uA723 voltage regulator viable in 21st century?

[rsjsouza]

Thanks for sharing; that is quite interesting to show how the real world is much more complex than plain datasheet specifications. I remember stories told by the greybeards about how the manufacturer and sometimes even the country or origin of a part could introduce unexpected results for a design. This was much more common in the early days of high scale integration. 

A point that made me cringe a bit was how the other user was completely ignored by the OP, but I digress...

[Richard Crowley]

A point that made me cringe a bit was how the other user was completely ignored by the OP, but I digress...

I a the OP.  Please help me here. What "other user" are you referring to?  And how did I completely ignore them?

I came here to simply ask a question about whether the 734 was still alive and kicking and a really interesting discussion ensued.  I learned a lot about modern linear regulator design. I wasn't trying to ignore anyone.

[rsjsouza]

A point that made me cringe a bit was how the other user was completely ignored by the OP, but I digress...

I a the OP.  Please help me here. What "other user" are you referring to?  And how did I completely ignore them?

I came here to simply ask a question about whether the 734 was still alive and kicking and a really interesting discussion ensued.  I learned a lot about modern linear regulator design. I wasn't trying to ignore anyone.

Hah... It was on the thread linked by the post just above mine. 

[mike_mike]

Does anybody know if the LM/UA723 will still be manufactured and how long time 723 will be manufactured from now ?
I am asking this question because I want to build a few 723 based power supplies.

[Wolfgang]

Does anybody know if the LM/UA723 will still be manufactured and how long time 723 will be manufactured from now ?
I am asking this question because I want to build a few 723 based power supplies.

Hi Mike,

of couse I dont know how long the 723 "will be" manufactured but I am confident that it will be another decade(s) from now at least.
Its available from all major distributors either unter uA723 or LM723. I use it routinely in a lot of supply circuits and it works.

Some hints here:
https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf (oldest appnote I found)
https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/

have fun
  Wolfgang

[not1xor1]

Some hints here:
https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf (oldest appnote I found)
https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/

have fun
  Wolfgang

I started to read "a collection... etc" but...
1) there is no buried zener in 723s
2) what they call minimum drop-out voltage (10V) is just the minimum supply voltage

I did not read any further

that is a case of fake EE 

[Wolfgang]

Some hints here:
https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf (oldest appnote I found)
https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/

have fun
  Wolfgang

I started to read "a collection... etc" but...
1) there is no buried zener in 723s
2) what they call minimum drop-out voltage (10V) is just the minimum supply voltage

I did not read any further

that is a case of fake EE 

Well, thats easy.

- make a google search about "LM723 buried Zener"or just "Zener". Surprised ?
- try to run an LM723 with just a few volts on Vcc and tell me how it was

Here is one of the first datasheets of the LM723 I found, found 1968:
https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf

[schmitt trigger]

What an extraordinary app note!

No one writes such a thorough and detailed app note anymore.

[Wolfgang]

Yeah, one of the most profound appnotes I have seen. I got it from EEVBlog member Cody, thanks again to him for digging it out.

I also have an old Siemens book with a lot of elaborate LM723 circuits ("Lineare Spannungsregler"), but only on paper. Its a feeble paperback so it will fall apart hen I try to put it into my scanner. These people also discussed a lot more circuits than today, one of the interesting ideas is to use the CL transistor (in reverse, as a BE junction Zener) as a prestabilizer for the 723s own supply voltage in order to improve CMRR.

[Richard Crowley]

... if you buy 100 pieces or more you can get down to 10 to 15€Cents.
Its an active part, from TI, ST and others, there is no end of life warning, so no surprise ... 

Both DigiKey and Mouser show all the more modern, plastic (DIP, SMD) packages as "OBSOLETE"
And the original round metal can (TO-100) package is selling for US$10-12 each.
It certainly makes it appear to be on its way out. Perhaps that is just TI?

[Wolfgang]

... if you buy 100 pieces or more you can get down to 10 to 15€Cents.
Its an active part, from TI, ST and others, there is no end of life warning, so no surprise ... 

Both DigiKey and Mouser show all the more modern, plastic (DIP, SMD) packages as "OBSOLETE"
And the original round metal can (TO-100) package is selling for US$10-12 each.
It certainly makes it appear to be on its way out. Perhaps that is just TI?

I got the news that ST has discontinued it. TI bought National, but on their page the *uA723* is still active in DIP, SMD, TO-99 and CERDIP. TI has marked the National nomenclature *LM723C* as obsolete.

TI still sells military and even space-grade LM723QML varieties as active parts on their webpage.

I looked at Mouser today and found a whole lot of uA723 parts deliverable, prices being a few ten cent depending on volume for the commercial versions, about 10€ for TO-99.

My bet is that it will still be sold in ten years. I hope this Methusalem IC does not survive me

[not1xor1]

Well, thats easy.

- make a google search about "LM723 buried Zener"or just "Zener". Surprised ?
- try to run an LM723 with just a few volts on Vcc and tell me how it was

Here is one of the first datasheets of the LM723 I found, found 1968:
https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf

I did search the net and the only result was an old application note (NSC AN173 November 1976) where they suggested to use an LM129 (i.e. a real buried zener) as external reference for LM723.

Of course you can find various people stating 723s have buried zener.
There is no lack of self proclaimed experts on internet, but as far as I'm concerned, manufacturers datasheet and application notes are the only reliable source.

Apart from that, drop-out is usually the difference between input voltage and output voltage and in the case of LM723, as stated by NSC, that ranges from 3V up to 38V both for LM723 and LM723C while 9.5V is the lowest limit of the "Input Voltage Range".

Please do not take that as a personal offence and forgive me if I have been a bit too harsh. 

