Simulate LED in LTSpice

Discussion in 'Electronic Design' started by Dr Mitch, Aug 8, 2007.

  1. Dr Mitch

    Dr Mitch Guest

    How can I tell if an LED is on or off in Spice model? Currently, I'm
    looking at the current and voltage drop, (~20mA and ~1.7V
    respectively) but when I do this design with an actual circuit, I get
    bupkis.
    Dr Mitch, Aug 8, 2007
    #1
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  2. "Dr Mitch" <> schrieb im Newsbeitrag
    news:...
    > How can I tell if an LED is on or off in Spice model? Currently, I'm
    > looking at the current and voltage drop, (~20mA and ~1.7V
    > respectively) but when I do this design with an actual circuit, I get
    > bupkis.
    >


    Hello,

    You don't tell SPICE when a diode is on or off, you only specify model
    parameters.

    Example.for a model specification of a LED with 20mA, 1.7V.

    ..model LED1 D(Is=1e-19 N=1.6 Rs=2.5 Eg=2.1)

    Replace the value D of your diode in the schematic with LED1 and
    place the model specifications on your schematic as a SPICE-directive.

    I recommend to read some text about the basics of SPICE.

    Best regards,
    Helmut
    Helmut Sennewald, Aug 8, 2007
    #2
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  3. Dr Mitch

    Martin Guest

    On Aug 8, 10:01 am, Dr Mitch <> wrote:
    > How can I tell if an LED is on or off in Spice model? Currently, I'm
    > looking at the current and voltage drop, (~20mA and ~1.7V
    > respectively) but when I do this design with an actual circuit, I get
    > bupkis.


    Most likely you have miswired your actual circuit (LED wrong way
    around perhaps)

    Also, LEDs are very long lasting when operated within their allowable
    parameters, but if you miswire and subject the LED to excessive
    current or reverse voltage, you can destroy it in much less than a
    second. If you did that previously, it will most likely look like an
    open (infintitely high resistance) to the rest of the circuit now.
    Martin, Aug 8, 2007
    #3
  4. "Helmut Sennewald" <> schrieb im Newsbeitrag
    news:f9cp1t$7c2$02$-online.com...
    > "Dr Mitch" <> schrieb im Newsbeitrag
    > news:...
    >> How can I tell if an LED is on or off in Spice model? Currently, I'm
    >> looking at the current and voltage drop, (~20mA and ~1.7V
    >> respectively) but when I do this design with an actual circuit, I get
    >> bupkis.
    >>

    >
    > Hello,
    >
    > You don't tell SPICE when a diode is on or off, you only specify model
    > parameters.


    Hello again,

    Maybe I haven't correctly understood all questions when I answered first.

    Just probe the current flowing through the LED in LTspice to see
    whether it's "on" or "off". If a few milli-Amperes will be shown,
    the LED will light in a real circuit.

    Best regards,
    Helmut

    >
    > Example.for a model specification of a LED with 20mA, 1.7V.
    >
    > .model LED1 D(Is=1e-19 N=1.6 Rs=2.5 Eg=2.1)
    >
    > Replace the value D of your diode in the schematic with LED1 and
    > place the model specifications on your schematic as a SPICE-directive.
    >
    > I recommend to read some text about the basics of SPICE.
    >
    > Best regards,
    > Helmut
    >
    >
    Helmut Sennewald, Aug 8, 2007
    #4
  5. Dr Mitch

    D from BC Guest

    On Wed, 08 Aug 2007 07:01:27 -0700, Dr Mitch <>
    wrote:

    >How can I tell if an LED is on or off in Spice model? Currently, I'm
    >looking at the current and voltage drop, (~20mA and ~1.7V
    >respectively) but when I do this design with an actual circuit, I get
    >bupkis.


    Nahhh..It can't be...I hope you don't expect to see the LED symbol to
    actually light up?


    D from BC
    D from BC, Aug 8, 2007
    #5
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