LM3886T , How to drive a big load?! - diyAudio
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Old 8th July 2011, 11:16 PM   #1
epilot is offline epilot  United States
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Default LM3886T , How to drive a big load?!

Hello guys.

I just need help please.
I have 2 questions as bellow:

I have several LM3886T amplifier chips. The first question is how can I use one or more of them so that drive a 1 ohm load?

The other question is that if I bridge them then what would be the Minimum of drove load?

Thanks a bunch for any help
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Old 8th July 2011, 11:38 PM   #2
! is offline !  United States
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There is a graph in the LM3886 datasheet showing approximately 18W power output at slightly over 2 ohms. You can parallel two of them to double that, but they really aren't suited for 1 ohm load, why not use different speakers instead and use your LM3886's to build a few amps that drive typical speakers?
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Old 8th July 2011, 11:53 PM   #3
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Yes, this Overture Series IC can be configured with 4 in parallel for 1 ohm applications. See Page 2 in section '3.0 Conclusion'.

http://www.national.com/an/AN/AN-1192.pdf

As far as normal bridging goes with these, you can only bridge up to 2 devices and the load impedance needs to be 8 ohms.

Or, you can mix the bridge and parallel configuration, bridge 2 ICs, parallel 2 ICs, to be able to drive 4 ohms. Regardless it's all on that data sheet.
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Old 9th July 2011, 12:46 AM   #4
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What specifically are you driving, multiple drivers in parallel? If so, it would make more sense to wire them in series, or if it's whole speaker speaker systems with passive crossovers, just use one chip amp per system. A one ohm load is going to be tough on just about any amp.

Mike
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Old 9th July 2011, 12:57 AM   #5
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Oh yeah, for the second part of your question, when you bridge amps, you must de-rate output capability by a factor of two, so an eight ohm load effectivly becomes a four ohm load. So to drive a one ohm load in bridge mode you would need to parallel four amps on both sides of the bridge for a total of eight per channel.

Mike
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Old 9th July 2011, 01:18 AM   #6
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Whoops, my stupid old brain didn't do the math right, to drive a one ohm load in a bridge, which is the same as 1/2 ohm single ended, you would need eight amps per side for a total of sixteen per channel. I don't think you want to go there.

Mike
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Old 22nd July 2011, 04:20 AM   #7
eccdbb is offline eccdbb  United States
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What is the desired power output? Describe your PSU specs.

+/- 30V PSU could deliver...but 30A is well....dang. Expected power ~900w into 1ohm. Need more?
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Old 22nd July 2011, 09:52 AM   #8
AndrewT is online now AndrewT  Scotland
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Well done. Our questions have driven this Member into oblivion.

I really mean "well done". Simple logical thought has shown him the error of his idea.
__________________
regards Andrew T.
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