AN4376 Application note 10 W wide range non-isolated high power factor LED driver using HVLED815PF Federico Levati Introduction This application note describes the performances of a non-isolated 10 W, wide range, regulated LED driver using the HVLED815PF device, with a high power factor and a constant output current regulation. The maximum power and form factor have been designed for the lighting market, facilitating the replacement of the incandescent lamps. In fact the architecture is based on a single-stage buck-boost topology and it has been used the STMicroelectronics® HVLED815PF device with a primary side control to achieve an LED current regulation within ± 5% and a high power factor. The patented primary side regulation, the internal high-voltage primary switcher operating directly from the rectified mains and the high-voltage start-up generator contained in the HVLED815PF device allow a very cost-effective solution for an LED driving. Figure 1. EVLHVLED815W10A demonstration board January 2014 DocID025380 Rev 1 1/37 www.st.com Contents AN4376 Contents 1 Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 EVLHVLED815W10A - main characteristics and circuit description . . 8 2.1 LED current definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 LED current ripple definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 DMG pin and OVP setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.4 External compensation network of the voltage loop . . . . . . . . . . . . . . . . . 10 2.5 Power factor corrector function and ILED pin modulation with the input mains voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.6 High-voltage start-up generator and VCC capacitor . . . . . . . . . . . . . . . . .11 3 Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5 Component layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6 Measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2/37 6.1 LED driver performance at nominal load 70 VDC - 140 mA . . . . . . . . . . . 16 6.2 Line regulation at nominal load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.3 Power factor at nominal load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.4 Total harmonic distortion (THD) at nominal load . . . . . . . . . . . . . . . . . . . 17 6.5 Driver efficiency at nominal load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.6 LED driver performance varying the number of LEDs . . . . . . . . . . . . . . . 18 6.7 Line regulation at different LED load number . . . . . . . . . . . . . . . . . . . . . . 19 6.8 Power factor at different LED load number . . . . . . . . . . . . . . . . . . . . . . . 20 6.9 Total harmonic distortion (THD) at different LED load number . . . . . . . . . 21 6.10 LED driver efficiency at different LED load number . . . . . . . . . . . . . . . . . 22 DocID025380 Rev 1 AN4376 7 Contents PFC waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1 Input and output LED driver waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.2 Transition mode operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.3 ILED pin modulation with the line voltage . . . . . . . . . . . . . . . . . . . . . . . . 25 7.4 Controller startup and light-ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7.5 OVP protection and no load behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.6 Short-circuit and output current limitation . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.7 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.8 Harmonic content at nominal mains voltage . . . . . . . . . . . . . . . . . . . . . . 34 7.9 Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . . . 35 8 Supporting material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 DocID025380 Rev 1 3/37 37 List of figures AN4376 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. Figure 40. Figure 41. Figure 42. Figure 43. Figure 44. Figure 45. Figure 46. Figure 47. Figure 48. 4/37 EVLHVLED815W10A demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Flyback (FL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Buck-boost topology (BB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 TM (transition mode) flyback currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 TM (transition mode) buck-boost currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 TM (transition mode) flyback waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 TM (transition mode) buck-boost waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 ILED pin modulation with the input mains voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 EVLHVLED815W10A demonstration board schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Top side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Bottom side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 LED current vs. AC line voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Power factor vs. AC line voltage at nominal load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Total harmonic distortion vs. AC line voltage at nominal load . . . . . . . . . . . . . . . . . . . . . . 