Plot2d-Question: How to plot 2 changing functions economically



Hello,
first of all, i'm new to this mailing list - Please excuse my language, 
as it's not my first.

Well, I want to simulate an electrical circuit, which has two operation 
condition, each of them is discribed with a diffential equation. After a 
certain time i want to switch to the other equation.
1. Equation: 'diff(I,t)=(U-R*I)/L (eg. 1 second in this operating 
mode=t_equation1)
2. Equation: 'diff(I,t)=-(R*I+U)/L (eg. 2 second in this operation 
mode=t_equation2)
Well, I solved them with ode2 and ic1 for some certain points. Eg: t=0 
and I=0. But I want to plot I for a longer periode to see how I 
develops. I would wish myself a function where I can plot a continous 
flow of current.
The function I would wish should look like 
I(U,R,L,t,t_equation1,t_equation2).

Dear experts, how can I construct such a function? Thank you in advance 
for your help!
Michael Heidinger