need urgent help with phototransistor based circuit plzzzzz!

Discussion in 'The Projects Forum' started by arq, Jun 3, 2009.

  1. arq

    Thread Starter Member

    Nov 2, 2008
    16
    0
    I am posting a circuit diagram of simple circuit of phototransistor driving a relay. This is a simple circuit i have found yet. I am new to phototransistors. The diagram i am posting includes npn phototransistor . BUT at this time i have pnp phototransistor302C 40. There is no datasheet of this phototransistor availiable on the internet. So i want to ask if someone can help me with the same circuit implementing with a PNP 302C 40 phototransister. I shall be thankfull. I am in a urgent need.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    PNP photo transistors are not so common.
    If it is really a PNP transistor the emittor should be more positive than the collector.
    In your schematic the PNP transistor would have the collector and emittor turned over.

    Greetings,
    Bertus
     
  3. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    so your PNP emitter goes to +v, collector through a resistor to ground. then the base of the relay NPN through resistor to photo PNP collector. this allows NPN base to be pulled down when photo stops conducting.

    or, make the PNP collector resistor ~1.5k and then add a 200k pot in series (after the 1.5k) to ground. wiper of pot goes to NPN base. this gives you sensitivity control.
     
    Last edited: Jun 3, 2009
  4. pdc

    Member

    Mar 1, 2009
    10
    0
    Was googling for a similar way to drive a relay and found this thread. I am using a radioshack phototransistor (278-0145) tied to the base of a 2n2222 and was planning on using a voltage divider attached to the phototransistor emitter (12 volt source) to get the 6 volts the 2n2222 datasheet lists for vcbo and a trimpot on the voltage divider output to control sensitivity to the 2n2222 base. Basically a sunup, sundown relay. Sound feasible? Sort of like this (the zz's are resistors)

    PT
    !
    Z
    Z
    !------Trimpot--2n2222 base
    Z
    Z
    !
    =


    Also, is the diode in the diagram for when the relay field collapses?

    Thanks,

    Paul
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Why guess?
    Throw away the junk photo-thing that does not have a datasheet.
    Buy a name-brand photo-thing from a real electronic parts distributor and get its detailed datasheet.
     
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