17 Efficiency vs. AC line voltage at nominal load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Line regulation at different LED load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Power factor versus AC line voltage at different LED load . . . . . . . . . . . . . . . . . . . . . . . . . 20 THD versus AC line voltage at different LED load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Efficiency versus AC line voltage at different LED load . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Input and output PFC waveforms at 100 VAC - 50 Hz - PF = 0.9889 . . . . . . . . . . . . . . . . 23 Input and output PFC waveforms at 230 VAC - 50 Hz - PF = 0.9211 . . . . . . . . . . . . . . . . 23 Transition mode operation at 100 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Transition mode operation at 100 VAC - 50 Hz -zoom of signals . . . . . . . . . . . . . . . . . . . . 24 Transition mode operation at 230 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Transition mode operation at 230 VAC - 50 Hz - zoom of signals . . . . . . . . . . . . . . . . . . . 24 ILED pin operation at 85 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 ILED pin operation at 100 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 ILED pin operation at 130 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 ILED pin operation at 175 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 ILED pin operation at 230 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 ILED pin operation at 265 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Startup at 100 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Startup at 230 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Load disconnection at 100 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 No load behavior at 100 VAC - 50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Load disconnection at 230 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 No load behavior at 230 VAC - 50 Hz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Short-circuit of the output connector at 100 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Short-circuit removal at 100 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Short-circuit of the output connector at 230 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Short-circuit removal at 230 VAC - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Top side thermal map with 23 LED load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Bottom side thermal map with 23 LED load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Top side thermal map with 25 LED load - 10.5 W output . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Bottom side thermal map with 25 LED load - 10.5 W output . . . . . . . . . . . . . . . . . . . . . . . 33 Measurement at 100 VAC, 50 Hz, PIN = 10.95 W, POUT = 9.5 W, PF = 0.9880 . . . . . . . . . 34 Measurement at 230 V, 50 Hz, PIN = 10.88 W, POUT = 9.48 W, PF = 0.9220 . . . . . . . . . . 34 100 VAC and 23 LED load - phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 DocID025380 Rev 1 AN4376 Figure 49. Figure 50. Figure 51. List of figures 100 VAC and 23 LED load - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 230 VAC and 23 LED load - phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 230 VAC and 23 LED load - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 DocID025380 Rev 1 5/37 37 Theory of operation 1 AN4376 Theory of operation Most applications for an LED driver are designed using a common isolated flyback for decoupling the secondary side and the load from the input mains, but sometimes the use of transformers could be costly and is not always needed. In the bulb replacement market the buck-boost topology without isolation and a transformer is often considered when isolation is not requested by regulations. Figure 2. Flyback (FL) Figure 3. Buck-boost topology (BB) /('ORDG /S /('ORDG 9RXW /S ,RXW ,RXW 9LQ 9RXW 9LQ 7 7 $0 $0 Figure 2 and Figure 3 show the differences, the flyback is derived from the basic buck-boost topology and in fact it could be considered as a flyback with a unity primary to secondary turn ratio. As a consequence the output of the buck-boost is floating and the negative side of the output capacitor is not at GND but connected to the input mains. Note then that the transformer of Figure 2 has been substituted by a simple inductor in Figure 3. Then in both situations, when the switch T is ON, the energy is stored in the inductor for the BB or primary side for the FL, when the switch is OFF, the energy is transferred to the output