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LM3886 BTL Configuration. Help needed
LM3886 BTL Configuration. Help needed
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Old 10th March 2020, 08:50 PM   #1
Placido is offline Placido
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Default LM3886 BTL Configuration. Help needed

Hello, good evening to y'all
I'm a senior ECE student and currently working on my graduation project, in which I need to design a power amplifier circuit to drive a subwoofer, long story short, the signal I'm amplifying is a single tone of 50Hz, and the power being fed to the speaker is in the range of 100-120 watts
I'm using a single-tone generator in the first stage followed by a preamp to bring the signal level up to an adequate level then the power amplifier will provide the wattage gain.

I have attached an image of the circuit design I have built which I'm pretty sure has alot of flaws and I hope someone can help me with it because I actually feel lost and can't really be sure if this design will work in practice.
Thanks in advance

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Old 10th March 2020, 09:22 PM   #2
FauxFrench is offline FauxFrench  France
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I cannot read the value of D3.
Your lower LM3886 circuit will not work. You cannot make an inverting channel for BTL just by swapping the inverting and non-inverting inputs of the LM3886.
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Old 10th March 2020, 09:22 PM   #3
Nisbeth is offline Nisbeth  Denmark
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LM3886 BTL Configuration. Help needed
Quote:
Originally Posted by Placido View Post
Hello, good evening to y'all
I'm a senior ECE student and currently working on my graduation project, in which I need to design a power amplifier circuit...
1) No offence, but why are you asking us if you are supposed to be designing it?

2) The LM3886 is pretty well documented - data sheet and other information - so why don't you start from there?
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Old 10th March 2020, 09:26 PM   #4
rayma is offline rayma  United States
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Yes, just look at the data sheet for the standard circuit. If you are using a BTL circuit,
use an op amp connected as a unity gain inverter to get the opposite polarity input signal.
Please study about op amps, you cannot be a credible EE without basic analog knowledge.

Last edited by rayma; 10th March 2020 at 09:33 PM.
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Old 10th March 2020, 09:36 PM   #5
FauxFrench is offline FauxFrench  France
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Look here for inspiration: The LM3886 BTL amplifier under Other Circuits -60637- : Next.gr
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Old 10th March 2020, 11:04 PM   #6
Placido is offline Placido
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Quote:
Originally Posted by FauxFrench View Post
I cannot read the value of D3.
Your lower LM3886 circuit will not work. You cannot make an inverting channel for BTL just by swapping the inverting and non-inverting inputs of the LM3886.
D1 and D3 in the mute circuit were meant to block the current out of pin 8 until it's breakdown voltage has been reached. Anyhow, for this application it might not be necessary. Thanks for the insight, I will look for more information regarding the bottom side of this design. The link you posted in the last reply is empty.

@Nisbeth
1) I was supposed to design it but I hadn't acquired enough knowledge for that matter so I decided to ask for help/guidance.
2) I have read the datasheets and documents and that design was actually just how far I could go with those.

@rayma
I would not mind studying before beginning to design but with all the documents I had, that was the furthest I could reach, maybe I just need to do more digging and research


I would really appreciate it if any guidance to topics I can further read on in order to get this design right, even the slightest...
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Old 11th March 2020, 08:29 AM   #7
FauxFrench is offline FauxFrench  France
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Hi Placido,

The link I posted works repeatedly for me. If you still cannot make it work, search yourself for "LM3886" and "BTL" and look through the images.
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