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 Class D Switching Power Amplifiers and Power D/A conversion

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lorylaci
diyAudio Member

Join Date: Aug 2008
Location: Dabas, Hungary
Quote:
 Originally Posted by Dzony988 Thank you pafi. I measured 19turns. thats it. But accidentally i found ETD29 core with gap 2x0.5mm gap, from PC smps. Do someone know materia nuber (27 or 87). how can i calculate number of turns. From datasheet I see that N27 has variant with only 0.1mm gap on one half of core, and N87 has variant with 0.5mm (one half) gap and Al value is 201nH. That means from calculation 10 turns for 20uH, or what. Is that calculation for one half or all core? How many number of turns for whole core. One galf gas 0.5mm gap and whole core has 1mm Thank you
The maximum reccomended frequency for N27 is 100kHz, N87 can take up to 300kHz, so its much better.
2x0,5mm gap is not enough, as you can see the required turns is not enough, it might saturate. Wind it with 18 turns, and put paper between the two half cores, until its inductance decreases to 20uH.
Attached there is a zipped spreadsheet to calculate cores.
Attached Files
 vasmag gerjesztés.zip (8.8 KB, 469 views)
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Pafi
diyAudio Member

Join Date: May 2004
Location: Budapest
Quote:
 Originally Posted by lorylaci The maximum reccomended frequency for N27 is 100kHz, N87 can take up to 300kHz, so its much better.
N27 is perfectly usable for output filter inductor, since most of the current is in the audio band. The ripple current is too low to make any problem in a properly sized core. Those freq limits are only guidelines for pure HF excitation (SMPS transformer).

Quote:
 2x0,5mm gap is not enough, as you can see the required turns is not enough, it might saturate.
For 1 kW it's not enough indeed, but I don't know if he wants to build such a big amplifier or a smaller one. Basically the ETD29 is not enough for this high power, regardless of gap height.

Quote:
 Attached there is a zipped spreadsheet to calculate cores.
"Utáp" (Vcc) is a little too high, 150 V would be enough for 2 kW.

To the users: Attention! K1 and K2 are also from datasheet, they are different for different cores!

Last edited by Pafi; 30th April 2011 at 09:42 AM.

 30th April 2011, 11:19 AM #1073 Dzony988   diyAudio Member   Join Date: Apr 2010 Location: Nis, Serbia I maked output coil, and on full power is very little little warm, its beter then other core. previously core, when i conected and turn on amlifier, without signal, came up big spark in gap and stay until I switched off amp after few seconds Thank you Laci and Pafi
electroconico
diyAudio Member

Join Date: Jun 2010
What material could it be this toroid ?

I want to use it but i dont have any specification.

any sugestion??

Color gray-yellow.

External diameter = 1 1/5" (1.5inches) - 38.1mm

Internal diameter = 13/16" (0.8125inches) - 20mm

wide = 9/16" (0.5625inches) - 14.28mm

-images atached

regards!
Attached Images
 unknown toroid.jpg (49.5 KB, 1301 views)

Pafi
diyAudio Member

Join Date: May 2004
Location: Budapest
Quote:
 Originally Posted by electroconico What material could it be this toroid ? I want to use it but i dont have any specification. any sugestion?? Color gray-yellow. [...] regards!
I guess it's ferrite. You should measure AL!

If you don't have inductance meter, there are many other ways! You have to find some AC voltage source with a few kHz output (for example your sound card), put a resistor (for example 100 ohm) in series, attach the coil with 10...30 turns, and measure the voltage accross the coil (again, with your sound card input, and some SW)! You have to chose/altern such resistor/number of turns/freq so that Vcoil=0.02...0.3*Vsource!

You can differentiate between ferrite and metal powder with a very simple test: wind 20 turns, and put it in series with your regularly used tweeter (4 or 8 ohms, dinamic type!). If high tones are almost completely gone, then it's ferrite, if highs only slightly decreased, then it's metal powder. In the second case you can try to use it. In the first case first you need to break it into 2 or 4 pieces in order to avoid saturation!

An other way to differentiate between ferrite and metal powder: try to saw it! If you can do it easily, then it's not ferrite.

Last edited by Pafi; 1st May 2011 at 07:45 AM.

 2nd May 2011, 10:50 PM #1076 Dzony988   diyAudio Member   Join Date: Apr 2010 Location: Nis, Serbia Hi to all. During holidays, during party,my d class amps (3 of them, stereo) are worked 9 hours without stoping on full power, and survived all of them. Cold heatsinks, all components except resistors for TIP41 and LM311. One of them is on +-60V with IRFP240 and it was worked on 2ohm load per chanel all the time. Transistors are survived although I thought it would not to submit 2 ohm load for a long time at full power..
opor
diyAudio Member

Join Date: Nov 2005
Quote:
 Originally Posted by lorylaci Yesterday my firend told me the main problem: "you have pin 1 on gnd, so your comp output swings between 0 and 3V, not enoguh to turn on the transistors next to". I put pin 1 to -3V. Now everything works. With some setups my switching frequency reached 400kHz. But now I use the following schematic as a test: The switching freq is at 320kHz (3,1us periodic time). (the same feedback with other connecntiion was at 250kHz)
Following this schematic. Is noise eliminated?

lorylaci
diyAudio Member

Join Date: Aug 2008
Location: Dabas, Hungary
Quote:
 Originally Posted by opor Following this schematic. Is noise eliminated?
I had only probelem with noise in the first prototypes. So far I had no problem with noise. But noise mainly depend on your layout and connection, in my setup its eliminated.
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opor
diyAudio Member

Join Date: Nov 2005
Quote:
 Originally Posted by lorylaci I had only probelem with noise in the first prototypes. So far I had no problem with noise. But noise mainly depend on your layout and connection, in my setup its eliminated.
And how about DC offset?

lorylaci
diyAudio Member

Join Date: Aug 2008
Location: Dabas, Hungary
Quote:
 Originally Posted by opor And how about DC offset?
DC offset is easily eliminated if you put a 10uF cap in series with the 820r resistor. I don't care about a small DC offset (one of my board it was 0,2V, in some other it was 70mV, with the cap it is less than 50mV), and there are hundred ways to correct DC offset, so I don't know why everybody is so upset about it.
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