Graphs set to zero in a two graphs plot

Hello,

When I run this code with non-zero values for Ieq and Req I just get the second function (I2) on the graph. I don't know why the first function (I1) in constantly zero despite the fact that it shouldn't be so. Vd_vec is equal to 0:0.001:Ieq*Req.

    function [ Vd,Id ] = solve_diode_graph( Ieq,Req,Vd_vec )
     V = Vd_vec;
     I1 = Ieq - (V/Req);
     I2 = (10^-12)*(exp(V/0.026)-1); 
     figure();
     plot(V, I1, V, I2);
     legend('Id1', 'Id2')
     Vd = [ ];
     Id = [ ];
    end

[KSSV]

Give the values of Ieq,Req,Vd_vec .

[yackhaton]

Ieq = 1, Req =2, Vd_vec = 0:0.001:Ieq*Req

Answer 1

[KL]

if I1 is zero, it comes simply from the line I1 = Ieq - (V/Req);, which are your function inputs.

Nevertheless, according to your equations, I1 should start from Ieq and eventually would become zero in its final timestep since V(end) = Ieq*Req.

[yackhaton]

On the plot, I2 is shown normally but I1 is just 0. No other value. The strange thing is that if Iplot just I1 alone it takes its real value.

[KL]

that's because of the scale, since your Ieq = 1, I1 starts from 1 and meets zero in the end which you cannot see on the graph because I2 starts from 0 and grows exponentially. use the right side y axis with proper limits and you'll see both on the same graph

[KL]

or a subplot

figure();
subplot(2,1,1)
plot(V, I1);
title('Id1')
subplot(2,1,2)
plot(V, I2)
title('Id2')