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Tuesday
Jun292010

LED Backlights for LCDs

LED vs CCFL
General Digital’s LED (Light Emitting Diode) backlight design is an efficient alternative to typical CCFLs (Cold Cathode Fluorescent Lamps). While each technology has its own distinct advantages, LED backlit displays tend to be superior to CCFL displays in terms of longevity (50,000 hours minimum), much greater resistance against shock and vibration, reduced power consumption, brighter intensity and precise control of the intensity, among several other attributes. Due to their solid-state design, they do not require an inverter as they typically require only 5 Vdc of power to operate, though they can be configured to run with 12 Vdc.

In an LCD display, the light from the LEDs is diffused to light up the viewing area evenly. General Digital offers array and edge-lit LED configurations. An array-lit configuration consists of many LEDs mounted uniformly so as to distribute the light evenly. An edge-lit configuration has all of the LEDs mounted on one side of the display (usually the top), which makes for a thinner package and reduces power consumption, albeit at a slight deficit in uniformity.

Uses and Benefits of LED Backlights
LEDs are ideally suited to sunlight readable and NVIS (Night Vision Imaging Systems) applications. The military and heavy industrial industries can benefit greatly from their longevity, superior brightness control, and resistance to shock, vibration and weather extremes. Operating at reduced power levels can be achieved while keeping the thermal levels within the OEMs’ original spec. Other benefits include reduced EMI emissions, operation at low temperatures (-40° C), and virtually instantaneous full brightness for those mission-critical situations. Other applications that could benefit from LED backlighting include digital signage, construction, and aviation.

Compared to Conventional CCFL Backlights, Consider that LED Backlights:

  • Have Lower Power Consumption
  • Have Lower Heat Emission
  • Have a Lower Operating Temperature; Will Operate at -40° C (-40° F)
  • Have a Lower Voltage, Allowing Operation at High Altitudes
  • Have a Lower IR Signature; Ideal for NVIS (Night Vision Imaging System) Applications
  • Have a Longer Life
  • Are More Robust for Rugged Environments
  • Have No Mercury Content
  • Require No Inverters, Thereby Reducing Both EMI Emissions and Dependence on Outside Contractors
  • Have No Cadmium Sensors (No Waiver Required)
  • Have a Reduced Lead Time

Additional Features:

  • General Digital-designed LED Backlight Controller Board (BCB)
  • LED BCB Drives Up to 4 LED Rails (2 Sunlight Readable, 2 NVIS)
  • LED BCB Operates from +12 Vdc to +18 Vdc
  • In Sunlight Readable Mode, Maximum Current is Monitored and Controlled to Prevent “Thermal Runaway”
  • Serial-Parallel Design Ensures Monitor Remains Lit and Operable
  • LED BCB is Programmable at the Factory for Specific Applications
  • Solid-State Technology

Conventional Designs
Most commercial LED rails for LCD displays are designed to be driven serially. The primary advantage of this design approach is that the associated controller requires only a very low output current. Typically, the controllers occupy a small footprint since the low output override requires only small traces. However, the glaring disadvantage of a serial driven LED rail, and associated controller, is that there is no soft failure mechanism in the event of an individual LED failure. A failure of a single LED will render the entire rail inoperable. The other disadvantage is that the LED controller will produce a very high output voltage (100 Vdc typical), which constitutes a hazardous voltage and complicates its integration.

Our Design
General Digital’s™ LED backlight designs are designed to provide a very low cost of ownership by ensuring extended operational life of the LEDs. Our LED rails use a serial-parallel design philosophy, whereby we drive the LEDs in groupings of three or four. When grouped in pairings of three, the controller requires a 12 Vdc input, for pairings of four, a 15.3 Vdc input. However, what differentiates our design approach from others’ is that each of the LED groupings is driven in a parallel manner. The primary benefit is that a single LED failure will only affect its immediate grouping (soft failure), but will not affect any of the other groupings of LEDs. The benefit is that singular or multiple LED failures will not render the monitor inoperable, and in most cases will still provide a very uniform backlight. This non-catastrophic failure condition is essential for mission critical applications. The secondary advantage is that the General Digital™ LED controller's output voltage does not exceed 15.8 Vdc. It should also be noted that our LED Controller can support up to 10 amps of output current. This is far greater than typical current regulated LED module drivers, which only support 1 amp per module. Prior to the advent of our LED controller, our typical sunlight/NVIS backlight for a 19" display required six LED modules to drive our LED rails. Substituting our LED Controller saves considerable expense, mechanical space and weight. Furthermore, our controller eliminated the need for technician time to calibrate each of the individual modules, providing further cost savings.

About General Digital Corporation
For over 30 years, General Digital has been a leading industry designer and manufacturer of commercial-, industrial- and military-grade rugged flat panel monitors. The diverse product line includes numerous LCD monitor configurations:

General Digital’s Optical Bonding Laboratories uses film laminations, brightness enhancements and optical bonding to efficiently improving the brightness, contrast, shatter resistance and overall performance of your LCD monitor.
Going hand in hand with its technological expertise, General Digital provides software testing and engineering services, primarily for aerospace and avionic software applications.

GeneralDigital.com

GDOptiLabs.com

Local and International: 860.282.2900

Toll-Free in North America: 800.952.2535

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