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I need help for phototransistor circuit

  1. Feb 14, 2015 #1
    I need help to calculate the resistance values for the attached circuit diagram. I have also attached the data sheets. Can you help me.

    Attached Files:

  2. jcsd
  3. Feb 14, 2015 #2


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    hi there yaasir
    welcome to PF :)

    for the IR LED (or any LED for that matter), choose a resistor that will limit the current (I) to a chosen value at an assumed Vf. And we have both of these.

    R = (V - Vf) / I

    R = the resistor
    V = The supply voltage
    Vf = the LED voltage drop
    I = the LED current

    Vf and I can be obtained from the datasheet you posted

    see how you go :)

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