over coming an Overshoot

Discussion in 'The Projects Forum' started by simorq, Aug 1, 2013.

  1. simorq

    Thread Starter New Member

    Aug 1, 2013
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    Hello Every Body
    I have problem with my newly design circuit :
    it had a 50% overshoot .
    in multisim the simulator said there are some errors and asked if I want to resolve the problem , after solving the problem now there is a long risetime !:(
    and I don't know what to do and which result to relay on ?
    by the way the results in proteus 8 are as same as multisim before solving Problems ...

    any body can help ?
    any body has any Idea to overcome overshoots in analog circuits ?

    thanks a lot
     
  2. LvW

    Active Member

    Jun 13, 2013
    674
    100
    A high overshoot is an indication for a phase margin that is too small.
    However, in any case you should show us your circuit. Otherwise no real help is possible.

    EDIT: An overshoot of 50% corresponds with a phase margin of 25 deg. approximately.
     
    Last edited: Aug 2, 2013
  3. simorq

    Thread Starter New Member

    Aug 1, 2013
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    0

    Thanks a lot .

    Here is my circuit ...

    actually I should say that my circuit is more than this but this part is causing the Line Voltage to Overshoot.
    and by the way the Overshoot takes place on the Line which we can take the 5 ohms resistor .
    and one other thing to say :
    the 5k ohms resistor should be a 15 ohms resistor .
    thanks again ,...

    http://www.4shared.com/office/KBKXZoI0/PPC.html
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't see a 5 ohm resistor.

    LTspice only shows 1.8% preshoot at the drain when the gate voltage goes high.
    Perhaps you should show what is in the circuitry that you omitted.
     
    Last edited: Aug 2, 2013
  5. simorq

    Thread Starter New Member

    Aug 1, 2013
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    Dear Ron ....
    There is a five ohm resistor in the middle of the page !
    and I should say that,
    this part of circuit is causing the line Voltage to Overshoot!
    the other parts may confuse you and the others ...

    thanks for your response !
    actually I'm very in need of a solution ...
    May God Help me and the others ...
     
  6. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    I can not get a view of the 5 ohm resistor. I can not expand the right half of the drawing. I can not agree that the rest of the drawing would confuse the people here. (That is almost an insult.)

    Please post your circuit on this site so we can see it. .PNG is a good format.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Simorq has changed what he posted on the sharing site. Now there is a complete schematic, but I don't see any values on it.
    I tried the download, but my antivirus program blocked it.

    As #12 said, post it as a .png file.
    Just click on Go Advanced, then scroll down to Manage Attachments, click on it, and follow the instructions.
     
  8. simorq

    Thread Starter New Member

    Aug 1, 2013
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    Dear Friends....
    Hello again ...
    the format changed to .PNG
    and the Circuit is complete with the Values on it !

    The Link :
    http://upload7.ir/images/55812502049355387816.png

    and the file is attached to the "reply" too .

    /thanks for your attentions ...
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Your first schematic had a MOSFET. Now you have a BJT. It has no base current limiting resistor.
    Does this still have the overshoot problem? Where does it occur?
    If you are trying to reduce the power dissipation of the 7805, that is a very inefficient way to do it.
     
  10. simorq

    Thread Starter New Member

    Aug 1, 2013
    5
    0

    after I tried the BJT I found it's better than the MOSFET .
    I'm dealing with a 24v Voltage which should be switched by only a 5v Voltage or even less (Coming out from an AVR or ARM or ...)

    see, the overshoot occurs at the Start of the circuit. if you simulate it with Proteus you'll find ...

    again I'm thankful, you & the others are helping me ...
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I don'tuse Proteus. I use LTspice.
    Can you post the Proteus waveform?

    What is the maximum current load on your voltage regulator?
     
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