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Thread: Ideal Diodes Question

  1. #1 Ideal Diodes Question 
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    For my university assignment one of the questions is about ideal diodes and I have NO idea how to do it!
    Unfortunately I also have no idea how to draw a circuit on this forum to show you what the question looks like.
    But if anyone could explain to me, in more simple terms than my crazy lecturer, how to find unknown currents and voltages in a simple ideal diode circuit, it'd be so great!
    Thanks in advance to anyone who can help me.


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  3. #2  
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    I'm afraid we will need more information. If you want to post a drawing on this site, you will have to upload the image to an image hosting site, like Photobucket, then post a link here to the uploaded image.
    By "ideal diode" do you mean one that has zero resistance in the forward direction and infinite resistance in reverse?


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  4. #3  
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    Quote Originally Posted by TheDoofus View Post
    For my university assignment one of the questions is about ideal diodes and I have NO idea how to do it!
    Unfortunately I also have no idea how to draw a circuit on this forum to show you what the question looks like.
    But if anyone could explain to me, in more simple terms than my crazy lecturer, how to find unknown currents and voltages in a simple ideal diode circuit, it'd be so great!
    Thanks in advance to anyone who can help me.
    If your definition of "ideal" is as Harold14370 asks, then the diode either appears as a short circuit (wire) or open circuit. If you can't figure out by inspection which of these two possible states the diode is in, sometimes a method based on reductio ad absurdum will help. Simply assume that a diode is in a particular state, then see if that assumption leads to a contradiction (e.g., the current flows the wrong way). If so, then you know that the assumption is wrong.
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  5. #4  
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    Conventional current flows in the direction the diode symbol points, and from + to -. If the diode is pointing backward, no current flows and the entire voltage appears across the diode; if it's pointing forward, current flows and no voltage appears across it.

    If it's an ideal diode, anyway. Real diodes leak a little bit in the reverse direction, and will "break down" and be destroyed if too strong a reverse voltage is applied across them.

    A real diode will exhibit 0.7 (pure silicon diode, like a 1N400x) or 0.3 (germanium diode, like used in old-fashioned AM "crystal radios") or a very low forward bias voltage like 0.1V or below (high tech super-diodes, given various trade names. For reference here is a catalog page: http://www.diodes.com/catalog/fast_s..._rectifiers_8/. The rest of the voltage from the source will appear across the rest of the components.

    It is therefore necessary (kids playing with experimenter kits please note) to put enough resistance in the circuit to prevent the current from burning the diode. Unlike a resistor it won't burn or make a smell, it just stops working. The amount of heat that destroys an LED or a germanium diode is so small you won't even notice it. So remember to always put enough resistance in the circuit to keep it from burning.
    Last edited by Schneibster; March 16th, 2014 at 04:13 PM.
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  6. #5  
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    Quote Originally Posted by TheDoofus View Post
    For my university assignment one of the questions is about ideal diodes and I have NO idea how to do it!
    Unfortunately I also have no idea how to draw a circuit on this forum to show you what the question looks like.
    But if anyone could explain to me, in more simple terms than my crazy lecturer, how to find unknown currents and voltages in a simple ideal diode circuit, it'd be so great!
    Thanks in advance to anyone who can help me.
    I presume that you have been taught the underlined part of the question.
    Substituting the characteristics of an ideal diode for a real diode gives you the answer. All other circuit elements remain unchanged. Simple really, quit worrying.
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  7. #6  
    KJW
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    Maybe "ideal diode" refers to a diode that satisfies the Shockley diode equation.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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