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Direction of DC and AC current with diodes.

Discussion in 'General Electronics Discussion' started by IntruderCell87, May 9, 2011.

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  1. IntruderCell87

    IntruderCell87

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    May 9, 2011
    Hey guys I'm having a hard time grasping the concept of how diodes change the direction of current in DC and AC circuits. Im also a little confused about how AC current flows. As an audio student, I understand AC current fluctuates but in circuits I dont understand how it flows. Is it positive and negative current going in the same direction or is it constantly going all over the place back and forth? I am stressed with the idea further and maybe I misread here and there but do diodes work with DC current? If so if DC current flows in only one direction already do diodes reverse the direction sending the positive or negative current back to its terminal?

    If AC current flows through a diode what happens when the AC current is reversed? Where does it go besides other components and back into the AC terminal (Wall/outlet). I just have this mind boggling idea of batteries exploding and houses blowing up!

    I have pictures to further elaborate my questions.

    [​IMG]

    [​IMG]

    Sorry for the poor quality graphics. The yellow is the load. I shoulded added a load in the AC diagram but I understand DC or AC cant have a complete/live circuit without one just wanted to demonstrate where Im at so far with understanding direction of currents and direction of currents with diodes.
     

    Attached Files:

  2. Laplace

    Laplace

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    Apr 4, 2010
    When drawing a diode never forget to also draw the diode band which is used to indicate the forward direction of current. Just think of the diode as a switch. When current wants to flow in the forward direction, then the switch is closed. When current wants to flow in the reverse direction, then the switch is open.

    Think of an AC power source as two batteries connected to a DPDT switch. When the switch is in one position it connects one battery to the X & Y terminals. When the switch is in the other position it connects the other battery to the X & Y terminals. The batteries are flipped in polarity so that every time you throw the switch the X & Y polarity changes. Flip that switch back and forth 60 times per second; what you have is 60 Hz AC power at the X & Y terminals.

    So to analyze AC operation, flip the battery switch to one side and analyze which direction the current wants to flow in the circuit from the battery. Determine if the current wants to flow in the reverse direction through any diode switch. If it does, then open the diode switch. Then flip the battery switch to the other side and analyze which direction the current wants to flow in the circuit from the other battery. Determine if the current wants to flow in the reverse direction through any diode switch. If it does, then open the diode switch.

    And that is how you conceptually analyze the way current flows in a diode circuit.
     
  3. IntruderCell87

    IntruderCell87

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    May 9, 2011
    Thanks for the concept. It makes more sense as a switch than "valve".
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    no the diode is still a valve, it only lets current flow in one direction :)

    Dave
     
  5. Ratch

    Ratch

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    Mar 10, 2013
    IntruderCelll87,
    This member has not intruded for almost 7 years, so he has probably passed on to the great beyond. However, others can possibly benefit from this answer. No one explained to him that a diode passes charge (not current flow) like a one-way valve. When the voltage is in the forward direction, the charge flows. When the voltage is reversed, the current does not exist It is as simple as that.

    Diodes by themselves don't change the path of current in a bridge circuit, the change of voltage polarity does.
    Ratch
     
  6. Minder

    Minder

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    Apr 24, 2015
    Diode.
    Hence the check valve symbol!
    (shown backwards, courtesy Ben. Franklin)!
    M.
     
    Last edited: Oct 28, 2020
  7. Martaine2005

    Martaine2005

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    May 12, 2015
    Oh no @davenn ,
    You know "current flow" is incorrect.
    It literally means "charge flow flow".
    But it was in 2011 so all is forgiven

    Martin
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Please do not (again) resurrect this nasty discussion on current and charge flow :(
     
    Martaine2005 likes this.
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