G. S. SPAGNOLO ET AL.
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Figure 13. Curve of the Operating Point (Q) defined by circuit.
[7] ITE, “Vehicle Traffic Control Signal Heads (VTCSH)”
and “VTCSH Part 2: LED Vehicle Signal Modules,” In-
stitute of Transportation Engineers, Washington DC.
that using a pair of yellow and orange LEDs, it is possi-
ble to adjust the chromaticity in the temperature range
indicated by the standard, only acting on their intensity
ratio. For what concern the stability of in tensity, we have
seen a circuital setup able to counteract the drop in lu-
minous efficiency with increasing temperature. The in-
teresting aspect of the proposed circuit is related to the
calibration of its parameters (RS and VREF), which are
able to provide any trend of intensity-temperature for a
cluster of LE D.
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Assuming a signal consistin g of a matrix of yellow and
orange LED types, it will be possib le to use and calibrate
a couple of circuits for these two clusters of colors. As
we said, this configuration allows to secure the thermal-
stability of intensity, bu t also the inten sity trend to fo llow
a predetermined temperature pattern. In this way it is
possible to feed the clusters independently at any tem-
perature, according to our design, and to obtain the opti-
mal intensity ratio for the compliance of chromaticity
over the whole range of temperatures.
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[12] A. Groh, S. Brückner and T. Q. Khanh, “The Tempera-
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REFERENCES [13] OptoSemicondutors OSRAM, LS E6SF, LR E6SF, LA
E6SF, LO E6SF, LY E6SF, datasheet.
http://catalog.osram-os.com/catalogue/catalogue.do?act=d
ownloadFile&favOid=0200000200008f8a000200b6
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