Electronics > Beginners

Characterizing diode via scope XY mode

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MikeK:
I'm trying to setup my scope to characterize a 1N4001 diode.  This should be a plot of voltage across the diode (X-axis) versus current through the diode (Y-axis).  But I'm not getting the full results I expect.

I have my function generator outputting a triangle wave to the series connection of the diode and a 10 ohm resistor.  Amplitude is set to max.  On my scope, I have X measuring the voltage across the diode and Y is the voltage across the resistor (to get the current).

It took me a while to get the settings where I can see something recognizable.  I set the generator for two frequencies, 1k and 39k.  I'm assuming that I'm getting no reverse current, because the reverse threshold is much higher than the voltage my function generator outputs.  But what the heck is happening at 39k?  Also, why is the plot so grainy?  It has 1MSa/s in XY mode, which should still give me a nice smooth curve, no?

Rerouter:
hmm, if i had to guess either its some inductance in what your measuring, or the recovery of the diode, though i would think more the first because the specced frequency of a 1n4001 should be much much higher,

MikeK:
I just ran a 5.1V zener.  No strange behavior.

But the scope acts strange when I set the function generator to a large integer factor of the scope sample rate.  I get "connect the dots".

slateraptor:
In agreement with Rerouter on the first; what you're seeing is likely hysteresis.

For the second, I suspect aliasing.

Mechatrommer:

--- Quote from: MikeK on April 08, 2012, 12:27:04 am ---But what the heck is happening at 39k?  Also, why is the plot so grainy?  It has 1MSa/s in XY mode, which should still give me a nice smooth curve, no?

--- End quote ---
try to increase the freq (MSps) more, then you'll realize the limitation of rigol built in XY plot mode.

edit: didnt realize this...

--- Quote from: MikeK on April 08, 2012, 12:51:50 am ---But the scope acts strange when I set the function generator to a large integer factor of the scope sample rate.  I get "connect the dots".

--- End quote ---
ahhh! here they are!