dimmable led driver solutions

1 Confidential Proprietary

Dimmable LED Driver Solutions

2 • Template • Nov-12 Confidential Proprietary2

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


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


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


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)


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

http://en.wikipedia.org/wiki/File:3Way_bulb_diagram.jpg


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


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


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


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


How Does this Approach Work?

No Dimmer

With Dimmer

100VMOSFET


Principle Scales up for 230 Vac Inputall Bipolar Solution, Dimmer Compatible

Design Note DN05047


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


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


Example Design – LV5011Non-isolated TRIAC dimmable buck-boost

Snubber in input creates extra current

during input voltage step


TRIAC Shimmer due to Holding Current

These current levels can be different causing “shimmer” (50 or 60 Hz content)


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


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


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

Presenter

Presentation Notes

LV5012のワンページャです。是1pger。


“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”


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


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


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


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


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


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


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)


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


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)


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


Appendix


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

dimmable led driver solutions

Technology

dimming curve

new dimmer

light output

logstep dimming

confidential proprietary24

confidential proprietary29

light level

visible light