LM-324 op amp

[chuckrr]

What is standard procedure for tying off unused op-amp inputs?

If for instance there is a circuit which uses only (2) of the (4) available op-amps in a DIP package,
what is the normal protocol for dealing with these unused units?

Can the unused inputs just be left floating? Doing do on an LM-324 runs the output at around 7.45 volts
when the chip is operating from a single 9 volt supply. Does doing this draw more current than tying off inputs to GND?

Thanks, Chuck

[Bill van Dijk]

Ty the unused inputs to ground with a 10K resistor, float the unused outputs.

Bill

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[David Forbes]

The standard way is to connect it as a unity gain buffer. Connect the non inverting input to Gnd and connect the inverting input to the output.

[David Forbes]

Bill,

That's not a good idea. It is likely to oscillate. See my other reply.

[peter bunge]

Why are you using a 324 Op Amp? Older OpAmps are asking for problems with instability and common mode input range as well as output swing limits.

I suggest you look at something like the TLV2371 series that is available as single, dual, and quad. Inputs and outputs are rail to rail. 

Yes, connect as unity gain buffer. You don't want extra resistors.

If you want retro design and a challenge use a uA702 and good luck with getting it stable.

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[Toby Thain]

Here's one guide. There are others. And there are deep dives online by
the likes of Bob Pease and Paul Rako if that's what you're into.

https://www.ti.com/lit/an/sboa204a/sboa204a.pdf

--Toby

[Bill van Dijk]

David,

 

You are correct, I had a brainfart. My mind was on a CMOS logic chip. Thanks for the correction.

 

Bill

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[chuckrr]

Using LM-324 because I have them here and they work extremely well in the application.

 

---- Original Message ----
From: "peter bunge" <bung...@gmail.com>
Sent: 4/1/2021 10:25:42 AM
To: neoni...@googlegroups.com
Subject: X-IMail-SPAM-Connection Re: [neonixie-l] LM-324 op amp
 

Why are you using a 324 Op Amp? Older OpAmps are asking for problems with instability and common mode input range as well as output swing limits.

I suggest you look at something like the TLV2371 series that is available as single, dual, and quad. Inputs and outputs are rail to rail. 

Yes, connect as unity gain buffer. You don't want extra resistors.

If you want retro design and a challenge use a uA702 and good luck with getting it stable.

On Thu, Apr 1, 2021 at 10:06 AM David Forbes <nixie...@gmail.com> wrote:

Bill,

That's not a good idea. It is likely to oscillate. See my other reply.

 

On Thu, Apr 1, 2021, 6:37 AM Bill van Dijk <theold...@gmail.com> wrote:

Ty the unused inputs to ground with a 10K resistor, float the unused outputs.

Bill

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[chuckrr]

Thank you David.  Makes good sense.   -Chuck
 

---- Original Message ----
From: "David Forbes" <nixie...@gmail.com>
Sent: 4/1/2021 10:03:25 AM
To: "NeoNixie" <neoni...@googlegroups.com>

Subject: Re: [neonixie-l] LM-324 op amp
 

The standard way is to connect it as a unity gain buffer. Connect the non inverting input to Gnd and connect the inverting input to the output.

On Thu, Apr 1, 2021, 5:53 AM chuckrr <chu...@all2easy.net> wrote:

What is standard procedure for tying off unused op-amp inputs?

If for instance there is a circuit which uses only (2) of the (4) available op-amps in a DIP package,
what is the normal protocol for dealing with these unused units?

Can the unused inputs just be left floating?   Doing do on an LM-324 runs the output at around 7.45 volts
when the chip is operating from a single 9 volt supply.   Does doing this draw more current than tying off inputs to GND?

Thanks,    Chuck

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[chuckrr]

That actually sounds kind of like the old military practice of grounding unused TTL inputs through a 1k resistor.

---- Original Message ----
From: "Bill van Dijk" <theold...@gmail.com>
Sent: 4/1/2021 9:40:44 AM
To: neoni...@googlegroups.com
Subject: RE: [neonixie-l] LM-324 op amp

Ty the unused inputs to ground with a 10K resistor, float the unused outputs.

Bill

-----Original Message-----
From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com] On Behalf Of chuckrr
Sent: Thursday, April 01, 2021 8:53 AM
To: neoni...@googlegroups.com
Subject: [neonixie-l] LM-324 op amp

What is standard procedure for tying off unused op-amp inputs?

If for instance there is a circuit which uses only (2) of the (4) available op-amps in a DIP package, what is the normal protocol for dealing with these unused units?

Can the unused inputs just be left floating? Doing do on an LM-324 runs the output at around 7.45 volts
when the chip is operating from a single 9 volt supply. Does doing this draw more current than tying off inputs to GND?

Thanks, Chuck

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</theold...@gmail.com>

[chuckrr]

David,

 

Since you responded to my question about LM-324, I have another thing I need to consult you about:

 

I have tried several times to contact you at your nixiebunny emal address with no response back.

What this is in reference to is my interest in obtaining and setting up a rubidium oscillator so that I can construct a much more

accurate free-standing clock than the ones I currently have.    I did some digging on this, and have a general idea of how to do it.

