# Multisim and Ultiboard

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## How to setp up LED red to 1.8V and blue with 2.7V?

Hello,

here I have an image which explains the reason for this thread.

https://imgur.com/a/5JgXHfS

From a video, it was showed that in the following circuit only red LED glows:
9V battery, 3.9K Ohm resistor, 2 LEDs blue (2.7V) red (1.8V).

I build the circuit and both LED are emitting light.
https://i.imgur.com/eCUGlp4.png

Thank you.

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## Re: How to setp up LED red to 1.8V and blue with 2.7V?

No one has an idea? Or is my question to beginner like?

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Solution
Accepted by topic author xan137

## Re: How to setp up LED red to 1.8V and blue with 2.7V?

Hello,

The LEDs color selection is not related to the corresponding voltage that the LED needs for a proper functionality (is more like a matter of aesthetics).

This is not implemented in its model.

You can use the Ion parameter to adjust the voltage across LEDs, using a series resistor with them.

However, this is not the best approach, since for a VD voltage of 0.6V, the LED easily opens, behaving like a regular diode, and not an LED.

This issue is taken into account and transmitted further, with the hope another component will be added in the future.

Thank you for your input on this matter.

Monica Ignat

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## Re: How to setp up LED red to 1.8V and blue with 2.7V?

Why does the LED closes already with 0.6V? This makes no sense.

Message 4 of 7
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## Re: How to setp up LED red to 1.8V and blue with 2.7V?

В модели диода настройте ток поджига так, чтобы падение н

апряжения соответствовало вашему желанию
В варианте с произвольным спайс блоком нужно подобрать ток IS в модели, взятой из спайс нет листинга
Поскольку в синем лэде получался слишком маленький ток, я взял модель красного светодиода и подставил в синий, отрегулировав IS под нужное напряжение(можно было ещё чуть чуть увеличить, чтобы ровно 2,7 вольт получить)

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## Re: How to setp up LED red to 1.8V and blue with 2.7V?

I'm using the live Multisim, https://www.multisim.com/create/, the one running in the browser.

Message 6 of 7
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## Re: How to setp up LED red to 1.8V and blue with 2.7V?

Возьмите модели из 14 версмии и перенесите в live

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