Datasheet

R
NTC
[k
ΩΩ
]
you calibrate the NTC used with your ACULED in your specific application. To achieve accurate
measurements of the resistance, a four-terminal sensing circuitry (4T) is the best choice.
20
18
16
14
12
10
8
6
4
2
0
10
0 mA
700 mA
20 30 40 50 60 70 80
T B [°C]
Figure 17
Typical curve of resistance R vs.
temperature T of an NTC:
Left: typical SMD NTCs.
Right: ACULED chip level NTC
in the typical ACULED T B range
for different currents I F of the
chips (RGBN-ACULED DYO).
I
F
[mA] No. of Chips
per Chip
0 0
c T
[°C]
c
R
[k Ω ]
26.3 25.6
Table 2
Coefficients to be used with
equation 12 to calculate T B from
R NTC (given in kΩ).
700 1 21.8 26.4
700 3 22.3 26.3
Using a Photo Diode with the ACULED DYO
With the ACULED DYO, a photo diode (PD) can be placed on a chip pad. PDs can be used to
measure light and are hence a good instrument to control the light output of the LEDs. When
using a multi-color ACULED with a PD, e.g. an ACL01-OD-RGBP, it can even be used for easy
color control and adjusting by turning on and measuring each LED separately and sequentially.
This can be done during the off-time of the other chips at a PWM pulse or in a specific
calibration mode during off-hours of a lamp application. PDs can also be used to measure the
ambient light, for example to switch on and off the ACULED according to the surrounding light in
lamp applications. Also, light barrier applications in reflection mode are possible. However, we
need to consider that no optical barrier is between the PD and the neighbored LED chips
leading to a strong optical crosstalk by both direct light from the LEDs and reflected light from
the ACULED ring and encapsulation-to-air surface.
Figure 18
V R = -5 V
Pin 1, 3, 5 or 7 Pin 2, 4, 6 or 8
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Symbol and reverse biased
connection of a photo diode with
the ACULED VHL.
Driving the ACULED® VHL™ 17