Audio Amplifier. Which class should I use?

[Shayaan_Mustafa]

By the way , think on this issue , until i come back : why the voltage across the out put inductor is AC ? an AC square wave !!!!! . try to find a reason for it .

I thought about it. And I am confused. Inductor blocks AC. Right?

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I have some question sir;

1) We have made Buck regulator. Why can't we use linear voltage regulators?

2) And when I was searching for this Buck regulator (Switched mode converter). I found that it was under the section of DC to DC converters. What is this? Will you please help me out of this?

3) What is free-wheeling operation? What is free-wheeling diode?

4) Capacitors for switched regulators are chosen on the basis of effective series resistance (ESR).
I found this statement in the link which I provided you in the post#438. So will you please elaborate this? I have never heard about ESR.

5) Most of the switched supplies needs a minimum load, in order to ensure that the inductor carries current always. If the current flow through the inductor is not continuous, regulation may become poorer.
Why is it necessary for current to be continuous? I also found this statement on the given link.

 

[goldsmith]

Hi shayaan

I thought about it. And I am confused. Inductor blocks AC. Right?

the reason isn't this ! don't forget that inductor won't block AC ! it will has a reactance instead of AC signal. if the value of L be high , and XL be high , thus we can say that it blocks AC . but here another thing is the reason ! see below , please :
**broken link removed**
You understand ?

1) We have made Buck regulator. Why can't we use linear voltage regulators?

Sorry if my descriptions weren't as clear as enough . again :
I assume you want achieve 400 watts audio amplifier . it means Vout across the 2 ohms load should be around 40 volts . ok ?( (vpp^2)/8RL )
As you probably know , your audio signal , is not in constant amplitude . it has variations . so , if your regulator is linear it means if you need 40 or 45 volts at the out put , you have to use at least 60 or 65 volts as input DC voltage ( unregulated ) . and current for 400 w = 40/2=20A ok ? so , dissipated power across the regulator will be 20*25=500W . with this large value of dissipation as heat , you can bake cake and sweets for a big celebration !!!!! it is very fun that you want achieve 400w and then loss the power around 500W . isn't it ?
So , now if you consider that you have a Buck regulator , suppose that the input voltage is 100 volts and out put ( after filter ) is 40 volts . don't forget that the voltage before filter , is a square wave with amplitude , around 100 volts . suppose D.C is around 0.4 . consider your mosfet is IRFP450 . if Rdson is 0.5 ohms . dissipation will be D.C*(Rdson*Idmax^2) 0.5*20^2=200 =====>200*0.4=80W . is 80W reasonable or 500W ? is there any unclear thing in my explanations , available ? if yes , tell me , please i'll simplify that .

2) And when I was searching for this Buck regulator (Switched mode converter). I found that it was under the section of DC to DC converters. What is this? Will you please help me out of this?

Of course . it called DC/DC converter , because the input voltage is unregulated DC voltage and out put voltage is regulated DC voltage .

3) What is free-wheeling operation? What is free-wheeling diode?

Can you remember the diode that we have putted to prevent damages of mosfet and recovering the energy , to recharging the out put capacitor ? that diode called freewheeling diode or fly back diode . ok ?

4) Capacitors for switched regulators are chosen on the basis of effective series resistance (ESR).
I found this statement in the link which I provided you in the post#438. So will you please elaborate this? I have never heard about ESR.

ESR is derived from Equivalent Series Resistor . each capacitor in this world has ESR . it is a low value resistor , that created internally and it is unwanted ! it created because of rolling ! ( rolling the conductor ) . as you probably kno each conductor has a low value of resistance . ( R=p*(L/A) did you know this ? ) .
We should select capacitors with lowest value of ESR , but because these capacitors are a bit expensive , i usually using some capacitors in parallel . by the way , do you know about equivalent model of a real capacitor ? it is pretty important .

5) Most of the switched supplies needs a minimum load, in order to ensure that the inductor carries current always. If the current flow through the inductor is not continuous, regulation may become poorer.
Why is it necessary for current to be continuous? I also found this statement on the given link.

You can put each load in out put of your SMPS . i will talk about continuous and discontinuous mode of operation . be patience . it is not for this time .
By the way , it is very good , that you started to search about SMPS in the net . it can increase your knowledge . keep this action .
Best Wishes
Goldsmith

 

[Shayaan_Mustafa]

Hi shayaan
the reason isn't this ! don't forget that inductor won't block AC ! it will has a reactance instead of AC signal. if the value of L be high , and XL be high , thus we can say that it blocks AC . but here another thing is the reason ! see below , please :
**broken link removed**
You understand ?

Sir your given link is not opening. I am getting this page when I click above link.

