A question about Q factor

[overmars]

I saw a Q factor in many materials, for capacitor Q=ω•C•Rp and for inductor Q=(ω•L)/Rs

Rp is the equivalent parallel resistor of capacitor and Rs is the serial one for inductor.

What those Q factors mean?

Thanks

Regards!

 

[alberr]

Q-factor means quality of device. The more Q factor the less resistive loss will be.

 

[lladnar23]

Q stands for Quality Factor, and is a common figure of merit.

Q is the ratio of energy stored per cycle to energy dissipated per cycle: Q = X/R, where X is the reactance and R is the resistance. This is for a reactance and resistance in series, and is often labeled as Qs.

Alternatively, for a reactance and resistance in Parallel, you can define Qp = B/G , where B is the susceptance (1/X) and G is the conductance (1/R). So for an inductor, Q=wL/R (L and R are in series). For a cap, use the second definition: Q=(wC)/(1/R)= wCR (C and R are in parallel)

Another property of Q is that it equals the Bandwidth/center frequency, where BW is usually the 3dB BW.

Hope this clears it up.

 

[rakesh_aadhimoolam]

https://en.wikipedia.org/wiki/Q-factor

 

[tarakapraveen]

hi friends small doubt,

What will happen if we go for higher Q-value in our circuits .

1)Is it advantage or diadvantage?

2)What about the sizes of the circuit elements at high values of Q-factor?

3)Is there any instrumetns present to measure the Q-factor directly plz tell me?

Thanks,
tarak

 

[ender84567]

a q factor is a ratio of reactance to resistance measured at a certain frequency, so high q factor is good at the frequency you want to use the component at. it really doesnt have much to do with size. again q factor is measured at a specific frequency, so a RLC meter can do it if it has frequency adjustment, a VNA with s-parameter test set is also an expensive way to do it, but usually they are listed in the data sheet.

Added after 1 minutes:

another note, if you have components with different q factors, the overall circuit Q will be driven by the lowest one.

 

[jasmin_123]

> What will happen if we go for higher Q-value in our circuits.
>
> 1)Is it advantage or diadvantage?

A too large Q may be very bad: the larger Q the longer transients in the time
response of the resonant circuit: 2.2Q/(pi f0).

>Q is the ratio of energy stored per cycle to energy dissipated per cycle: Q = X/R,
>where X is the reactance and R is the resistance.

The factor of 2pi is missed here.

 

[tronix]

hi all
In continuation to earlier posts, Q factor also represents the peak of the distribution at the central frequency. The larger the Q factor the more sharp will be the curve and similarly smaller the Q factor more flat would be the curve.
Now let say we have a ckt for radio receiver. A high Q factor receiver will produce a good quality at a precise central frequency (fine tuning) whereas a low Q factor receiver will give average quality over a range of frequencies around the central one.


Regards
tronix

 

[Amarbir]

Hi,
some More question .I Have Seen That LCRQ Meter Test Q Factor For Inductors Not Capacitors [I Have One Like this ] ,does this Mean Q Factor is Mot there In Capacitors .Seeing The Above discussions i think it is .Fo Are There Devices To Measure That

Amarbir

 

[jasmin_123]

One more disadvantage of too great Q: too narrow receiver bandwidth may demand a too precise transmitter tuning.

 

[ender84567]

The factor of 2pi is missed here.

2pi is only missing if you are working in Hz instead of radians per second, its all relative based on your conversion

 

[jasmin_123]

The factor of 2pi is missed here.

2pi is only missing if you are working in Hz instead of radians per second, its all relative based on your conversion

Q=wo energy stored/average power dissipated in the resistor
Q=2pi energy stored/energy dissipated in one cycle

© Desoer and Kuh

How do you eliminate 2pi in the second equation?

 

[springf2000]

the Q is more high, the loss is smaller, this is very important when design LNA and LC filter, thanks

 

[E-design]

High-Q filters have higher insertion losses.

 

[Yarafat]

Q factor is a ratio of stored energy to loss energy. example in RL circuit, Q is inductive energy to energy dissipated in resistance.

 

[jasmin_123]

Q factor is a ratio of stored energy to loss energy. example in RL circuit, Q is inductive energy to energy dissipated in resistance.

Q=2pi energy stored/energy dissipated in one cycle.

 

[ch1k0]

reactance X contains frequency w.
Xc for caps, XL for coils, no pi is missing from Q=X/R .

Energy dissipated per cycle equals Power * Period .

Q = W * AVERAGE_ENERGY_STORED_PER_CYCLE / AVG_ENERGY_LOSS_PER_CYCLE

W = 2*PI/PERIOD

all is right, above.

Question for hard brains:

Calculate Q of RL or RC with NON-LINEAR REACTANCE ... How ?

Hint: Not in Desoer-Kuh. Large-signal is key! General case treats hysteresis... Try q = C(v) * v only ...

 

[Julian18]

but how do you guys get
Q=X/R
directly from the general definition of Q factor?

 

[hrazadi]

In fact Q factor is an important parameter of a device. It means: Quality of device. that is the ratio of energy stored in it to the ratio dissipated in it. For example, in the case of capacitor, the modeling shows that a parallel resistor can show the dissipated power and therefore you can state Q=ω.c.R.

 

[xulfee]

it is basicaly quality factor,u can find it for any frequency dependent circuit by ωc/(ωh-ωl),where ωc is center frequency or resonent frequency,ωh is higher stop band & ωl is lower stop band,converse for stop band