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led properties 10.1 VS 11.0

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Hi,

 

In Multisim 10.1 I can change the LED Forward Voltage under properties>value. In 11.0 this option is gone.

I am using 5W  UV Leds in a real life situation. The "old school" LEDs typicaly have a 1 or 2V  Vf @ about 20ma , but the new power LEDs have a much higher Vf and typical 650 to 750 ma current.  The circuit I am using has 6.8 Ohm current liniters and a 12V supply. (4 Leds)

 

Is there a file I can modify to change the Vf so multisim 11.0 works liek 10.1 in this LED simulation? Better yet is ther a way to import a 5W led to the database?

 

Thanks,

 

Alan

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This message is for any NI reps out there. I am more of a LabVIEW guy, just started playing with Multisim, so forgive me if my questions here are a bit naive. If there is no answer for my above question can you explain why NI took out a usefull feature between Multisim 10.1 and 11.0?

 

Thanks

 

Alan (CLAD)

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Hi Alan,

 

Sorry for taking so long to answer your question. It's not naive at all - it helps us understand better our motives as to why we took that function away. The reason is because it doesn't quite mimic the realistic physical behaviour of a normal diode if you set the Vf to a very high level. It's the current flowing through the diode that's making a difference to the functionality of a LED, not the Vf. However, there are ways to customize diodes to meet your needs i.e. set Vf to an arbitrary level. We've constructed a diode model for you. You can open the attached file and modify the model parameters. The weakness of this approach is that the LED won't bloom as it's supposed to. But if your purpose is just to play around with the Vf and see how the circuit behaves this should be enough.

 

 

Derek Z.
National Instruments
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Thanks Derek,

 

I will try this out later this afternoon. NI's model of a realistic LED is out dated. High Power LED's are all the rage. In fact incandescent light bulbs are being phased  out arcos the planet and in their place High Powered Diodes with a high forward voltage and high current and wattage are being installed. The LED model in Multisim 10.0 is much more realistic in the NEW real world. In fact in 10.0 I can simulate the high powered LED's of today and in 11.0.1 I can not.

 

Alan (CLAD)

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Hi Alan,

 

Ok, Thanks for your feedback. I will forward your suggestion to our senior developers. Should you have any further questions, please feel free to ask.Smiley Tongue

 

 

Derek Z.
National Instruments
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Hi Derek, 

 

I was looking for an answer to a similar issue i have when i want to simulate a circuit with LEDs, your file helped me to change the Vf but basically I'd like to know how also can change the current, I'm working with LEDs which have 3.0, 3.5 and 5 V with currents around 180 mA and 300 mA.... 

I hope you're able to help me!

 

really appreciate it 

Regards!

Ray

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Hello rai005

 

Have you tried to create a custom LED? Using another SPICE model.

 

Regards

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Hi,

I am just curious why the online Multisim simulates "LED" as a normal diode - at least concerning the forward voltage drop. In normal Multisim (standalone version 13) one can see at least three different voltage drops (1.79V for RED, 2.08V for GREEN and 3.38 V for BLUE.. it fails for IRED - also 1.79V, could be rather 1.1 V). The online multisim has 717mV for all colors. 

It is very stupid to show beginners (students) these numbers for LEDs.. . 

Of course there are modern LEDs made of strange compositions, typically high brightness ones, that have different forward voltage...but I guess none of them has 0.7V...

Regards,

 Vojtech  

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