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Class D Switching Power Amplifiers and Power D/A conversion

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Old 28th March 2007, 06:09 AM   #381
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No, I have not built this specific Delta-Sigma Class D amp yet. My designs are rather different to this. From the photo, it looks like aluminium-oxide.
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Old 28th March 2007, 06:12 AM   #382
BWRX is offline BWRX  United States
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In a past thread Bruno mentioned that it was a ceramic (alumina oxide) insulator.

http://www.diyaudio.com/forums/showt...903#post487903
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Old 28th March 2007, 10:44 AM   #383
alfsch is offline alfsch  Germany
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ok, some testing:
to-220, capacitance (drain)case--heatsink

to220+mica+grease: 70pf
to220+mica : 27pf
to220+silpad: 11pf
to220+ceramic: 5pf


ceramic is alu.ox. , 1,5mm thick
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Old 28th March 2007, 11:55 AM   #384
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Hi, Alfsch,

Thanks for the test I think I will use silpad (I can buy them here).

Complemenary mosfet class D (Pch+Nch) seems will not experience this effect, since all Drains are DC.
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Old 30th March 2007, 07:42 AM   #385
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I read somewhere that for highside 12V supply better use bootstrapp compared to using floating 12V from transformer.

What happens if I use floating 12V for highside 12V supply?
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Old 3rd April 2007, 05:29 PM   #386
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Hi, Alfsch,

I measure some insulation material. Maybe my capacitance-meter is not too accurate :

TO-247 plastic (dioda) with grease or not = 27pf

TO-220 plastic (mosfet) with grease or not = 17pf

TO-247 metal (mosfet) :
-bare mica = 92pf
-mica+goop = 85pf
-single silpad = 34pf
-double silpad = 25pf
-polymatech 2mm = 20pf

TO-220 metal (mosfet)
-bare mica = 47pf
-mica+goop = 39pf
-single silpad = 25pf
-double silpad = 19pf
-polymatech 2mm = 19pf

A strange thing is in my measurement, when a mica is with silicon grease, the capacitance drops.

In your experiment, when mica is with silicon grease, the capacitance raises.
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Old 4th April 2007, 06:44 AM   #387
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Quote:
Originally posted by lumanauw
I read somewhere that for highside 12V supply better use bootstrapp compared to using floating 12V from transformer.

What happens if I use floating 12V for highside 12V supply?

CROWN, POWERSOFT IT, ECLER, HOTSOUNDPRO, TECHNICAL PRO all in their Class-D use high side Floating 15V supply.....Does anything happens to them??
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Old 8th April 2007, 05:24 PM   #388
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Hello!

I am still developing a switching amplifier based on the IRS20954 floating input gate driver! The first versions had problems with the power stage (as we discussed in another topic), the second version is free from powerstage shutdowns, but have problems with the modulation itself!

it looks like this:
http://ftp.torespont.hu/solarian/ucd20.jpg
http://ftp.torespont.hu/solarian/ucd21.jpg

It is modular for easier developing!

The schematic:
http://ftp.torespont.hu/solarian/ucd-kapcs-3.png

The comparator is TL3106, VBus is +-32V, there are some minor changes in real life, but mostly around the powerstage!
The problem is that, that the switching frequency highly depends on the 'input impedance', if i attach a cable or ground it, or attach some device, the switching frequency varies(100-600k)! I have tried it with a non-inverting amplifier(like this: http://ftp.torespont.hu/solarian/ucd-kapcs-2.png), and the problem is the same, sometimes it just would not oscillate!

Do you guys have any idea about this?

Thanks for the advices in advance, Mark
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Old 19th April 2007, 07:12 PM   #389
blmn is offline blmn  Brazil
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Hi,

Ive just finished my UcD using 70V rails (Philips application note and ne5532 differential at input-very similar to Classd from ru UcD2.5), and I have some interesting behaviour that I like to share.

Im using IRF640, fosc is near 330kHz, rgate is 27ohms, and, at 8 ohms load, near 60v peak-to-peak there is some noise at the top of the wave (sinus) and a behaviour like its going to clipping, just at the positive side.

The efficiency is very good and, using 100ohms load the swing reaches, without problems, almost 140v peak-to-peak. Using 4ohms load the maximum peak is near 40v peak-to-peak till noise occurs.

Im using an 18uH n. 2 Micrometals toroid core.

I think the problem is aty the upper gate or pcb layout at upper mosfet side.

Any thoughts?

Best Regards,
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Old 19th April 2007, 07:24 PM   #390
luka is offline luka  Slovenia
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Hi

Can you post some pic?
- Like before LC filter
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