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Class D Switching Power Amplifiers and Power D/A conversion

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Old 11th January 2013, 05:25 PM   #211
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KiCad does not allow to set different clearances, as a function of position, for a filled area.
Nevertheless the necessary structures below the comparator would be OK for most PCB manufacturers even with 70µm copper.
So I added manually a GND grid.

Edit: The track thickness and and clearance setting for the grid is 0.35mm.
Attached Images
File Type: jpeg triplecomp_grid.jpeg (821.2 KB, 409 views)

Last edited by ChocoHolic; 11th January 2013 at 05:27 PM. Reason: track thickness & clearance
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Old 13th January 2013, 02:55 PM   #212
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Default Multi Outline of Comparators

Today I set up a small jig for testing the intended multi outline before going on with the layout.
Also this is helpful for comparing the comparators.
The jig is build with identical routing as intended for the amp.
Attached some pictures showing the different positions of LM306 or MAX913 or LM361.
All comparators are working correctly with the intended routing.
The electrical testing was done with input signals of +/-10mV and a frequency of 2MHz.
LM306 is the slowest and shows slightly more self disturbance when driven with rectangles, but for a so called 'scrappy' comparator it is really good.

Besides measurements with rectangles, I also measured with +/-10mV triangles.
And there we can see, why I am stating that the fastest high end comparators are not the best choice for classD. When driven with small and slowly creeping signals these ultrafast high gain devices start to show serious jitter.
MAX913 performs great with rectangular input signal of reasonable size, but for input signals with low dv/dt it generates by far more jitter than a LM306 or LM361.
I am curious if we will see impact from this effect on the noise figures of the amp.

Overall the LM361 seems to perform very well.
My thanks to Kanwar that you pushed me to add it, despite its unpleasant size.

Edit:
All measurements were done with 10:1 probes.
Upper trace is the input voltage of the comparator.
Lower trace is the output voltage of the comparator.
Attached Images
File Type: jpg LM306jig_640x853.jpg (442.7 KB, 330 views)
File Type: jpg LM361jig_853x640.jpg (441.6 KB, 286 views)
File Type: jpg MAX913jig_853x640.jpg (448.9 KB, 257 views)
File Type: jpg LM306rect_853x640.jpg (496.8 KB, 231 views)
File Type: jpg LM361rect_853x640.jpg (502.7 KB, 43 views)
File Type: jpg MAX913rect_853x640.jpg (515.1 KB, 37 views)
File Type: jpg LM306tri_853x640.jpg (512.2 KB, 40 views)
File Type: jpg LM361tri_853x640.jpg (456.6 KB, 38 views)
File Type: jpg MAX913tri_853x640.jpg (508.7 KB, 41 views)

Last edited by ChocoHolic; 13th January 2013 at 03:01 PM. Reason: see Edit
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Old 14th January 2013, 08:20 AM   #213
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The modulator stage was not stable in open load, actually blown power switches without load.
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Old 14th January 2013, 10:23 AM   #214
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Quote:
Originally Posted by ionutgaga View Post
The modulator stage was not stable in open load, actually blown power switches without load.
huh?
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Old 14th January 2013, 12:13 PM   #215
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Quote:
Originally Posted by ionutgaga View Post
The modulator stage was not stable in open load, actually blown power switches without load.
Which power stage and with reference to which design?
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Old 14th January 2013, 12:28 PM   #216
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Power stage Irfb4332+ir2110, +/-107v, 4r dummy load, with load works ok, but not superior to ucd at clip, frequency drop the same.
This is what i have in hand for a little experiment (ucd-like builded about 3 years ago, but works ok even in 2r, offcourse-with power supply sag):
Attached Images
File Type: jpg mod1.jpg (82.5 KB, 146 views)
File Type: jpg mod2.jpg (87.4 KB, 158 views)
File Type: jpg ucd.jpg (90.3 KB, 185 views)
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Old 14th January 2013, 02:56 PM   #217
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Quote:
Originally Posted by ionutgaga View Post
Power stage Irfb4332+ir2110, +/-107v, 4r dummy load, with load works ok, but not superior to ucd at clip, frequency drop the same.
This is what i have in hand for a little experiment (ucd-like builded about 3 years ago, but works ok even in 2r, offcourse-with power supply sag):
ouch, how did you even get your circuit to work, its looks like a forest.
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Old 14th January 2013, 04:21 PM   #218
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Hi Ionut,
your posting does not show any key information.
You are stating that you tried a class D amp as 3D pin2pin construction and it was not better than an older design with a GND plane construction.
Considering that the layout makes 50% of the design of a class D amp, your findings are not surprising.

Regarding circuitry I can only guess you tried one of the modulator schemes of this thread with a completely different power stage and higher rails.
If done right, 3D pin2pin can operate in a satisfying way also for class D.
But I have to disappoint you - in the moment my priority is clearly to bring forward my design rather than debugging yours.

I understood that you did some comparative measurements before your experimental set up died.
If you could post details of your experiment and screenshoots of the measurements it might be interesting to have a look at.

Well, there is still your UcD amp.
IMHO UcD is a reasonable benchmark.
I have no UcD amp on hand, but we could use measurements from yours to set the mark.
I.e.
- Screen shots from clipping ( 2R and no load )
- Screen shots from the output signal of a 10kHz sine wave at high output levels, say 10% below clipping
- Screen shots from load dump
- THD measurements
- 10kHz rectangle into 2R and no load
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Old 14th January 2013, 04:37 PM   #219
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Please don't get me wrong, i hope that your modulator design is better, because actually i have to counteract the cracking sound at clip with a pre-clipper tracking power supplies and i feel that is not right. This cracking sound happened to be worst when feeding 2-3 way loudspeakers and almost imperceptible from feeding a woofer only, even running to 2khz. I think that frequency drop at clip inside the audible range of a HF driver.
I donot have a good scope at hand, only one very old. The waveforms looks like in this post: Hard clipping classD
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Old 14th January 2013, 04:59 PM   #220
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Hm, the wave forms shown in your thread are looking much better than your verbal description. Your words are pointing more to the direction that the amp falls into interuptive operation... - which is not easy to catch without a storage scope. ...but already with a cheap USB DSO it should be possible to find.
I guess you already followed Jens' hint and tried larger caps for the bootstrap and floating supply?
Edit: I see - you tried...

Last edited by ChocoHolic; 14th January 2013 at 05:05 PM. Reason: Edit: I see - you tried...
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