Datasheet

The output voltage is proportional to the photo current and thus to the irradiance E
e
or the
illuminance E
V
at a given spectral distribution of the radiation or light reaching the photo diode; an
example is given in table 4. Since the sensitivity of a PD depends on the wavelength as shown
in figure 21, the resistance R
N
has to be adjusted according to the amount of light and its spectral
distribution. To learn more about the amplification circuitry of PDs, please refer to the appropriate
published literature.
R N
I Ph
-
+
V Out
-
V R
+
Using a photo diode with an RGBP ACULED DYO
Figure 20
Typical circuitry utilizing operational
amplifiers (op-amps) as current-to-
voltage converter with reverse biased
voltage V R.
Figure 21
Spectral sensitivity of the PD.
In this section we will see a specific example how the photodiode can be used based on an
RGBP ACULED DYO, which means an ACULED equipped with a red, a green and a blue LED
chip and the PD. In figure 22 we can see how the photo current of the PD depends on the
current of the LEDs and the temperature of the board. The red LED leads to the highest photo
current due to the spectral sensitivity of the PD as shown in figure 21 with its maximum at
approx. 850 nm (IR). Table 5 shows the numbers at 25 °C board temperature. Please note that
these numbers and figures depend on the intensity ranks of the specific ACULED and are for
example only. The results were taken without any environmental light, so an important question
is how these measurements would be influenced by ambient light. Table 4 shows the photo
current of the PD induced only by ambient light typically for office illumination to get a picture of
it. Since the values are very low compared to the photo current induced by the LEDs, ambient
light does not matter in many applications. However, if it is an issue, you should synchronize the
www.excelitas.com Driving the ACULED® VHL™ 19