Orcad PSpice Diode

Discussion in 'General Electronics Chat' started by BBB, Feb 3, 2010.

  1. BBB

    Thread Starter New Member

    Jan 13, 2010
    Hey everyone, I wonder if someone may be able to help me with this problem.

    I am trying to compare in theory the effect of increasing a diodes active surface area. I wanted to set up a model in orcad and then iterate it so I get a graph showing perhaps power in vs power out parametrised by surface area. Does anyone know if this is possible? and I cannot seem to find how to alter the active area of diodes when using the capture schematic editor.

    Many thanks.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I know how to do this in LTSpice. I suggest you do some reading on the Diode Model in Spice. It has settable area and perimeter parameters. These parameters can be set at the netlist level using a text editor. I suspect that PSpice's graphic user interface is getting in your way...
  3. Darren Holdstock

    Active Member

    Feb 10, 2009
    Editing models in OrCAD PSPICE isn't intuitive, you may need to jab at the F1 key a few times. There's a separate little program that does the editing (OrCAD is a bit of a Frankenstein's monster when it comes to build structure), and the last time I did this - which was a while ago, so my recollection is fuzzy - there was an error window that popped up that required ignoring. I do recall that once I worked out the magic incantation to enable the model editor, I felt the need to write the procedure down and refer to this just about every time thereafter.
  4. BBB

    Thread Starter New Member

    Jan 13, 2010
    thanks for the help guys, I have found the model editor and I am just gonna start by editing the 1N4148 diode model:

    .model D1N4148 D(Is=2.682n N=1.836 Rs=.5664 Ikf=44.17m Xti=3 Eg=1.11 Cjo=4p
    + M=.3333 Vj=.5 Fc=.5 Isr=1.565n Nr=2 Bv=100 Ibv=100u Tt=11.54n)

    This is the info I can find on the model. How can I find out what each abbreviation refers to?

    Thanks again.
  5. BBB

    Thread Starter New Member

    Jan 13, 2010
    Okay, so I have found this:

    Is = Saturation current
    N = Emission coefficient
    Rs = Parsitic resistance
    Ikf = Flicker noise coefficient
    Xti = IS temperature exponent
    Eg = Activation energy
    Cjo = Zero-bias junction capacitance
    M = Junction grading coefficient
    Vj = Junction potential
    Fc = Forward bias depletion capacitance coefficient
    Isr = ??
    Nr = ??
    Bv = Reverse breakdown voltage
    Ibv = Reverse breakdown current
    Tt = Transit time

    not sure what Isr and Nr are, something to do with Is and N I'm guessing! So how do I adjust the active surface area?