Favorite (LM324) quad op-amps for industry?

Harry Bissell harrybissell at prodigy.net
Thu Mar 23 03:44:19 CET 2000


Hey everybody...

Don't get me wrong... the LM324 does indeed have its place. I used it in an
industrial
control system where the low power drain, output that approaches ground on a single
supply, and well... its "quadness" were plusses... My design pulls down to 200mV of
the negative rail (that be "ground" in this case...) much better than the
transducers that input to the unit (at 700mV for 'zero'). They (the other transducer
designers...) also used the LM324... shame on them for not getting closer to zero
!!!

OTOH using the LM324 in an envelope generator (which was an early design of mine and
has certain deficiencies) on a bipolar supply resulted in the dreaded "latch-up"
condition (after several years of sucessful use...). Replacing the #@$ (oops thats
324...slip of the shift key....) with another 324 did not help. Using a TL084 did...
so what its in a CV app. Easier than redesign at this stage of the game...

The 324 is ok... but is 'gotta know its role...'

H^)   harry

Jim Patchell wrote:

> Tim Daugard wrote:
>
> > LM324 - Distortion highly visable as the negative input crosses from greater
> > than to less than the plus input reference level. Doesn't mater what the
> > supply is the cross over distortion has to be from switching some internal
> > trasistors. - This was more evident in a log amp than a straight amp. I
> > wanted to use the 324 for natural frequency rolloff but distortion was
> > outrageous.
> >
>
>     The LM324 has a class B output stage.  Because of the slow slew rate, you
> will see the crossover notch even at low frequencies.  By putting a resistor
> from the output to the negative rail, you cause the amplifier to be biased
> closer to class A, eliminating the cross over notch.  Still, if you are
> interested in audio of any sort, LM324's are not the answer.  They are very nice
> to use in DC applications where the input bias current is not a problem.  And
> the input common mode rage goes from V- to V+ -1.5 volts, which by the way,
> matches the range of voltages that the output will go over.  I stand also stand
> with those who do not dismiss this part out of hand.  It has it's uses.
>
> > Tim Daugard
> > Lurking and trying to make a living at real estate.
>
>     -Jim




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