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MPC-WORKSHOP FEBRUAR 2013
DC Forward Model of High-Power LED’s
Abstract—Exact models of electronic components
are necessary for the development of electronic
circuits. Manufacturers of light emitting diodes
(LED) make only standard diode Spice models
available, particularly for the active region of
LED’s, the DC forward voltage range. In our work
we present a DC-model for the forward active region,
which exactly characterizes the behavior of
high-power LED’s in a large current/voltage range.
Index Terms—High-power LED, DC forward model,
Spice model.
I. INTRODUCTION
The development of high-power LED’s makes their
usage in measurement and signal technology as nearly
monochromatic light sources possible. Furthermore,
high-power LEDs are used as white light sources in
lightning technology, where they have a very high
potential due to their high energy efficiency in contrast
to conventional light sources [1].
Basically, a LED is nothing else than a diode and
can be described with the Spice model of a pn junction
[2]. The DC forward Spice parameters are the saturation
current IS, the emission coefficient N and the
serial resistance RS. Only these basic parameters are
in general provided by manufacturers of LED’s. Neither
the temperature behavior, which is described in
the Spice model by the saturation current temperature
exponent XTI and the energy gap EG nor deviations
from the ideal diode behavior like generationrecombination
and high-level injection effects [3] can
be modeled by the information given by the manufacturer.
The knowledge of the exact electrical description
and the temperature behavior for LEDs working
under different ambient conditions are necessary to be
considered in electric circuit development to increase
e.g. energy efficiency.
In the following, we present the development of a
general model for the entire DC forward operating
range of a LED. We applied the model to different
high-power LED’s, showing the universality of the
Volker Lange, volker.lange@hs-furtwangen.de, Brenton Sherston,
brenton.sherston@hs-furtwangen.de, Robert Hönl, robert.hoenl@hs-furtwangen.de,
Hochschule Furtwangen, Computer
and Electrical Engineering, Robert Gerwig Platz 1, 78120
Furtwangen.
Volker Lange, Brenton Sherston, Robert Hönl
Figure 1: Forward IV- characteristic of a green light emitting LED
model. First results on temperature effects and ambient
light influence will be shown.
II. EXPERIMENTS
Measurement and data analysis has been done with
Agilent Technologies ICCAP software (rev. 2012.01).
With this tool it is possible to drive the measurement
equipment, acquire the data and to perform the Spice
analysis. For this purpose, several tools like sensitivity
analysis and parameter optimization algorithms are
available. We used high accuracy source monitor units
(HP4142B) to take the current voltage data. Current
measurements down to pA with a resolution of tenth
of fA with 1% accuracy are possible. We made measurements
on different high power LED’s from Seoul
Semiconductor F50381 RGB-LED. Temperature control
was performed with the LED mounted on a
Temptronic TP34 controlled temperature chuck. The
temperature was additionally measured with a KTY-
10 temperature sensor in direct contact with the LED.
III. MODEL DEVELOPMENT
The development of the DC forward model will be
discussed on a measurement example of a LED emitting
green light of 533 nm (figure 1). It is obvious, that
such an IV characteristic cannot be characterized by a
simple diode model. Modeling such curve, we take
into consideration the influences of only standard
electronic components on the characteristic curve [1]
and follow a step by step procedure for the diode
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