LED Applications & Lighting Systems - fonarevka

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The LM3445 includes a bleeder circuit to ensure proper TRIAC operation
by allowing current flow while the line voltage is low to enable proper
firing of the TRIAC. A passive power factor correction circuit ensures
good power factor by drawing current directly from the line for most of
the cycle, and provides a constant positive voltage to the buck regulator.
Additional features include thermal shutdown, current limit and undervoltage
lockout.
NXP: World’s First Integrated
Dimmable Mains LED Driver IC
NXP Semiconductors, the independent semiconductor company
founded by Philips, launched the SSL2101 - the world’s first integrated
dimmable mains LED driver. The NXP SSL2101 is a small form factor
Switched Mode Power Supply (SMPS) controller IC specifically designed
to drive LED devices and provide dimming capabilities to further improve
the energy efficiency of LED lighting.
Typical application circuit of the LM3445
The LM3445 TRIAC dimmable LED driver maximizes the light output for
systems while maintaining ENERGY STAR® power factor requirements
in a typical application, positioning it among National’s PowerWise®
family of energy-efficient products.
Today’s TRIAC wall dimmers are designed to interface with a resistive
load such as incandescent or halogen light bulbs. Since an LED bulb
does not appear as a resistive load to the TRIAC wall dimmer, dimming
an LED bulb using a conventional TRIAC wall dimmer does not yield
optimal dimming performance. LED drivers available today cause either
a 120Hz flicker of the LEDs or do not enable the full 100:1 dimming
range. National’s LM3445 overcomes this challenge by translating the
TRIAC-chopped waveform to a DIM signal and decoding it for a fullrange
of uniform, flicker-free dimming. The driver’s patent-pending
control architecture maintains constant ripple through the LEDs, which
extends the life of the LEDs.
National’s LM3445 LED driver enables direct LED bulb replacement of
existing incandescent or halogen bulb systems connected to standard
TRIAC wall dimmers. In addition, the LM3445 allows master-slave operation,
enabling the control of multiple strings of LED bulbs.
Technical Features:
Offered in a 10-pin mini SOIC package, National’s LM3445 is an adaptive
constant off-time AC-DC buck (step-down) constant current controller
that includes a TRIAC dimming decoder. The decoder allows wide-range
LED dimming, using standard TRIAC dimmers. The high-frequency
capable architecture allows the use of small external passive
components.
Block diagram of the SSL2101
The dimming capabilities offered by the SSL2101 create unique opportunities
for lighting system designers to produce more energy efficient systems.
With the high integration level, this cost effective device reduces the
number of total electronic components and allows designers to fully reap
the benefits of dimmable LEDs while minimizing precious board space.
The SSL2101 is fully compatible with today’s lighting infrastructure and
can operate directly from rectified mains power supply in combination
with a phase cut dimmer. The SSL2101 includes a high-voltage power
switch and can start-up directly from the rectified mains voltage, so no
external startup circuit is required. To support its dimming capabilities
the SSL2101 contains two integrated high voltage-switches for bleeder
operation and an input that can be used to sense lamp power usage and
activate additional bleeder action when needed.
www.led-professional.com LED professional Review | Mar/Apr 2009 | page 12