trying to simulate two LED's in my circuit but I don't understand the Vf @ 1A parameter. How do you insert specific values for a specific LED. I have two I'd like to simulate: Vf 3.95 @ 80mv and another at Vf 3.65 @ 110mv. If you have the time id prefer to be taught to fish over you giving me a fish... In other words I'd like to understand how to calculate this on my own. Appreciate any help you can offer.

 

So do we assume you are asking about the icircuit app?
http://icircuitapp.com/
The Vf of an LED is listed in the datasheet for that specific LED..
Why the designers of icircuit chose to use @1A or if that can be changed would be a question you would need to ask them..

I don't have the program but if I was using it I would put the Vf from the datasheet that closely matches the amps I'm supplying to it..
I suspect you may only be able to modify the Vf value and would hope that it uses the same Vf at whatever current you are driving it at..

Here is the user manual for that program too.. It mentions how to edit a components parameters..
http://icircuitapp.com/usermanual/

 

yes im referring to the icircuit app. Unfortunately I dont have the data sheet for these LED's and an exhaustive search has turned up nothing. I could create a curve from bench testing them but I'm trying to understand the app and how it works so i don't have to do that in the future ;-).

havent had any luck with icircuit responding to my questions. The manual you attached does not address this specifically, ive gone through that already.

Ill try playing around with it in the manor you suggest and see if that gets me anywhere. Thanks for the reply!

 

Who is the manufacturer of the LED and whats the part number?
(Or is it just junk you picked up from ebay,etc..?)

But just placing a power supply, resistor of a know value and the LED and just look at how much current is going through the LED (I assume the simulator tells you that) is enough to answer your doubts..

 

I picked them up at fry's a few weeks ago and there was no data available for them other than what came on the package which only indicated min. Vf. I don't recall those values. I searched around quite a bit for a data sheet and came up empty. I put them on the bench and drove them with my PSU to the point i want them to run at. (those are the values i listed). BTW - I'm building a aquarium light with blue and white led's in two parallel series strings. I have done the rough math and can of course build the circuit on a breadboard to tweak to my liking, I'm just trying to understand the logic they use for inserting custom led parameters into these simulators. It would be really cool if you could just punch in VF at a specific current. Now that i think about it... that's probably impossible since every led has a unique curve and as you change other parameters the LED properties would change and be inconsistent. Probably why ltspice doesn't allow me to change that parameter for led models. I think i just answered my own question.... Is my answer the proper way to think about this? Thanks for being patient with me ;-)

 

Well.. The Vf of an LED will also change with temperature so...

I'd suspect (and you can easily verify) that the Vf entered is used no matter how much current is going through the LED in that simulator and the fact they put @1A is probably irrelevant..

And just in case.. LEDs in parallel is fine assuming each series string has its own current limiting resistor.

 

understood. i did check and it doesn't stay constant... I can't figure out what they did, oh well. 10-4, yes i have resistor on each string, each string draws different currant and has different V drop totals.

 

understood. i did check and it doesn't stay constant... I can't figure out what they did, oh well. 10-4, yes i have resistor on each string, each string draws different currant and has different V drop totals.

just fudge the Vf @ 1Amp in iCircuit until they hit the desired Vf at measured current for Your LEDs.