Lm4702

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#322
Re: Heat problems

routhun said:
This version also may suffer similar heat problems as the commercial one because the power transistors for both the channels are close on the heat sink. What is the power output these boards are targetted for?
Routhun.
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Mine can deliver about 2 x 100W (THD - 0.001%). I will use two of this boards to make symmetrical amplifier (+ OPA1632). Spaces between transistors are big enough and LM4702 won't be mounted on the same heat sink.
 
#323
Re: Re: Heat problems

veteran said:


Mine can deliver about 2 x 100W (THD - 0.001%). I will use two of this boards to make symmetrical amplifier (+ OPA1632). Spaces between transistors are big enough and LM4702 won't be mounted on the same heat sink.
Click to expand...


I have been running a similar amp for months now, but my power modules are separate from the driver, and can be just about anything. My prototype uses SAP16s. I actually have a whole thread about it.

http://www.diyaudio.com/forums/showthread.php?postid=949032#post949032

It is working quite well, but I think I am onto something I like even better. 🙂

I have not posted to the thread in a while, a lot of the PCBs/schematics have actually changed, but the concept is the same, and works quite well.

I have also designed (but not implemented yet) over current protection and a soft start thanks in no small part to my friend Mauro Penasa.

Cheers!
Russ
 
#325
Re: Heat problems

routhun said:
This version also may suffer similar heat problems as the commercial one because the power transistors for both the channels are close on the heat sink. What is the power output these boards are targetted for?

Routhun.
Click to expand...

You make a correction for the length of the heatsink. The correction factors are on Aavid Thermalloy's website.
 
#326
GeWa said:


Can this be used for other amp designs to?

Regards
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Well the only part I have finished is the soft start (it works great) and it is good for 10amps or so. So any amp that draws less then that from the mains should be fine. It is its own PCB. It also works for either 110 or 220 volt mains just by changing a couple values.

I will keep you posted on the over-current protection. That one is a lot more tricky to get right and needs to be tweaked for each particular circuit.

Cheers!
Russ
 
#329
jackinnj said:
You can use the mute function on the 4702 for over-current protection -- although you can't smoothly cut off the drive -- use a comparator and a flip-flop so that the offending condition can be rectified (are male teenage son's offending conditions?)
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A very good point/suggestion, and worth trying. I may see if I can work this out. I may post something for you guys to look at. Protection circuits are still new to me.
 
#330
To add to the mute pin usefulness, I think Pinkmouse suggested a while back using the mute pin coupled via capacitors to make a soft start. I'll have to look back for the exact circuit, but the gist was the charging of the caps brought the mute pin up and turned the output on. I believe that was from a National data sheet originally. . . .

Oh well, I can't remember specifics, but it seemed a great idea at the time and was quite straight forward if memory serves.

David

Duh! I just found the thread here
 
#334
New Version for 4702C

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#336
VLSI said:
Has anyone experimented with the capacitor between source & sink (LM4702) NS have Cb3/5 as 0.015/1250v polyprop (I used a 0.015/300v Mica) Have tried other value caps but the 0.015 sounded best?
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I haven't done any sound comparisons, but I've seen a huge range of values of the capacitor in this position (across the Vbe multiplier). 0.015uF is on the low side, 47uF electrolytic is the highest I've seen, in Randy Sloan's book. Without it I think there is high frequency distortion at high output levels. 0.1uF seems to be a very common compromise. Because the cap is in a NFB loop its sonic signature would be miniscule.
 
#339
Re: Re: New design for LM4702CTA

veteran said:
Lovely, now you can use few different output stages with one, LM4702-base board 😉
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You and I have both done the math for that one! My bet is that the power from the LM4702 wouldn't be up to scratch for driving more than one board. I think you would have to put an intermediate current gain stage before the output boards to drive more than one. Of course I don't have the numbers for that particular system, but my back-of-the-envelope math says "not quite."

David
 
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