LED Applications & Lighting Systems - fonarevka

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LTM8040: 1A LED Driver &
Current Source Protects LEDs
Linear Technology Corporation introduces the LTM8040, the first of a
new family of DC/DC uModule LED drivers that contains all the circuitry,
including the inductor, in a compact 9mm x 15mm x 4.32mm surface
mount package. Driving an LED string with the LTM8040 is as simple as
adding the input capacitor and connecting the LED string. The LTM8040
can drive from 0A to 1A through a string of LEDs with ±2% accuracy at
full load current. The device protects against an accidental open LED
string with its output voltage clamp circuitry and against short-circuit
incidents with a frequency foldback scheme. The LTM8040 has applications
in 2-cell Li-Ion battery packs, rectified 12VAC and industrial 24V for LCD
backlighting, portable lighting, and wide area lighting.
Typical application circuit for LTM8040
Features:
• True Color PWM delivers constant color with 400:1 dimming
• Wide input range: 4V to 36V
• Up to 1A LED current
• Adjustable control of LED current
• High output current accuracy is maintained over a wide range from
35mA to 1A
• Open LED and short-circuit protection
• Grounded cathode connection
• Small footprint, low profile surface mount LGA package
Applications:
• Automotive and avionic lighting
• Architectural detail lighting
• Display backlighting
• Constant current sources
The LTM8040 can convert an input voltage range of 4V to 36V to a
lower voltage ranging from 2.5V to 13V, suitable for driving a wide
variety of color and white LEDs with different voltage-drops (VD). The
device also features both analog and True Color PWM dimming,
allowing a 400:1 constant color dimming range. The LED current
amplitude can be linearly controlled from 0A to 1A with a single resistor.
The default switching frequency is 500kHz, which can be adjusted with
a resistor for up to 2MHz operation.
The LTM8040 is housed in a 9x15x4,32mm land grid array (LGA) package
and is offered in two temperature grades of 0ºC to 125ºC and -40ºC to
125ºC (internal package temperature).
Driver Family Extension
Meets Demands of Next
Generation LEDs
The RCD series of constant current LED Drivers from Recom has been
extended to a maximum of 1200mA to provide the higher currents
needed by the next generation of high brightness LEDs. The RCD-24-1.0
and RCD-24-1.2 DC/DC converters deliver a stable maximum current of
1A or 1.2A respectively from a wide input voltage range of between 5V
and 36VDC. The modules measure only 22mm x 12.5 x 8.5mm and yet
are fully complete plug-n-play units requiring no external components,
thus reducing the circuit footprint compared with alternative discrete
solutions by up to 50%.
The RCD series have two independent dimming inputs: a PWM control
that allows simple interfacing with microprocessors and digital
controllers and an analogue voltage input that is suitable for lighting
controllers or rheostat dimmers. Both dimming inputs are linear and the
dimming range covers 0%-100%. The PWM input can also be used to
shut down the converter to draw only 200µA from the supply.
The sophisticated feedback control circuit used in the RCD family of LED
drivers ensures excellent load and current regulation, resulting in LED
current stability of ±1%, a residual output ripple of less than 200mV
and efficiencies of up to 96%. The low internal power dissipation of
only 800mW permits the ambient operating temperature range of
-40°C to +71°C for the 1000mA version and -40°C to +65°C for the
1200mA version. The drivers also feature short circuit protection and
thermal shutdown.
The drivers have been designed to be as reliable as the LEDs they are
driving and contain no electrolytic or tantalum capacitors.
National Semiconductor:
TRIAC Dimmable LED Driver
National Semiconductor Corp. (NYSE:NSM) introduced a new constantcurrent
controller that enables off-line, uniform, flicker-free dimming of
high-brightness light-emitting diodes (LEDs) with a conventional TRIode
for Alternating Current (TRIAC) forward or reverse phase-control wall
dimmer. The LM3445 TRIAC dimmable LED driver enables a full 100:1
range of dimming capability and can maintain greater than 1A of
constant current to large strings of LEDs in a variety of residential,
architectural, commercial and industrial applications.
www.led-professional.com LED professional Review | Mar/Apr 2009 | page 11