Benefits, such as small size, extremely long life, low power
consumption and enhanced dimming capability are the catalyst for the
wide spread adoption of HB LED DRLs and headlights. Several
manufacturers, such as Audi, Mercedes and most recently, Lexus and
Honda have used LEDs to design very distinctive DRLs as “eyebrows”
or “underlines” around the headlights as part of their unique
branding. Not only are these applications very distinctive from a
design perspective, they also create several design challenges to
offer a reliable and cost effective solution. As HB LEDs are adopted
into both the low beam and high beam of the headlights, these
challenges become even more pronounced.
It is well known that the primary function of headlamps is to
provide forward illumination at night or in less than ideal weather
conditions such as rain, snow and fog. The need for a higher level
of illumination has been the primary driver for the evolution of the
headlamp. In the 1980’s, Halogen based lights became the industry
standard, with 50W of electrical power they could deliver
approximately 1,500 lumens of light which was a 50% improvement over
their tungsten filament predecessors. This translates into an
efficacy, (known as light output per watt) or light delivered per
watt, or 30 lumens/watt (lm/W). In the mid 1990s, xenon based high
intensity discharge (HIDs) lamps became popular as they could
deliver up to 80lm/W, enabling manufacturers to deliver even greater
total light output.
However, they also have shortcomings such as the need to be
accurately adjusted so as not to blind oncoming traffic, relatively
short operational lives of 2,000 hours, the use of toxic mercury gas
and are expensive to manufacture. As the efficacy of HB LEDs
continues to improve they have become more desirable for headlight
applications. Five years ago, production HB LEDs offered efficacies
of 50lm/W which were not sufficient for headlight applications,
however current LED designs offer 100lm/W with estimates that this
will exceed 150lm/W in the next few years surpassing even the best
HID lamps. The ability of LEDs to offer roughly the same amount of
light output per watt and their other benefits of long life,
ruggedness and environmentally friendly design, makes them
particularly attractive to power the next generation of head lights.
The benefits of using LEDs in automotive headlights and DRLs have
several positive implications. First, they never need to be
replaced, since their solid state longetivity of up to 100K+ hours
(11.5 service years) surpasses the life of the vehicle. This allows
automobile manufactures to permanently embed them into the vehicles
bodywork without requiring accessibility for replacement. This also
enables styling to be dramatically changed as LED lighting systems
do not require the depth or area as HID or Halogens do. HB LEDs are
also more efficient than Halogen bulbs (and are soon to surpass
HIDs) at delivering light output (in lumens) from the input
electrical power. This has two positive effects. First, it drains
less electrical power from the automotive bus, which is especially
important in EVs and hybrids, and equally important, it reduces the
amount of heat that needs to be dissipated in the housing
eliminating any requirement for bulky and expensive heat sinking.
Finally, by using arrays of HB LEDs in headlight arrays and
electronically steering or dimming them, they can easily be designed
to optimize lighting for many different driving conditions.
In order to ensure optimal performance and long operating life, LEDs
require an effective drive circuit. This means that the driver ICs
must deliver an accurate and efficient DC current as well as
accurate LED voltage regulation regardless of the variations of the
input voltage source. Secondly, they must offer a means of dimming
and also provide a wide array of protection features just in case a
LED open or short circuit is encountered. In addition to operating
reliably from the electrically caustic automotive power bus, they
must also be both cost and space effective.
Stop/Start, Cold Crank & Load Dump Conditions
In order to maximize fuel mileage while minimizing carbon emissions,
alternative drive technologies are continuing to evolve. Whether
these new technologies incorporate electric hybrids, clean diesel or
a more conventional combustion engine designs, the chances are that
they will also need to incorporate a stop-start motor design.
Already prevalent in virtually all hybrid designs throughout the
world, many European and Asian and car manufacturers have been
incorporating these designs into conventional gas and diesel
vehicles as well. In the USA, Ford recently announced that it will
incorporate stop-start systems into many of its forthcoming domestic
The concept of a stop-start system for the engine is
straight-forward, the engine is shut off when the vehicle comes to a
stop and then restarted immediately before the vehicle is required
to move again. This eliminates the fuel used, and emissions
generated, while the car is stopped in traffic or at a stop light.
This stop-start design can reduce fuel consumption and emissions
between 5% and 10%. However, the biggest challenge for these designs
is making the entire stop-start scenario imperceptible to the
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