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Old 12th September 2008, 01:54 AM   #1
icko is offline icko  Sweden
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Default output network

Iam trying to build a subwoofer amp using TDA8920BJ IC and I am trying to figure out some stuff from the schematic in the datasheet.
Click the image to open in full size.

And I can't understand what resistors R14,R9 and cap C24,C32 do. Anybody know?


After looking around in application note for phillips class d amplifier they are sometimes omitted and sometimes only on one of the outputs. Both for BTL applications.
http://www.nxp.com/acrobat_download/.../AN10436_1.pdf
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Old 12th September 2008, 03:48 AM   #2
djQUAN is offline djQUAN  Philippines
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they are there so that the output stage doesn't blow up when the amp is powered without any load or drives a reactive load.
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Old 12th September 2008, 05:00 AM   #3
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These components damp the output LC filters. Without these there would be severe ringing or overshoot at the natural frequency of the filter.
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Old 12th September 2008, 07:03 AM   #4
icko is offline icko  Sweden
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thanks!
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Old 12th September 2008, 01:00 PM   #5
icko is offline icko  Sweden
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Can somebody explain what the symbols at each input is?

I assume that the half-circle denotes the input but the circle with ground through the circle and on top of it. Is it an american standard symbol?
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Old 12th September 2008, 01:22 PM   #6
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RC is to diminish the Q of the filter for not very resistive loads. Speakers are highly inductive above audio.

The symbols are typical schematic symbol for a jack socket.

Adam
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Old 12th September 2008, 02:07 PM   #7
icko is offline icko  Sweden
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no matter. i figured it out
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Old 13th September 2008, 02:38 PM   #8
icko is offline icko  Sweden
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Default Power Inductor

Thanks for all replies so far.

My highly speculative calculations show that the highest current will be around 7 A through the output network.

Anybody knows where to buy an inductor with ~25-16 uH that is capable of those currents? Best i've come up with are http://www.coilws.com/ but their shipping prices are horrifific.

Where do you buy your filter inductors?
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Old 13th September 2008, 03:14 PM   #9
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heya,
where do you buy the TDA8920?

cheers
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Old 13th September 2008, 05:07 PM   #10
icko is offline icko  Sweden
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haven't bought it yet but i plan to buy it via nxp website.
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