But I did want to open up a discussion with you regarding this, because I know that you have a rubidium oscillator running as the time base

for one of your nixie clocks.      Thanks again   -Chuck
 

---- Original Message ----
From: "David Forbes" <nixie...@gmail.com>
Sent: 4/1/2021 10:07:56 AM
To: "NeoNixie" <neoni...@googlegroups.com>
Subject: Re: [neonixie-l] LM-324 op amp
 

Bill,

That's not a good idea. It is likely to oscillate. See my other reply.

 

On Thu, Apr 1, 2021, 6:37 AM Bill van Dijk <theold...@gmail.com> wrote:

Ty the unused inputs to ground with a 10K resistor, float the unused outputs.

Bill

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[Ian Vine]

Ua702 :) I wonder what they go for ?

Ian

On 1 Apr 2021, at 17:49, chuckrr <chu...@all2easy.net> wrote:



To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/202104010921689.SM628587%40ADT-IM1.

[John Rehwinkel]

> That actually sounds kind of like the old military practice of grounding unused TTL inputs through a 1k resistor.

I thought the military practice was to tie unused inputs high (instead of grounding them) through a resistor: TTL takes less current to pull high than to pull low.

- John

[gregebert]

An op-amp is a high-gain amplifier, so if both inputs are tied to the same voltage, then noise will amplified thru the op-amp and cause the output to jump around. As others have said, this can lead to oscillation. Noise is not just what is present at the inputs; it's also inherent in the op-amp itself. Even the pullup or pulldown resistors you use are a source of noise.

By tying the unused output to the inverting input, you have a stable unity-gain amplifier, thanks to the internal compensation. You can then tie the non-inverting input to gnd, vcc, or preferably something inbetween.

[chuckrr]

Makes perfect sense.  Thank you.   So far I've used op amps for a few simple things but still need lots of study and practice to become more proficient with them.

To date my experience with op amps has all been cookie-cutter cookbook applications.   They work, but much more study is required.  At least I now know a little more

about the proper way to tie off the unused ones.   Thanks.   -Chuck
 

---- Original Message ----
From: "gregebert" <greg...@hotmail.com>
Sent: 4/1/2021 7:36:20 PM
To: "neonixie-l" <neoni...@googlegroups.com>
Subject: Re: [neonixie-l] LM-324 op amp

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[Nick]

I would strongly recommend getting a copy of the excellent "Opamps for Everyone", 5th ed. by Bruce Carter  & Ron Mancini. It's one of my go-to books...

https://www.amazon.co.uk/Op-Amps-Everyone-Bruce-Carter-dp-012811648X/dp/012811648X 

This is a highly revised version of the original Rev B version of Texas Instruments' book by Mancini that is available for free from TI's at https://e2echina.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-52-01-00-00-04-59-46/OP-amp-for-everyone.pdf

TI (and others) have great free analogue design guides... for some more of TI's, see

https://www.ti.com/amplifier-circuit/op-amps/technical-documents.html

HTH

Nick

[Mac Doktor]

On Apr 1, 2021, at 8:52 AM, chuckrr <chu...@all2easy.net> wrote:

Doing do on an LM-324 runs the output at around 7.45 volts
when the chip is operating from a single 9 volt supply.

This reminds me of an aspect of the LM324 worth including in this thread. It's the kind of real-world issue that doesn't come up until the second or third chapter of an operational amplifiers textbook. I doubt that it's a concern for the original poster but I'm a bit hazy on details myself so I'm hoping that someone else can remind me.

The LM324 is capable of working reliably on both bipolar and single power supplies. This versatility combined with its low price makes it a good all-around choice for a wide variety of less critical applications.

A friend of mine, someone much cleverer than I'll ever be, ran into what he assumed to be limitation imposed by its single supply capability. He was designing a circuit with a bipolar PS and simply couldn't get the 324 to behave. IIRC, he told me that there's glitch that occurs when the output crosses zero volts while slewing from negative to positive.

He ended up using something else, problem solved. Has anyone else heard of this?

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com/

“...the book said something astonishing, a very big thought. The stars, it said, were suns but very far away. The Sun was a star but close up.”—Carl Sagan, "The Backbone Of Night", Cosmos, 1980

[gregebert]

If the loop-gain is sufficiently low, any non-linearities at the output will get self-corrected (because of the negative feedback) at low-frequency. If the signal frequency is high-enough, or if there is low-bandwidth in the feedback network, then the output will definitely behave differently than you would expect due to the frequency response of the OP-amp (or your feedback network, such as an RC filter that isn't properly designed).

This is where SPICE simulations are imperative. I wont use an OP-amp unless the manufacturer provides a SPICE model.

[chuckrr]

I have used the LM-324 op amp for several things here over the years exactly because of its ability to operate from a single power supply, namely +9 volts DC and GND.
 

---- Original Message ----
From: "gregebert" <greg...@hotmail.com>
Sent: 4/5/2021 7:29:22 PM
To: "neonixie-l" <neoni...@googlegroups.com>
Subject: Re: [neonixie-l] LM-324 op amp

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