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photo diode/transistor

Discussion in 'General Electronics Discussion' started by jcurrie, Dec 20, 2013.

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  1. jcurrie


    Feb 22, 2011
    the question i have , would one be able to sub a phototransistor for a diode it it for a model rr dector cir. plans call for a diode but i was given a huge bag of transistors they are T1 housing look just like doide the only diff i can fine is the gain of the transistor over the diode any one out with more exp than me have any sage words?

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Whilst the junctions of a transistor act as diodes, they're not optimised to be used that way. This would be especially true of a phototransistor.

    Can you show us the circuit and identify what diodes you want to replace with these transistors?
  3. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    If it were a NPN transistor then as along as reverse voltage and current is low then they make very good diodes. Much better temperature tracking if using more than one transistor, than using diodes. Tie the base of a transistor to its collector and now this can be used as a low power diode. But as Steve points out you might not get good results with a photo transistor, I have never tried it.
  4. jcurrie


    Feb 22, 2011
    thanks for the input , while looking for a printer friendly copy of circuit i was planing on using found a circuit for the same purpose that uses a phototransistor its simpler and uses less componets which leads me to another thought the p/t's are npn 35v but dont list wave length but will breadboard it first to see if they will fuction with ambient light
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