R1
note:
1) passive sign convention
2) each plot corresponds to
a specific subcircuit
vS
+
-
A
i
+
+ vR -
v
-
p3-8 revisited, repeat for
Circuit B
Rest of
the
circuit
B
Circuit A
iA
i
iR
i
A
+
-
+
+
vA
-
1/R 1
R
vS
vS
vR
-
vA
R1
vR
But iA= -i, so flip source over and use negative voltage
i
iA
iS
vA
+
i
+
iR
A
+
R2
-v S
v
-
-v S
Rest of
the
circuit
B
vA
Circuit B
A
Now let’s consider the output of the combined voltage source and resistor (note that I’ve flipped the
reference on v to adhere to passive sign convention within the subcircuit).
i
R1
-v S
+
i
-
+ vR -
v
+
1/R 1
vs/R1
v
-v S
v=0 when vR=vS
Finally, let’s flip the reference direction on v to put the "the rest of the circuit" in terms of passive
sign convention as viewed by the subcircuit. Thereby flipping the plot relative to the vertical axis.
Confusing? Yep. Too many steps and lots of opportunity
for mistakes. But you have to know how to manipulate
plots.
i
R1
-v S
+
i
+
v
-
vs/R1
-1/R 1
vS
v
Starting from scratch, return to Circuit A at the top of this
sheet, forgetting about the preceding plots. Determine
what v leads to i=0, next find what i leads to v=0, finally
plot these two points in the i-v plane (much easier).