If you want an accurate Schmitt function, rather than a fast one......

[whit3rd]

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

 

[server]

On Wed, 12 Jan 2022 17:34:26 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

If you are doing timing with an RC, you can charge the cap through a
resistor from the same voltage that sets the thresholds. Then the
power supply voltage drifts don\'t matter much.

We use an RC and a dac+comparator to make programmable time delays. If
the charging supply is ratiometric on the DAC reference, it\'s stable.



--

I yam what I yam - Popeye

 

[Spehro Pefhany]

On Wed, 12 Jan 2022 17:34:26 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?

Available and near ideal (but requires an external reference and $$)
LTC1042

https://www.analog.com/media/en/technical-documentation/data-sheets/1042fa.pdf

Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

I\'ve used an non-RR op-amp switching a CMOS analog switch, say 1/3 of
a 4053. You can use a voltage divider from a reference for the
thresholds. Easy-peasy.
--
Best regards,
Spehro Pefhany

 

[bitrex]

On 1/12/2022 8:34 PM, whit3rd wrote:

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

Cheep and cheerful:

<https://www.dialog-semiconductor.com/products/greenpak/slg46120>

 

[Phil Hobbs]

whit3rd wrote:

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

An RRO comparator such as a TLV7031 and two resistors. Run the op amp
off an LP2951 to get decent rails.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

Phil Hobbs wrote:

whit3rd wrote:
what do you use?

I want to know the high and low switch thresholds, precisely,
and for them  not to drift.

A \'555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least.   It\'s as dead
as the XR2206, though.

You can drive the \'555 reference, but that\'s a tad messy.

So, what IS still available that\'s near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.


An RRO comparator such as a TLV7031 and two resistors.  Run the

comparator

off an LP2951 to get decent rails.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com