lm324 op amp

T

timmmmayyy!

Guest
Has anyone found this problem,

When a negative voltage is connected to the input of this op amp the output
will go positive, and the other outputs will go slightly positive.

Do you know what causes this?

Thanks
 
timmmmayyy! wrote:

Has anyone found this problem,

When a negative voltage is connected to the input of this op amp the output
will go positive, and the other outputs will go slightly positive.

Do you know what causes this?

Thanks



How negative? Are you going below the negative rail?
Click to expand...

http://www.analog.com/library/analogDialogue/Anniversary/6.html

Search for "phase inversion".

All the parts are on one die, so if you do something that lets the
electrons escape it'll affect all the other units on the die (this can
give you fits on multiple-input ADC's; somehow the datasheet doesn't
stress what happens to the other channels when you "safely" turn on the
protection diodes).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Sat, 9 Oct 2004 20:34:09 +0100, the renowned "timmmmayyy!"
<timmmmayyy@nospamplease.com> wrote:

Has anyone found this problem,

When a negative voltage is connected to the input of this op amp the output
will go positive, and the other outputs will go slightly positive.

Do you know what causes this?

Thanks
Click to expand...
It's called "output phase reversal" and it's a well-known "feature" of
the LM324 and other op-amps. You will only see it if you violate the
datasheet Absolute Maximum rating of -300mV (@ 25°C) input voltage.

It's caused by current flowing from the input (forward biasing
isolation junctions) into the substrate, which b*ggers things up in
one way or another.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Sat, 9 Oct 2004 20:34:09 +0100, "timmmmayyy!"
<timmmmayyy@nospamplease.com> wrote:

Has anyone found this problem,

When a negative voltage is connected to the input of this op amp the output
will go positive, and the other outputs will go slightly positive.

Do you know what causes this?

Thanks
Click to expand...
If you go below the negative supply, even a few tenths of a volt, a
324 (or similar-process parts, like LM339) will go crazy internally;
charge is being sprayed everywhere. There's a tiny fine-print footnote
on the original National datasheet, and some hints in the application
examples near the end.

Also: If one section of a 324 swings to the output rails, it can/will
also mess up the other amps in the same can. It's a nasty part,
overall.

LM35 and other National parts have similar problems. Pease promised me
he'd fix the LM35, maybe 10 years ago, but he hasn't so far.

John
 
On Sat, 09 Oct 2004 17:20:22 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:


Ah, give Pease a chance.
Click to expand...
---
<CHORTLE> :)

---
Visualize whirled Pease.

--
John Fields
 
On Sat, 09 Oct 2004 17:20:22 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Sat, 09 Oct 2004 13:40:48 -0700, the renowned John Larkin
jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On Sat, 9 Oct 2004 20:34:09 +0100, "timmmmayyy!"
timmmmayyy@nospamplease.com> wrote:

Has anyone found this problem,

When a negative voltage is connected to the input of this op amp the output
will go positive, and the other outputs will go slightly positive.

Do you know what causes this?

Thanks



If you go below the negative supply, even a few tenths of a volt, a
324 (or similar-process parts, like LM339) will go crazy internally;
charge is being sprayed everywhere. There's a tiny fine-print footnote
on the original National datasheet, and some hints in the application
examples near the end.

Also: If one section of a 324 swings to the output rails, it can/will
also mess up the other amps in the same can. It's a nasty part,
overall.

LM35 and other National parts have similar problems. Pease promised me
he'd fix the LM35, maybe 10 years ago, but he hasn't so far.

John

Ah, give Pease a chance.
Click to expand...
20 points!

John
 
John Larkin wrote:
...a 324 will go crazy internally...It's a nasty part,
Click to expand...
What ubiquitously available quad would you recommend instead?
 
In article <4168740c$0$22860$afc38c87@news.optusnet.com.au>,
Clifford Heath <no@spam.please.net> wrote:
John Larkin wrote:
...a 324 will go crazy internally...It's a nasty part,

What ubiquitously available quad would you recommend instead?
Click to expand...
If the design is finished, put a LT1014 in place of the LM324.


--
--
kensmith@rahul.net forging knowledge
 
On Sun, 10 Oct 2004 09:28:12 +1000, Clifford Heath
<no@spam.please.net> wrote:

John Larkin wrote:
...a 324 will go crazy internally...It's a nasty part,

What ubiquitously available quad would you recommend instead?
Click to expand...
Why a quad? Duals are a lot more flexible, and don't take much more
room. Decent old/cheap amps are LF353 (dual jfet) and LM1458, basicly
a dirt-cheap dual 741. But there are hundreds of nice opamps around
nowadays: cmos, rail-to-rail, micropower, precision, low-noise,
superfast, whatever.

I use a lot of LM7301's, a SOT-23 bipolar r-r amp. It's a single, so
you just plop one down wherever you need it.

John
 
On Sun, 10 Oct 2004 09:28:12 +1000, the renowned Clifford Heath
<no@spam.please.net> wrote:

John Larkin wrote:
...a 324 will go crazy internally...It's a nasty part,

What ubiquitously available quad would you recommend instead?
Click to expand...
And nothing over a dime or two, please. ;-)


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article <8atgm0113d1anqnj6bcv5vkk81llesoiua@4ax.com>,
John Larkin <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:
[...]
Why a quad? Duals are a lot more flexible,
Click to expand...
Have you ever tried bending one?

