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Dimmable LED Driver Solutions


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- All LEDs are dimmable, the issue is how the driver is designed to be dimmed

- Legacy wall dimmers present a unique set of compatibility issues and challenges

- New standards are being established like NEMA SSL7 to support new dimmer and bulb designs

- “Smart dimmers” can enable dimming for any application without legacy interface issues

Published in: Technology, Business
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Dimmable LED Driver Solutions

  1. 1. 1 Confidential Proprietary Dimmable LED Driver Solutions
  2. 2. 2 • Template • Nov-12 Confidential Proprietary2 Basic LED Dimming Concepts Digital – Pulse Width Modulation(PWM) – Can dim <5% depending on driver – Less wavelength shift (still ∆Tjº) Analog – Amplitude Modulation(AM) – Highest Efficiency – No Flicker, more color shift LED “A” ∆CCT = 411K 350-1500mA; 35-105˚C LED “B” ∆CCT = 31K 350-1500mA; 35-105˚C OutputCurrent Time Source:OSRAM
  3. 3. 3 • Template • Nov-12 Confidential Proprietary3 Dimming Light Sources • All light sources shift in color when dimmed • Many reasons to adjust light level – Situation control (reading/watching TV/etc) – Energy saving (Occupancy/Daylight harvesting) – Color tuning or mixing • Control Interface key to dim LED Driver Source: NEMA LSD-60
  4. 4. 4 • Template • Nov-12 Confidential Proprietary4 Dimming Control Interfaces • Control part of AC Power – Leading Edge Control (Triac) – Trailing Edge Control (MOSFET) • Control interface separate from Power Delivery – 0/1-10 V (IEC 60929) – DALI (IEC 62386) or custom PWM – Bluetooth/WiFi/Zigbee/Proprietary – Infra-red • Integrated Control – Ambient light sensing – Occupancy/motion sensing
  5. 5. 5 • Template • Nov-12 Confidential Proprietary5 AC Line Dimming • Line dimming especially TRIAC is of high interest for retrofit LED lighting and TRIAC dominates in US as no special wiring is needed • Compatibility requires special design effort in LED Driver – Driver needs to look like a resistive load (high power factor) – EMI filter has to be designed and optimized, big issue with input surge current – Driver must present minimum load for driver compatibility Leading Edge (TRIAC) ELV Dimmer Wiring Trailing Edge (ELV)
  6. 6. 6 • Template • Nov-12 Confidential Proprietary6 Dimmable Bulbs in US Households • 3 way have 2 dimming steps – Step 1 – Range 68-85% – Step 2 – Range 15-32% Source: CFL Market Profile, September 2010, Energystar • ~ 150 m installed in North America • ~ 100 m installed in Western Europe Dimmer Types in USA
  7. 7. 7 • Template • Nov-12 Confidential Proprietary7 Review of TRIAC Dimmer Operation • TRIAC must see a minimum latching current (Io) to stay on • Given abrupt turn on of the TRIAC there is ringing in the dimmer and the load • Problem is big since most LED drivers look capacitive (EMI filter) • If total load current drops below holding current (IH), TRIAC will turn off Current in TRIAC with resistive load
  8. 8. 8 • Template • Nov-12 Confidential Proprietary8 TRIAC Latching & Holding Current Even an incandescent can cause a dimmer to flicker with added capacitance (100nF Capacitor || 15w Bulb) Flicker is caused when dimmer fires multiple times per cycle
  9. 9. 9 • Template • Nov-12 Confidential Proprietary9 Designing for TRIAC Dimmer Compatibility • Step 1: Driver should look as much like a resistive load – PF ~ 1 – Very little line to neutral capacitance – Load current must be enough to stay above holding current of Triac • Step 2: If driver has capacitance due to EMI filter, extra latching current may be needed to deal with ringing in EMI filter • Step 3: Driver may need to switch in artificial load to present extra holding current to dimmer, dependent on: – LED Driver Load – Dimming Curve – Range of dimmer compatibility
