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Can anyone tell me how to set up a sweep that would show a diode characteristic curve.

Take a look at this circuit: Run a DC sweep -- it sweeps the voltage from -1 to +1 volts, and plots the current at each applied voltage.

Mike,

It works great! Thanks for your help!

Great site!

Dan

But beware, if you really need to see a diode curve in this much detail, a simulation is likely to be inadequate.

Real diodes have curvature at the top and bottom ends of the curves, they're not perfectly straight on a log graph.

And they don't all cross the 1mA line at 560mV, they can vary several hundred millivolts, depending on the exact recipe they used.

They also have some really weird time-dependent effects, especially if they're "gold-doped" for extra conductance. They can have delayed conductance-- a wild overshoot that can last nanoseconds, and even a slight memory effect that lasts milliseconds!

You won't see these little details in most diode models.

( Also the diode model in Circuitlab does NOT have the very significant 2mV drift per degree C, a very important effect when you're engineering a circuit that has to run in the real world of high and low temperatures ).

So enjoy the simulations, but always remember that it's just a simulation, the real world is going to be a bit different.

Our diode models are pretty good, in my opinion. Then again, I wrote them :)

As far as DC behavior, we do model a series resistance component which leads to eventual linear I-vs-V behavior at higher currents, not exponential forever. We do model different diodes having different emission coefficients, saturation currents, so different diodes in our simulator really do behave quite differently! Pick some datasheets and give it a try.

Time dependent effects are weird, yes. But we do model them! I recently responded to a question about reverse recovery time, talking about how the space charge in diodes affects the turn-off (and to much smaller degree, turn-on) dynamics. Check out my "Diode Reverse Recovery Time Demo" circuit:

I think your "wild overshoot that can last nanoseconds" is basically the "forward recovery time", and "slight memory effect that lasts milliseconds" is basically the "reverse recovery time". (In my circuit above, I show the 1N4007 has a reverse recovery time of about 2us, but that's because I let the space charge get neutralized through an external reverse bias voltage. If you truly just switched the diode to be open circuit, you would see a charge remain for milliseconds or more, as the hole-electron pairs would just have to randomly recombine in the bulk semiconductor.)

You're right that we don't currently do any thermal modeling.

All of these effects really come out when you try an application like switching an inductive load. Take a look at "MOFSET switching inductive loads" from our homepage:

Try swapping D1 from a 1N5817 (a fast Schottky diode) to a 1N4007, and you'll see it has a problem turning off fast enough when the MOSFET starts conducting again. Or put in a 1N4148 (a tiny signal diode) and you'll see that it can't handle the current without letting the drain voltage get dangerously high.

Hope that helps!