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Can I connect GNDs?

Discussion in 'General Electronics Discussion' started by holex, Aug 19, 2014.

  1. holex

    holex

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    Jun 2, 2014
    Hi, I have a transformer and two circuits will connect to this transformer and I want to make the GND common. Can I connect GND-1 and GND-2 or I make a short circuit by doing this?
     

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  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You could do that. You would just be connecting the two bottom halves of the bridge rectifiers in parallel.

    Connecting diodes in parallel isn't a good idea unless they are closely matched and held at the same temperature. That's because one of them will have a slightly lower forward voltage than the other, and it will take more of the current, which will make it get warmer, and its forward voltage will drop, and so on, until it's carrying most or all of the current.

    I don't know why there are two separate bridge rectifiers on the same transformer secondary, driving separate DC circuits. I would use a bridge rectifier rated at twice the current and supply both circuits from it, unless there's a genuine reason why you can't.
     
  3. holex

    holex

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    0
    Jun 2, 2014
    One of the cicruits is only a power resistor, so I don't need capacitor after the bridge rectifier. The other circuit is a microcontroller based circuit with a DC-DC converter and a MOSFET to turn on/off the power resistor.

    If I would use only one rectifier the resistor would drain the energy of the capacitor very fast so the microcontroller reset. Thats why I need two circuits. But the GND must be common because of the MOSFET.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    How about using a single bridge rectifier feeding the resistor directly, then a series diode to the smoothing capacitor and the rest of the circuit. The series diode will prevent the resistor current from discharging the smoothing capacitor. There would only be one 0V rail.
     
  5. holex

    holex

    21
    0
    Jun 2, 2014
    Oh, thank you, it's a good idea! :)
     
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