Negative and Positive Bridge rectifier

Discussion in 'The Projects Forum' started by JamesNichols, Oct 8, 2011.

  1. JamesNichols

    Thread Starter New Member

    Oct 8, 2011
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    I'm new in electronics and I'm learning to work with AC and DC.

    I want to build a bridge rectifier and be able to select the output between negative AC part or positive. I'm posting a picture to explain it better:

    When the push switch is pushed the output is positive
    When it's not pushed it's negative.

    I've no idea how to build the circuit and the diodes I need to use.

    The only way I've thought is the one you can see in the second file attachment. Is correct?
     
    Last edited: Oct 8, 2011
  2. Wendy

    Moderator

    Mar 24, 2008
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    You are over complicating this concept. Where you pick ground to be is what defines + or -. Put a switch to move ground on the DC side and there you go.
     
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  3. JamesNichols

    Thread Starter New Member

    Oct 8, 2011
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    So you mean that don't touch the AC side and only switch the ground of the dc side. I understand that the only thing I need to do is to change the DC connections from the bridge. If don't touch the original configuration I will get positive, and If I want negative simply I change the connections from + and - to - and +. Right?
     
  4. Georacer

    Moderator

    Nov 25, 2009
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    Yup, that's what he said. If you want to do it automatically, you might find double rotary switches that will suit you. Be careful not to short-circuit the + and - terminal.
     
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    In your first schematic you're showing 240VAC coming into a box, and rippled DC coming out; showing a power switch and a DPDT switch.

    I most certainly hope that you plan on having a transformer in there somewhere. Working with mains power is quite dangerous. You need to isolate your circuit from the mains power by using a transformer.
     
  6. JamesNichols

    Thread Starter New Member

    Oct 8, 2011
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    Thank you very much to all

    And how is it a half wave bridge rectifier? I'm only interested to get the negative part of the wave in the output
     
    Last edited: Oct 8, 2011
  7. MrChips

    Moderator

    Oct 2, 2009
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    In reality, there is little difference between positive and negative. It is just a matter of where you connect your ground.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    And, as Wookie suggested, the transformer is not optional.
     
  9. Adjuster

    Well-Known Member

    Dec 26, 2010
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    A bridge rectifier is a full wave rectifier. If you are looking to obtain only the negative-going or positive-going half-cycles from the input, then you need to use something different.
     
  10. JamesNichols

    Thread Starter New Member

    Oct 8, 2011
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    I'm interested in getting this:
    http://www.eecs.tufts.edu/~dsculley/tutorial/diodes/halfWaveOut.jpg

    Half wave rectification. Well, when I connect the AC input I only want to get the negative pulses without the positive ones. In the last question I asked to get the full wave rectification and connect the wires to get the negative part. Now I want to know how to get only the negative part withouth the positive. Like I show in the picture. The voltage it doesn't matter since in the picture you can read 5 Volts, but I'm not interested in any quantity by now.
     
  11. dataman19

    Member

    Dec 26, 2009
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    So you want a half wave rectifier... Not a Plus (+) and Minus (-) bridge rectifier output...
    Simple...
    Use a center tapped transformer..
    On one leg put a Diode Rectifier oriented to give a positive voltage.
    On the other put a Diode Rectifier oriented to give a negative voltage.
    Use the transformer center tap of the secondary winding for the common (ground?).
    ..
    This will give you what you want (a positive and negative half wave rectifier). Using a bridge rectifier with a center tapped transformer secondary will only give you a positive and negative voltage. You are looking for half wave rectifications - which calls for a single diode, not a bridge.
    Dave
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Have a look at the attached. It's a half-wave rectifier using a single diode connected to the secondary side of a low-voltage transformer.
     
  13. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Surely you do not mean something this simple?

    Edit: Too slow, as usual.
     
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