through the output diode. The primary current coming from the mains is in red and the current flowing into the output is in blue. Approaching the real LED driver, the LED load has been represented by the average LED current in black. Considering n as the transformer turn ratio, if n = 1, it is easy to represent the current and waveforms for the buck-boost (Figure 5). Figure 4. TM (transition mode) flyback currents %XFNERRVW )O\EDFNQR 3ULPDU\FXUUHQW W 21 Figure 5. TM (transition mode) buck-boost currents 'LRGHFXUUHQW ,QGXFWRUFXUUHQW W 21 W 2)) $0 6/37 DocID025380 Rev 1 'LRGHFXUUHQW W 2)) $0 AN4376 Theory of operation Waveforms are represented in case of transition operating mode that is on the boundary between continuous and discontinuous conduction mode, this is the most efficient and an easy way to design EMI compliant low power single-stage LED drivers. Figure 6. TM (transition mode) flyback waveforms Figure 7. TM (transition mode) buck-boost waveforms %XFNERRVW )O\EDFN 9GV 9GV 95 95 9LQ 9LQ W W ,/ ,S W Q W Q ,' ,V W W 9V 9V 9287 9287 W W W 21 W 2)) W 21 W 2)) $0 $0 Figure 6 and Figure 7 represent the split current. To design a single-stage LED driver with a high power factor it is enough to modulate the peak current of Figure 5 with a sinusoidal reference like in a common PFC in order to put the input voltage with input current into phase. DocID025380 Rev 1 7/37 37 EVLHVLED815W10A - main characteristics and circuit description 2 AN4376 EVLHVLED815W10A - main characteristics and circuit description The main characteristics of this single-stage LED driver demonstration board are: Line voltage range: 85 to 265 VAC Line frequency (fL): 47-63 Hz LED string voltage drop: 70 V nominal LED nominal current: 140 mA ± 3% LED current ripple: 100 mA Rated output power: 10 W Power factor > 0.9 Efficiency: 86 - 88% at full load Maximum ambient temperature: 50 °C Conducted EMI: in accordance with EN55022 Class-B Protections against overvoltage, load disconnection and short-circuit The LED driver provides a constant nominal current of 140 mA to an LED string with a nominal voltage drop of 70 VDC in all the wide range input mains [85 - 265] VAC. Due to the power factor correction, the input current of the driver is almost in phase with the mains voltage and the power factor is close to the unity. The power supply utilizes a typical non-isolated buck-boost converter topology with a simple inductor to transfer energy to the LED load. The inductor T1 (layer type, with standard ferrite size EF-20 and manufactured by Magnetica) is charged by the internal Power MOSFET when it is turned on, and it discharges into the three output parallel capacitors C11, C12, C16 (with 100 VDC rating see Figure 9 on page 12) and into the LED load when Power MOSFET turns off. In this demonstration release the auxiliary winding is used to sense the inductor current demagnetization, to sense the input line voltage for the voltage feed forward compensation, to trigger the overvoltage protection and to self-supply the IC during normal operation. An external high-voltage start-up circuitry is not needed because it is already embedded into the IC. Also the buck-boost switch is embedded into the HVLED815PF in order to maximizing the current sensing and the gate driving. The board power cell has been designed using the procedure described in the AN1059 (See 2. in Section 8: Supporting material on page 36) used to design a standard high power factor flyback; this document has been used as 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 with the reflected voltage of the flyback. Additional information has been reported in Section 2.1. 8/37 DocID025380 Rev 1 AN4376 2.1 EVLHVLED815W10A - main characteristics and circuit description LED current definition The sense resistors R2 = 1.2 ± 1% and R3 = 1.8 ± 1% sense the current flowing into the inductor primary side and fix the output LED current according to Equation 1: 1 02 0 14 2 1 8 1 2 A . V. / . / . 1 2 e Ds En Le s VCR D E IL Equation 1 Where VCLED = [0.192 - 0.2 - 0.208] V is the equivalent internal voltage that includes Gi, Iref, R parameters. and it is an internal parameters of the controller (see the HVLED815PF device datasheet for more details [See 1. in Section 8: Supporting material on page 36] ). 2.2 LED current ripple definition The output capacitor size and the LED current ripple definition have been calculated with Equation 2: Equation 2 For this demonstration board 3 parallel capacitor of 68 F-100 V have been selected to have a current ripple of less than 100 mA pk-pk with 23 LEDs each with a dynamic resistance of 0.8 . 