Why was the LM3900 discontinued ?

Well, my guess is, they may have a better part that can replace it. Why can't you change your schematic? Are you trying to fix an old board?

For the LM3900's I replaced them with NTE992.

PS. Votre anglais est bien. Félicitation à vous.

Are there in fact any other quad Norton amplifiers out there? LM3900 is no ordinary op-amp.

Isn't the NTE992 merely an LM3900 with different numbers stamped on it and a higher price? NTE is not a manufacturer -- they're a marketer and relabeler.

It served really no purpose.

I can remember when it came out, and it was born with a big datasheet or application note that was loaded with things you could do with it. But, most of it was novelty, "oh look, here's an LED flasher but you can do all kinds of other things with it".

It got press early on, but it was rarely used in constructin articles in the hobby magazines, unless someone used one of those novelty applications. You had to add a whole IC just to flash an LED? The sorts of things where it might be really useful, as a very low current LED indicator, you wouldn't want to devote the space to.

I don't remember it as being particularly available, it must have been but it never saw the saturation in places that sold to hobbyists that would indicate it was a popular part.

I've never seen one in any piece of commercial equipment I've taken apart, which does seem to be an indicator of how little use it saw in commercial products.

It lasted for decades, but never really served much purpose.

ONe of the odd things is how long a lot of ICs have lasted. In the early days there was so much turnover, as logic family A was replaced with logic family B and so on, and as op-amps evolved until they got good. In retrospect, it's a surprise that a lot of ICs did last so long, because then the expecation seemed to be that something better would come along soon to replace anything; after all that had already happened.

A lot of ICs have come and gone, often far more useful or interesting than the 3909. I can't really fathom why the 3909 lasted so long.

Michael

Michael Black ( snipped-for-privacy@FreeNet.Carleton.CA) writes: Oops, ignore this, I read "3909" (the flasher) instead of "3900" (the norton amplifier).

Michael

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Whoa. LM3909 = low-voltage LED flasher. LM3900 = quad Norton amplifier. Both are discontinued.

The LM3909 was useful -- it would flash a red LED from a 1.5-volt source, if I recall correctly. At one point I reverse-engineered it and designed a discrete-component substitute.

The LM3900 -- well, I couldn't see what it could do that an op-amp couldn't.

The NTE992 is probably an LM3900.

Do you seriously think they have them made separately ?

Graham

Sure, but NTE still sells them, while National Semiconductor doesn't.

Look at the date codes on the NTE stuff. It's old stock that may be gone, any day.

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My impression (possibly wrong) is that NTE occasionally buys up the rights to the original mask/wafer designs of certain parts and has them fabbed.

It appears that TI is still making the LM3900, in both PDIP and SOIC formats. DigiKey has only the SOIC in stock. Mouser has both.

Motorola apparently used to make an LM3900-compatible Norton quad (MC3401) but it looks as if it didn't make the quantum-leap over to On Semiconductors.

So, the NTE992 might be old-stock NatSemi LM3900s which have been relabeled, or TI LM3900s which have been relabeled, or parts made by J-random-fab based on licensed (or non-licensed) designs of one or another heritage. I don't think there's any way to know for certain, unless one works for NTE.

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Until they run out of stock.

Graham

I see 1500+ of the DIP TI LM3900N in stock at Digikey, but the LM3900NE4 is non-stock. Offhand I don't see the difference-- they're both listed as RoHS on the datasheet.

Terrible matching on the current inputs (+/-10%).. makes an LM324 look like a precision device. I used them in a couple of designs way back-- sort of like BJTs.

Best regards, Spehro Pefhany

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I've heard them described as being a bit like a super-high-beta BJT.

I ran into an interesting use of them a couple of years ago - in the audio and squelch stages of a receiver for an amateur-radio repeater. Best as we could figure out, they were used because they allowed the design to operate on a single-sided 12-volt power supply (regulated down to around +8 internally) with a minimum amount of interstage DC-blocking caps and bias networks being required.

These days, of course, much better parts for this application would be used, but I don't think there were any good low-voltage, rail-to-rail- capable op amps in common use back when this receiver design was finalized.

Sure was puzzling for a while there, though. My cohort-in-crime and I were tweaking the audio gain and equalization, and changed the feedback resistor around the amp... and its output pinned at one of the rails. Led to a puzzled session of headscratching, before the flashbulb went off and I said "Oh, hell.. LM3900... that's not an op amp, that's a Norton!"

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Retarded Michael running out of stream? Go get killed in IRAQ NOW stupid jerk!

Quit following my thread dummy Mikhell.

snipped-for-privacy@earthlink.net...

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Useless tidbit. Phase Linear used the LM3900 in the model 1000 autocorrelator in the notch filters. It was an interesting alternative to the Burwen noise reducing box. IIRC Burwen had a sliding corner lowpass while Phase used 3 broad notch filters / gated by program material in the respective band. The Phase Linear worked better after removing the RC4136 (?) opamp and replacing it with a TL075.

GG

I wrote:

Or they might have enough to meet the demand for another century. There's no way to tell.

I wasn't proposing that anyone should design the NTE992 into a new product. But if you have something that already uses an LM3900 or NTE992, it doesn't appear that reengineering it needs to be a crash priority.

Eric

I disagree. Its gain-bandwidth product is 3 MHz., triple the gbw of the venerable LM324, which is why I designed it into (and still use it) in the RST-523 Aircraft Navigation Receiver, still in production.

Jim

-- "If you th>> Anybody knows why National discontinued the LM3900 ? It seems