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Bridge Rectifier Circuit

  1. Feb 18, 2015 #1

    Zondrina

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    1. The problem statement, all variables and given/known data

    The output of the transformer is a sinusoidal AC signal with ##10.6V## RMS amplitude, and acts as an input to the bridge rectifier.

    Explain the operation of the following bridge rectifier circuit.

    Then sketch the output waveform ##V_L## assuming the ##0.7V## drop model for the silicon diodes.

    Screen Shot 2015-02-18 at 11.41.58 AM.png

    2. Relevant equations


    3. The attempt at a solution

    I want to make sure I understand the operation of this circuit correctly.

    The output of the the transformer acts as the input to the bridge rectifier circuit, call the input ##v_s##. The input will have a maximum amplitude given by ##V_p = (10.6 V)\sqrt{2} = 15 V##.

    During the positive half cycles of the input voltage, ##v_s## is positive, and current is conducted through ##D_1, D_L, R_L## and ##D_4##. The diodes ##D_2## and ##D_3## are reversed biased during this time. The output voltage ##V_L## will be lower than ##v_s## by two ##0.7V## diode drops and a ##1.5V## LED drop (I've been told to assume LEDs have a 1.5 V drop). So the maximum amplitude of ##V_L## would be ##12.1 V##.

    During the negative half cycles of the input voltage, ##v_s## is negative, so ##-v_s## is positive. Current will be conducted through ##D_2, D_L, R_L## and ##D_3##. The diodes ##D_1## and ##D_4## are reversed biased during this time. The output voltage ##V_L## will be lower than ##v_s## by two ##0.7V## diode drops and a ##1.5V## LED drop. So the maximum amplitude of ##V_L## would be ##12.1 V##.

    Does this sound okay? Thank you for your help in advance.
     
  2. jcsd
  3. Feb 18, 2015 #2

    Svein

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    Yes.
     
  4. Feb 19, 2015 #3

    Merlin3189

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    Your logic sounds fine except for the LED drop. It may be I am misreading your diagram, but VL seems to include the LED and the RL because the arrows point to the top and bottom conductors and the + and - signs are placed at those points, not at the top and bottom of RL.
    Either way, you have the correct understanding.
     
  5. Feb 19, 2015 #4

    Zondrina

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    So the max amplitude of ##V_L## should actually be lower by just the two diode drops, i.e 13.6 V.
     
    Last edited: Feb 19, 2015
  6. Feb 20, 2015 #5

    Merlin3189

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    That's what I thought.
    Since you correctly show how you got the result, if it's clear where you are measuring VL then you can't be wrong.
     
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