Specifyng Diode Forward Voltage in PSpice Schematics

Discussion in 'Digital Circuit Design' started by akhuller, Jul 28, 2016.

  1. akhuller

    Thread Starter New Member

    Jul 28, 2016
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    Hi! I'm new to using PSpice Schematics, and I was wondering how one can specify the forward voltage of a diode.

    The circuit is here below, with it continuing till the 10 th capacitor, C10. What diode model should I use, and how do I specify the forward voltage to be 1.4 V? I've uploaded my efforts for your reference as a .sch file.

    [​IMG]

    Thank you so much!
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Here's some detailed information from the LTspice manual. Depending on how elegant your modeling needs to be, you can either choose a stock diode, or model the IV curve manually. I don't think you'll find a "normal" diode with a 1.4 V forward drop though, but you can synthesize that with a couple of diodes in series.

    Eric
     
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  3. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    The diode model determines the forward voltage.
    Just select a diode with the required reverse voltage and forward current rating.
    What type of diode has a 1.4V forward drop?
    Just putting two silicon junction diodes in series will give about a 1.4V drop.
     
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  4. akhuller

    Thread Starter New Member

    Jul 28, 2016
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    Thank you so much!! I'm putting two 1n4002 Diodes to get 1.4V forward voltage, since I read that they are Silicon diodes, and have 0.7 V FV approximately. I hope that's correct.
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yep.
    And...if you want to experiment some, many LEDs have about a 1.4 Volt forward drop.
     
  6. akhuller

    Thread Starter New Member

    Jul 28, 2016
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    Awesome!! Thank you so much! I have one last question for me to be done with this circuit. I need to measure the current vs time across the last capacitor (100uF) in the picture.
    How do I do this?
    When I press simulate, I get a graph. I changed the X-axis variable to I(current across that capacitor) and for the Y--axis, I put user-defined 0s to 10000Ms. Is this correct?
    Thanks again.
     
  7. SLK001

    Well-Known Member

    Nov 29, 2011
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    You use a transient analysis to do time dependent simulations.

    Looks like you are trying to make a voltage multiplier for high voltages. A lot of high voltage diodes are two (or more) diodes in series, thus the 1.4V forward voltage. Your 1N4002 has a low breakdown voltage - you might want to use a 1N4007, which has a breakdown voltage of 1000V. You need to make sure your diodes can take the voltage. What ultimate voltage are you looking for?
     
  8. Bordodynov

    Active Member

    May 20, 2015
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    i=is*(exp(Vd/(25.8mV *n))-1) ==> standard is=1e-14 ==>
    n=(Vd/25.8mV)/ln(i/is) i=100mA=0.1 Vd=1.5 is=1e-14 ==> (1,5/25,8e-3)/ln(0,1/1e-14) = 1,942283013879 ==>
    .model d1_5V d is=1e-14 n=1.942283013879

    Draft317.png
     
    Last edited: Jul 29, 2016
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  9. akhuller

    Thread Starter New Member

    Jul 28, 2016
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    Thank you for your reply. The final voltage should be 1200V.
     
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