how i can increase this to 20w? please help!

 

I would start with using a proper driver for the mosfets. Then you could try increasing the voltage in the output stage.

 

how i can do? can you help me for this please

 

For 20W into 8 ohm, you need at least 18Vp at the output. That requires symmetrical supply to the output stage of at least +-18V.
Also, you should be using an comparator instead of operational amplifier.
V2 needs to be biased to cca 2.5V to make the circuit even work. (or add a 10u cap in seris with R3)

Then you can look on the output stage, and replace the transistors with some half-bridge mosfet driver IC.

 

so if i send my project documents to you could you please help me to drive mosfets??it is so important for me...please(

 

What are you trying to do?

 

i am trying to make a 20w d class amplifier. if i can't do this, i won't graducate, please help

 

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To get 20W in 8Ω you need at least V_lod = √2*20*8 = +/- 18V
Your supply voltage is 12V so max power that you can get is P_max =6^2/16 = 2.2W

 

I think OP needs to define the classes first if he/she wishes to graduate


I made a dooozy....

 

I attached tutorial for class D
http://www.edaboard.com/thread141833.html#post612674

 

I attached tutorial for class D
http://www.edaboard.com/thread141833.html#post612674

Hmmm!! nice one jony

 

I guess the OP doesn't know enough about simple electronics to graduate.

 

i made this. i can't speak english very well, sorry. please help...

 

With an 18v supply, the max undistorted output into the 8 ohm load is about 5.0W.
If the supply is 36V or plus and minus 18V as was said before then the max undistorted output is about 19.8W.

If you don't care about distortion then your latest schematic can produce a square-wave of 10W into 8 ohms.

 

U know What OP...we cannot graduate you....
It's up to you to do it...if we did it, you will learn nothing.

So .please stop begging and do some research from the documents provided

 

what am i doing? can you draw shametics it please?

 

Ur circuit is OK...what others are telling is that u need to increase the power supply to increase the power.
Don't you understand simple English?

 

I wonder why he doesn't ask in his own language on a website in his own country.
I also wonder why he doesn't ask his teacher.

 

i only wanted your help. Thanks for everything.