[Wolfgang]

The point is that a manufacturer does not tell you how he has implemented the "temperature stabilized" Zener component. One way to find out if it was a buried or a surface Zener is looking at noise level. The ones with a very low noise level are most probably the buried ones. A lot of datasheet explicitely mention the word "Zener" and not  "Bandgap". When you look at TIs datasheet showing the internals of the chip the 6.2 zener is explicetely drawn.

In the course of chip shrinking over the decades manufacturers have sought ways to replace the Zener by a bandgap or similar circuit with some tempco improving circuitry. One of them was ST, and the results were mixed. The new chips have a much higher drift factor than the old ones (I keep a box of all kinds of 723s from different manufacturers and dates). They (TI the same) had (before discontinuing the part altogether) some customer response claiming problems with drift values a lot higher than the datasheet suggests. The explanation was a "trapped charge" problem you never have with a subsurface Zener. So, they tried to cut corners.

An "official" bandgap 723 clone product was the SG3532, with about 2.5V of reference voltage, more accurate current limiting, overtemp protection and some other gimmicks. It was discontinued because the LM723 was good enough for most users and the SG3532 niche was too small.

Mil versions are a totally different story. The drift for a few days, and then stay tack sharp for a long time. The old ones were definitely aged and temp cycled, and most probably used a buried Zener.

https://electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/

has some details about the stability experiences with several 723 types, including long-term results.

I am OK with the definition of drop-out voltage as the minimum input/output voltage where the part still provides regulation. In the case of the 723, the built-in reference needs at least 9.5V (varies by datasheet) on the Vcc pin. The Vc pin can be lower, agreed. So, the manufacturers took the maximum of both voltages to be correct. When you look at my "best practices" you see exactly this ("headroom"). The minimum Vc voltage can be computed from the minimum output voltage (2V), the drop on the current limiting resistor, plus some headroom for the 723s internal pass transistor, so you end up with something in the ballpark of 4-5V, at not too high currents.

Apology accepted if you promise me that you read stuff to the end.

[not1xor1]

The point is that a manufacturer does not tell you how he has implemented the "temperature stabilized" Zener component. One way to find out if it was a buried or a surface Zener is looking at noise level. The ones with a very low noise level are most probably the buried ones. A lot of datasheet explicitely mention the word "Zener" and not  "Bandgap". When you look at TIs datasheet showing the internals of the chip the 6.2 zener is explicetely drawn.

It is just not possible to prove the non-existance of something, so it is to you the onus of proving that (the existance of a buried-zener 723). 

Besides that 723 is about a decade older than the first subsurface zener (LM199).
Producing subsurface zener requires more resources (i.e. costs more) so it would make just no sense to produce a more expensive version of 723 with the same part-code or without clearly mentioning it in press releases and datasheets

BTW temperature dependance and long term stability of 723 is about the same of the cheaper and ubiquitous bandgap 431 and while noise might be lower than that of a cheap LM317 and similar ICs you can design low noise PS with many other different parts.

[Wolfgang]

Hi,

I try to dig out an old paper where the "buried" Zener was explictely referenced.

With the noise issue, there have been comparative studies of integrated voltage regulators showing that the 723 is still top:

https://www.bartelsos.de/dk7jb.php/rauschen-von-spannungsreglern (click on the download link)

This is a german paper, but the curves say everything you need.

[iMo]

Where the 2mVpp noise comes from? (ie. your mil 723j).

[Wolfgang]

Hi Imo,

what exactly are you referring to ?

[iMo]

 I've been referring to the output of LM723J - see your graph below. I can see a similar <1mVpp @Vref low freq fluctuations with my samples (see my "723 baking" topic). I compared with other low cost Vref sources and those show typically 20-50x lower fluctuations.

[Wolfgang]

Hi,

thanks, now I know what you are saying. No, thats not noise, thats all kind of RFI sampled in one minute intervals. A look at the physical measurement setup photo explains everything.
A data logger like the M300 has not shielded inputs, but a little "patch panel" with open wire outputs. Its meant for low frequency measurements and not RF or high immunity. Accuracy
is fine (6 1/2 digits) but of course there is RFI. For drift measurements this is no problem.

When looking at LM723 noise you need a fully shielded, all coaxial environment, best with battery power. The noise measurements in the german paper mentioned did it like that.
For other noise measurements I built battery powered supplies, like here:

https://electronicprojectsforfun.wordpress.com/power-supplies/battery-operated-power-supplies/

[iMo]

@Wolfgang: try to measure an 1.5V AA battery with your logger, I bet  you will see no noise like the above one..

[Wolfgang]

I did (9V battery), with similar results. When you look at the scale of the measurements and the free-fly cabling, its no surprise. What does make a difference if you use the (shielded) internal multimeter path of the M300 and coax cabling. If you do that, you have less noise, but you can do only one measurement at a time. This is not why you have a data logger. I measured supply voltage, output voltage, supply current, ambient temperature and case temperature at the same time. Then you need to go over the terminal block. Photo here:

electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/lm723-long-term-stability-results/

Just as a hint: in this setup the readings change if you switch on the light (just sub-mV, but they do). Not a problem for a long-term measurement, but unusable for noise.

[mike_mike]

Hello,

I asked TI about UA/LM723 and I got the answers from the attached images.

[glarsson]

723, 555, 2N3055, 1N4148,... will live forever. :-)

[Richard Crowley]

Isn't LM723 the same part as UA723? 
Aren't those just the new (TI) and old (National) part numbers for the same product?
Was LM723 some sort of TI "remake"(?) of the original National uA723?

[schmitt trigger]

723, 555, 2N3055, 1N4148,... will live forever. :-)

Also the 7805. And the 1N400x diodes.