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Phototransistor vs LDR

  1. Oct 20, 2006 #1
    I'm wondering what the difference between a light dependent resistor and a phototransistor is. Am i correct in assuming they are the same if the third lead of the phototransistor is not connected to anything?
  2. jcsd
  3. Oct 21, 2006 #2


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    From my somewhat limited experience with electronics I seem to recall that phototransistors can amplify the current produced and therefore have a greater sensitivity that of a photodioide, the response times are slower however. This question may be better placed in the Engineering forums (perhaps Berkeman could take a look).
  4. Oct 21, 2006 #3
    Yes, this question should be in one of the Engineering forums.
    A photodiode has an ability to produce large light to dark current ratio. The current produced by a photodiode is of few micro-amperes. A normal transistor has a property to amplify the input current by [itex]\beta[/itex] times where [itex]\beta[/itex] ranges from 50 t0 300 and is known as current amplification factor. A Phototransistor combines the advantages of a photodiode as well as a normal transistor.

    LDR as the name suggests is a Light Dependent Resistor whose resistance changes according to the intensity of the light incident on it.
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