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Class D Switching Power Amplifiers and Power D/A conversion

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Old 25th August 2010, 06:03 PM   #451
RaiTulo is offline RaiTulo  Finland
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Default Elfa Sverige

Quote:
Originally Posted by Tekko View Post
I plan on replacing the LM311 if i find something better. I tried to sample an LT1016 but they wont accept free email adresses anymore, and at 16 dollars minimum on ebay, its way outta my budget.

Suggestions ? Pin compatible would be nice, so i could just pop it into the prototype for testing.
Elfa (All prices are in SEK exclusive of VAT and freight charges)

https://www.elfa.se/elfa3~se_en/elfa...c;node=0;id=2;
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Old 25th August 2010, 06:12 PM   #452
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Elfa is very expensive!!! I can only go for free samples.
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Old 25th August 2010, 06:53 PM   #453
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I may try this when my samples from maxim arrives in a few weeks:
Click the image to open in full size.
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Old 25th August 2010, 08:02 PM   #454
savu is offline savu  Romania
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Quote:
Originally Posted by AP2 View Post
Hi all,
I hear interesting speeches from Savu or Baldin and job of Tekko But I do not understand the insistence to use a comparator lm311 on audio? is a poor comparator for audio. then it is normal that there is no difference of THD with 250kHz (at 1KHz) you try 2 or 3 high frequency signals and measure intermodulation if you want to see the difference, eg. at 400KHz.
Savu: for my experience (I can demostrate with Measure) TC44xx is not good for driving on 2-3Kpf on gate MOSFET ( Because internal use mosfet complementary and Have rds-on) not good for fast. A very good amplifier requires a chain of solutions, for this reason the concept is simple but very difficult to obtain.

Regards
Hello AP2 ...
IMHO I think that this amp is crap. At lest the original version is.
I do not militate on using LM311 comparator.
I militate for using LT1711 and other fast comparators to reduce propagation delay at the imput stage.

Regards,
savu
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Old 26th August 2010, 09:12 AM   #455
AP2 is offline AP2  Italy
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Hi Savu,
I was referring in general lm311.
yes, fast comparator is important for resolution and clearly helps to reduce the propagation time But more speed equals more "glish" and artefact, RFI etc and requires a very nice development of the PCB. very good Class D is ... "bastard in side".
sooner or later I will a Amp with direct-conversion, eliminated some stages.. ..(comparator and mosfet only)

Regards

Last edited by AP2; 26th August 2010 at 09:14 AM.
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Old 26th August 2010, 09:18 AM   #456
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Yes the original version of this amp is crap, i used LM311 because it happened to be what i had available in my parts box.

I currently have 187nS propagation delay from comparator output to after the fets before the output filter in my simulation.

With that much propagation delay, i wonder if a comparator with super low propagation delay is really improving anything, unless it adds to the other propagation delays.

Im pretty sure a MAX913 will be a drastic improvement opver the LM311 atleast. And geting rid of that ltp thing with the 4 transistors is likely a big improvement as well.

Last edited by Tekko; 26th August 2010 at 09:20 AM.
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Old 26th August 2010, 09:34 AM   #457
AP2 is offline AP2  Italy
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Quote:
Originally Posted by Tekko View Post
Yes the original version of this amp is crap, i used LM311 because it happened to be what i had available in my parts box.

I currently have 187nS propagation delay from comparator output to after the fets before the output filter in my simulation.

With that much propagation delay, i wonder if a comparator with super low propagation delay is really improving anything, unless it adds to the other propagation delays.

Im pretty sure a MAX913 will be a drastic improvement opver the LM311 atleast. And geting rid of that ltp thing with the 4 transistors is likely a big improvement as well.
Hi,
First of all for improve performances you have to redesign Q3-q4 stage because actually is very slow (it is passive jmp with very small current).
PWM does not work well at the limits of range.
Then ,not have sense change only comparator.
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Old 26th August 2010, 09:54 AM   #458
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This circuit yields 6nS propagation delay in the level shifter:
Click the image to open in full size.
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Old 26th August 2010, 10:41 AM   #459
savu is offline savu  Romania
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Quote:
Originally Posted by AP2 View Post
Hi Savu,
I was referring in general lm311.
yes, fast comparator is important for resolution and clearly helps to reduce the propagation time But more speed equals more "glish" and artefact, RFI etc and requires a very nice development of the PCB. very good Class D is ... "bastard in side".
sooner or later I will a Amp with direct-conversion, eliminated some stages.. ..(comparator and mosfet only)

Regards
you are right, but if you use all smd package like sop, or even bga or lga, with board make out of copper coated in silver (for better rfi performance) and use shields like in mobile phones you can get some pretty results.

regards,
savu
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Old 26th August 2010, 10:45 AM   #460
AP2 is offline AP2  Italy
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Hi,
this yes but...runnig only if low side have low voltage,in this case 18v.
and ..you put a heatsink on this bjt?
also, high thd introduce becouse base current is very high!
A part not really possible 6ns. 15-18 ns is allready good...if solve dissipation first, then add other bjt and
story is infinite.

Last edited by AP2; 26th August 2010 at 10:49 AM.
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