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Class D Switching Power Amplifiers and Power D/A conversion

Class D Design Issues
Class D Design Issues
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Old 28th October 2018, 06:17 PM   #131
dipolar is offline dipolar  India
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Quote:
Originally Posted by nigelwright7557 View Post
I use a T106-2 10uH with 470nF at 250KHz and it barely gets warm.

I know on mine I got a little residual carrier but I don't think its anything to worry about. The speaker wont reproduce 100KHz.
I will try that again and come back.

Last time I tried 15uh / 0.4uF in Tl074 based amp (my first one), and mosfet were dead,so bit more cautious and reserved with this new trial.
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Old 28th October 2018, 06:22 PM   #132
dipolar is offline dipolar  India
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I had also noted that while doing audio sweep at around 10khz to 13khz there is almost 3-4db peak, thats like this amp is behaving like a peak filter ??
Oscilloscope output was across speaker terminal and I was sweeping from 20HZ to 20khz manually from PC soundcard.

Could it be due to some speaker (4ohms) resonance or LC filter or feedback?

(But before that to be explored I had to sort out the sine wave in output.)
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Old 29th October 2018, 02:30 PM   #133
irs20957 is offline irs20957  Russian Federation
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Quote:
Originally Posted by dipolar View Post
I had also noted that while doing audio sweep at around 10khz to 13khz there is almost 3-4db peak, thats like this amp is behaving like a peak filter ??
Oscilloscope output was across speaker terminal and I was sweeping from 20HZ to 20khz manually from PC soundcard.

Could it be due to some speaker (4ohms) resonance or LC filter or feedback?

(But before that to be explored I had to sort out the sine wave in output.)
Feedback before output filter, do post filter feedback.

Last edited by irs20957; 29th October 2018 at 02:32 PM.
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Old 29th October 2018, 06:40 PM   #134
dipolar is offline dipolar  India
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Quote:
I use a T106-2 10uH with 470nF at 250KHz and it barely gets warm.

I know on mine I got a little residual carrier but I don't think its anything to worry about. The speaker wont reproduce 100KHz.

Reduced the Fsw by changing he feedback resistor to 2.2k and 100pf.
OP LC remain original 30uH/0.47uF

Now the FLoating voltage diode Mur1100e heats considerably ,finger burns.
The waveforms are as in images below.

Now the new problem is amp becomes unstable beyond certain amplitudes ,
When input volume is increased beyond certain level , music begins to distort and suddenly dreaded HUm is heard which goes away when amp is restarted.
Probably amp starts to oscillate .

attached the image of wave when sudden hum is heard.

Also the output zobel 10 ohm resistor heats up too much almost to smoke.


Quote:
Feedback before output filter, do post filter feedback.
Thank you ,I will try the filter and see.
Attached Images
File Type: jpg 1.jpg (86.0 KB, 181 views)
File Type: jpg 2.jpg (110.5 KB, 177 views)
File Type: jpg HUm wave.jpg (88.2 KB, 176 views)
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Last edited by dipolar; 29th October 2018 at 06:50 PM.
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Old 30th October 2018, 12:37 PM   #135
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by dipolar View Post
Reduced the Fsw by changing he feedback resistor to 2.2k and 100pf.
OP LC remain original 30uH/0.47uF

Now the FLoating voltage diode Mur1100e heats considerably ,finger burns.
The waveforms are as in images below.

Now the new problem is amp becomes unstable beyond certain amplitudes ,
When input volume is increased beyond certain level , music begins to distort and suddenly dreaded HUm is heard which goes away when amp is restarted.
Probably amp starts to oscillate .

attached the image of wave when sudden hum is heard.

Also the output zobel 10 ohm resistor heats up too much almost to smoke.




Thank you ,I will try the filter and see.
You need to design the output low pass filter very carefully on the right speaker impedance, post feedback is not needed for cure the peak, this is because of output filter, maybe wrong core or such. Postfeedback can be used but fase shifts make feedback more difficult see pdf.

https://www.hobbielektronika.hu/foru....php?id=253790

regards

Last edited by kees52; 30th October 2018 at 12:49 PM.
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Old 30th October 2018, 08:54 PM   #136
dipolar is offline dipolar  India
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Quote:
Originally Posted by kees52 View Post
You need to design the output low pass filter very carefully on the right speaker impedance, post feedback is not needed for cure the peak, this is because of output filter, maybe wrong core or such. Postfeedback can be used but fase shifts make feedback more difficult see pdf.

https://www.hobbielektronika.hu/foru....php?id=253790

regards
Thank you for this document ,exactly what I was looking for.
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Old 31st October 2018, 01:13 PM   #137
kees52 is offline kees52  Netherlands
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