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Old 11th February 2008, 08:35 AM   #1
TroelsM is offline TroelsM  Denmark
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Default PLaying with ClassD again

Hi.

Here's a small peak at my latest classD-fumblings.

I concentrated on the output-stage at first. It's build around a IR2110 and two FQB19n20L.

Here's a few pics of the output-waveforms before the filter. First a 115Vpp square and the rising/faling edge. Rise/fall-time is approx. 35nS (10%->90% of voltage-range). Looks promising.

Click the image to open in full size.
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Click the image to open in full size.

Next on the to-do is the modulator-scheme. Most likely selvf-osc in some form. Any ideas? What's your favorite-scheme of the day?

Please click this link to see more info: http://kofoedmejer.squarespace.com/classd-amplifier/

Regards TroelsM
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Old 11th February 2008, 08:39 AM   #2
luka is offline luka  Slovenia
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Hi

I have tried clocked version, works great. Ucd's are also great...really hard to say what to go for... ucd is more simple if you make it all discrete

Hope you will have bigger cap for upper gate drive, when you will go into hard clipping

Are those pics befere or after LC filter?
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Old 11th February 2008, 08:42 AM   #3
TroelsM is offline TroelsM  Denmark
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Waveforms are taken before filter. Just edited my prev. post to reflect this.

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Old 11th February 2008, 08:48 AM   #4
luka is offline luka  Slovenia
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Hi

Bit you to it Before LC you won't have really any problems, you should connect LC filter too, and see what you get there...
Do you have any rail-rail decoupling caps on board?
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Old 11th February 2008, 08:54 AM   #5
TroelsM is offline TroelsM  Denmark
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Hi.

Each rail has a 330uF/100V e-cap and a smaller film-cap. There is no caps from rail to rail. Why?
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Old 11th February 2008, 08:55 AM   #6
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Is there any good clocked classD schematic with feedback taken after LC filter?
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Old 11th February 2008, 09:03 AM   #7
luka is offline luka  Slovenia
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Hi

@ TroelsM

You will need noise free rails as much as possible, this is why you should have rail-rail cap too, 2x100n or 1x220-330nF, try to find some good ones

@lumanauw

Yes there is as far as you ask me, made by fredos and then redesigned by alexclaire
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Old 11th February 2008, 01:34 PM   #8
TroelsM is offline TroelsM  Denmark
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@Luka

Output filter was connected at the time, but the plot shows the pre-filter waveform.

The cap on the floating supply is not very big, but I will change it later. Right now its not the biggest problem.

Thanks for the help. Re-visit the tread later to see more.

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Old 20th February 2008, 06:10 AM   #9
TroelsM is offline TroelsM  Denmark
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Doh!

Click the image to open in full size.

Regards TroelsM
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Old 20th February 2008, 06:48 AM   #10
luka is offline luka  Slovenia
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Hi

What are you trying to say?
It is better then my...
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