Why are my LTSPICE results so different from the 1N4148 datasheet and real life?

[makiyoung]

I plotted the IV curve for a 1N4148 diode and obtained this. The simulation shows about 60 mA of current at 0.8 V while the datasheet shows about 30 mA. I also checked this datasheet and it also shows 30 mA. In real life I measure 26.4 mA at 0.8 volts.

Considering this is supposed to be a model of that actual diode, the result seems rather far off.

 

[Alec_t]

Did you mean to add links or attach something?
Interesting though. At Vfwd=0.8V Vishay's datasheet shows a spread from 9mA to 20mA, NXP's datasheet shows ~40mA and Fairchild's shows 30mA. So on balance it looks like the Spice model is wrong.

 

[(*steve*)]

The slope of the curve is very steep. I would be happy that it's within cooee of the result you're getting. The value is also likely to be pretty temperature dependent too.

(Within cooee is similar to within a bull's roar, but less than a packed lunch and a waterbag. Probably closer than Woop-woop unless you're already well beyond the black stump)

 

[Audioguru]

Why do you need the sim to show one voltage/current that you cannot buy? You get whatever they have because they cannot be made to all be the same.
Are you trying to match a diode to the base-emitter of a transistor or to another diode? You can't unless you buy many, test them all and sort them.

The text in the datasheet shows the range of voltage and current. The curves in the datasheet shows only a "typical" one that you can't buy and many are minimum and others are maximum.

Maybe the datasheet measures the forward voltage immediately and before the diode heats but maybe the sim waits for the temperature of the heating diode to finish rising.

 

[Harald Kapp]

The text in the datasheet

e.g. NXP:

max. forward voltage even at 10 mA is 1V.
So much for tolerances.

 

[Arouse1973]

I make mine 0.758 mV at 30 mA at 25 deg C.
Thanks
Adam

 

[Audioguru]

Is 25 degrees C the temp of the chip or the temp of the ambient air?
But we do not want the forward voltage of your diode because it is different for most 1N4148 diodes.They cannot all be made exactly the same, they have a range of forward voltage.

 

[Harald Kapp]

Even LTSPICE offers two different models:

• 1N4148
• MMSD4148

These will deliver different characteristics. Some models fpr 1N4148 from different vendors that you can find on the internet have again other parameter values.

It's a good thing you do not take the simulation result as a given truth but you question this result. I hope more users of simulators were that thorough.