  10. 10. 10 • Template • Nov-12 Confidential Proprietary10 Device Application Topology Input Voltage Input Power Power Factor THD NSIC2030B LED Lighting Linear 100 to 130 Vac 6.7 W 0.98 22% Design Note DN05046 Parallel to Series on Low Mains (120 Vac) Phase dimmer compatible Efficiency ~72% (3 LEDs/string) to 94% (4 LEDs/string) CREE MX-6S LED, VF = 20 V/LED Small Capacitor 2.2 nF
  11. 11. 11 • Template • Nov-12 Confidential Proprietary11 How Does this Approach Work? No Dimmer With Dimmer 100V MOSFET
  12. 12. 12 • Template • Nov-12 Confidential Proprietary12 Principle Scales up for 230 Vac Input all Bipolar Solution, Dimmer Compatible Design Note DN05047
  13. 13. 13 • Template • Nov-12 Confidential Proprietary13 PFC Flyback EMI Filter Optimization •Excess EMI filter capacitance degrades power factor •Larger inductors provide filtering with less effect on PF and resistors across inductors dampen resonance • Moving transient limiter RV1 after inductors can increase filter effectiveness •C1 normally controls EMI, but can interfere with TRIAC dimmer so this is can be reduced in size or eliminated and inductor values L1, L2, and L3 should be increased •Open magnetic path inductors (drum type) can create audible noise with TRIAC dimmer so closed-path or shielded inductors should be used
  14. 14. 14 • Template • Nov-12 Confidential Proprietary14 NCL30000 TRIAC调光 NCL30000 Triac Dimming 通过改变调光器位置来在350 mA至1.7 mA调光的性能 Dimming performance from 350 mA to 1.7 mA by changing dimmer position 施加电压 Applied voltage @ 100 V/div 线路电流 Line current @ 333 mA/div
  15. 15. 15 • Template • Nov-12 Confidential Proprietary15 Example Design – LV5011 Non-isolated TRIAC dimmable buck-boost Snubber in input creates extra current during input voltage step
  16. 16. 16 • Template • Nov-12 Confidential Proprietary16 TRIAC Shimmer due to Holding Current These current levels can be different causing “shimmer” (50 or 60 Hz content)
  17. 17. 17 • Template • Nov-12 Confidential Proprietary17 Optional Bleeder can add Holding/Bleed Current for Low Power Applications •ACS Comparator senses input line voltage level • When input voltage is too low, external load is added which presents extra current to TRIAC
  18. 18. 18 • Template • Nov-12 Confidential Proprietary18 LV5029M MOS FET REF OUT CS MOS FET OUT2 ACS LV5026MLV5011MLV5012M HV Vin ◆LV5026 Adjustment Dimmer ・External Bleeder control ◆LV5011 Adjustment Dimmer ・Built-in POWER FET (LV5026+POWER FET) ◆LV5012 Adjustment Dimmer ・Built-in Start-UP HV FET ・Built-in TRIAC Stabilized LV5011LV5026LV5012 HV MOSFET BLEEDER FET TRIAC Driver Functional Comparison
  19. 19. 19 • Template • Nov-12 Confidential Proprietary19 Unique Features Application DataBenefits Market & Applications Others Features • TRIAC Dimming Light Bulb • Dimmable LED Downlights ・PWM Topology ・Built‐in Start UP MOSFET ・Built‐in BLEEDER MOSFET for TRIAC light control • Holding Current Circuit Package Information ・Good adaptability of TRIAC Dimmer ・ Improvement Power factor ・Reduced # of external  components ・Isolation or Non‐Isolation ・Low noise switching System Step Drive switching & 5 Stage skip Frequency ・Integrated Triac Dimmer Compatibility ・ Improvement power factor ・LED current line regulation ±3% (180V‐264V) ・Built‐in TRIAC holding current function  ・Over current protection ・Thermal Shut down (TSD) LV5012MD Single Stage (PSR) LED Dimming Controller MFP14S Internal BLEEDER &HV FET
  20. 20. 20 • Template • Nov-12 Confidential Proprietary20 “Smart Dimmer” Issues • Night Light and Smart Dimmers – MCU steals current from line to stay powered even when dimmer is off – LED Driver must provide a current path all the time for proper operation Dimmer Operating ILOAD Vin Dimmer Off “60W Bulb”
  21. 21. 21 • Template • Nov-12 Confidential Proprietary21 Dimmer Compatibility • Very little standardization in place globally • LED lamp vendors and dimmer manufacturers have to test for general compatibility • For US Market there has been some standards developed – NEMA SSL-6 … Recommended Dimmer Characteristics – NEMA SSL-7A … Future Compatibility (New Dimmers/New Lamps) Philips LED Bulb Example
