### Author Topic: How do I model a custom LED with TINA?  (Read 1870 times)

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#### DiTBho

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##### How do I model a custom LED with TINA?
« on: April 28, 2021, 09:50:26 am »
I am using DesignSoft TINA v8 to simulate a couple of circuits. Everything is fine, except its library only supports a few models for the LED component and none of these models looks fine because with 5V I need a low Current-Limiting Resistor  to turn the LED on.

LEDs are constant current devices with a predictable forward voltage drop based on the amount of current flowing through them.  These I-V current-voltage curves are available in the datasheet for specific LEDs. The CQX35 shows it nicely, so if you want to drive one of these LEDs with a forward voltage of 1.5V off a 5V power supply, you need something in that circuit to absorb the extra (5-1.5)V. The easiest way to absorb extra power in a circuit is to use a simple resistor.  You need to know the intended LED to define the resistor using V=IR, but the math is very straightforward once you determine your system parameters.  If you want to drive that 1.5V LED at 5mA, you need to absorb (5-1.5)V at 5mA in a resistor.  (5-1.5)V = 5mA * R.  Solving for R gives a resistor value of 700 ohm.

700 ohm looks ok, but it's definitively too small far from what I'd like to achieve with my simulations, since I would like to have 1K ohm, so I would like to model a different LED.

Unfortunately I can edit the properties of the component, but I am bit lost with too many parameters

Code: [Select]
#       Name    Parameter                    Units      Default Example  Area1       IS      Saturation current             A         1e-14   1e-14    *2       RS      Ohmic resistance               Ω         0       10       *3       N       Emission coefficient           -         1       1.04       TT      Transit-time                   s         0       0.1ns5       CJO     Zero-bias junction capacitance F         0       2pF      *6       VJ      Junction potential             V         1       0.67       M       Grading coefficient            -         0.5     0.58       EG      Activation energy              eV        1.11    1.11 Si                                                                 0.69 Sbd                                                                 0.67 Ge9       XTI     Saturation-current temperature exponent  3.0     3.0 jn                                                                 2.0 Sbd10      KF      Flicker noise coefficient      -         011      AF      Flicker noise exponent         -         112      FC      Coeff. for for.-bias dep. cap. formula   0.513      BV      Reverse breakdown voltage      V         ∞       40.014      IBV     Current at breakdown voltage   A         1.0e-315      TNOM    Parameter measurement temp.    °C

I was expecting to find just two parameters: "If" and "Vf". There many more.

I haven't yet understood how to import a PSPICE model into TINA, I am not sure I can do it with version 8, I haven't enough budget to upgrade to v12.

Anyone has already tried to create a custom LED model for TINA? If so, let me know
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