Compared to conventional CCFL backlights,
LED backlights...
· Have
lower power consumption...
...meaning
less heat disipation and reduced cooling rates
· Have
solid-state technology...
...making them more robust for rugged environments
· Have
no mercury content...
...which results in flicker-free
operation over the entire brightness range, nor are any hazardous
material waivers required
· Require
no inverters...
...thereby reducing
EMI emissions, cost and lead time, and eliminating the cost and design
time of custom inverters
· Have
a lower IR signature...
...which is ideal for NVIS
(Night Vision Imaging System) applications
· Have
a wider operating temperature...
...making them especially suited
to outdoor applications for the commercial, industrial and military
markets (rom -40° C to +85° C)
· Have
a lower voltage requirement...
...meaning they’re better suited to high altitude
applications
· Have
a “truer” white...
...resulting in a more accurate
graphical representation and an aesthetically more pleasing
appearance
· Have
a longer life...
...saving cost and time associated
with backlight replacement
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
LED Backlights are available on most General
Digital
LCD monitors. To determine
what configuration best suits your application, please
contact a Sales Engineer.
Length 2:38
Overview
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 5Vdc of power to operate, though they can be configured
to run with 12Vdc.
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.
LEDs are ideally suited to sunlight readable and NVIS
(Night Vision Imaging System) 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.
LED Backlight Controller Board General
Digital’s™ LED Backlight Controller
has been designed to support LCD Monitor applications that require sunlight
readability, as well as nighttime vision (NVIS) performance. This controller
is optimally designed to drive up to four (4) LED rails (up to two sunlight
readable rails and up to two NVIS rails). The controller will operate
from +12 Vdc to +18 Vdc and drives LED’s up to 10 amps in sunlight
readable mode, and 3 amps (6 Vdc) in NVIS mode. The maximum and minimum
brightness for each mode of operation (sunlight readable/NVIS) is programmable.
The controller allows brightness control from full off to full brightness
in both modes of operation, providing 256 steps and more than 1000:1
dimming. It accepts both push button brightness control via a membrane
switch or mechanical buttons or a 10K analog potentiometer. In sunlight
mode, the maximum current is monitored and controlled to prevent “thermal
runaway” under extreme temperature conditions,
assuring long life for the LED’s Operators may select between sunlight
mode and NVIS mode via a two-pin input from a mechanical switch or TTL
signal.
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 LED’s. Our LED rails use a serial-parallel design philosophy,
whereby we drive the LED’s 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 LED’s. 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.
Programmability
The performance of the LED controller is programmable at the factory
to meet the specific requirements of each application. The following
parameters are programmable:
Maximum/Minimum Brightness of Sunlight Readable
LED Rails
Maximum/Minimum Brightness of NVIS LED Rails
Current Limiting of Sunlight Readable & NVIS
LED Rails
Monitor Maximum Output of Sunlight Readable Rails to
Prevent Thermal Runaway Under Extreme Thermal Environments
Ensures Long Life of LED’s
Define Brightness of Sunlight Readable and
NVIS Modes When Switching Modes
Brightness Algorithm Choices
Default Brightness (value defined by user)
Last Brightness (recalls last setting)
Based on Potentiometer Position
Custom
Features and Benefits of General Digital’s LED Backlight Controller
FEATURES
BENEFITS
Support
for Brightness Sensors (Up to Two)
-
One (1) LED Rail – Sunlight Readable (SR) and Night Vision
Imaging System (NVIS)
Consistent
and Predictable Luminance
Sensors provide real-time brightness feedback from the LED backlights to the
microprocessor so that the brightness can automatically be corrected for changes
due to ambient temperature fluctuations, increased current draw of the LEDs,
decay of the LED, etc. Ensures consistent performance from one monitor to another
despite inherent component tolerances.
-
One (1) Ambient Light with Proximity Sensor
Maximizes
Backlight Life, Power and Energy Savings
Allows for automatic brightness/dimming control of LED backlights
based on ambient lighting conditions. Use only as much brightness
as the working environment demands. A proximity sensor determines
if the optical sensor is obstructed, thereby preventing false readings
or unintended brightness adjustments.
Custom Brightness Profiles
Custom control profiles (firmware) can be created by General Digital
for the LED Controller to meet specific customer requirements.
Support for
Multiple Temperature Sensors
- Embedded on
LED Rail
Prevent Critical
Hardware Failures
Provides real-time temperature feedback from the LED rails. This
data is used by the over-temperature brightness/power control algorithm
to automatically reduce backlight power consumption (brightness)
in response to excessive temperatures, which reduces heat generation
and prevents critical failure of the LCD or associated electronics.
- Other
Monitor other
critical temperature hot spots within the integrated solution/monitor.
Current Limiting
for LED Rails (SR and NVIS)
Inherently,
LEDs will draw more current as they heat up. After a certain temperature
threshold is exceeded, the LEDs power efficiency and brightness
will degrade; furthermore, as the LEDs lose brightness, they will
continue to draw more current and dissipate more heat.
Prevention of Thermal Runaway
The LED controller monitors the current to each LED rail and automatically
reduces the current if it exceeds a predetermined value that
is stored as a constant in the controller’s memory/firmware.
Power Efficiency
Proactive control of the backlight current prevents the backlights
from demanding more power after they have exceeded their optimal
luminance threshold.
