Lm4702

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#361
Re: As simple dual opamp?

Russ White said:
Just wondering, is there any reason you could not simply tie the "sink" and "source" pins together and use the 4702 as a high voltage opamp? I know it can only do about 4-6ma, but I was just wondering if it would work. It seems thats what the test circuit shows in the datasheet. But I was not sure what the implication are.

Any thoughts?
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Russ, I have run these chips in just that configuration for a while to do testing and measurements on the chips themselves absent the output stage, and I didn't have any problems at all. This is NOT saying there are no implications for this, but I never had any problems as long as I had a good sink on the chip. I like the idea of using the chip this way.

David

PS, What software you are using to sim? I don't immediately recognize it.
 
#363
Thanks. I have been using p-spice, just because that is what I learned to work with lo these many years ago, but I absolutely hate it. (which probably accounts for why I am not as proficient as I would like to be with it. 🙁 ) I think it is time to switch.
 
#364
Russ, do you have a spice model for the LM4702? National seems to have a ton of other device sims, but I can't find any of the audio chips, and I was wondering what you were using.

Thanks!
David

PS LTSpice seems pretty good. Much more intuitive than PSpice. Thanks for the tip.
 
#365
dfdye said:
Russ, do you have a spice model for the LM4702?

PS LTSpice seems pretty good. Much more intuitive than PSpice. Thanks for the tip.
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Hi David,

Yes LTSpice is very nice, especially for the price! 🙂

As for the model I just used the universal op amp model in my test, I don't think there is a published model for the 4702 yet. if you find one please let me know. 🙂

Cheers!
Russ
 
#366
Russ White said:
Yes LTSpice is very nice, especially for the price! 🙂
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Lol, yes, that math is indeed quite skewed, but I always factor my time of LEARNING TO USE the software into what I pay. If I do that math, it is still quite nice, which I can't say for a lot of other free ware (Eagle being the most applicable exception that also represents a good "free" value.) Knowing Spice basics definitely helps, but this still seems pretty easy and VERY well documented.
As for the model I just used the universal op amp model in my test, I don't think there is a published model for the 4702 yet. if you find one please let me know. 🙂
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I just scoured the National web page and couldn't come up with anything, not even an alternate recommendation. OnSemi has me a little spoiled. Since the sink/source issues would create a pretty big difference vs "normal" opamps, I would indeed like a better model than the generic. I'll definitely post if I find something.
 
#368
jackinnj said:
Take a look at the "sink-source" connection in the test circuit.
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I have. That is how I have tested a bunch of configurations. I don't really follow. . . . .

If you connect the two, the chip acts like a normal opamp, but for simulation purposes I would like the sink and source in two different outputs.

David
 
#374
anyone notice this

peculiar -- i have a 2x125W LM4702 which I have been running through its paces -- there seems to be an intermediate power region in which the amplifier experiences some "unhappiness" -- that is, at very low levels no problems, at very high power levels no problems, at about 10W output there is some "notchiness" in the output, on the positive halves of the sine cycle.
 
#376
the problem seems to occur with a 350mV input -- at 1.2V in there is no problem. 'have to check the bias -- i set it for 100 mA per device.

the other thing about the '4702 is that it takes quite a few seconds for the distortion to settle down...seems like it wants to warm up like a bunch of 6550's.
 
#379
lm4702

Hallo members
i have a question about the output with fet transistor i have seen a shematic with driver transistor before the fets and without driver.
wat is right?
I want to make an amp with IRFP240 IRFP9240 at -+ 54V.
is it better to take 2 in parallel or is 1 pair enaph?
I want to buy 3 pcb for lm4702 where can i buy them and how can ipay them?

greetings Rapunzelelch :Popworm:
 
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