Thevenin Equvialent circuits

Discussion in 'Homework Help' started by jayemtee91, Feb 20, 2013.

  1. jayemtee91

    Thread Starter New Member

    Feb 20, 2013
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    Hello,

    My professor gave me the following assignment and I am having trouble with parts c through e. I am unsure how to handle the dependent sources and the positioning in of some of the independent voltage source in part d. I would like assistance in the steps needed to take to solve them, not the answer. Thank you for your help!
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Please post your attempt to solve them (or at least one of them) in order to give us a springboard for the discussion. Don't worry if what you post isn't correct, it just works better if we have a starting point.

    Keep in mind that there is nothing special about the analyses involved here. You can use mesh current, node voltage, superposition, or whatever ad-hoc method seems appropriate. But you do need to keep in mind that you can't "turn off" a dependent source.
     
  3. jayemtee91

    Thread Starter New Member

    Feb 20, 2013
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    Okay, so I posted the first steps that I have for each part, but I'm not even sure if I have the right approach to these :confused: What I tried to do is break the first piece off that had current flowing through it and try to find what the value the dependent sources needed. That's where I get kind of fuzzy because I know I need to solve for the open circuit voltage, then find the equivalent resistance, but I get lost in between there.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    One of the first things that will help you is to be more organized in your work. In your work for part (c), for instance, it's very hard to follow your thought processes because you've got work done off to the right and work done below and it's hard to tell how or if they relate.

    You also have a 1V source inserted between the outputs but it appears you don't include it in your analysis off to the right or immediately below but do include it in the stuff a bit further below. You need to make it clear what circuit goes along with each portion of your work.

    Then you have two nodes labeled 'A'. So when you have V_A in an equation, which node is it referring to.

    Then there is the really big one. You don't track your units. You throw units in here or there but they are just after thoughts. You need to consistently track and check your units throughout your work. If, at any point, the units don't work out you need to stop and find out why not. Most errors (not all) you make will mess up the units and if the units are wrong, you KNOW the answer is wrong.

    If you address these things your work will be much easier for everyone, including yourself and the grader, to follow.

    Despite all this, it appears you have everything correct up to this point. But what will you have when you solve the three equations? You'll know the currents when the load it a 1V source and you will know the open circuit voltage. Is that enough to find the Thevenin equivalent circuit? Yes, but it is not the easiest way. Instead, turn off the independent sources and then put in your 1V test source and find out how much current flows into the circuit and you can find the Thevenin resistance directly.

    you've got a 1V source across the output but it's unclear whether this i
     
  5. jayemtee91

    Thread Starter New Member

    Feb 20, 2013
    3
    0
    I attempted to get through the first one, part c, and this is what I got and my Vab for the thevenin/norton do not match up to the voltages across Vab in the original circuit. I tried to be a bit more clear with my work, but I would like to know where I went wrong. Thanks!
     
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