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Old 21st April 2008, 02:59 AM   #1
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Default Lm4950

Hi,
Has anyone used LM4950 in stereo mode? The data sheet shows a value of 470uF for Cout. Is this a misprint or what? After a quick search at Farnell, 100uF bi-polar electrolytic is the highest availabe. Strangely there is no Cout in mono mode. I would have thought a 10uF is sufficient for decoupling the chip from the speakers. Any suggestions.
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K K
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Old 21st April 2008, 09:24 AM   #2
boholm is offline boholm  Denmark
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Default Re: Lm4950

I haven't tried it at all. But i can read in the pdf that it is intended for sound in flat panels.

470 F for Cout is adequate, since it is not intended to give deep bass. Lower frequency limit calculated to 86 Hz. The circuit on p4 of the National pdf has only an amplification of 1 => a buffer and a voltage swing of max. +/- 9 volts - in bridged mode +/- 18.

A 10 F for decoupling sufficient? Sorry, but I don't understand . . . ?

What do you wish to use it for?
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Bo
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Old 21st April 2008, 06:57 PM   #3
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Both amplifiers' output are biased to Vdd / 2 in idle, so this is a typical chip of one-supply solutions.

For the stereo amplifier you DO NOT need bi-polar capacitor on the output. Cout should be a normal electrolytic capacitor, 470 or 1000uF (maybe paralell with a n*100nF ceramic capacitor).

BUT! Cin must be definitely bi-polar, maybe a ceramic one.

Yes, there's no Cout in the mono application, because the two amplifiers working in bridged mode, with 180 degrees phase shifting... (with no output half Vdd should be measured on both pins of the speaker)

http://cache.national.com/ds/LM/LM4950.pdf
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Old 23rd April 2008, 07:42 AM   #4
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Thank you guys.
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