Question 2.SP.24: Sketch the i-v input characteristic of the network of Fig. 2......
Sketch the i-v input characteristic of the network of Fig. 2-39(a) when (a) the switch is open and (b) the switch is closed.
The solution is more easily found if the current source and resistor are replaced with the Thévenin equivalents V_{Th} = IR and R_{Th} = R.
(a) KVL gives v = iR_{Th} + IR, which is the equation of a straight line intersecting the i axis at -I and the v axis at IR. The slope of the line is 1/R. The characteristic is sketched in Fig. 2-39(b).
(b) The diode is reverse-biased and acts as an open circuit when v > 0. It follows that the i-v characteristic here is identical to that with the switch open if v > 0. But if v ≤ 0, the diode is forward-biased, acting as a short circuit. Consequently, v can never reach the negative values, and the current i can increase negatively without limit. The corresponding i-v plot is sketched in Fig. 2-39(c).