Hi guys,
I want to integrate into my design an IR emitter and a phototransistor. I want to experiment with the emitted power and the viewing angle, so I picked up some emitters based on that:
https://eu.mouser.com/Search/LwCompareProducts.aspxAlso, I am looking at the following phototransistor from Mouser
https://eu.mouser.com/ProductDetail/?qs=DkZGzo4b%252BTLpMYDw%2FNdTDA%3D%3DTo match the emitter and receiver with respect their wavelength, I picked up both to have a peak sensitivity wavelength of
940nmI am a bit confused regarding the collector current of the phototransistor. The higher the Irradiance Ee (mW/cm2 ), the higher the collector current right? In the datasheet, there is a graph that correlates both parameters, but the graph goes up to 6mW/cm2. The high-power IR emitters a picked up for testing, e.g the SFH 4546 emits 130mW/m2. Could this destroy the phototransistor? In the datasheet of the phototransistor, I cannot find the max. collector current.
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From my experience:
The max collector current is limited by the 100mW max dissipation of this device and only 6mw of dissipation is realized at 5V Vdd. Higher irradiance would decrease Vsat but with a collector load resistance in the 1 to 10K of ordinary operation, 100mW at 5V would not be realized and Vsat would further be further reduced by increased irradiation, lowering dissipation.
IIMBG, depending on the distance of the radiating source from the phototransistor, the irradiating energy heating effect with the phototransistor touching the photo-emitter device would not be sufficient to raise the phototranistors temperature beyond the safe operating temperature. You could measure the max heating effect yourself with a thermistor or other temperature measuring device. The phototranstor's leads themselves would function as a heat spreader into the PCB or breadboard to dissipate any heating. The irradiance itself (IMHO) would likely not damage the phototransistor, apart from any heating effect.
You emitter is 130mw/steradian, a unit of angular area
https://en.wikipedia.org/wiki/SteradianThe further the distance, the lower the power density (with the square of distance), as the surface area covered goes up (also with the square of distance)since the LED emits a fixed angle width beam.