# Transfer function of an RLC circuit

I'm trying to simulate an RLC circuit using transfer function. Circuit is there: http://i.stack.imgur.com/MC8ME.png (I'm a new user therefore I cannot post images)

But I can, L.Motl...

Main current (I) is the output and V is the input. So far, I'm stuck at this:

TF = (Q1(s) + Q2(s)) / ((30 + s)(Q1(s) + Q2(s)) + 20 * Q1(s))

I need to get rid of Q1 and Q2, but I cannot find a way.

• Best to ask your teacher next week. – Johannes Jan 22 '11 at 17:29
• This looks very like a homework problem, so I doubt you will find anyone to give you the answer here. For this reason I have also voted to close the question. However, I will point you in the right direction: What you are looking for is Kirchoff's laws (en.wikipedia.org/wiki/Kirchoff%27s_circuit_laws). – Joe Fitzsimons Jan 22 '11 at 18:02
• Homework problems should be tagged as such (which I did) and only be answered with hints - besides that they are perfectly valid questions for this site. – Sklivvz Jan 22 '11 at 20:37
• @Sklivvz is right. There is no reason to close this question, as long as it is tagged as homework. – Noldorin Jan 22 '11 at 21:37
• Although the physics people can certainly help you out, you are probably better off posting this on the Electrical Engineering stack exchange. Joe is pointing you in the right direction, use Kirchoff's laws to get a system of equations (only two in this case) and from the system you can eliminate the variables. – docscience Oct 5 '16 at 22:29

\left\{\begin{aligned} &V_I e^{i\omega t}= R (I_1(t)+I_2(t)) + j \omega L (I_1(t)+I_2(t))+ R I_1(t) \\ &V_I e^{i\omega t}= R (I_1(t)+I_2(t)) + j \omega L (I_1(t)+I_2(t))+ \frac{1}{j \omega C} I_2(t) \\ \end{aligned}\right. or, if you aren't interested to know $I_1$ and $I_2$ in separated rings you can consider the parallel of R2 and C:
$$V_I e^{i\omega t}= RI(t) + j \omega L I(t) + \frac{1}{\frac{1}{j\omega L}+ j\omega C}I(t)$$