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Old 14th March 2003, 09:23 PM   #1
Toucan is offline Toucan  United States
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Default Bridge/Parallel LM3886 Amp

DJBassamp got me thinking.....

The BPA 200 amp (Bridge/Parallel LM3886) detailed on page 10 of this Application Note
http://www.national.com/an/AN/AN-1192.pdf
has been referred to a few times on this forum. After reading the document it appears that more than just 2 LM3886's can be paralleled on each side of the bridge. This could be used to build a much higher power amp than the 200W one shown in the schematic.

In section 4.4 of the App Note it says "By paralleling the two bridged sets of ICs, the amount of output power attainable is essentially limitless". And the last sentence in section 4.5 says "Another variation would be to add more ICs in parallel to further reduce power dissipation, allowing low impedance loads to be driven to obtain even higher output power levels".

So it sounds like, say, 5 IC's can be paralleled on the positive side and 5 IC's can be put on the negative side. Or more, let's say 10 or 15!

Can the subcircuit of the LM3886 & LF412 just be added on again and again, or will modifications be needed? It looks like it would work fine but I don't have enough knowledge to figure it out myself.

Does anyone have any thoughts on this? Any words of wisdom? Non-flame type words of wisdom, of course!
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Old 15th March 2003, 04:18 AM   #2
rdunnit is offline rdunnit  United States
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I am interested in finding out about the same questions. I was thinking 5 IC's on the positive side and 5 on the negative side as well. I am in the process of obtaining the necessary parts to build a bridge-paralleled 3886 using 10 IC's. As I am on a very limited budget, I am slow at obtaining the necessary parts. I have taken advantage of the sample parts available from various Semiconductor manufacturers but am still looking for a company that offers transformers as samples. I am looking at the transformers from ApexJr; especially the Signal BL1733. Low cost is a necessity for me.
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Old 15th March 2003, 11:46 AM   #3
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Please note that paralleling a lot of ICs will not automatically
give you more power. For a given speaker impedance, the
maximum power is limited by the supply voltage to the ICs,
which is limited by the voltage rating of the ICs. The only
thing you achieve by paralleling ICs is to increase the current
capability. Hence, to make use of many ICs parallelled you need
low-impedance speakers. I don't remember any exact figures
for these ICs now, but I think more than two LM3886 in parallel
for each half of the bridge is probably not useful for 8 Ohm
speakers. For 4 Ohm speakers, maybe it is useful if the speaker
impedance has a big dip, to say 2 Ohms, somewhere. However,
paralleling many ICs may still be useful, since each IC will
dissipate less power and require less cooling. The distorsion
will probably also be lower since they are operating at lower
power.
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