Modeling I-V Characteristics in LTSpice

[crono1009]

I'm trying to model the I-V characteristics of a few diodes in LTSpice. Though doing the DC sweep I have in the picture doesn't seem to give me what I want. I'm sweeping from -80V (It's breakdown is 75V) to 2V, in 1V increments.

What kind of simulation do I have to run across the diode to get a nice curve representing the I-V characteristics of a diode?

Thanks!

[vk6kro]

Make the resistor 0.1 ohms. Vary the voltage from 0 to +2 volts in steps of 0.01 volts.
View the current in the diode.

Run the simulation then left click on the vertical axis and set the maximum current to 100 mA with 10 mA ticks.

This gives a fairly good version of the forward characteristic.

[crono1009]

Thanks for the tips. I am happy with my cut-in voltage, around 0.7V where it should be.

Though I'm having another dilemma, I want to display my breakdown voltage characteristics also. The breakdown voltage of my 1N4148 diode is 75V. So I swept my DC voltage source from -100V to +2V in 0.01V increments, though as you can see from my graph my diode does not conduct in reverse bias at all.

Any thoughts?

[vk6kro]

LTSpice does not seem to use maximum ratings although they are listed in the diode characteristics. I couldn't see anywhere to turn this on.

I started a trace at -1000 volts and a 75 V diode did not conduct until it was forward biased. It was also able to conduct hundreds of amps where this was unlikely in practice.

If you want a reverse breakdown, try using a Zener diode. LTSpice has quite a few of them.

Use very small steps like 0.01 volts and remove the 1 K resistor because that affects the shape.

[vk6kro]

I had a play with this.

Go to
c:\Program Files\LTC\LTspiceIV\lib\cmp\standard.dio
and in the description for the 1N914 edit the text to add "bv=75" after Cjo

Restart LTSpice and reload the simulation.

The simulation now includes a breakdown at -75 volts.