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Homework Help: Zero Point Switching with transformer

  1. Jul 17, 2012 #1


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    So with my final test tomorrow I thought to sneak in another question...

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

    The following circuit applies switch at the load RL via Zero Point Switching. The ratio of the coil windings at the transformer is N1:N2 = 4:1. The introductory voltage is a sinusoidal type and its RMS value is 100 volts RMS at a frequency of f=40hz. The switch circuit activates switch S the following way:

    Every full uneven cycle (from 0 degrees to 360 degrees) the switch is used as a shortcircuit.
    Every full even cycle (from 0 degrees to 360 degrees) the switch is used as a disconnection.

    http://img42.imageshack.us/img42/2498/zpszps.jpg [Broken]

    1) Based on the data above, draw the voltage on the load at 4 cycles of Vin. In your drawing mark the max voltages positive and negative as well as significant times.

    2) Calculate
    A) VRL(RMS), IRL (RMS)
    B) VRL (AVG), IRL (AVG)
    C) PRL (RMS)
    D) Vptp

    3. The attempt at a solution

    http://img849.imageshack.us/img849/7163/wavewavy.jpg [Broken]

    http://img404.imageshack.us/img404/1545/theanswertothequestion.jpg [Broken]
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jul 17, 2012 #2

    I like Serena

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    Hey Fp.

    1) You graph looks good. :S

    2a) Your formula for Vrl(rms) does not look right.
    There should be a square root in it...

    2b) Good.

    2c) Same problem
    Actually here you should take the average of the powers in each cycle.

    2d) Vptp is the peak-to-peak voltage.
    What is the highest voltage you have (look at your graph)?
    And what is the lowest voltage you have?
  4. Jul 18, 2012 #3


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    30 mins before I need to take the test :)

    Vptp is 25 volts

    Are you sure?

    Hmm...we are told that if we're asked for the power with an AC current, we should always take it as RMS power.
  5. Jul 18, 2012 #4

    I like Serena

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    Then I'm probably too late. ;)
    Good luck!

    But peak-to-peak is -25 to +25, which is 50 V.

    It should be 25/√2 volt.

    Actually, RMS power and average power are the same.
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