2.3 DMG pin and OVP setting Due to the topology the LED string load is connected to a floating output and the loop is closed through a primary sensing regulation. From auxiliary winding, an accurate image of the output voltage is fed to the DMG pin that is the inverting input of the internal, error amplifier. Then R8 is connected to the auxiliary winding providing the inductor demagnetization signal to the DMG pin and turning on the internal MOSFET at any switching cycle. R8 value impacts on the voltage feed forward function and a 270 k resistor has been selected for improving the line regulation (see the HVLED815PF datasheet - section Voltage feed-forward block [1. in Section 8: Supporting material on page 36]). The divider composed by the R8 and R5 fixes the maximum output voltage VOVP at no load (in case of LED -load disconnection) with Equation 3: Equation 3 V 8 8 8 . 3 V 1 5 . 2 Ω k 3 3 V 1 5 . 2 Ω k 0 7 2 8 . 3 N V 1 5 . 2 P V O V 1 5 . 2 5 8 R R N V N = 3.8 ± 2% is turn-ratio between primary and auxiliary winding. DocID025380 Rev 1 9/37 37 EVLHVLED815W10A - main characteristics and circuit description 2.4 AN4376 External compensation network of the voltage loop The compensation network composed by C6, C7 and R7 is placed between this pin and GND to achieve stability and good dynamic performance of the voltage control loop. Normally it is not working and operates only during an OVP. 2.5 Power factor corrector function and ILED pin modulation with the input mains voltage Once the signal at the current sense pin has reached the level programmed by reference signal on the pin ILED, the internal MOSFET turns off. The network composed by R15, R17, R21, R20 and R4, R22 and modulated by Q2, works as a divider and it provides to the ILED pin of the HVLED815PF the information of the instantaneous input voltage which is used to modulate the current flowing into the inductor. Through this network the controller works as a power factor corrector. 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 maximizing the power factor performances. Referring to Figure 8 on page 11, a voltage Vx proportional to the input rectified mains is summed on the average voltage present on the ILED pin trough the CLED capacitor generating a voltage reference proportional to the input voltage (AC coupling). Equation 4 R R ︳ L C A L ︳ H ︳ C A C A R N ︳ k p k p X VI V The ILED pin voltage is compared with the CS pin voltage, generating a primary current proportional to the input voltage reaching the high power factor condition. The average value of the ILED pin is not depending from the Vin input voltage (AC coupling), as a consequence the desiderated output current can be programed trough the current sense resistor Rsense according to Equation 1 (see the HVLED815PF device datasheet for more details [1. in Section 8: Supporting material on page 36] ). 10/37 DocID025380 Rev 1 AN4376 EVLHVLED815W10A - main characteristics and circuit description Figure 8. ILED pin modulation with the input mains voltage 9,1 '5$,1 5$&B+ ,UHI ,/(' &/(' 5$&B/ 2)) 5 5$&B/ &I LOWHU 3:0 /2*,& && /RJLF 6: 4 5 '(0$* /2*,& 4 6 ,)) 5I I $8; '0* /RJLF )HHGI RUZDUG 5GPJ 5I E &6 6285&( 5VHQVH $0 In Section 7.3: ILED pin modulation with the line voltage on page 25 is showed the behavior of the ILED pin depending on the action of the switch represented by the BJT Q2 (SW in Figure 8, Q2 in Figure 9). At the low line the switch is Off (BJT base is low) and the pin is modulated by the divider composed by RAC_H and RAC_L1. When, at the high line, the BJT is ON the pin ILED is modulated by a different ratio of the divider (RAC_H and the parallel of RAC_L1 with RAC_L2) in order to keep the same dynamic on the ILED pin. 2.6 High-voltage start-up generator and VCC capacitor At a startup, a 5.5 mA internal current source of the HVLED815PF device [1. in Section 8: Supporting material on page 36] charges the VCC capacitor (C8), until the voltage on the pin Vcc reaches the start-up threshold, and then it is shut down. With a 22 f of the VCC capacitor, the device turns-on typically in: 52 s m 13 55 A Vm g r e a h c 22 . ︳ F N O C VCI c c CV p u t r a t TS Equation 5 The T1 auxiliary winding (pins 4 - 5) and a diode D2 and a limiting resistor R9 generate a constant VCC voltage that powers externally the HVLED815PF device during normal TM (transition mode) operation. See the real behavior in Section 7.4: Controller startup and light-ON on page 26. DocID025380 Rev 1 11/37 37 12/37 & 10 N & Q) 9; DocID025380 Rev 1 5 N 5 N 1$ 5 10 1$ & Q) 5 N 4 %&& 5 N & Q) '0* & Q) & X) & X) & Q) ,/(' 5 5 9&& 5 5 ' %$9: *1' 5 5 8 +9/('3) 9&& '5$,1 5 N 5 N 5 N '5$,1 ' %=9& ' N 5 N &6 5 N / P+ 5 & Q) 9; N 6285&( '5$,1 '0* & X) 5 / P+ '5$,1 10 5 $9)DVW ) 9,1 1$ - &21 - &21 %' +'7 '0* 5 $X[ 5 N 5 N 3ULB'UDLQ 3ULB5HFW 5 5 5 7 ' & X) 9 677+/8 & X) 9 & Q) 9;< & X) 9 & 10 & 10 5 - N 9RXW $0 +,*+92/7$*( 121,62/$7(' '$1*(5 & 10 - 9RXW 3 5 Electrical diagram AN4376 Electrical diagram Figure 9. EVLHVLED815W10A demonstration board schematic &203 AN4376 4 Bill of material Bill of material Table 1. Bill