presentation lt3799

8/6/2019 Presentation LT3799

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LT3799Universal Input, Isolated LED Controllerwith Active PFC


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2010 Linear Technology

An isolated regulated current source for driving LEDs using a single-stage active PFC flyback topology without an optocoupler

Compatible with standard TRIAC in-wall dimmers

Active Power Factor Correction > 0.97

Low harmonic distortion

Regulates LED current (typically 5%) Open- and shorted-LED detection and protection

Boundary mode operation improves efficiency and EMI

Multiple CTRL inputs allow flexibility(CTRL pins can be used to reduce LED current at high ambienttemperatures, at low line voltages, or at high ambient light levels)

Ideal for up to 100W+ of LED Power

LT3799 Features


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LT3799 Main Advantages Isolated LED Driver solution featuring standard TRIAC dimming, active

PFC, and well-regulated LED current with no optocoupler.

Small solution size with a minimum of external components;

the LT3799 utilizes a single-stage PFC Flyback topology, which

requires only one FET and one transformer and no opto-coupler;

most other isolated solutions require an additional 20-30 discrete

components (for bleeder and damper circuits, and for secondary-

side LED regulation circuitry / optocoupler feedback circuitry)

Active PFC has higher efficiency and lower harmonic distortioncompared to passive PFC (many competitive ICs use passive PFC)


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LT3799 - Typical ApplicationUniversal TRIAC-dimmable 20W LED Driver; 85% Efficient; PFC >0.97

No OptocouplerIsolated output with

regulated LED current

Complete LT3799Schematic

(20W LED Power)


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LT3799 Demo CircuitDC1744A, ~4W

40mm diameter; 22mm height;this board is optimized for

small size


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LT3799 Power Factor Correction LT3799 typical PFC is > 0.97

Even though PFC is required only at power levels greater than ~75W,

many LED fixture manufacturers and industry experts have recognized

the need for PFC even at power levels less than 10W (due to the fact that

a large building may contain several hundred light fixtures, and when the

total load is added together, the total power required from the power gridcan be much more than 75W)

Currently, most LED light fixtures and replacement light bulbs are not

isolated and do not provide PFC; for those that do provide PFC, manyuse passive PFC


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LT3799 - VIN and IIN Waveforms (active PFC)

LT3799 Active PFCPFC = 0.977

Competition Passive PFC

PFC = 0.913

Active PFC topology provides smoother input current waveforms,resulting in lower harmonic distortion.

Sharp edges of passive valley-fill PFC technique generate harmonics.


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LT3799 Harmonic Content In addition to the importance of PFC, there has been a lot of discussion

recently about the importance of the Harmonic Content of LED fixtures,

even at power levels under ~10W (again, due to the fact that a largebuilding may contain several hundred light fixtures, it seems wise to

design even low power LED fixtures to have good harmonic distortion)

There are IEC requirements for the amount of current drawn on each of

the odd harmonics

The LT3799 waveform shape provides low harmonic distortion


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LT3799 Measured Harmonic Content

Complies with IEC 61000-3-2, Class C Lighting Equipment Harmonics Requirement

Test data obtained using Demo Circuit DC1595A (20W LED power),operating with 110VAC input, 1.1A LED current.


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LT3799 Dimming with TRIAC Dimmer

Data taken using democard DC1595A (20W LED power),operating with 110VAC input.

Notice that TRIAC Dimmers do not reach 180 Phase, even when turned fully on.

Currently, TRIAC dimming range is ~10:1, and no flicker is present.


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LT3799 Full Load Efficiency (Without TRIAC Dimmer)

Data taken using democard DC1595A (20W LED power),operating at 1.1A LED current.

Some tradeoffs are made in Efficiencyto operate over wider VIN range.


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LT3799 Target Applications The LT3799 is targeted at customers who want a small solution size

offline LED driver with isolation, PFC, and low-harmonic distortion;

many high-quality / high-reliability customers want UL Class 2

certification, which requires that the LEDs to be isolated

Also works well for high-voltage DC and AC applications that do not need

triac dimming, and non-isolated applications

Some potential applications:

Architectural lighting

Street Lighting

High-end Fixtures and Lamps

Commercial Lighting / High-Bay Lighting


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Description Final SiliconSamples

Data Sheet Release

LT3799 Isolated Flyback LEDController with Active PFC

January 2010 December2010

February2011

LT3799 Embargo date & Release Schedule


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presentation lt3799

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