Phone-Activated Lamp Controller

Discussion in 'Homework Help' started by Point_Man, Feb 22, 2004.

  1. Point_Man

    Thread Starter New Member

    Feb 22, 2004
    3
    0
    For an assignment, I have to analyze the following circuit:

    http://www.geocities.com/spc_point_man/homework.txt

    (Click here if the above link does not work)

    However, I've been sick the last few classes, and am falling behind. Is there anyone here who can please explain how the current flows through the circuit so I can answer some problems relating to it?

    Ex: 1) Determine the current through R3 when the optocoupler is activated.


    I am lost and really need help. Any help at all is greatly appreciated!

    Thank you in advance! :D
     
  2. Point_Man

    Thread Starter New Member

    Feb 22, 2004
    3
    0
    Nevermind - I got it all figured out. :D
     
  3. Battousai

    Senior Member

    Nov 14, 2003
    141
    44
    What is that U1 circuit element? :blink:
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    :huh: I have no idea, it looks like half a diode! :blink:

    Unless its a test point, but I've never seen one drawn like that.
     
  5. Point_Man

    Thread Starter New Member

    Feb 22, 2004
    3
    0
    It's called a Shockley Diode... but its not a diode :huh:
    It's more like two BJT's connected together with only two external connections available.
    In essence, this device acts like two cutoff transistors until the voltage across Anode to Cathode exceeds the breakdown voltage VBRF, at which point minority carrier current flowing through one device into the base of the other device turns it on. The second device now turns the first device on, establishing lots of current to keep both devices turned on.
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Ah, so its exactly like a BJT, but with an increased breakdown voltage. Strange device <_<
     
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