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Why does this rectifier have a large AC output voltage?

  1. Jun 30, 2006 #1
    I made a (bridge) rectifier for a simple circuit that would make several LEDs light up. When it was finished, I used a multimeter to measure the voltages between several points and got the readings you can see in http://users.pandora.be/k-a-d/rectifier.jpg". Why is there still an AC voltage between the two points that were supposed to be DC-only? And why is it almost twice the original transformer voltage? The resistor code is pretty blurry in the image; it's 2.2k if it helps.

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    Last edited by a moderator: Apr 22, 2017
  2. jcsd
  3. Jun 30, 2006 #2


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    How are you getting that 20V AC number? I'm guessing it's with a multi-meter of some sort. A cheap way to make AC voltage measurements is to use half a bridge rectifier, measure peak voltage, and multiply by 2.

    You could test this by measuring the AC voltage of a battery using the same tool.

    P.S. You might want to stick a capacitor in there to clean up the power supply. Otherwise it will be noisy.
    Last edited: Jun 30, 2006
  4. Jun 30, 2006 #3
    Indeed, the reading comes from a multimeter. I simply switched between "V DC" and "V AC".
  5. Jun 30, 2006 #4


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    Take a look at http://www.allaboutcircuits.com/vol_3/chpt_3/4.html" [Broken] to see where you're getting the AC.

    Last edited by a moderator: May 2, 2017
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