[sdiy] 4136??

[Happy Harry]

LOL !!!

Hah you are correct.

I did a design with the LM324 (25 years ago)... it worked
fine for many years, then suddenly started to latch up.
New and NOS LM324 opamps would still fail to work. Careful
review (with +25 years experience) showed the problem was in
the design from day one. Why did it run at all... I'll never know.

So just "Hey, it works..." is not enough. "Why and How" are much
more important.

H^) harry


>From: Martin Czech <czech at Micronas.Com>
>Reply-To: Martin Czech <czech at Micronas.Com>
>To: bahi0387 at terra.com.br
>CC: synth-diy at node12b53.a2000.nl
>Subject: Re: [sdiy] 4136??
>Date: Thu, 15 Mar 2001 11:13:22 +0100 (MET)
>
>
>:::Torbjörn Hörnfeldt wrote:
>:::>
>:::> Wasn't there one IC with the same pin-out - the TL075? Or is my
>:::> memory going?
>:::
>:::
>:::Yes. It's right. The only equivalent inthis world, I think.
>
>Just a few comments to the swapping IC business:
>
>I had a look into IC OP AMP genealogy yesterday.
>
>741,101,1458 are NPN diff input stage, two stage devices.
>A/B class output stage.
>Very similar.
>
>The 4136 is based on a single unit package I have forgotten now,
>however a PNP diff input stage is used. The overall two stage
>topology is the same, though. A/B class output stage.
>Parasitics are very different,
>however.
>
>075 is a jfet device IMHO. A completely different branch of the
>family tree. Parasitics are completely different, because
>process is different. I'm not sure, but output stage might not be A/B.
>
>So, even if bandwidth, slew rate, offset voltage etc. of two
>op amps are similar, you can not just swap.
>Because there are pesky effects like input zenering (latchup),
>ie. limited differential range or limited common range.
>Sometimes there are internal protection resistors and clamps
>(OP07), sometimes they are omitted (OP37) in favour of low noise.
>Just swaping devices can be dangerous, especially in the moment
>of power turn on and off, or if exessively large signals
>are applied (which is the case in turn on/off).
>Did I mention specs for bias current, offset current, and all the drifts?
>
>A very close look to the data sheet (abs max, and simplified
>circuit diagram, recommendations and basic applications)
>is a must if you want to swap and be sure that no pesky side
>effects will come up. Compared to that the pinout is of
>very little importance, you could use some adaptor, or change the pcb.
>Sometimes the manufacturers of a new part provide you with information
>how to replace older parts (mostly 741) with that new design.
>That is likely to work.
>
>If one is not so experienced (e.g. me), the only safe way is to plug in
>exactly the same type. Odd designs may require even the same
>manufacturer, which is of course very bad.
>I would not rely on "let see what happens", because what seemed
>to work yesterday can blow up today if I do not know what exactly I'm 
>doing.
>
>Proof by "it works" is no accepted engineering methodology.
>{People who argue like that will be thrown out of our design dept. here.
>Quite a lot of people had to go because of this "habit".}
>
>Proof by "I have understood and can explain that to others experienced
>in the art" is accepted.
>
>m.c.
>

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com