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Class D Switching Power Amplifiers and Power D/A conversion

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Old 8th December 2011, 03:19 PM   #1501
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Ok..thanks alot!
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Old 10th December 2011, 04:06 PM   #1502
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Quote:
Originally Posted by CPX View Post
Ok..thanks alot!
Have you managed to solve the noise and distortion problems?
After changing output filter, have you managed to get out more power?
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Old 10th December 2011, 05:26 PM   #1503
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Not yet..i only changed output transitors to irfb4321 and unforcenetly i got the same efficiency as with irfp540z.arround 80% in 1 ohm load..very low...so power is lost during switching and not by rds .
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Old 10th December 2011, 07:46 PM   #1504
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Update
Tested with lm319...Switching frequency has increased from 380 la 520 khz but distorsions have increased at 50 hz and 20 hz..no change at 15khz and above(also tested with aditional capacintace to obtain ~300khz)..so a faster comparator means more distorsions in my case....why???

Last edited by CPX; 10th December 2011 at 07:52 PM.
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Old 10th December 2011, 08:01 PM   #1505
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Quote:
Originally Posted by CPX View Post
Update
Tested with lm319...Switching frequency has increased from 380 la 520 khz but distorsions have increased at 50 hz and 20 hz..no change at 15khz and above(also tested with aditional capacintace to obtain ~300khz)..so a faster comparator means more distorsions in my case....why???
Increased switching frequency shows the reduced propagation delay, so it means good.
Something is wrong with freqs at 20-50hz. For this circuit the imput frequency should cound nothing if it is much lower than switching freq. Isn't it because of your signal generator?
What is your power supply? How much is the supply decoupling capacitor?
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Old 10th December 2011, 08:34 PM   #1506
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Yes..something is wrong at frequencies<100hz..and >10kHz.

I tried adding filtering capacitance(from 10mF to 15mF)..no change,but added 1uF at output and i saw a small decrease in distorsions at 50 hz and 1A increase in current before distorsions at 18khz.
I then added 2.2uF but i saw a huge increase in distorsions ..it seems residual was to small so i decreasied switching speed but that generated oscilations with no load(1kohm dummy load) at high frequencies input,so i do not think it will work with 7.5uF output capacitance at 380khz.....maybe 2-3uf ..
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Old 10th December 2011, 08:46 PM   #1507
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Quote:
Originally Posted by CPX View Post
Yes..something is wrong at frequencies<100hz..and >10kHz.

I tried adding filtering capacitance(from 10mF to 15mF)..no change,but added 1uF at output and i saw a small decrease in distorsions at 50 hz and 1A increase in current before distorsions at 18khz.
I then added 2.2uF but i saw a huge increase in distorsions ..it seems residual was to small so i decreasied switching speed but that generated oscilations with no load(1kohm dummy load) at high frequencies input,so i do not think it will work with 7.5uF output capacitance at 380khz.....maybe 2-3uf ..
How do you measure distortion? Did you see clipping distortion, or what other non-linearity?
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Old 10th December 2011, 09:04 PM   #1508
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I am using my ears..i have very sensitive hearing..

I listen the difference between no load and load..i know exactly how a clean sine sounds..and those are big distorsions but rarely visible on the digital scope(some are visible especially at high frequencies).

I will make sound card distorsions measurements after i will be unable to pick up with my ears any change in signal in load/noload tests.
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Old 10th December 2011, 09:12 PM   #1509
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Quote:
Originally Posted by CPX View Post
I am using my ears..i have very sensitive hearing..

I listen the difference between no load and load..i know exactly how a clean sine sounds..and those are big distorsions but rarely visible on the digital scope(some are visible especially at high frequencies).

I will make sound card distorsions measurements after i will be unable to pick up with my ears any change in signal in load/noload tests.
So you put a loudspeaker at output, and listen to it? But then what load and no load means?
Even if you ears are good, your brain is the most unrealiable source for comparison... so stay with oscilloscope, Fourier-transforms or other.
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Old 10th December 2011, 09:18 PM   #1510
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I am using resistive load(1 ohm)..no speaker..i have headphones connected to the output with a resistive network.
Any way 50hz and 20 hz distorsions that i hear are not visible on the scope/fourier..
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