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Old 1st February 2013, 06:58 AM   #1
child1 is offline child1  Denmark
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Default TDA7294 capacitor polarity

Hi all!

I'm building an amplifier based on the TDA7294 chip and have had a look at some different schematics. One thing puzzles me a bit (on attached schematic) the C8 lytic has positive side to gnd. However on other schematics it is the other way around (with nothing else changed). Can it be both ways or what is the correct orientation of the cap?

Thanks

-Mads
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Old 1st February 2013, 11:35 AM   #2
DUG is offline DUG  Canada
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If the input devices are NPN then there will be a slight negative voltage on the cap.

input current x R5...not much but still there.

If the input devices are PNP then positive voltage.

I would put two (double value) in series (- together). Then it will not matter if the input is NPN or PNP. (or FET)

But that is just me.

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Old 1st February 2013, 12:29 PM   #3
child1 is offline child1  Denmark
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Do you mean like this?
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Old 1st February 2013, 12:45 PM   #4
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The voltage that appears across the capacitor is too low to warrant a polarity as it is decoupling the feedback loop and controls the overall gain of the device. R4 + R5 / R4 = gain of device.
Most electrolytic capacitors don't mind a volt or so reversed across them.
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Old 1st February 2013, 01:39 PM   #5
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Quote:
Originally Posted by child1 View Post
I'm building an amplifier based on the TDA7294 chip and have had a look at some different schematics. One thing puzzles me a bit (on attached schematic) the C8 lytic has positive side to gnd. However on other schematics it is the other way around (with nothing else changed). Can it be both ways or what is the correct orientation of the cap?
As far as I know, the C8 cap's polarity is reversed in your schematic . Please look at the datasheet from ST and zoom in the PDF file in order to see that cap. You'll notice the right polarity as given by the manufacturer.
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