Transfer Function for Passive Low Pass Filter. Attached Snapshot.

[AJAB]

Hi,

I have a low pass filter as below and I need to generate transfer function for this. (My ultimate goal is to plot frequency response of this circuit.)
How do I derive it?

I was thinking (Xr+Xc2)/Xr+Xc2+XL)...But what to do about Xc1?

Do I need to consider the RC branch for plotting the frequency response?


I will be using this circuit at the output of D amplifier. So does this RC in anyway has to do anything with speaker load?

Need Help! :|
Thank you.

Regards,
Archana.

 

[LvW]

I suppose, the input is at the most left and the output at the most right side - OK?
(Note, to avoid misunderstandings, always show input and output nodes.)
Of course, each branch must be considered.
The calculation of the transfer function is relatively simple.
* step 1: Calculate the equivalent impedance Z2 of the parallel braches.
* step 2: Write the voltage division rule for Z2 and sL1 (s is the complex frequency variable):
* step 2: Rearange the expression to get a polynominal (in "s") in the numerator as well as the denominator.

 

[AJAB]

ok. I followed below steps...
Xx = Xc1 || (Xc2+R)

Then Vout/Vin = Xx/(Xx+XL)
The Plot I get with this calculation does match with the simulated one.
Thank you.

And yes I will surely specify the I/O nodes next time.

Thanks LvW.

 

[AJAB]

Hi,

I have one more query for this ckt, regarding the DC power dissipation in the inductor.
If V is the supply to the internal MOSFETS of Class D amplifier, F is the switching frequency of PWM output, and IndR is the DC resistance of Inductor.
Can I say, Current through Inductor IL = V/2*F*L
And Power Dissipation = IL * IndR

Is this approximation correct?

Thanks,
Archana.