Can't ground a bridge rectifier?

Discussion in 'Homework Help' started by GregJ7, Jun 7, 2014.

  1. GregJ7

    Thread Starter New Member

    Jun 7, 2014
    18
    2
    Self-assigned homework: I thought I would try some different capacitance values in a simple bridge rectifier circuit. For me, step 1 is to make a working bridge rectifier circuit before adding capacitors. I basically recreated one of the many online bridge rectifier schematics, but a time-dependent voltage graph of the output shows I have failed. I checked the wires and diode orientations a half dozen times. I am guessing that the problem is with my grounding, since that isn't displayed in the diagram I am copying. Multisim (trial) won't run circuits without a ground and there must be a good reason for it. What have I failed to grasp in my attached circuit diagram?

    A quick off-topic question unworthy of its own post: I understand why each of the forbidden topics in the ToS for this forum exists, except one. What is the background on posting questions about non-transformer power supplies?
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Its the ground reference for the scope thats the problem, what does the scope consider to be ground/measurement reference point.?
    I use LTSpice.
    E
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,798
    1,103
    Powering projects from the mains without an isolating transformer is potentially (pun intended) LETHAL !!
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    Instead of grounding the source, put the ground on the load output.
     
  5. GregJ7

    Thread Starter New Member

    Jun 7, 2014
    18
    2
    Moving the ground as suggested worked. Now, looking at the circuit, I can see that is the way it must be. However, what is the thing I need to learn about so that I would have known that? If it's just, "read about AC circuits," that's fine. I realize I need to do that. I have mostly been learning about components under DC power.

    I think I learned something new about transformers, too: it isn't always a bad thing when one burns out. :)

    Thanks all!
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    It's sort of a continuing process as you learn more about circuits. Remember that a circuit ground (common) is just a reference point from where all the other voltages are measured, there's nothing magical about it otherwise. You can place it at any node in the circuit but it's commonly done at the negative voltage for a positive supply rail.

    Bridge circuits can be a little tricky because you can't ground both their input and their output, it has to be one or the other. Typically you ground the output since that gives the normal reference point for the circuits (load) powered by the bridge output.
     
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