I'm getting a little turned around here. With regards to the lab, are you saying that my current measurements for steps 6 and 7 are backwards? (i.e. I should be showing negative current on the left side?)
Yes, you should be, and your graph should look like the one I posted in #9. (Minus the leftmost steep part, because you have never entered that region). That said, the shape of the answer box strongly hints that the author of the instruction expects the drawing like the one you've done in #1. Problem is, such answer is objectively wrong. Here's why.
Diodes are normally measured in a test setup which looks like that:
(from
http://www.mouser.com/pdfdocs/IVChrzDIodes2450_AN1.PDF -- actually, read the whole thing)
(1) Per convention, the HIgh potential is usually higher up on the image and the LOw potential is lower. Let's say that the Force_LO connector is held at 0V w.r.t. ground, and the Force_HI connectors is at potential V_F>0 w.r.t. to the ground. The diode is now polarized
forward (anode is at higher potential).The current is flowing from higher potential to lower potential, i.e. out of the Force_HI terminal, downward through the diode, and into the Force_LO terminal. Observe the diode symbol is simply an arrow which shows you which direction the device will treat as forward! The whole idea behind the diode is that it will conduct current which enters through anode and exits through cathode, but not vice versa!
(2) To measure reverse current, we have to put the anode and lower potential than the cathode. If you can afford a proper characterization device (like the one in the PDF) then you simply tell it to put the Force_HI terminal at some voltage -V_R<0, while keeping Force_LO (and thus Sense_LO) at ground. Since the current in the circuit obeys the laws of physics, it will again flow from higher potential to lower potential, i.e out of the Force_LO terminal, upwards through the diode and into the Force_HI terminal. However, since the current is now flowing
into the Force_HI terminal, and
backward through the diode, then this current is negative (and the meter will indeed show negative current). Further, as the diode itself is concerned, the current is now flowing
into cathode. So from the diode's POV, it is being forced to conduct reverse (i.e. negative) current.
(3) If you cannot afford proper equipment, observe that the same effect (i.e. forcing the diode to conduct the current backwards) can be achieved by keeping the Force_HI terminal at positive voltage +V_R>0 and instead connecting the diode backwards (i.e. so that its arrow points upwards). Since the diode is now reversed, its anode is now at
lower potential. Remember, the diode "wants" to conduct current in the direction of its arrow symbol, i.e. upwards; alas, we have put it in the circuit which forces downward current flow,
into cathode, so as far as the diode is concerned -- it is again operating in the reverse region, so the current is backwards, i.e. negative.
---------- Post added at 10:18 PM ---------- Previous post was at 10:09 PM ----------
Note the red lead will usually have the negative battery terminal of the ohmmeter circuit, and the black lead the positive battery terminal.
That's backwards. The standard convention is:
red - positive w.r.t. COM/GND
black - COMmon / GrouND
blue - negative w.r.t. COM/GND
