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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 this image. 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.

    Attached Files:

  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 this to see where you're getting the AC.

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