Author Topic: uA723 voltage regulator viable in 21st century? (Read 54569 times)

Wolfgang · « **Reply #50 on:** July 05, 2018, 01:57:00 pm »

Hi,

I am not sure if you are aware that improved LM723 chips have existed (SG3532, LAS1000, LAS1100) but were discontinued due to insufficient demand. They provided a lot of features you have been asking for, like:
- lower dropout voltage (they had a 2.5V reference)
- overtemperature protection
- better current sensing with less drop and more accuracy
- enable pin
- better PSRR and loop amplifier gain

I would appreciate to see better chips again, but with 40V/150mA capabilities. All the hyped new regulators are low voltage only.

GigaJoe · « **Reply #51 on:** July 05, 2018, 03:14:32 pm »

" low noise heated reference (LM399, LTZ1000)"
lm - not a really low noise - 3 uV pp ltz - are better but, really

, consider the price ...

IR led diodes gives a lowest noise; then regular led, - all this thing has to be measured ... a significant fluctuation depend on manuf. and current flow

Wolfgang · « **Reply #52 on:** July 05, 2018, 08:17:00 pm »

Agreed, but you can kill the noise a little bit by a lowpass (see Horowitz and Hill 2nd edition) using an RC lowpass with a large foil capacitor.
If you need extreme performance I do not know any alternative to an LTZ1000. The problem with LEDs is aging and drift.

If you have alternatives please let me know.

Kleinstein · « **Reply #53 on:** July 05, 2018, 08:25:37 pm »

Just for low noise some of the old zener diodes like 1N829 are supposed to be relatively good. The Chinese 2DW232 from a certain manufacturer are supposed to be even lower noise than the LTZ1000 - though with unknown (and likely worse) long term stability.

The LED based references are kind of bandgap type, though with relatively large current and a higher band-gap.

David Hess · « **Reply #54 on:** July 05, 2018, 10:51:53 pm »

Quote from: Wolfgang on July 05, 2018, 08:17:00 pm

Agreed, but you can kill the noise a little bit by a lowpass (see Horowitz and Hill 2nd edition) using an RC lowpass with a large foil capacitor.

It is better to start out with lower noise than to try and filter low frequency noise which is especially a problem below the flicker noise corner frequency.

Wolfgang · « **Reply #55 on:** July 06, 2018, 09:07:59 am »

If you have the choice, no noise is always better than filtered noise.
Just to add another weird idea, you could consider cooling your reference instead of heating it.

BravoV · « **Reply #56 on:** July 06, 2018, 10:26:33 am »

Re-reading the datasheet, just realized as I spotted that the TO-100-10 package doesn't have the V_Z pin as other packages.

precaud · « **Reply #57 on:** July 06, 2018, 01:27:50 pm »

Quote from: Giuss on July 05, 2018, 01:27:30 pm

I think it is a very good chip: stable, reliable, easy to use and cheap.

In all the instruments I've serviced/repaired, I've never seen a bad 723...

Wolfgang · « **Reply #58 on:** July 06, 2018, 07:40:26 pm »

The datasheet says than if you want a TO-99 version you need to add the Zener externally. It is certainly on the chip, but there was no pin left to connect to.

Thats why I used a DIP version for my heated LM723 reference. If you insist on hermetic packages, you could still by a 723J in CERDIP package (not very cheap, however, between 5 and 20€ on eBay).

David Hess · « **Reply #59 on:** July 06, 2018, 08:12:32 pm »

Quote from: BravoV on July 06, 2018, 10:26:33 am

Re-reading the datasheet, just realized as I spotted that the TO-100-10 package doesn't have the V_Z pin as other packages.

The V_Z pin is used where the output compliance of the error amplifier is not sufficiently low. The minimum output voltage at the V_out pin is 2 volts.

iMo · « **Reply #60 on:** July 07, 2018, 10:14:49 am »

I wonder if the 723 could "ovenize" its own chip die - for example:
1. the current sense transistor (B-E) as the temperature sensor, and
2. the output transistor as the heater..
.. and then you may find the zero tempco of the zener (if any)..

David Hess · « **Reply #61 on:** July 07, 2018, 11:03:59 am »

Quote from: imo on July 07, 2018, 10:14:49 am

I wonder if the 723 could "ovenize" its own chip die - for example:
1. the current sense transistor (B-E) as the temperature sensor, and
2. the output transistor as the heater..
.. and then you may find the zero tempco of the zener (if any)..

Apparently an old article in EDN or Electronics magazines showed a self ovenized 723 reference. The idea has been reinvented periodically:

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

I found the example below from Elektor:

Wolfgang · « **Reply #62 on:** July 08, 2018, 06:58:42 pm »

Hi,

I tried to collect all sources of information about heated 723 references on my webpage, including the suggestions from Elektor and the EDN circuit where a LM723 stabilizes a CA3046 chip temperature.

What is still missing is the "pure 723" variant from EDN. Does anybody have an original circuit ?

Thanks and best regards

leonababy · « **Reply #63 on:** July 08, 2018, 09:16:34 pm »

I just recently got back into electronics experimenting, and went searching my shelves for power supplies. I have multiple linear supplies in the 12V +/- 2V range, but only ever had one that was 5V. It is a Sierracin open frame monstrosity, with three outputs. 5V, 8V and 12V, the 5V has the highest current capacity and two pass transistors. There is a 723 for each supply. Years ago, I had an issue with it of some sort, and pulled the circuit board off to do some testing. I misplaced most of the mica insulators and all mounting hardware. Today I have no idea what I thought went wrong in the 5V supply, but I bought the mounting hardware and a supply of 723's NOS off Ebay. With some careful testing, I determined that nothing was actually wrong with it, and I teamed up the 8V and 12V supplies to get the 20+V I need for VFD experimenting. I just bought a used precision Keysight bench supply off Ebay that will do 0-50V (hopefully it will work right out of the box), but the old clunker Sierracin is cranking along just fine. You can buy em on Ebay cheap, probably salvaged out of old equipment.