of material Ref. Value Description Manufacturer PCB - HVLED8XX HPF NI WR BULB EB rev. 2.0 TECNOMETAL BD1 HD06-T Bridge diode HD06-T 600 V 0.8 A Minidip Diodes C1 100 nF CAP X2 305 V MKP P. 10 EPCOS C2 220 nF CAP X2 305 V MKP P. 15 EPCOS C4 100 nF Cap. ± 10% X7R 50 V 0805 KEMET C5 2.2 F Cap. ±1 0% X5R 25 V 0805 KEMET C6 470 nF Cap. ±1 0% X7R 25 V 0805 KEMET C7, C17 2.2 nF Cap. ± 5% C0G 50 V 0805 MURATA C8 22 F Cap. ± 20% EL. 50 V 105 °C rad. D5 P 2.5 mm Panasonic C10 2.2 nF CAP X1 Y1 250 V CERAMIC P.10 Murata C11, C12, C16 68 F Cap. ± 20% EL. 100 V 105 °C LL LOW ESR rad. D10 P 5 mm Nichicon C13, C14, C15, C20 N.M. - - C19 4.7 F Cap. ± 10% X5R 50 V 1206 TAIYO YUDEN D2 BAV20W Diode rect. 150 V 200 mA SOD123 Diodes D3 STTH2L06U Diode rect. UFAST STTH2L06U 600 V 2 A SMB STMicroelectronics R13 120 k Res.1/4 W 1% 100 ppm 1206 SMD VISHAY D7 BZV55-C18 Zener 18 V ± 5% 500 mW MINIMELF NXP F1 1 A - 250 V - fast Fuse 1 A 250 V fast radial 8.4 mm x 7.7 mm P 5 mm MULTICOM 2 J1 +Vout Cable color red 0.5 mm L.50 mm, stripped and tinned 5 mm - J2 CON1 Cable color brown 0.5 mm2 L.50 mm, stripped and tinned 5 mm - J3 -Vout Cable color black 0.5 mm2 L.50 mm, stripped and tinned 5 mm - 2 J4 CON1 Cable color brown 0.5 mm L.50 mm, stripped and tinned 5 mm - L1 L2 2.2 mH Choke RF 2.2 mH 250 mA axial D 6.5 L 12 mm EPCOS Q2 BC847C NPN SML SIG G.P. AMP SOT23 NXP R2 1.2 Res.1/4 W 1% 100 ppm 1206 SMD Panasonic R3 1.8 Res.1/4 W 1% 100 ppm 1206 SMD Panasonic R4 120 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R5 33 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R7 10 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R8 270 k Res.1/4 W 1% 100 ppm 1206 SMD VISHAY R9 180 Res.1/8 W 1% 100 ppm 0805 SMD VISHAY DocID025380 Rev 1 13/37 37 Bill of material AN4376 Table 1. Bill of material (continued) Ref. Value Description Manufacturer R10 62 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R12, R21 51 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R11, R19 N.M. - - R15, R17 180 k Res.1/4 W 1% 100 ppm 1206 SMD WELWYN R16 0 Res. 0 0603 SMD VISHAY R20 20 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R22 6.2 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R23, R24 4.7 k Res.1/8 W 1% 100 ppm 0805 SMD VISHAY R25, R26 3.9 Res.1/4 W 1% 100 ppm 1206 SMD VISHAY T1 2267.0001 Inductor L = 1.1 mH 0.6 A core EF20 Magnetica U1 HVLED815PF Offline LED driver HVLED815PF SO16 STMicroelectronics 14/37 DocID025380 Rev 1 AN4376 5 Component layout Component layout Figure 10. Top side Figure 11. Bottom side $0 DocID025380 Rev 1 $0 15/37 37 Measurement results 6 AN4376 Measurement results The EVLHVLED815W10A non-isolated LED driver demonstration board has been tested using the following instrumentations/load: 6.1 Agilent Technologies 6813B AC source ® watt meter YOGOGAWA WT210 ® Tektronix DP07054 500 MHz digital oscilloscope Tektronix TCP0030 current probe TELEDYNE LECROY PPE4kV 100:1 400 MHz high-voltage probe KEITHLEY 2000 digital multimeter Avio TVS-200 P thermal video system CHROMA TECHNOLOGY CORP® 6314 DC electronic load SEOUL SEMICONDUCTOR Z-Power LED P4 LED series LED driver performance at nominal load 70 VDC - 140 mA First measurement set has been collected using a nominal load with an LED voltage drop of 70 VDC. Following Equation 1 the current flowing into the LED is set by: R2 = 1.2 ± 1% and R3 = 1.8 ± 1% at 140 mA. 6.2 Line regulation at nominal load Figure 12 shows the measured average output current versus line voltage at the nominal load: Figure 12. LED current vs. AC line voltage 1RPLQDOORDG /('FXUUHQW >$@ 9LQ>9DF@ $0 The output current is 140 mA ± 1% over all the input voltage range [85 - 265] VAC. 16/37 DocID025380 Rev 1 AN4376 6.3 Measurement results Power factor at nominal load The “Power Factor” (PF) at the nominal load remains above 0.9 for every input mains voltage. Figure 13. Power factor vs. AC line voltage at nominal load 3RZHU)DFWRU 1RPLQDOORDG 9LQ>9DF@ $0 Total harmonic distortion (THD) at nominal load Figure 14 shows the total harmonic distortion versus line voltage: Figure 14. Total harmonic distortion vs. AC line voltage at nominal load 7+'>@ 6.4 1RPLQDOORDG 9LQ>9DF@ $0 The THD curve presents two minimum valley point corresponding to the Japanese and European nominal voltage. DocID025380 Rev 1 17/37 37 Measurement results 6.5 AN4376 Driver efficiency at nominal load The LED driver efficiency is up to 89%. Figure 15. Efficiency vs. AC line voltage at nominal load 1RPLQDO/RDG (IILFLHQF\>@ 9LQ>9DF@ $0 Efficiency at Japanese range is around 87% and increases to 88% at European voltage. 