Solutions to example problems (Sorry it’s a little messy, but I only had about 45
minutes to write this up)
At a glance, we see that the two current sources both send all of their current
through the 5k resistor, so the total current is 2 amps, so the voltage is 10 kilovolts.
Consider what would happen if the current source were not there, then we’d have
a balanced wheatstone bridge. Thus V would be zero in that case. If we add a
dependent current source based on that voltage, then we know that V being zero is
still the solution.
Since we have to find the behavior of several loads, we should first find the
Thevenin equivalent. Solving, we get that V_oc=8V, I_sc=40 mA, and R_th=200
Thus for the 200 ohm resistor, I_out is 20 mA.
For the 1800 ohm resistor, I_out is 4 mA
For the capacitor, I_out is 0
For the inductor, I_out is 40 ma
For the ideal diode, I_out is 40 ma
For the device with a piecewise I-V characteristic, we first assume that it
is in the V positive state. This gives us I_out=10 ma. We then verify that
our assumption is correct. Doing this, we find that the voltage across the
strange device is 8V, which is consistent with our guess.
We know that, for a diode, current increases with temperature. This increase in
current will lead to a further increase in temperature. Thus, one diode will keep
taking more and more of the current until it almost completely dominates the
current flow. This process is known as “thermal runaway”. This process also
occurs, for example, in microwave cooking (hot food generally absorbs
The first thing to realize is that we’re going to have two guesses-one for the diode