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Class D Switching Power Amplifiers and Power D/A conversion

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Old 27th January 2013, 06:05 PM   #231
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Hello ChocoHolic,

very interesting Thread

Quote:
Simulation showed that in this project the IRFP4668 would struggle hard with its body diodes.
Do you already have think about SIC or are they too expensive? Because I think these transistors are made for class-D.
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Last edited by moschfet; 27th January 2013 at 06:08 PM.
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Old 27th January 2013, 06:21 PM   #232
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@ Choco just a quick question: Why did you choose the MBR40250 over V30200? With a 164V bus, 250V diodes are not needed.
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Old 27th January 2013, 06:53 PM   #233
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@MoschFet:
SIC are great, but I am not aware of types for reasonable voltages.
More in the voltage range of 600V and above with pretty high Rdson.
I am intending to set my overcurrent protection above 50A, consequently not just the body diode but also the Rdson is important.
My personal guess is that over the next 5 years GaN will evolve as most fortunate for normal class D applications. You never know. GaN was already promoted 3 years ago, but then they noticed that the dynamic Rdson was more than an order of magnitude higher than the static values which had been used as design criteria and promoted by the semiconductor design guys. In the mean time they seem to have overcome this issue and I am hoping that not to much further surprises will come up.


@Tom:
MBR40250 or V30200:
Both are perfectly fine to me.
From simulation including PCB parasitics the 200V types are easily enough, fitting to your statement.
I am settling a file with alternatively usable components for the power diodes, power MosFets and comparators. The file will show if it is already tested or not and which adjustments might be necessary to fit (i.e. OCP settings with other MosFets).
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Old 31st January 2013, 07:37 PM   #234
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...here the updated schematic.

Compared to the older schematics it has improved low noise voltage references for the modulator without adding tons of components and a faster output filter and accordingly optimized loop gain parametrization.
==> Resulting in improved large signal step response into low impedances.
C201, C202 are kept NIP, but most likely I will have to place 47pF to avoid catching RF noise. Further changes can be expected when I start building and debugging...
Keeping you updated.
Attached Files
File Type: pdf SystemD_2k4_Modulator_V1dot1.pdf (122.2 KB, 207 views)
File Type: pdf SystemD_2k4_Power_V1dot1.pdf (151.1 KB, 207 views)
File Type: pdf SystemD_2k4_Supply_V1dot1.pdf (75.4 KB, 162 views)
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Old 31st January 2013, 08:20 PM   #235
IRSound is offline IRSound  Germany
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Hi,

why are you using 6*330nF capacitor for filter section ?
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Old 31st January 2013, 08:44 PM   #236
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SystemD_2k4_Power_V1dot1.pdf:

There is a connection dot missing at the upper gate drive R327 / R328. Or is my acrobat reader not displaying it right?
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Old 31st January 2013, 09:46 PM   #237
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@IR:
IMHO the only high quality solution.
...just compare the effective parasitic series inductance of one huge MKP with LS22.5 vs 6 small paralleled MKP with LS5 each.
A single large cap will show at least one order of magnitude more parasitic inductance vs the six small paralleled ones.
Also Mundorf, Jantzen etc. cannot overcome physics.
I am using them as input caps and for cross overs, but it would not be clever for the output filter of a class D amp.
Another ignorant approach would follow the spirit of the age by and place a completely overdriven and distorting SMD XR7.
Very hip these days, because it's 'small and cheap'.

@Tom:
Absolutely right. Many thanks. It is not caused by your PDF viewer. I rechecked it in KiCad.
The schematic editor also does not display this dot, but the ratsnest has the connection. ...software wonders everywhere.... Fortunately the gerber data seems to be fine.
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Old 4th February 2013, 07:04 AM   #238
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I was once foolish enough to use paralleled X7R SMD caps as the output filter, in a low power (30W) UCD-style amp. Even though there were 4 caps in parallel and post-filter nfb, the measured distortion was over 3 times high than with film caps.
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Old 5th February 2013, 05:42 PM   #239
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...only cowards read manuals and data sheets..


The deltaC vs. voltage graph would have kept you from trying.
Well, I am also a never-read-manuals-macho. Unless ignorance strikes back.
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Old 6th February 2013, 04:25 AM   #240
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Choco don't you know that sometimes
"Ignorance is bliss for many"
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