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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th September 2011, 07:10 AM   #1311
CPX is offline CPX  Romania
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I have 4 grounds(Speaker Gnd,Capacitor Gnd,Digital Gnd and Signal Gnd) they all go to star Gnd .. i tried all kinds of gnd versions and wire positions..they all have noise,feeadback wire (even shielded) picks it up from my gapped toroid and oscillation bus...anyway i measure it with mai ear glued to the speaker..i am comparing to my receiver which sounds completly dead,like unplugged....
I will try the resistor to see if it changes anything.....

Thanks Dzony988 for your help..if i have better results or more questions i will post again.

Last edited by CPX; 15th September 2011 at 07:20 AM.
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Old 15th September 2011, 09:11 AM   #1312
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Adding the resistor had no effect...
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Old 15th September 2011, 02:27 PM   #1313
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Doyou have noise when you short input direct on pcb?
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Old 15th September 2011, 04:19 PM   #1314
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Yes..all noise tests are beeing done with shorted input..
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Old 15th September 2011, 05:12 PM   #1315
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Try to put 470uF or 1000uF 100V near by fets on power rails. (near drain and gnd on + and source and gnd on -). Paralel with them put 100n 100V. Output coil conect accros a wire few centimeters away from board
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Old 15th September 2011, 05:15 PM   #1316
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I already have 2x220uf, 1x470uf and 6x100 nF on each rail (4x100nF and 470uf cvlose to mosfets)
I also tried conecting coil far for the board..
I do not understand what is wrong..now i have distorsions starting 10 volt before clipping point..

Last edited by CPX; 15th September 2011 at 05:17 PM.
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Old 15th September 2011, 05:34 PM   #1317
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what is percent of THD 10V befere clip? What is supplay voltage and what is imedance of load?

What bridge do you use? If you use fast diodes, you will never kill 50Hz noise ( some of harmonics will pass accros diode). for main bridge you have to use slowest diode because the most slowest diode on the world is stll very fast to distroy 50Hz noise. You have to slow your bridge with 4x 100nF in parallel with all 4 diodes in bridge
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Old 15th September 2011, 05:36 PM   #1318
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Quote:
Originally Posted by CPX View Post
I already have 2x220uf, 1x470uf and 6x100 nF on each rail (4x100nF and 470uf cvlose to mosfets)
I also tried conecting coil far for the board..
I do not understand what is wrong..now i have distorsions starting 10 volt before clipping point..
Could you send the exact schematic and pcb layout you have? And if you can the photo of the test setup! I am sure i can give lots of ideas.

What type of core do you use? Gapped toroid in my opinion is worse then a gapped EE, ETD or RM ferrite. Iron powder (micrometals material -2) toroids are usually good, and has the pro that magnetic field is same all around. In a gapped toroid the B function has a shift around the gap, leaking radiation.

For example try some of the Coilcraft shielded flat-wire wound inductors. They are extremely good, two of VER2923-103K connected series will give you 20uH 5mOhm, and >30A saturation current.

Quote:
have 4 grounds(Speaker Gnd,Capacitor Gnd,Digital Gnd and Signal Gnd) they all go to star Gnd
Use one big ground plane! If you can, use a two-sided board, even if you have no wire on top, use top layer as a big ground plane! See Bruno's ideas about star-ground vs ground plane.
Only if necessary separate ground planes as told in IR's manual (analog input, V- the common of IR2110, and power otuput ground)
My experiments have shown much reduced noise and EMI with one big ground plane.

Are you still useing the old IRF540 (no N no Z)? Even with the schottkys, it will produce EMI.
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Old 15th September 2011, 05:56 PM   #1319
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Laci, can I try with this core?
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Old 15th September 2011, 07:49 PM   #1320
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Quote:
Originally Posted by Dzony988 View Post
Laci, can I try with this core?
I reccomend NOT to use that core for class D audio.
Core losses will be high at the switching freq, saturation current is not high enough. This core material is not so suitable for this use.

Use micrometals -2 or -6 instead, if iron powder you want. Or use gapped ferrite. RM cores are amongst the best, since they provide shielding, low PCB space. The previously given coilcraft one was an only an example, but it is one of the bests for this use.
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