LCD Failure Protection
By directly limiting the power consumption of the backlight and
indirectly reducing the heat generated, the LED controller prevents
over-temperature conditions from developing. If allowed to go
unchecked, what could occur is temporary or permanent failure
of the liquid crystal material and/or the LCD’s optical
films and diffusers.
Controlled Brightness Under Extreme Temperature
This feature is especially important for applications that have
high ambient temperature requirements or that will be mounted
in sealed enclosures without active cooling provided.
Hardware Protection
Critical Failure
Detection
In the event that the microprocessor or either of the digital potentiometers
fails, the backlights will be intentionally shut off. This will prevent
the LEDs from entering a “runaway” thermal condition
that could lead to permanent damage of the LCD and its infrastructure.
Critical Failure
Protection
In response to over-temperature conditions reported within the monitor
from an integrated temperature sensor, the controller can be programmed
to automatically reduce brightness and power consumption of the LED
backlights, thereby reducing internally generated heat. Default code
will reduce brightness to 80% at the first over-temperature failure,
60% for the second failure, and will shut off the backights if the
third temperature limit is exceeded. Backlights will be turned on
and brightness increased as internal temperature decreases below
each established temperature limit. Custom firmware can be developed
to establish a specific number of temperature limits and the percentage
of brightness for each limit.
- Minimum/Maximum
Sunlight Readable Brightness
Consistent and
Predictable Luminance
The firmware can be configured to ensure that the minimum brightness
does not go below a specific luminance, and the maximum brightness
does not exceed a specific luminance. The results are more accurate
when using the optional brightness sensors.
- Minimum/Maximum
NVIS Brightness
Consistent and
Predictable Luminance
The firmware can be configured to ensure that the minimum brightness
does not go below a specific luminance, and the maximum brightness
does not exceed a specific luminance. The results are more accurate
when using the optional brightness sensors.
- Current Limits
Maximizes Backlight
Life/Critical Failure Protection
Prevents thermal runaway under extreme thermal environment variations
and increases LED longevity.
- Define Brightness
of Sunlight Readable and NVIS Modes when Switching Between Modes
Consistent and
Predictable Luminance
The brightness can be programmed to be a default brightness (defined
by customer), or last brightness (recalls last setting made), based
on potentiometer position, or a custom setting.
Supports
General Digital’s Serial-Parallel LED Backlight Designs
Soft Failure
Design
General Digital’s LED backlight rails utilize a serial-parallel
design philosophy that provides applications with a hardware “soft
failure” mechanism, which minimizes the risk of a critical
failure due to the failure of a single, or multiple, LEDs.
Further improve your display's optical performance with our optical
enhancement products and services. For details, visit our Optical Bonding Laboratories web site now.
1 Data reflects display manufacturer
specifications (using CCFL backlights) and General Digital-derived
measurements after LED backlights were installed. 2 TN panels are more transmissive (more light output
per watt); IPS/VA panels incorporate wide viewing technologies with
better contrast.
Maximum
Ratings3
Symbol
Parameter
Value
Unit
Vin
Supply Voltage
1.00 to 20.00
Vdc
Vsig
Voltage to All Input Pins
-0.7 to 5.25
Vdc
Imax
Input Current
10
Adc
Pmax
Output Power
138
Watts
Top
Operating Temperature
-40 to +75
°C
Tst
Storage Temperature
-60 to +150
°C
3 Maximum ratings denote the
values beyond which damage will occur.
Recommended Operating Values
Symbol
Parameter
Typical Value
Unit
Vin
Supply Voltage
12.0 to 15.3
Vdc
Lhigh
Logic Input High
1.27 to 5.00
Vdc
Llow
Logic Input Low
0 to 0.70
Vdc
Din
Dimming Potentiometer
0 to 5.00
Vdc
Physical Characteristics
Weight
Size
PCB Thickness
74.2 Grams
4.000" x 3.000" x 0.625"
0.062
Ordering Options
Part Number
Description
21-101
LED Backlight Controller Board with
Sunlight Readable and NVIS Support
21-127
LED Backlight Controller Board with
Sunlight Readable Support
General
Digital’s™ LED Backlight Controller
has been designed to support LCD Monitor applications that require sunlight
readability, as well as nighttime vision (NVIS) performance. This controller
is optimally designed to drive up to four (4) LED rails (up to two sunlight
readable rails and up to two NVIS rails). The controller will operate
from +12 Vdc to +18 Vdc and drives LED’s up to 10 amps in sunlight
readable mode, and 3 amps (6 Vdc) in NVIS mode. The maximum and minimum
brightness for each mode of operation (sunlight readable/NVIS) is programmable.
The controller allows brightness control from full off to full brightness
in both modes of operation, providing 256 steps and more than 1000:1
dimming. It accepts both push button brightness control via a membrane
switch or mechanical buttons or a 10K analog potentiometer. In sunlight
mode, the maximum current is monitored and controlled to prevent “thermal
runaway” under extreme temperature conditions,
assuring long life for the LED’s Operators may select between sunlight
mode and NVIS mode via a two-pin input from a mechanical switch or TTL
signal.
General Digital’s™ LED backlight designs are designed to
provide a very low cost of ownership by ensuring extended operational
life of the LED’s. Our LED rails use a serial-parallel design philosophy,
whereby we drive the LED’s 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 LED’s. 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. 
LED Backlight Controller