Audio Amplifier. Which class should I use?

[Shayaan_Mustafa]

no no... I mean if you not post your solution then I could post mine and then it would be same as yours.

My english is bad that's why I am not getting what should I write that you understand what I am trying to say.

In short. I have done it. My answer is same as yours.

 

[goldsmith]

Well , if we simplify it more and more we can write something like this : AV= XC/XC+XL . now can you write vc , ( vc is out put voltage ) according to these formulas : IC=c*dv/dt and VL=-L*di/dt ?

 

[Shayaan_Mustafa]

Seriously I am not getting how to use IC and VL formulae in finding output voltage. Any hint?

 

[goldsmith]

Ic=c*dv/dt can you tell me what is the VC ? ( solve this differential equation )

 

[Shayaan_Mustafa]

OK. So I have to integrate it. Right?

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I am getting this,

I have integrated this equation from 0 to t.

Vc = V0(1-e^(-t/T0))

Where,
T0=Time constant.

Is it right sir?

 

[goldsmith]

No it is not correct ! it is a simple first order differential equation , see here :

You understand ?

 

[Shayaan_Mustafa]

OK. So similarly for VL. Right?

 

[goldsmith]

Now : VL= L*di/dt . can you calculate IL ?

 

[Shayaan_Mustafa]

Here is attachment.

 

[goldsmith]

Congratulations !
Now can you remember VC ? i/Cintegral over Ic dt ? so what is Ic ? can we write it according to the IL ? ( Ic=IL ) . show me the result .

 

[Shayaan_Mustafa]

Are you there?

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Now can you remember VC ? i/Cintegral over Ic dt ? so what is Ic ? can we write it according to the IL ? ( Ic=IL ) . show me the result .

Sir I didn't get what you mean by Ic=IL. I know the current in series is same. But Ic is under the integral of Vc's equation (equation for capacitor voltage). I have to differential the equation in order to separate Ic from there.

BTW: I have attached the image what I did.
Here it is . Tell me, am I right anyhow?

 

[goldsmith]

Humm , what is your idea about this equation ? see below , please :

Did you understand what this circuit is for ?

 

[Shayaan_Mustafa]

Is it low pass filter? But this has not RC network. So it may not be a low pass filter.

That is what I know and I guessed it.

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Now I want to say one more thing sir. In our university math teacher has not teach us how to evaluate double integrals.

 

[goldsmith]

Of course it is a low pass filter . it is a 2nd order low pass filter . but it is an integrator too ! ( average taker ) ha ha ! got it now ? what i tried to say ?
see below please :

Both of the circuits that you can see above , are integrators and of course LPF . but those are first order . if you remove resistors and connect circuits together it will given the circuit that we have talked about it at past .
By the way , do you know why that LC circuit is LPF ? ( i think you understood why it is integrator after looking at my latest literature ?
By the way do you know meaning behind word order in filters ?

 

[Shayaan_Mustafa]

it is a 2nd order low pass filter

We have double integral that is why it is 2nd order. I think.

By the way , do you know why that LC circuit is LPF ?

It will allow to pass the frequency that are lower than cutoff frequencies. Is that you are asking for sir?

 

[goldsmith]

Humm ! let me clarify those definitions !
2nd order means 6dB attenuations at cutoff frequency and first order means just 3dB attenuation . however it means : 2nd order has two pole , but first order has just one pole . the phase shift of a first order can't exceed from 90 degree but for 2nd order can be around 180 degree .
RC filters at high powers are not reasonable choices but LC families are pretty reasonable .
And about that LC filter : as you probably know impedance of each inductor will increase by increasing the frequency right ? and for capacitor vice versa . ok ? what does it mean ? can you think about this sentence and the configuration of that LC circuit ? if yes tell me what you can understand from it ?

 

[Shayaan_Mustafa]

2nd order means 6dB attenuations at cutoff frequency and first order means just 3dB attenuation . however it means : 2nd order has two pole , but first order has just one pole . the phase shift of a first order can't exceed from 90 degree but for 2nd order can be around 180 degree .

I already know these points you described here.

RC filters at high powers are not reasonable choices but LC families are pretty reasonable .

I don't know this thing. Now I have knowledge about this when to use LC family and when to use RC. LC for high powers and RC for low powers.

And about that LC filter : as you probably know impedance of each inductor will increase by increasing the frequency right ? and for capacitor vice versa . ok ? what does it mean ? can you think about this sentence and the configuration of that LC circuit ? if yes tell me what you can understand from it ?

Xc=1/(2*pi*f*C)
If frequency increases then impedance of capacitor will decrease.

XL=2*pi*f*L
If frequency increases then impedance of the inductor too.

I think this is what are you asking for by the statement "can you think about this sentence and the configuration of that LC circuit ? if yes tell me what you can understand from it ?"

 

[goldsmith]

As you saw , we have an LC filter . with a series inductor and a parallel capacitor in out put ( with this assumption that load resistor is pretty high ) . if you increase input frequency , the XL will increase and then XC will decrease as well . then out put voltage will decrease . you understand ? it means it is LPF . are you agree with me ?

 

[Shayaan_Mustafa]

OK OK.. It is new to me. Now, I get it.

So if I say,
"we have an LC filter . with a series capacitor and a parallel inductor in out put. If we increase input frequency , the Xc will decrease and then XL will increase as well . then out put voltage will increase. So is this refers to the High pass filter?"
Am I right sir?

 

[goldsmith]

Surely you are right !

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So , now i think i can continue ! can you remember that mosfet and square wave issue ? we have needed a circuit to take average ? ok ? now we can use this circuit :

But this circuit has a problem . can you tell me what is that ? ( assume that mosfet is used as a switch and we have an LC LPF in out put ! ( Inductor and switch ! ) ) tell me the problem if you can .