6.6 LED driver performance varying the number of LEDs The performance of the LED driver has been collected varying the LED number and as consequence the string voltage drops after a thermal warm-up (T = 1 h). In Table 2 are shown the descriptions of the loads applied and corresponding to a total voltage drop after a warm-up: Table 2. LED string voltage specification 18/37 LED number String voltage drop Variation respect to nominal voltage 23 LEDs 68.3 VDC - 2.4% 25 LEDs 74.0 VDC + 5.7% 21 LEDs 62.3 VDC - 11% 18 LEDs 53.2 VDC - 24% DocID025380 Rev 1 AN4376 Line regulation at different LED load number Figure 16 shows the measured average output current versus line voltage at different numbers of LEDs applied: Figure 16. Line regulation at different LED load /(' 1RPLQDOORDG /(' /('FXUUHQW>$@ 6.7 Measurement results /(' /(' 9LQ>9DF@ $0 When the LED string voltage drop is passing from 75 VDC to 50 VDC the controller is able to maintain the current practically stable in all the input mains range. DocID025380 Rev 1 19/37 37 Measurement results 6.8 AN4376 Power factor at different LED load number Following relation of the AN1059, the power factor performance is directly related to the output voltage of the buck-boost. For this reason when the load is composed only by 18 LEDs corresponding to a load 30% lower the nominal specification, the power factor remains above 0.9 only at low mains till 200 VAC. A good power factor performance for the light market can be reached decreasing the load from 23 LEDs to a minimum level of 21 LEDs. Figure 17 shows the measured power factor (PF) at different LED load. Figure 17. Power factor versus AC line voltage at different LED load 3RZ HU)DFWRU /(' 1RPLQDOORDG /(' /(' /(' 9LQ>9DF@ $0 20/37 DocID025380 Rev 1 AN4376 Total harmonic distortion (THD) at different LED load number Figure 18 shows the total harmonic distortion (THD) versus the line. Figure 18. THD versus AC line voltage at different LED load 7+'>@ 6.9 Measurement results /(' 1RPLQDOORDG /(' /(' /(' 9LQ>9DF@ $0 THD at nominal input voltage (Japanese - European) is lower than 20% applying different loads. Also the distortion of the PFC current is increasing, decreasing the number of LED. DocID025380 Rev 1 21/37 37 Measurement results 6.10 AN4376 LED driver efficiency at different LED load number Figure 19 shows the efficiency versus the line. Figure 19. Efficiency versus AC line voltage at different LED load /(' 1RPLQDOORDG /(' /(' (IILFLHQF \>@ /(' 9LQ>9DF@ $0 Varying the number of the LEDs , the efficiency remains comparable with the nominal load, of course increasing the load to 25 LEDs means increasing the converter output power till 11.5 W. Section 7.7: Thermal measurements on page 29 shows that the HVLED815PF device is not overeating and is able to support this load properly. Note: 22/37 Important: In this design a sort of short-circuit protection has been previewed, the R25 and R26 in series with the diode have been added to sense the short-circuit of the output connectors. If this function is not needed, the two parallel resistors could be removed and the converter efficiency will increase of 1.5%. DocID025380 Rev 1 AN4376 PFC waveforms 7 PFC waveforms 7.1 Input and output LED driver waveforms The waveforms of the input current and drain voltage at the nominal input voltage mains and nominal LED load are illustrated in this section. Drain voltage is modulated by the sinusoidal shape of the input mains voltage and the peak increase with the line. The input current is in phase with the input voltage and a high power factor is achieved (PF > 0.9). Figure 20. Input and output PFC waveforms at 100 VAC - 50 Hz - PF = 0.9889 CH1: DRAIN CH2: INPUT PFC CURRENT CH3: VOUT CH4: LED CURRENT Figure 21. Input and output PFC waveforms at 230 VAC - 50 Hz - PF = 0.9211 CH1: DRAIN CH2: INPUT PFC CURRENT CH3: VOUT CH4: LED CURRENT Also the LED current and output voltage have been checked. Note that the regulated LED current remains constant all over the input mains voltage. The LED pk-pk ripple is the ± 27% of the average current. Increasing the value of the output capacitor it is possible to decrease the LED current ripple following (Equation 2 on page 9). For this demonstration board 3 parallel capacitors of 68 F have been selected to have a current ripple of less than 100 mA pk-pk with 23 LEDs each with a dynamic resistance of 0.8 . DocID025380 Rev 1 23/37 37 PFC waveforms 7.2 AN4376 Transition mode operation During ON-time, the peak drain current is modulated by a signal proportional to the ILED pin. This reference sets the turn-off of the MOSFET. The MOSFET turn-on depends on the DMG signal that senses the demagnetization of the drain current realizing a transition mode operation. Figure 22. Transition mode operation at 100 VAC - 50 Hz CH1: DRAIN CH2: CS CH3: ILED CH4: DMG CH1: DRAIN CH2: CS CH3: ILED CH4: DMG Figure 24. Transition mode operation at 230 VAC - 50 Hz CH1: DRAIN CH2: CS CH3: ILED CH4: DMG Figure 23. Transition mode operation at 100 VAC - 50 Hz -zoom of signals Figure 25. Transition mode operation at 230 VAC - 50 Hz - zoom of signals CH1: DRAIN CH2: CS CH3: ILED CH4: DMG A primary inductance of 1.1 mH has been selected in order to obtain the converter switching frequency into the interval [35 - 70] kHz (Magnetica PN-2267.0001). 