LM3886 BTL Configuration. Help needed

Placido

Member
2020-02-25 4:04 pm
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

BrWVsAh
 

Nisbeth

Member
2001-01-29 9:58 pm
Denmark
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?:confused:

2) The LM3886 is pretty well documented - data sheet and other information - so why don't you start from there?
 

rayma

Member
2011-04-29 8:37 pm
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:

Placido

Member
2020-02-25 4:04 pm
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...
 
1) No offence, but why are you asking us if you are supposed to be designing it?:confused:
Asking is FINE, doublechecking never hurts and in any case this is s Forum where people is suppossed to help others .

2) that said, Placido is
senior ECE student and currently working on my graduation project
so it´s a test where he must PROVE he´s skilled enough to be given a State endorsedProfessional Licence.

*Checking* a design is fine, as I said above, but the expected outcome is: "fine, it will work properly as shown".

IF "your" design is "done by others" because you can´t (and the schematic above has gross errors) then you can´t, with a clean conscience, ask for and get a Professional Degree based on what you don´t actually know.
Don´t like to use the word "cheating in an exam" but sincerely can´t find a more approppriate one.

Proper answer and course of action, of course, is to study more until you are fully qualified, in which case you will have honestly earned your degree.

Just as a side note, dissing nobody but commenting on real world experience, I do actually manufacture for over 50 years now and depend on lots of suppliers for custom parts I use, meaning sheet metal stamping and fabrication, lathe operators, plastic injecting, rubb er molding, galvanizing, custom aluminum sheet fabrication, paints and chemical treatment, etc.

When I ask them "are you hiring people?" a sadly common answer is "I´m trying to keep older workforce working ever after retirement" :eek: , "kids know nothing even with a shiny fresh degree under their arm and are untrainable" , etc.

Not dissing them but **poor education**
Schools in general but even Universities have been dumbed down a lot; simulation has all but replaced all workshop practice and even Physics or Chemistry or Metallurgical labs experiments.
At best experiments are made by Professors or University staff and pupils "Look", not the same by a Country mile.
Courses have been compacted and reduced, say Hydraulics and Hydraulic machines compacted into one, Industrial Electricity and Electrical Machines same thing, and so on.
Our 60's 6 year 56 Course typical Engineering career has been reduced to 5 years and 30/40 courses, depending on specialty/orientation.
FWIW *our* graduation project was designing and building the power and control system for a rotative paper/magazine printing press, where some 18 motors running HUGE printing and transport cylinders must run in perfect unison or the **20 km** continuous roll of newspaper will either tear or make a messy mountain of fresh inked paper if just one turns even a little faster or slower than needed.
All of this was done before microprocessors and such.
Oh well, rant mode OFF
 

Placido

Member
2020-02-25 4:04 pm
Something like it
Thanks, I read that article and I have gained some insight.

Asking is FINE, doublechecking never hurts and in any case this is s Forum where people is suppossed to help others .

2) that said, Placido is
so it´s a test where he must PROVE he´s skilled enough to be given a State endorsedProfessional Licence.

*Checking* a design is fine, as I said above, but the expected outcome is: "fine, it will work properly as shown".

IF "your" design is "done by others" because you can´t (and the schematic above has gross errors) then you can´t, with a clean conscience, ask for and get a Professional Degree based on what you don´t actually know.
Don´t like to use the word "cheating in an exam" but sincerely can´t find a more approppriate one.

Proper answer and course of action, of course, is to study more until you are fully qualified, in which case you will have honestly earned your degree.

Just as a side note, dissing nobody but commenting on real world experience, I do actually manufacture for over 50 years now and depend on lots of suppliers for custom parts I use, meaning sheet metal stamping and fabrication, lathe operators, plastic injecting, rubb er molding, galvanizing, custom aluminum sheet fabrication, paints and chemical treatment, etc.

When I ask them "are you hiring people?" a sadly common answer is "I´m trying to keep older workforce working ever after retirement" :eek: , "kids know nothing even with a shiny fresh degree under their arm and are untrainable" , etc.

Not dissing them but **poor education**
Schools in general but even Universities have been dumbed down a lot; simulation has all but replaced all workshop practice and even Physics or Chemistry or Metallurgical labs experiments.
At best experiments are made by Professors or University staff and pupils "Look", not the same by a Country mile.
Courses have been compacted and reduced, say Hydraulics and Hydraulic machines compacted into one, Industrial Electricity and Electrical Machines same thing, and so on.
Our 60's 6 year 56 Course typical Engineering career has been reduced to 5 years and 30/40 courses, depending on specialty/orientation.
FWIW *our* graduation project was designing and building the power and control system for a rotative paper/magazine printing press, where some 18 motors running HUGE printing and transport cylinders must run in perfect unison or the **20 km** continuous roll of newspaper will either tear or make a messy mountain of fresh inked paper if just one turns even a little faster or slower than needed.
All of this was done before microprocessors and such.
Oh well, rant mode OFF
First off I would like to apologize for not making it clear the time I started this thread that I was looking for resources to begin with but I recall including that in a reply afterwards, however, I had not realized then that the documentation provided by TI was more than enough, and I have dug more into it until now and the design is almost ready for wiring.

Your reply caught my attention though, and I would like to reply to every part of it.
1. I was asking, the circuit diagram seemed sloppy and simulating it gave no results, I felt hopeless at the time because my college professor had no idea how to help and I knew something was wrong.
2. It is supposed to be a test where I must prove that I'm skilled enough, YES, but that is the case when given a proper education and taught how to properly design an amplifier stage, but that never happened, and I'm not complaining because it was my responsibility to learn these things and not expect it to be fed to me but it just happened, I'm sorry.
3. I was not expecting someone to do the design for me, if I did I would have asked a freelancer or a graduate engineer and given them money for that.
4. I appreciate you took the time to reply in my thread given that you're a very experienced engineer, I will be a fresh graduate in less than a month, I have not acquired enough skills to be hired in a reputable business but I'm telling you that I'm one of the most hard-working students in my class and I'm still doing my best just because I'm pretty sure the education I'm being fed is not right and won't get me anywhere, and as you can imagine my classmates who should have had a participation in this project didn't even bother to "reasearch" and expected me to do it for them, like you said, and they will be given the precious State endorsed Professional License you didn't want me to get.
5. I'm happy for you that you were given the right tools and proper education, and was taught/learnt how to design such a complicated system, but I hope you also know that the electronics lab in my college doesn't have multi-meters, signal generators nor adjustable power supplies (I'm just saying that it was more difficult for me than it must've been for you, but whatever).

Thanks, I have actually used the PA100 design since it was mentioned to be a better solution when driving a 4ohm load speaker.

Thanks! These links are very helpful, I'm currently reading the first thread.