quality factor

niga

New Member

• Jun 25, 2005

• #1

hello

I read that Q,the quality factor of series resonant circuits is wL/R
------------>1/R sqrt(L/C).This i understand

1.but for parallel resonant it is R/wL....hmm but why is that?this i don quite get.why shud it be XL not Xc?

2. what do u mean by loaded resonant circuit and unloaded resonant circuit?


Thanx for ur time and help.

 

L

ljcox

Well-Known Member

• Jun 25, 2005

• #2

The difference is that for a series circuit, the R is assumed to be in series with the L. But for parallel, it is assumed to be in parallel.

Impedance of a series R + L is R + jwL

Admittance = 1/(R + jwl) = (R - jwL)/ (R^2 + (wL)^2)

So the conductance is not 1/R it is R/ (R^2 + (wL)^2) which implies that the resistance for the parallel case is much greater than for the series case - as you would expect.

Len

 

niga

New Member

• Jun 25, 2005

• #3

ok len thats fine,Thanku

but its a parallel RLC resonant circuit.
R is in Parallel with C and L.........so why is C not so important?

 

L

ljcox

Well-Known Member

• Jun 26, 2005

• #4

niga said:

but its a parallel RLC resonant circuit.
R is in Parallel with C and L.........so why is C not so important?

Click to expand...

Capacitors have less loss than inductors.

The main loss in a capacitor is the dielectric loss. This can be represented by a parallel resistor. But inductors have copper loss and possibly magnetic losses such as eddy currents.

So in a RLC circuit, most of the loss is due to the inductor.

Len

 

niga

New Member

• Jun 26, 2005

• #5

i see.okay,thankyou for ur immediate reply.
wats a loaded resonant circuit?

 

L

ljcox

Well-Known Member

• Jun 26, 2005

• #6

One that has a load. The load may be the input resistance of an amplifier such as in a radio receiver.

Len

 

niga

New Member

• Jun 26, 2005

• #7

oh, the usual term load...yup.
thanx len

 

niga

New Member

• Jun 26, 2005

• #8

just one more thing...how do i calculate the Q of a loaded rlc circuit?

 

niga

New Member

• Jun 27, 2005

• #9

Please help.....
say, i have an XL as the load with a parallel RLC it becomes a loaded resonant circuit.
the Q for the parallel connt is
R/XL

so what do i do ..... :? please help?