rev 2 AN4314 8 Conducted emission pre-compliance test Conducted emission pre-compliance test The following graphs show the average measurements of the conducted noise with a 23LED load and nominal mains voltages. The limits shown on the diagrams are those of EN55022 class-B, which is the most popular standard for European equipment. As visible, good margins with respect to the limits are present in all test conditions. Increasing the CX capacitor value of the EMI filter will improve the safety margin but will affect the PF. A compromise has been found in this design. Figure 34. 100 Vac/50 Hz - phase Figure 35. 100 Vac/50 Hz - neutral $09 $09 Figure 36. 230 Vac/50 Hz - phase Figure 37. 230 Vac/50 Hz - neutral $09 $09 Note that a CY capacitor between the negative output pin of the converter and ground has been placed to filter common-mode noise flowing into the demonstration board. A small filter capacitor between the SEA05L output (pin 5) and SEA05L GND (pin 2) has also been placed for the same reason. The C20 capacitor between the drain and source of Q3 acts as a snubber and it has been foreseen to increase the safety margin. DocID024821 Rev 2 27/31 31 PCB layout 9 AN4314 PCB layout Figure 38 and Figure 39 show the layout of the PCB. The demonstration board has been designed to fit in a typical LED driver case so the maximum height is 20 mm, maximum length is 90 mm and the maximum width is less than 65 mm. Of course the form factor could be further reduced depending on the capacitor value. Here a very narrow current ripple has been defined as a specification, but accepting a higher value, the capacitor size could be further reduced. Figure 38. Bottom layer 28/31 Figure 39. Top layer DocID024821 Rev 2 AN4314 10 References References 1. AN1059 - Design equations of high-power-factor flyback converters based on the L6561 2. AN1060 - Flyback converters with the L6561 PFC controller 3. L6564H - datasheet 4. SEA05L - datasheet 5. STI8N65M5 - datasheet 6. X42182 LED - datasheet (Seoul Semiconductor) 7. STPS3150U - datasheet 8. STTH2L06 - datasheet DocID024821 Rev 2 29/31 31 Revision history 11 AN4314 Revision history Table 4. Document revision history 30/31 Date Revision Changes 18-Jul-2013 1 Initial release. 29-Jul-2013 2 Corrected rendition errors in Figures 14 to 29. DocID024821 Rev 2 AN4314 Please Read Carefully: Information in this document is provided solely in connection with ST products. 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