Sorry if my descriptions weren't as clear as enough . again :
I assume you want achieve 400 watts audio amplifier . it means Vout across the 2 ohms load should be around 40 volts . ok ?( (vpp^2)/8RL )
As you probably know , your audio signal , is not in constant amplitude . it has variations . so , if your regulator is linear it means if you need 40 or 45 volts at the out put , you have to use at least 60 or 65 volts as input DC voltage ( unregulated ) . and current for 400 w = 40/2=20A ok ? so , dissipated power across the regulator will be 20*25=500W . with this large value of dissipation as heat , you can bake cake and sweets for a big celebration !!!!! it is very fun that you want achieve 400w and then loss the power around 500W . isn't it ?
So , now if you consider that you have a Buck regulator , suppose that the input voltage is 100 volts and out put ( after filter ) is 40 volts . don't forget that the voltage before filter , is a square wave with amplitude , around 100 volts . suppose D.C is around 0.4 . consider your mosfet is IRFP450 . if Rdson is 0.5 ohms . dissipation will be D.C*(Rdson*Idmax^2) 0.5*20^2=200 =====>200*0.4=80W . is 80W reasonable or 500W ? is there any unclear thing in my explanations , available ? if yes , tell me , please i'll simplify that .

I have understood why we are using this regulator of course 80W is reasonable. But tell me where does this 25 came (highlighted in bold caps)?

Of course . it called DC/DC converter , because the input voltage is unregulated DC voltage and out put voltage is regulated DC voltage .

Our input is a square wave. In books I have read two types of non-sinusoidal signals; one is square wave and other is triangular wave. But here you said our input is DC voltages so it's mean square is DC voltage?

Can you remember the diode that we have putted to prevent damages of mosfet and recovering the energy , to recharging the out put capacitor ? that diode called freewheeling diode or fly back diode . ok ?

Great definition.

as you probably kno each conductor has a low value of resistance . ( R=p*(L/A) did you know this ? ) .

Yes I know this.

We should select capacitors with lowest value of ESR , but because these capacitors are a bit expensive , i usually using some capacitors in parallel . by the way , do you know about equivalent model of a real capacitor ? it is pretty important .

I didn't get what you said here. What is meant by as you said, "I usually using some capacitors in parallel."
About a real model I just know capacitor has some internal resistance like every conductor. Is there something more to know about a real model?

You can put each load in out put of your SMPS . i will talk about continuous and discontinuous mode of operation . be patience . it is not for this time .

I didn't get what you said. But I will wait for that time when you will teach me this too.

Thanks for this great explanation.

 

[goldsmith]

I don'et know why moderators have deleted it , but i attach it again :

see it , until i'm reading your above post .

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I have understood why we are using this regulator of course 80W is reasonable. But tell me where does this 25 came (highlighted in bold caps)?

It is simple : 65-40=25 ( 65 volts as unregulated voltage and 40 volts as out put of regulator .

Our input is a square wave. In books I have read two types of non-sinusoidal signals; one is square wave and other is triangular wave. But here you said our input is DC voltages so it's mean square is DC voltage?

I told you at past that when you don't understand each section , tell me before continuing and increasing the definitions . see below :

You understand ?

I didn't get what you said here. What is meant by as you said, "I usually using some capacitors in parallel."
About a real model I just know capacitor has some internal resistance like every conductor. Is there something more to know about a real model?

See below , please :

You understand ?

 

[Shayaan_Mustafa]

I don'et know why moderators have deleted it , but i attach it again :
View attachment 76678
see it , until i'm reading your above post .

I was thinking this and really I didn't get answer. But may be it is something related to capacitor, I guess.

It is simple : 65-40=25 ( 65 volts as unregulated voltage and 40 volts as out put of regulator .

So 25 is the difference of the output and input. But dissipation is always at a load so why don't we only account regulated output? Because in university until where we have measured power dissipation is just across the load so we take voltage across load and current through load. But here you are taking difference of output and input while calculating power dissipation.

I told you at past that when you don't understand each section , tell me before continuing and increasing the definitions .

Sorry sir, I know you told me. But at that time I had cleared everything. I just confused about DC voltages at input. While at input at Gate of MOSFET we have square wave. So this means square wave is not a sinusoidal nor a DC voltage.

See below , please :
View attachment 76680
You understand ?

I have now gotten it.

One more thing I want to ask. Here diode is not acting as rectifier diode. Right?
Here it is a free-wheeling diode. Right?

Let's say I have given a circuit with a diode, then how would I can recognize the diode whether it is free-wheeling diode or rectifier diode? Is it need an experienced eye to judge?

 

[goldsmith]

shayaan , now i have to go , tomorrow i will back and answer all of your questions in detail. i was in a trip for two days and today i came back but because i was in hurry it was pretty awful . hence i need a bit rest . see you tomorrow .
Best Wishes
Goldsmith

 

[Shayaan_Mustafa]

Sure sir. Good morning.
Thank you once again.

