Spice creates time-variant resistor
Vittorio Ricchiuti, Italtel, L'Aquila, Italy -- EDN, October 28, 1999
Figure 1 shows a subcircuit that represents the behavioral model of a linearly time-variant resistor in PSpice (Orcad, www.orcad.com). PSpice libraries include no models of such resistors, which you can use in various applications-for example, to simulate the fallback characteristic of a linear regulator in transient analysis. The suggested model uses the E-device in the PSpice analog-behavioral-modeling parts library. Listing 1 describes the subcircuit in Figure 1 for a time-variant resistor with the characteristic in Figure 2. The function in Figure 2 is the product of an independent voltage source, VCONTROL. The independent zero-voltage source VSENSE senses the current I(VSENSE) through the resistor. The voltage VR between nodes 1 and 2 of the time-variant resistor is VR=f(t)*I(VSENSE), where f(t) is a function of VCONTROL. (DI #2424)