LF353 (dual jfet) and LM1458,
Click to expand...
I'll second those suggestions.

[...]
I use a lot of LM7301's, a SOT-23 bipolar r-r amp. It's a single, so
you just plop one down wherever you need it.
Click to expand...
You can get r-r opamps and PICs in the SOT-23 package. This could make
designs even harder to copy.

--
--
kensmith@rahul.net forging knowledge
 
Ken Smith wrote:
In article <4168740c$0$22860$afc38c87@news.optusnet.com.au>,
Clifford Heath <no@spam.please.net> wrote:

John Larkin wrote:

...a 324 will go crazy internally...It's a nasty part,

What ubiquitously available quad would you recommend instead?


If the design is finished, put a LT1014 in place of the LM324.
Click to expand...
Make that the el cheapo Texas Instruments LT1013 family- and you are
only about 2x the National price on the LM324.
 
On Sat, 9 Oct 2004 23:50:54 +0000 (UTC), kensmith@green.rahul.net (Ken
Smith) wrote:

In article <8atgm0113d1anqnj6bcv5vkk81llesoiua@4ax.com>,
John Larkin <jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:
[...]
Why a quad? Duals are a lot more flexible,

Have you ever tried bending one?
Click to expand...
No, but I have stepped on both pin-up DIP8 and DIP16 packages
barefoot, and the 8-pins are much to be preferred.

John
 
Hi Fred,

Make that the el cheapo Texas Instruments LT1013 family- and you are
only about 2x the National price on the LM324.
Click to expand...
Or just stay with the LM324 and clamp off the negative peaks using a
reverse transistor, pre-biased diode etc. This would only add a few
cents to the design.

Regards, Joerg

http://www.analogconsultants.com
 
Joerg wrote...
Hi Fred,

Make that the el cheapo Texas Instruments LT1013 family-
and you are only about 2x the National price on the LM324.

Or just stay with the LM324 and clamp off the negative peaks
using a reverse transistor, pre-biased diode etc. This would
only add a few cents to the design.
Click to expand...
If a simple diode to ground, it had better be a Schottky diode.


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)
 
Hi Winfield,

Or just stay with the LM324 and clamp off the negative peaks
using a reverse transistor, pre-biased diode etc. This would
only add a few cents to the design.



If a simple diode to ground, it had better be a Schottky diode.


A regular one would have to be pre-biased so that it starts to clamp at
Click to expand...
less than 300mV. Schottkys are kind of pricey. I'd probably consider the
inverse transistor if the voltage swing in the other direction is always
below the breakdown.

Regards, Joerg

http://www.analogconsultants.com
 
Joerg wrote...
Hi Winfield,

Or just stay with the LM324 and clamp off the negative peaks
using a reverse transistor, pre-biased diode etc. This would
only add a few cents to the design.

If a simple diode to ground, it had better be a Schottky diode.

... Schottkys are kind of pricey.
Click to expand...
Not that bad... For example, Vishay BAT82S (44348 in stock),
SD101A (16922 in stock) are both $0.03, qty 1k at Newark, $0.05
in singles, and the LS101C smd part a bit more, $0.04 for 1k...


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)
 
"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:ckclm901in7@drn.newsguy.com...
Joerg wrote...

Hi Winfield,

Or just stay with the LM324 and clamp off the negative peaks
using a reverse transistor, pre-biased diode etc. This would
only add a few cents to the design.

If a simple diode to ground, it had better be a Schottky diode.

... Schottkys are kind of pricey.

Not that bad... For example, Vishay BAT82S (44348 in stock),
SD101A (16922 in stock) are both $0.03, qty 1k at Newark, $0.05
in singles, and the LS101C smd part a bit more, $0.04 for 1k...
Click to expand...
BAV70, dual SMD schottky.

SioL
 
Hi Winfield,

... Schottkys are kind of pricey.



Not that bad... For example, Vishay BAT82S (44348 in stock),
SD101A (16922 in stock) are both $0.03, qty 1k at Newark, $0.05
in singles, and the LS101C smd part a bit more, $0.04 for 1k...


That is a good price for a Schottky diode. Wish they were in SMT though.
Click to expand...
This could actually beat the transistor which can be had under 2 cents
but it needs a resistor for base current and that adds a penny back in.

The BAT54S is SMT but over 10 cents. Well, at least you get two in one
SOT23 pack for that. They are nice for building mixers.

Regards, Joerg

http://www.analogconsultants.com
 
On 10 Oct 2004 17:55:37 -0700, the renowned Winfield Hill
<Winfield_member@newsguy.com> wrote:

Joerg wrote...

Hi Winfield,

Or just stay with the LM324 and clamp off the negative peaks
using a reverse transistor, pre-biased diode etc. This would
only add a few cents to the design.

If a simple diode to ground, it had better be a Schottky diode.

... Schottkys are kind of pricey.

Not that bad... For example, Vishay BAT82S (44348 in stock),
SD101A (16922 in stock) are both $0.03, qty 1k at Newark, $0.05
in singles, and the LS101C smd part a bit more, $0.04 for 1k...
Click to expand...
Or the very available BAT54 (SOT-23) 200mA/30V $0.03 in 250 at Mouser
or Allied.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
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