# LC series Network

Discussion in 'Homework Help' started by buffon2009, Dec 29, 2013.

1. ### buffon2009 Thread Starter New Member

Dec 7, 2011
28
0
Hi everybody

if we want to design an LC series network as a matching network to get maximum power transfer from a power supply when Rl(load) > Rs(internal resistance of the power supply)

we enter Rs in our calculations or not???

i wanna know if we want to design a LC network any where in a circuit we must take care of all the capacitor and inductance and resistor before the network or just we care of the input voltage only!!!??

thank you

2. ### rsashwinkumar New Member

Feb 15, 2011
23
2
Please note that, the LC matching network is designed to match the load resistance RL to the series resistance Rs. For this particular network, the design equation should look like RL=Rs(1+Q^2); Q=RL/(w0*L). In general, if there are some parasitic inductances or capacitances already present in the circuit, you need to take them into account in your design.

3. ### buffon2009 Thread Starter New Member

Dec 7, 2011
28
0
i want to know we take Rs + Rl as the resistance in the RLC network or only Rl

4. ### rsashwinkumar New Member

Feb 15, 2011
23
2
Please elaborate more. What do you mean by "resistance in the RLC network" ?

5. ### buffon2009 Thread Starter New Member

Dec 7, 2011
28
0
we have two patterns for R,L,C network
series & parallel standard patterns
that for make calculation easier
so for any either pattern or configuration of R,L,C we convert it to series or parallel standard pattern or combined series & parallel standard patterns
so we must have in the end one R , one L, one C
so my question is that we take Rs + Rl to represent the Resistance in the series pattern standard

6. ### rsashwinkumar New Member

Feb 15, 2011
23
2
This could be reduced to a series RLC, with R=2*Rs @ w=1/sqrt(LC)

Last edited: Dec 29, 2013
7. ### buffon2009 Thread Starter New Member

Dec 7, 2011
28
0
so Rs in our calculation to define the response of the circuit RLC

8. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
The transformation to the series form (regardless of whether you are considering a high pass or a low pass match) ignores Rs and considers only the load Rl.

9. ### rsashwinkumar New Member

Feb 15, 2011
23
2
Yes, after transforming the parallel R-L combination to a series R-L, the network will resemble a series RLC having an effective loss resistance equal to Rs in series with the transformed RL, which at w=1/sqrt(LC) will equal to Rs.

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
The resonance condition at match won't be governed by that simple relationship with L & C being the actual circuit elements. Replace L with L' in that equation and you would be correct.

Last edited: Dec 30, 2013
11. ### rsashwinkumar New Member

Feb 15, 2011
23
2
Since for a high Q system, value of the inductance remains unchanged after the series to parallel transformation, I didnt add mention it explicitly. But yes to speak without loss of generality, L will change to L'=L(1+Q^2)/Q^2.

12. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Depends on the values one is trying to match. For instance if Rl=100 ohms and Rs=50 ohms then Q is 1.