David Hess · « **Reply #64 on:** July 09, 2018, 12:21:44 am »

Quote from: Wolfgang on July 08, 2018, 06:58:42 pm

I tried to collect all sources of information about heated 723 references on my webpage, including the suggestions from Elektor and the EDN circuit where a LM723 stabilizes a CA3046 chip temperature.

There are lots of examples where an external error amplifier temperature stabilizes a transistor array. Here the 723 has an advantage because of its built in reference although there are some combination operational amplifier and reference parts which could do it also but they are more expensive.

My favorite though is the discontinued LM389 audio amplifier which has 3 uncommitted NPN transistors stabilizing itself leaving one transistor free.

Wolfgang · « **Reply #65 on:** July 09, 2018, 08:55:13 am »

In Germany you can still buy this one for 67€Cent at Reichelt and other distributors. Its a smart part, I like it too.

dardosordi · « **Reply #66 on:** July 10, 2018, 09:33:53 pm »

Quote from: Wolfgang on July 08, 2018, 06:58:42 pm

Hi,

I tried to collect all sources of information about heated 723 references on my webpage, including the suggestions from Elektor and the EDN circuit where a LM723 stabilizes a CA3046 chip temperature.

What is still missing is the "pure 723" variant from EDN. Does anybody have an original circuit ?

Thanks and best regards

I contacted the author of this article http://www.cappels.org/dproj/1.024voltreference/portvoltref.html and asked for the schematics. Hopefully he can reveal the mystery since Im really curious about it.

Edit, relevant quote from the article:

Quote

I have an older voltage reference, which was based on Design Idea article in EDN Magazine back in the 1970's -its an LM723 voltage regulator chip connected so that the internal pass transistor acts as a heater, and the internal current limit transistor serves as a temperature sensor, so the chip could provide a stable temperature for the on-chip zener reference voltage. Back on March 1, 1979, I calibrated this against a differential voltmeter with calibration traceable to the NBS (Now NIST). I had set the output of this LM723 based reference to 1.00019 volts. I connected this LM723 based reference to a bench supply and watched it on one of my Fluke DVM's. After a minutes of warm-up time, the reading settled at 1.000 volts.

Wolfgang · « **Reply #67 on:** July 10, 2018, 11:00:38 pm »

Hi,

I also tried to contact Mr. Cappels and we emailed for a while. The bottom line was that the mystical EDN circuit could not be found, unfortunately.

This case would be easy to clear up if EDN magazine would keep a properly organized archive of their publications. In fact their older articles are full of missing graphs and broken links.
A shame in fact.

Wolfgang

EmmanuelFaure · « **Reply #68 on:** July 11, 2018, 12:11:43 am »

I've found the exact references :
Shah, M. J., Using transistor arrays for temperature compensation, published in Elecronics, April 12 1973, p. 103. The complete title might be "Electronics : the international magazine of electronics technology and business".
Shah, M. J., Self-regulating temperature stabilized reference, published in EDN, May 20 1974, p. 74-6
If anybody has a print version of those issues, or live nearby a college library that has them... If someone here happens to live in Switzerland, EPFL Lausanne seems to have the first one on their shelves, and ETH Zurich the latter.

dardosordi · « **Reply #69 on:** July 11, 2018, 04:53:28 am »

Quote from: EmmanuelFaure on July 11, 2018, 12:11:43 am

I've found the exact references :
Shah, M. J., Using transistor arrays for temperature compensation, published in Elecronics, April 12 1973, p. 103. The complete title might be "Electronics : the international magazine of electronics technology and business".
Shah, M. J., Self-regulating temperature stabilized reference, published in EDN, May 20 1974, p. 74-6
If anybody has a print version of those issues, or live nearby a college library that has them... If someone here happens to live in Switzerland, EPFL Lausanne seems to have the first one on their shelves, and ETH Zurich the latter.

This seems to be the 1974 article and it doesn’t use a LM723

http://www.seekic.com/circuit_diagram/Basic_Circuit/10_V_TEMPERATURE_STABILIZED.html

And here’s the 1973 one using the lm723 with the ca3046.

http://sigmambient.blogspot.com/2017/01/lm723-heater-circuit.html

But none is a standalone 723 heated reference. I guess the one in elector is the only one.

markce · « **Reply #70 on:** July 11, 2018, 09:25:51 am »

A circuit like the ones listed here, as well as the standalone 723 heated reference are in this document:
https://electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/

DimitriP · « **Reply #71 on:** July 26, 2018, 05:21:31 pm »

Quote from: Wolfgang on July 09, 2018, 08:55:13 am

In Germany you can still buy this one for 67€Cent at Reichelt and other distributors. Its a smart part, I like it too.

Stock up before prices magically go up.
(it may already be too late)

Kleinstein · « **Reply #72 on:** July 27, 2018, 12:07:54 pm »

There are still quite a few LM723 and µC723 to get. The µA 723 (DIP) even for under 40 cents.

Wolfgang · « **Reply #73 on:** July 27, 2018, 06:25:36 pm »

... 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 ...

iMo · « **Reply #74 on:** August 23, 2018, 09:48:30 pm »

Interesting reading for 723 fans

https://e2e.ti.com/support/power_management/linear_regulators/f/321/t/693040?UA723-Drift-is-a-one-time-thing-zener-walkout-that-stabilizes-after-time-Output-voltage-is-drifting-during-test-


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Author Topic: uA723 voltage regulator viable in 21st century? (Read 54569 times)

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