LME 49810 with NMOS output stage 1000W @ 4 OHM - diyAudio
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Old 21st September 2011, 09:43 PM   #1
NMOS is offline NMOS  Germany
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Default LME 49810 with NMOS output stage 1000W @ 4 OHM

I want try to drive NMOS output stage with LME 49810....

could this work ? look schematic


to get reliabale 1000W RMS MOSFET AMP is easy and the LME Chip assist baker clamp
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Old 22nd September 2011, 12:24 PM   #2
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The IRFP460 is quite a useful device, but the datasheet gives its maximum power dissipation as 250W. The circuit only shows two of them. You will need a few more for the sort of power levels you are talking about.

Another question is - why so much power in one amplifier?You might want to read this article:
http://sound.westhost.com/articles/pwr-vs-eff.htm

Last edited by ingenieus; 22nd September 2011 at 12:38 PM.
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Old 22nd September 2011, 12:42 PM   #3
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Quote:
Originally Posted by ingenieus View Post
The IRFP460 is quite a useful device, but the datasheet gives its maximum power dissipation as 250W. The circuit only shows two of them. You will need a few more for the sort of power levels you are talking about.

Another question is - why so much power in one amplifier?You might want to read this article:
Power Handling Vs. Efficiency

I know its important to add more devices for PA
but I want to know first could this design working without smoking ?
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Old 22nd September 2011, 02:20 PM   #4
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The basic idea is OK. Have you looked at the LME49830? It is specifically designed to drive MOSFETs.

I'm worried about the single pair of output devices. It looks like a potential smoke generator to me. I would at least one more pair in parallel. To be sure, make it four pairs in total.

Remember that at full power, your amp will be putting out about 300W in heat, so get a big heatsink.

Last edited by ingenieus; 22nd September 2011 at 02:32 PM.
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Old 22nd September 2011, 04:03 PM   #5
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I punched some the numbers into my calculator and it seems that the circuit is designed to deliver 500W into 8 ohm. The output devices are at their absolute maximum rating, but will be OK if you play music and not sine waves. 1000W into 4 ohm will definitely let out the magic smoke.
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Old 22nd September 2011, 05:49 PM   #6
alex mm is offline alex mm  Romania
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...... maybe you need something like this
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Old 22nd September 2011, 05:52 PM   #7
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This is a quasi complementary output stage.
If you use the Gamnut topology, the clipping behaviour is probably much more better.
Check out therefore this thread:
"Push-Pull" for push und "Push-Pull" for pull (like Gamnut) - whats the right name?
the simplified schema you will find about post #1
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Old 22nd September 2011, 05:58 PM   #8
riktw is offline riktw  Netherlands
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hmm, and how are you getting the heat away from the devices.
the Junction Case temperature resistance is 0.45 ohm.
if you have a infinite heatsink and no losses between the heatsink and the device it would be possible to remove roughly 150 watts of heat from the device.
in that case the junction would get over 90 degrees hot.
in the real world thats inpossible.
with a big heatsink and a proper conenction 75 watts of heat is possible per mosfet.
so want high power, get more mosfets.

in any case, read this:
Project 117
1.5KW amp and he uses 10 pairs of transistors.
I'd say that has a reason
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Old 22nd September 2011, 06:12 PM   #9
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schemtaics for amplifiers that can come arround so much power beyond P117 and the LME designs can be found in the internet very eassily .... most of them will sound also very good

The problem is that none of the schematics on this power have protection enough to protect the amplifier form it shelf ( suppose that the user will do all properly )

To be able to produce any amplifier for PA use anything more than 200 ( real watt ) you nead to study many Pa amplifier schematics understand what/ why/ how and many others arround the protections of the amplifier .....If you ever manage then go ahead ....other than that anything you built above 200W and used for PA will eventually blow

The schematic of one PA amplifier is only the 10 % of the job implementation and protection is the rest 90% .... obviously duarbility and reliability is more importand than power in PA bussines .

Sorry to say that this is a waste of time since all that has been allready told to you in many other "power hungry"threads you ve made ...but there you go ... once more ]

smoky regards
sakis
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Old 22nd September 2011, 06:18 PM   #10
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Quote:
Originally Posted by sakis View Post
The problem is that none of the schematics on this power have protection enough to protect the amplifier from itself
Well pointed out. I only see a DC protection which will protect the speaker, not the amp... For something to survive any reasonable length of time in PA duty you need an input signal limiter, DC protection, VI limiters and overtemperature protection, at the very least.
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