LTSpice LED

Discussion in 'General Electronics Chat' started by duxbuz, Dec 5, 2014.

  1. duxbuz

    Thread Starter Member

    Feb 23, 2014
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    Hi

    I am trying to add an LED model with these specs:
    Forward voltage(V): 2.0-2.2Current(mA): 20


    When looking at diode list in LTSpiceIV there is only Breakdown voltage but no value for Forward Voltage. (or is breakdown voltage the forward voltage?)

    I wondered if anyone knew if there a way to get some LED models with the typical LED values imported into LTSpice?

    What I mean by typical is this:
    http://www.electronics-tutorials.ws/diode/diode_8.html
    see section on colours

    Thanks.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Here is something that might work for you. I took a typical LED model (originally supplied by Linear) and modified the Emission Coefficient N. By stepping this using a parameter substitution, I generate the following family of V(f) curves:

    92.gif

    Here is the .asc file:
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    This short LTS mod file has some 'standard' LED models. Copy and Paste into your 'standard.dio' file
    Change the .txt extension back to .mod after downloading.
    Note the 'N' value, the LED's forward voltage is ~50% of the N value, so tweak the 'N' value to get a customised Vfwd.

    E
     
    • led.txt
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  4. duxbuz

    Thread Starter Member

    Feb 23, 2014
    133
    0
    Thanks Eric that's really helpful.

    Am not sure if I am utilising the file you sent correctly.

    I backed up the standard.dio, then I changed the standard.dio to a text file, copied the contents of the file you gave me. All sections with the asterisk are comments I take it.

    I then renamed the file as .dio.

    If I need to tweak the values I just change the N value, and maybe edit the comment where it states Vf for future reference.
     
  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    If you have added the models correctly, they should appear in the drop down list box when right clicking on the existing LED symbol on your circuit and choosing 'Pick New Diode'.
    Comments are after an asterisk.

    You may have noticed in the drop down list, the diodes, LED's, zeners, IMO are not in an easily accessible order.
    I have found it helpful to Edit the standard.xxx files by relocating the commonly used components near the top of the file listing.
    As always, make a backup copy before editing.;)
    Eric
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I always find the component I want is not one of my commonly used ones :). Just left-click on the title of any column in the drop-down list and you can instantly sort the data.
     
  7. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi alec,
    I tried that and its now reshuffled my preferred group sequence, drat.
    My commonly used ones were grouped at the top, not anymore?!:(
    Eric
     
  8. eetech00

    Active Member

    Jun 8, 2013
    650
    112
    Hi Duxbuz,

    Do not edit the standard.dio file. That file get updated occasionally and you could lose any modifications you've make to that file.

    Instead, Here's what you should do:
    1. Take the led.txt file Eric gave you and place it in the same folder as your schematic .asc file.
    2. In LTspice, open the schematic, then press F2, select the "LED" symbol, then place it on the schematic.
    3. Click anywhere on the schematic, press "t", select "SPICE directive". then type ".inc led.txt", without the quotes. Click OK, then place the text on the schematic.
    4. Right-Clk on the default LED value "D", then change the value to the name of the model you want to use in the led.txt file. For example, change "D" to "DLED3" (name from the led.txt file)
    5. That's it.

    eT
     
  9. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi eT,
    I have never lost a modified file entry during an LTS update.
    However your method should ensure that the asc files we post should be compatible with other users, providing the poster includes the led.text file.
    Eric
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Hi Eric.
    Sorry to hear you got shuffled. But, as you remind folk, you did have a backup file didn't you? ;).
    Like you, I've never had a problem with LTS updates over-writing third party model additions. LT has the good grace to build a discrepancy table as an initial stage in the update process and then takes care to avoid trampling on user-added models. Hopefully they'll continue with that considerate practice. (If you're listening, Helmut, thank you!).
     
  11. eetech00

    Active Member

    Jun 8, 2013
    650
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    hi Eric

    There is always a first time....;)

    At any rate, this subject always comes up a bazillion times on the Yahoo group.
    The recommendation from the LTspice group has been "don't modify files in the install folder hierarchy". But I'm sure users do it anyway...


    eT
     
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