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1 Confidential Proprietary
Dimmable LED Driver Solutions
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Basic LED Dimming ConceptsDigital
– 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 = 411K350-1500mA;
35-105˚C
LED “B”∆CCT = 31K350-1500mA;
35-105˚C
Out
put C
urre
nt
Time
Source:OSRAM
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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
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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
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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)
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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
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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 inTRIAC with
resistiveload
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TRIAC Latching & Holding Current
Even an incandescent can cause a dimmer to flicker withadded capacitance (100nF Capacitor || 15w Bulb)
Flicker is caused when dimmer firesmultiple times per cycle
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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
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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
SmallCapacitor
2.2 nF
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How Does this Approach Work?
No Dimmer
With Dimmer
100VMOSFET
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Principle Scales up for 230 Vac Inputall Bipolar Solution, Dimmer Compatible
Design Note DN05047
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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
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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
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Example Design – LV5011Non-isolated TRIAC dimmable buck-boost
Snubber in input creates extra current
during input voltage step
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TRIAC Shimmer due to Holding Current
These current levels can be different causing “shimmer” (50 or 60 Hz content)
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Optional Bleeder can add Holding/Bleed Current for Low Power Applications
•ACS Comparator senses inputline voltage level
• When input voltage is too low, external load is added which presents extra current to TRIAC
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LV5029M
MOSFET
REF
OUT
CS
MOSFET OUT2
ACS
LV5026MLV5011MLV5012M
HV Vin
◆LV5026Adjustment Dimmer
・External Bleeder control
◆LV5011Adjustment Dimmer ・Built-in POWER FET
(LV5026+POWER FET)
◆LV5012Adjustment Dimmer・Built-in Start-UP HV FET・Built-in TRIAC Stabilized
LV5011LV5026LV5012
HV MOSFETBLEEDER FET
TRIAC Driver Functional Comparison
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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 MOSFETfor TRIAC light control
• Holding Current Circuit
Package Information
・Good adaptabilityof TRIAC Dimmer
・ Improvement Power factor・Reduced # of external components・Isolation or Non‐Isolation
・Low noise switching SystemStep 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)
LV5012MDSingle Stage (PSR) LED Dimming Controller
MFP14S
InternalBLEEDER&HV FET
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“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”
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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
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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
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New 2013 NEMA SSL7A SpecificationEstablishes 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
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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”DimmableLED Driver
Passive IROccupancy Sensor
WirelessReceiver
IRReceiver
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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
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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
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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)
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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
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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)
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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
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Appendix
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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