Overview
Summary
The electrical design is part of the overall signal
The electrical design of an LED signal lamp has
several objectives. The first objective is to
operate the individual LED emitters at sufficient
drive current in order to generate sufficient
luminous flux to meet the lighting requirements.
The second objective should be to limit the
forward current through the individual LED
emitters so as not to exceed their maximum
internal junction temperatures and maximum dc
forward currents under worst-case conditions of
ambient temperature and input voltage. In
addition, the electrical design should protect the
LED array from automotive EMC transients.
Finally, the electrical design should provide
good intensity matching within the LED array.
The result of achieving these objectives will be a
maintenance-free LED signal light that operates
reliably for the lifetime of the passenger vehicle
or truck.
used in LED signal lamps and related circuit
design issues.
In addition to AB20-3, two companion electrical
design application notes are also available.
AB20-3A, titled “Advanced Electrical Design
Models,” discusses forward voltage models that
are more accurate and usable over a larger range
of forward currents than the simple linear models
shown in the “LED Emitter Modeling” section. In
addition, AB20-3A derives several additional
thermal-modeling equations from the basic
equations shown in the “LED Emitter Modeling”
section.
Application Note titled AB20-3B “SuperFlux LED
Forward Voltage Data” gives worst-case forward
voltage data for SuperFlux and SnapLED70
emitters. There are several potential electrical
models for LED emitters (linear, diode equation
models, etc.), each one optimized for an
Application Brief AB20-3 has been written to
simplify the electrical design of LED signal
lamps and is part of the Application Brief AB20
series. This application note has been divided
into three major blocks—Overview, Theory, and
Applications. The Overview consists of five
sections that discuss the electrical design
process and key electrical design concepts.
Theory consists of two sections that give an
in-depth overview of the electrical, optical,
and thermal properties of LED emitters and
mathematical modeling of their operation.
Applications consist of four sections that cover
specific types of circuit designs commonly
expected range of forward currents, and various
levels of “worst-casing” (i.e. min/max, average,
average ± one, two, three standard deviations,
etc.). In order to accommodate these various
needs, the data presented in AB20-3B gives the
nominal forward voltage and expected forward
voltage range for each SuperFlux LED
characterized over a range of forward currents
up to 70 mA. From this data, the desired
electrical model can easily be generated. The
latest forward voltage data for SuperFlux LED
emitters is available from your local Lumileds
LUMILEDS [ LUMILEDS LIGHTING COMPANY ]