  22. 22. 22 • Template • Nov-12 Confidential Proprietary22 NEMA SSL6 Compatibility NEMA SSL-6 Bulb A Bulb B 32% Light 10% Light • LED drivers can have very different dimming shapes • NEMA SSL-6 sets requirements targeting incandescent shape • Two bulbs both compliant could have dramatically different light output at low conduction angle
  23. 23. 23 • Template • Nov-12 Confidential Proprietary23 New 2013 NEMA SSL7A Specification Establishes Dimming Corner Points for New Dimmers/Bulbs Note: MLO = Maximum Light Output (no dimmer connected) • @ 130 degrees, light output must be > 75% • @ 40 degrees, light output must be < 30% • @ 45 degrees, there must be “visible” light
  24. 24. 24 • Template • Nov-12 Confidential Proprietary24 What about “Smart Lighting” • LEDs are easy to control and dim • Electronics opens up new functions – Built-in occupancy sensor – Power savings based on ambient light – Wireless interfaces eliminate need to change switches or wiring • Power saving techniques • Convenience and security Ambient Light Sensor “Smart Ready” Dimmable LED Driver Passive IR Occupancy Sensor Wireless Receiver IR Receiver
  25. 25. 25 • Template • Nov-12 Confidential Proprietary25 NCL30082 Smart Dimming Interface • Additional Features – Smart Dedicated Analog / PWM dimming Input – Programmable temperature foldback (TF) and over voltage protection (OVP) OVP TF ZCD CS GND VIN VCC DRV SD DIM
  26. 26. 26 • Template • Nov-12 Confidential Proprietary26 NCL30082 Dimming Control Pin Operation • The DIM pin combines analog and PWM dimming capability. • If a signal lower than VDIM100 is applied, the controller decreases the output current proportionally to the applied voltage. • If a signal higher than VDIM100 is applied to the DIM pin, the controller enters the PWM dimming mode and enables the drive pulses when VDIM > VDIMA. • Can also provide programmable soft start (RC from Vcc) • PWM and analog dimming can be combined also
  27. 27. 27 • Template • Nov-12 Confidential Proprietary27 NCL30082 Analog Dimming Iout VDIM • Iout of 5 LED load (purple), DIM input is ramped down slowly from 3 V to 0.75 V (Green) • VDIMA 100% level is 2.45V (typical)
  28. 28. 28 • Template • Nov-12 Confidential Proprietary28 NCL30083 Log-Step Dimming • Cost free dimming without a special dimmer switch • Target is control range of a triac < 10% • Output current decrease in discrete steps each time a low input voltage condition is detected. Dimming Step Iout ON 100% 1 70% 2 40% 3 25% 4 10% 5 5% Test Results with LEDTarget Output
  29. 29. 29 • Template • Nov-12 Confidential Proprietary29 How Log-Step Dimming is Done • The VCC capacitor must be able to supply the controller during a short brown- out condition (split supply for VCC)
  30. 30. 30 • Template • Nov-12 Confidential Proprietary30 Summary • All LEDs are dimmable, the issue is how the driver is designed to be dimmed • Legacy wall dimmers present a unique set of compatibility issues and challenges • New standards are being established like NEMA SSL7 to support new dimmer and bulb designs • “Smart dimmers” can enable dimming for any application without legacy interface issues
  31. 31. 31 • Template • Nov-12 Confidential Proprietary31 Appendix
  32. 32. 32 • Template • Nov-12 Confidential Proprietary32 Problem Description Driver Response Flashing/Flickering Repeated flashing, typically at dimmer upper range Add holding current, reduce EMI filter size Poor Control Range Cannot dim to desired light level, different response with different dimmers Accelerated Dimming Curve, equalizes bad dimmers Light Variation Line and load changes cause bulbs to get brighter or dimmer Limitation of constant power approach, closed loop current regulation LED on when dimmer is OFF Problem of smart dimmers needing current to keep memory alive Active Bypass Path to Dimmer Low Frequency Light Variation Light “variation” at lower dimmer position Add shimmer reduction compensation Night Light in Dimmer does not work LED Driver does not present a good DC path to the dimmer Active Bypass Path to Dimmer Common TRIAC Dimmable LED Issues