Rectifier with cap and zener

Discussion in 'Homework Help' started by scottfarcuz, Dec 9, 2012.

  1. scottfarcuz

    Thread Starter New Member

    Dec 9, 2012
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    Im lost as to how to calculate the Vripple (pk-pk) and Vaverage (Including Vripple) of the attached circuit.

    For Vsec I used
    75Vrms *sqrt(2) = 106Vpk then divided it by the turns ratio of 5 coming up with 21.21Vpk

    For the voltage at the top of the cap I just subtracted the 0.7V drop from the diode leaving me with 20.51Vpk

    Any help or links would be very appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    It seems you have misunderstood the question. The ripple voltage is at the top of C1. What you have found is the peak voltage of the transformer, and that is a good thing to do.

    There are 2 diodes in the path of each wave, so your .7 volts is a wrong belief.

    You need to find the amount of (mostly) dc on C1. Then calculate the current of the circuit in the DC section. Then calculate the p-p ripple voltage and describe that combined with the DC voltage on C1.
     
  3. scottfarcuz

    Thread Starter New Member

    Dec 9, 2012
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    I think I may have this problem solved, but would really appreciate anyones input.

    [​IMG]
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    I don't think anyone would want to help by looking at random equations on a piece of paper.

    Show your work in step form with appropriate comments.
     
  5. scottfarcuz

    Thread Starter New Member

    Dec 9, 2012
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  6. #12

    Expert

    Nov 30, 2010
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    Your third equation is wrong. The 200 ohm resistor doesn't go to ground. It goes to a 6 volt zener so the voltage is 19.8 minus 6.
     
    scottfarcuz likes this.
  7. scottfarcuz

    Thread Starter New Member

    Dec 9, 2012
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    Thank you. Not sure how I missed that, but it changed almost every eqatiion below it.

    [​IMG]
     
  8. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    You've got wrong units on Vripple2; they should be mV, not mA.

    Also, the voltage Vc1 can't be anywhere near 6 volts. It should be more like 19 or so volts.

    The current in the transformer secondary consists of very narrow, large amplitude pulses. These large pulses cause a larger voltage drop across the diodes than .7 volts each. This will cause the peak voltage across the capacitor to be somewhat less than it would otherwise be.
     
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