LM4780 (LM3886) impedance issues

Alfetta87 · 21st November 2006, 11:33 AM

The national semiconductor datasheet doesn't say if the bridged (or parallel) application of the LM4780 would hold on with a 4 ohms load, even with its maixmum voltage used.

Has anybody got some experience with that?

Same for the LM3886 in brdiged mode.

Thanks,

- dan

jackinnj · 21st November 2006, 02:35 PM

If you look at the "overture design tool" on National's website you can quickly determine the heat sink rating for a given rail voltage and impedance.

You can play around with the numbers and determine which heat sink/rail voltage combination is appropriate -- there's no need to guess.

I have used the LM4780 at higher PDMax than recommended by National by using forced air through the heat sink -- be mindful this causes the thermal protection to cycle on-and-off -- it's a nice experiment but something that you shouldn't try at home on your expensive speakers.

21st November 2006, 11:33 AM	#1
Alfetta87 diyAudio Member Join Date: May 2003 Location: Between northpole and southpole	LM4780 (LM3886) impedance issues The national semiconductor datasheet doesn't say if the bridged (or parallel) application of the LM4780 would hold on with a 4 ohms load, even with its maixmum voltage used. Has anybody got some experience with that? Same for the LM3886 in brdiged mode. Thanks, - dan __________________ It is worth to keep your mouth shut and let people think you’re stupid; rather than to open it and thus eliminate any doubts...

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21st November 2006, 02:35 PM	#2
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	If you look at the "overture design tool" on National's website you can quickly determine the heat sink rating for a given rail voltage and impedance. You can play around with the numbers and determine which heat sink/rail voltage combination is appropriate -- there's no need to guess. I have used the LM4780 at higher PDMax than recommended by National by using forced air through the heat sink -- be mindful this causes the thermal protection to cycle on-and-off -- it's a nice experiment but something that you shouldn't try at home on your expensive speakers.

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