Finding values with square wave input

Discussion in 'Programmer's Corner' started by brighton53, Jan 16, 2013.

1. brighton53 Thread Starter New Member

Jan 16, 2013
7
0
MATLAB - Forgot to add to thread title

Hi, this question is heavily based on my other thread http://forum.allaboutcircuits.com/showthread.php?t=79690
but I thought I would post another thread in there because It's more relevent and has more infomation.

So I'm generate 2 graphs with one being a current in the circuit and another a voltage across a capacitor.

Because I'm generating the square wave myself - I've been attempting to calculate the values with each of the sine waves that make up the square wave and add the results together. But Apparently my answer is incorrect - (my input is correct).

Can somebody take a quick look please !

Code ( (Unknown Language)):
1. %Constants
2. %%%%%%%%%%%%%%
3. T=1e-9;
4. omega = (2*pi)/T;
5. t = 0:0.1e-11:3e-9;
6.
7. c1 = 250e-12;
8. c2 = 250e-12;
9. c3 = 250e-12;
10. r1 = 0.5;
11. r2 = 1;
12.
13. zc1 = 1/(1i*omega*c1);
14. zc2 = 1/(1i*omega*c2);
15. zc3 = 1/(1i*omega*c3);
16. zr1 = r1;
17. zr2 = r2;
18.
19. zmatrix=[zc1,   -zc1,               0
20.         -zc1,   zc1+zr1+zc2+zr2,    -zr2
21.         0,      -zr2,               zr2+zc3];
22.
23. zinv = inv(zmatrix);
24.
25.
26. for n=0:200
27.     Vin = zeros(3, length(t));
28.     Vin(1,:) =  (1/(2*n+1))*sin((2*n + 1)*omega*t);
29.     Itemp = zinv*Vin;
30.     if n == 0
31.         I= Itemp;
32.         Vtotal = Vin(1,:);
33.         Vc3 = I(3,:)*zc3;
34.     else
35.         I = I + Itemp;
36.         Vtotal = Vtotal + Vin(1,:);
37.         Vc3 = Vc3 + I(3,:)*zc3;
38.     end
39. end
40.
41. figure(1)
42. subplot(311)
43. plot(t, Vtotal)
44. title('Input v(t)')
45. xlabel('time (s)')
46. ylabel('Voltage (V)')
47. subplot(312)
48. plot(t, I(2,:))
49. title('I(t)')
50. xlabel('time / s')
51. ylabel('Current (A)')
52. subplot(313)
53. plot(t, Vc3)
54. title('Voltage Cap 3')
55. xlabel('time (s)')
56. ylabel('Voltage (V)')
my output

and the outputs for I(t) and the voltage of capacitor 3 apparently should look like

2. MrChips Moderator

Oct 2, 2009
12,228
3,282
What are your units for r1 and r2? They seem rather low in value.

3. brighton53 Thread Starter New Member

Jan 16, 2013
7
0
Ohms - rather low but those are the values we where given.

4. brighton53 Thread Starter New Member

Jan 16, 2013
7
0
Any Ideas anybody?