I'm attempting to model a neon bulb as a circuit element. Bulbs behave oddly in that they have a region of negative differential resistance. I have (approximate) curves of voltage vs. current, so it seems appropriate to model the bulb as a resistor using the .model TABLE spline fitting. However, I have trouble getting the results to converge in some circuit configurations.
For example, the following circuit converges: I1 0 1 10u R1 1 2 100k R2 2 0 NE .model NE TABLE 0,0 100p,10 1n,60 100n,68 1u,70 10u,60 100u,55 1m,60 100m,65 1,68 order=1 DC results are V(2) = 60V, I(R2) = 10uA. The circuit will happily converge within the entire range, including the negative resistance portion. However, attempting to build a relaxation oscillator by adding a capacitor across the bulb produces a convergence failure, even with relatively small internal time steps. Adding a parallel resistor across the bulb, or a resistor in series with the cap, does not help (at least with values that should still produce oscillation. Any suggestions, either on how to get this circuit to converge or an alternate modeling technique that will produce convergence, would be appreciated. (I saw one suggestion online of using a comparator with hysteresis to switch the bulb between high and low resistance values; I'd prefer something more sophisticated, capable of modeling the nonlinear nature of the problem.) Thanks! Evan Daniel _______________________________________________ Help-gnucap mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gnucap
