Urgent Diode Analysis Help needed

[Sonia123]

Hey there folks,

I have a little problem with graphs. The cut-in voltage is 0.7V for the diode and am required to plot output voltage and diode current versus I1 over the range 0=<I1=<2mA. The circuits are in the attached file. My attempt is, I know very clearly that output voltage is I1 for the first circuit and diode current is zero and this condition remains true for I1<=0.7 but after that output voltage is 0.7 and diode current is I1-0.7 mA.
For the second circuit, output voltage is I1 and diode current is zero and this condition remains true for I1<=1.7 but after that output voltage is 0.7 and diode current is I1-1.7 mA.
For the third circuit, output voltage is 0.7V, the current for the first diode is I1 and second diode current is zero and this condition remains true for I1<=2mA but after that output voltage is 0.7 and diode current is I1-0.7 mA.

The concept is very clear but when it comes to plotting, am lost totally, please cn someone give a clear idea about plotting it since this is very urgent and I need to know it by today!
Thanks

 

[crutschow]

I don't understand all the different circuits. Are those provided as part of your homework?

The normal way to plot V vs. I for a diode is to use a power supply in series with a resistor (say 5k ohm) to provide the current source for the diode. Then you connect a sensitive voltmeter across the diode, slowly increase the voltage, and plot diode voltage vs. current. When the diode starts to conduct current, the diode voltage changes slowly so you need to adjust the current in about 0.1 mA steps to get good resolution of the voltage change.