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AC to DC

  1. Nov 21, 2011 #1
    Hi,
    I have to detect overvoltage on each of the 3 phases (individually) of a 3 phase AC signal. The 3 phase AC source has a neutral that is grounded and I have to use the same ground plane for my PCB.
    I was thinking of using a full bridge rectifier for each of the 3 phase but the problem is what do I reference the output to? Is there any other way or would I need a transformer?
    I have attached the schematic as an attachment.

    Thanks
     

    Attached Files:

  2. jcsd
  3. Nov 21, 2011 #2

    berkeman

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    Staff: Mentor

    The bridge seems like a reasonable approach. If you use a single diode and Neutral ground your PCB, you can see the peak of every other half waveform. Is that sufficient?

    BTW, using Neutral for your PCB ground means that your circuit is not going to be SELV. Is the whole circuit isolated from other SELV circuitry nearby?
     
  4. Nov 21, 2011 #3
    No, the need is full wave rectification as overvtg can occur on any of the cycle.

    For the second section, the neutral of the 3 phase is tied to the chassis/system gnd and pcb gnd is also tied to the same so , i guess the answer would be no.
    So, what are other options available to me?
     
  5. Nov 21, 2011 #4

    berkeman

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    Staff: Mentor

    What is your power source for your circuitry? You can still do the full-wave rectification, attenuate the voltage, and measure it differentially. You will need split power supplies (like +/-12V) to power the measuring circuitry.
     
  6. Nov 21, 2011 #5
    115vac 10amps. 3 phase. Can you send me the circuit. I am not sure of what to use as reference after full wave rectification.
     
  7. Nov 22, 2011 #6

    berkeman

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    Staff: Mentor

    What is the context of your question? Why are you being asked to design this circuit if you do not know how to do it?
     
  8. Nov 22, 2011 #7
    Hi,
    Oh! I guess there was a misunderstanding. What I meant was how do i attenuate. I beleive I have figured that out. Thanks for the idea though.

    Thanks,
    - Hemant
     
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