Re: How to set up a diff equation for circuit with a diode?

*To*: mathgroup at smc.vnet.net*Subject*: [mg62815] Re: How to set up a diff equation for circuit with a diode?*From*: "siliconmike" <siliconmike at yahoo.com>*Date*: Tue, 6 Dec 2005 00:03:11 -0500 (EST)*References*: <dn0v2m$8g2$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

I figured out this. Please comment: During forward bias, voltage across diode = 0.026 ln [10^12 I + 1] <- from diode equation During reverse bias, diode can be modelled as a large resistor, eg 10^12 ohms. voltage = I * R_Large So the differential equation looks like: V = IR + LI' + 0.026 ln[ 10^12 Abs[I] + 1] * U[I] + I * R_Large U[-I] where U is the Unit Step function (can be modelled as a continuous function using tanh). L and R are inductance and resistance in series with a source V(t) I modelled U as U[I] = (1+ Tanh[IB])/2 where B is a very large number, eg 10^12 Works great in mathematica using NDSolve. Mike siliconmike wrote: > I'm kind of curious how to set up a nonlinear differential equation and > then solve it using NDSolve in case of the following setup: > > Battery V in series with a diode, R and L. > > To simplify, we may assume that diode is a pure conducting device in > forward direction and pure blocking device in the reverse direction. > > Now how to set up a differential equation for the current I(t), that is > solvable using NDSolve? > > Thanks > Mike