24/37 DocID025380 Rev 1 AN4376 7.3 PFC waveforms ILED pin modulation with the line voltage From Figure 26 to Figure 31, the effect off the ILED pin modulation through a divider connected to the mains is represented. The effect is a very sinusoidal shape at nominal mains voltage 100 VAC and 230 VAC with high performance in terms of PF and THD. Figure 26. ILED pin operation at 85 VAC CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor Figure 28. ILED pin operation at 130 VAC CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor Figure 27. ILED pin operation at 100 VAC Figure 29. ILED pin operation at 175 VAC CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor DocID025380 Rev 1 25/37 37 PFC waveforms AN4376 Figure 30. ILED pin operation at 230 VAC CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor 7.4 Figure 31. ILED pin operation at 265 VAC CH1: VIN CH2: BJT-base CH3: ILED pin CH4: C5 capacitor Controller startup and light-ON With a VCC capacitor of 22 F (see Figure 9: EVLHVLED815W10A demonstration board schematic on page 12), the HVLED815PF turns-on in 50 ms. A light appears hundreds milliseconds later (see CH1-LED current). A capacitor C5 (2.2 µF) on the ILED pin is charging during the start-up phase and it is responsible of the LED current soft-start time. Figure 32. Startup at 100 VAC - 50 Hz CH1: LED current CH2: CS CH3: VOUT CH4: VCC Figure 33. Startup at 230 VAC - 50 Hz CH1: LED current CH2: CS CH3: VOUT CH4: VCC Acting on this C5 capacitor, it is possible to modify the soft-start time. In detail, to speed up the loop it is enough to reduce the C5 capacitor reducing the soft-start time. 26/37 DocID025380 Rev 1 AN4376 PFC waveforms 7.5 OVP protection and no load behavior During a load disconnection the HVLED815PF device senses the output voltage through the DMG pin and controls the voltage loop in order to regulate the output capacitor voltage to a level below its maximum rating (100 V) (see the HVLED815PF datasheet [1. in Section 8: Supporting material on page 36]). Figure 34. Load disconnection at 100 VAC - 50 Hz CH1: DRAIN CH2: IOUT CH3: VOUT CH4: DMG Figure 35. No load behavior at 100 VAC - 50 Hz CH1: DRAIN CH2: IOUT CH3: VOUT CH4: DMG Figure 36. Load disconnection at 230 VAC - 50 Hz CH1: DRAIN CH2: IOUT CH3: VOUT CH4: DMG Figure 37. No load behavior at 230 VAC - 50 Hz CH1: DRAIN CH2: IOUT CH3: VOUT CH4: DMG As shown in Figure 35 and Figure 37 the converter works in a burst mode during no load condition. No current is flowing into the LED load. DocID025380 Rev 1 27/37 37 PFC waveforms 7.6 AN4376 Short-circuit and output current limitation During a short-circuit of the output connector, all the energy stored in the output electrolytic capacitor is discharged into the output side loop, so that no current will flow to the external LED, thus preventing their failure. Figure 38. Short-circuit of the output connector at 100 VAC - 50 Hz CH1: output LED driver current CH2: DMG CH3: VOUT CH4: VCC CH1: output LED driver current CH2: DMG CH3:V OUT CH4:V CC Figure 40. Short-circuit of the output connector at 230 VAC - 50 Hz CH1: output LED driver current CH2: DMG CH3: VOUT CH4: VCC Figure 39. Short-circuit removal at 100 VAC - 50 Hz Figure 41. Short-circuit removal at 230 VAC - 50 Hz CH1: output LED driver current CH2: DMG CH3: VOUT CH4: VCC When the output capacitor is shorted, the HVLED815PF device works with the internal selfsupply function because no charging current came from the auxiliary winding. The controller doesn't stop switching but reduces the on-time to its minimum level. The selection of the R24 and R24 allows limiting the output diode current at a level of about 260 mA. Increasing 28/37 DocID025380 Rev 1 AN4376 PFC waveforms the two resistor value allows to regulate the output current at a lower level. Here a compromise between the output current limitation level and efficiency losses has been selected. 7.7 Thermal measurements To check the reliability of the design, the thermal maps have been checked with an IR camera. The LED driver has been stressed not only at a nominal load with 23 LEDs (Pout = 10 W) but also at 25 LEDs, here the requested output power is increased at 10.5 W across the input mains voltage range. Only minimum voltage range (85 VAC), maximum voltage range (265 VAC) and the two nominal mains voltages 100/50 Hz and 230/50 Hz have been reported. DocID025380 Rev 1 29/37 37 PFC waveforms AN4376 Figure 42. Top side thermal map with 23 LED load Vin = 85 VAC- 23 LEDs Point Temperature Description A B C D E F 58.2 °C 56.1 °C 58.7 °C 48.2 °C 49.3 °C 47.9 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 100 VAC - 23 LEDs Point Temperature Description