 

[goldsmith]

Hi shayaan

I was thinking this and really I didn't get answer. But may be it is something related to capacitor, I guess.

It is due to the lenz law , what AC does mean ? variation in polarity , right ? what is the polarity across the inductor ? see my latest drew picture about it again .

So 25 is the difference of the output and input. But dissipation is always at a load so why don't we only account regulated output

No consumption is across the load . dissipation means the power that we didn't use and we don't want to use it , but it will loss and it is out of interest of each designer . we should set it as low as possible .

Sorry sir, I know you told me. But at that time I had cleared everything. I just confused about DC voltages at input. While at input at Gate of MOSFET we have square wave. So this means square wave is not a sinusoidal nor a DC voltage.

When we have a 15 volts across the GS , it means we have a switch , just ! and nothing else ! . on or off .

One more thing I want to ask. Here diode is not acting as rectifier diode. Right?
Here it is a free-wheeling diode. Right?

Let's say I have given a circuit with a diode, then how would I can recognize the diode whether it is free-wheeling diode or rectifier diode? Is it need an experienced eye to judge?

You should be able to analyze your circuit ! you should know all things about the configurations before use !
Best Wishes
Goldsmith

 

[Shayaan_Mustafa]

Thanks all these reply step by step.

I understood.

And for AC across inductor; yes I have recognized it, it is due to Lenz's law.

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So we can say that if DC passes through the inductor then due to Lenz's law it may be AC. Is this statement correct?

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Sir I have to go now. It is 3:25am.

But you post what you want to teach me.

Good morning. May G O D bless you.

 

[goldsmith]

So we can say that if DC passes through the inductor then due to Lenz's law it may be AC. Is this statement correct?

Do you know what lenz law means ? if yes , can you show me ?

And good morning . see good dreams my friend .

 

[Shayaan_Mustafa]

Yes sir I think I know. It is the description of Newton's 3rd law of motion.

 

[goldsmith]

Hi shayaan
Let me simplify my meaning :
I think my description about this section was not as clear as enough , hence , see below , please :

Shayaan , i want describe an effect of inductor :
VL=-L*(di/dt)
A first law : we have a lovely effect that called inertia or in the other hand linear density . i think you are asking yourself that what does these words mean , no thing strange ! it means an inductor wants to do opposition with changes . it means when it has not any current and we want inject it a current it will try to keep it's initial condition . hence it will create a voltage against it !
See below , please :

You understand ? an inductor wants to keep it's initial or current situation ! i have created voltages nearby 200kv with a simple inductor and fast switch !!
And what does VL=L*(di/dt) mean ? it means if your switch be off , the dt is pretty low , and L is so large and di is large too and then VL ( voltage across the inductor ) can increase as large as some mega volts !!!!!!! or higher , if there won't be any path for it ! . so , that diode in our circuit will create a path for it , hence it won't destroy all things in our circuit ! it just will recharge the capacitor !
SO , what i have tried to say ?
see below , please :

Shayaan , i'm here to help you really , so , if you didn't understand them , tell me , please , and don't trick yourself . ok ?
Best Wishes
Goldsmith

 

[Shayaan_Mustafa]

Hello sir !

I hope you will be fine.

Due to my internet connection problem I am having difficulty in posting mostly but I have read your reply.

I want to say, I understand but I still have some problem. Can you make me understand in the most easiest way how AC across inductor?

Above reply is little bit confusing.

Shayaan , i'm here to help you really , so , if you didn't understand them , tell me , please , and don't trick yourself . ok ?

Thank you very much for this one.

 

[Shayaan_Mustafa]

Hello Sir !

I have read your post 4 to 5 times. And I got what you have said.
By reading 4 to 5 times, I understand what you tried to say to me.

Thank you.

 

[goldsmith]

Hi shayaan
I came back !
Are you sure that you have understood it ? i have decided to write another thing for you , today , but if you understood it , really , i think we can continue .

 

[Shayaan_Mustafa]

Yes sir. I am sure.
But if you want that you want to write that so you can. But really I have understood.

You may continue now.

Sorry for horrible internet connection.

 

[goldsmith]

Sorry for horrible internet connection.

Ha ha , my internet is pretty low speed too !
And i'm very happy because you have understood it .
So , let me ask you for an experiment ! did you connected a 1n4007 diode to the square wave source , with frequency around 1MHZ ? can you predict what will happen ? can you show me the result of simulations ?

 

[Shayaan_Mustafa]

I have connected 3 components, diode, square wave generator and a ground.

But I don't know how to change frequency, what should be PW, V1, V2, TR, TF, PER. ?

I am using PSpice version 16.

How use these? What should be their values?

 

[goldsmith]

Humm , i knew it that you will ask about those parameters !
Do you know what does rise time and fall time ? what about delay time ? ( i'm talking about a square wave )

 

[Shayaan_Mustafa]

How would I know all of that sir :-(