A B C D E F 52.6 °C 50.6 °C 55.5 °C 46.5 °C 49.0 °C 46.5 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 230 VAC - 23 LEDs Point Temperature Description A B C D E F 50.4 °C 46.7 °C 55.0 °C 47.0 °C 49.8 °C 47.9 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 265 VAC - 23 LEDs 30/37 Point Temperature Description A B C D E F 53.1 °C 49.0 °C 58.2 °C 49.0 °C 50.9 °C 48.7 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic DocID025380 Rev 1 AN4376 PFC waveforms Figure 43. Bottom side thermal map with 23 LED load Vin = 230 VAC - 23 LEDs Point Temperature Description A B C D E F G H 52.1 °C 52.9 °C 53.2 °C 52.6 °C 67.4 °C 56.7 °C 56.7 °C 48.5 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 23 LEDs Point Temperature Description A B C D E F G H 50.7 °C 50.4 °C 50.7 °C 50.2 °C 61.6 °C 54.5 °C 54.5 °C 47.9 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 23 LEDs Point Temperature Description A B C D E F G H 60.3 °C 59.0 °C 59.8 °C 57.9 °C 57.2 °C 52.3 °C 51.0 °C 47.4 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 23 LEDs Point Temperature Description A B C D E F G H 68.8 °C 65.8 °C 66.1 °C 64.8 °C 61.3 °C 54.7 °C 54.5 °C 47.9 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 DocID025380 Rev 1 31/37 37 PFC waveforms AN4376 Figure 44. Top side thermal map with 25 LED load - 10.5 W output Vin = 85 VAC- 25 LEDs Point Temperature Description A B C D E F 63.0 °C 62.3 °C 66.0 °C 50.6 °C 51.7 °C 50.6 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 100 VAC - 25 LEDs Point Temperature Description A B C D E F 55.5 °C 54.7 °C 60.2 °C 48.7 °C 50.9 °C 49.2 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 230 VAC - 25 LEDs Point Temperature Description A B C D E F 50.1 °C 47.6 °C 56.0 °C 48.7 °C 51.5 °C 48.4 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic Vin = 265 VAC - 25 LEDs 32/37 Point Temperature Description A B C D E F 49.5 °C 53.1 °C 58.7 °C 48.7 °C 52.0 °C 49.2 °C L1 L2 Drain T1 - magnetic T1 - winding T1 - magnetic DocID025380 Rev 1 AN4376 PFC waveforms Figure 45. Bottom side thermal map with 25 LED load - 10.5 W output Vin = 230 VAC - 25 LEDs Point Temperature Description A B C D E F G H 52.1 °C 52.9 °C 53.2 °C 52.6 °C 67.4 °C 56.7 °C 56.7 °C 48.5 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 25 LEDs Point Temperature Description A B C D E F G H 50.7 °C 50.4 °C 50.7 °C 50.2 °C 61.6 °C 54.5 °C 54.5 °C 47.9 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 25 LEDs Point Temperature Description A B C D E F G H 60.3 °C 59.0 °C 59.8 °C 57.9 °C 57.2 °C 52.3 °C 51.0 °C 47.4 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 Vin = 230 VAC - 25 LEDs Point Temperature Description A B C D E F G H 68.8 °C 65.8 °C 66.1 °C 64.8 °C 61.3 °C 54.7 °C 54.5 °C 47.9 °C D4 - 1206 resistor R13 R17 R15 HVLED815PF R25 R26 D3 DocID025380 Rev 1 33/37 37 PFC waveforms 7.8 AN4376 Harmonic content at nominal mains voltage 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 JEIDA-MITI Class-C standard and European EN61000-3-2 Class-C standard, at a full load and both nominal input voltage mains. Figure 46. Measurement at 100 VAC, 50 Hz, PIN = 10.95 W, POUT = 9.5 W, PF = 0.9880 0HDVXU HGYDOXH -(,7$0,7,&ODVV&OLPLWV +DUPRQLF FXUUHQW>$@ +DUPRQLF RUGHU >Q @ $0 Figure 47. Measurement at 230 V, 50 Hz, PIN = 10.88 W, POUT = 9.48 W, PF = 0.9220 0HDVXU HGYDOX H (1&ODVV&OL PLWV +DUPRQLFFXUUHQW>$ @ +DUPRQLFRUGHU>Q@ $0 Figure 46 and Figure 47 show as the harmonics respect the limits for the Class-C equipment. 34/37 DocID025380 Rev 1 AN4376 7.9 PFC waveforms Conducted emission pre-compliance test From Figure 48 to Figure 51 are the average measurements of the conducted noise with 23 LED load and nominal mains voltages. The limits shown on the diagrams are those of the 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. Increasing the CX capacitor value of the EMI filter will improve the safe margin but affecting the PF. A compromise has been fixed in this design. Figure 48. 100 VAC and 23 LED load - phase Figure 49. 100 VAC and 23 LED load - neutral Figure 50. 230 VAC and 23 LED load - phase Figure 51. 230 VAC and 23 LED load - neutral 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. DocID025380 Rev 1 35/37 37 Supporting material 8 9 AN4376 Supporting material 1. HVLED815PF datasheet: “Offline LED driver with primary-sensing and high power factor up to 15 W”. 2. AN1059: “Design equations of high-power factor flyback converters based on the L6561”. 3. AN4314: “25 W wide-range high power factor buck-boost converter demonstration board using the L6564H”. Revision history Table 3. Document revision history 36/37 Date Revision 09-Jan-2014 1 Changes Initial release. DocID025380 Rev 1 AN4376 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. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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