uA723 voltage regulator viable in 21st century? - Page 1
Forum section: electronics / projects

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 29, 2018, 04:43:44 pm
content: I can see why LM555 continues to be used, but why would antiques like uA723 and uA709 continue to be used in new designs?Over in the GeekSlutz forum I was helping a guy from Sweden fix his audio mixer apparently designed in the mid 2000s.The power supply is dead because the custom transformer (made by respected audio transformer maker Lundhal) has an open primary winding.But the regulator design just seems completely antique. It was obsolete when the thing was designed. If you need + and - 15V @ 200mA, then why wouldn't you just use a positive and negative 3-terminal regulator (LM7815 and LM7915 or a modern descendent).Service Manual PDF:https://data2.manualslib.com/pdf5/101/10098/1009764-satt_electronics/sam_82.pdf?373d3cacdef1450e71f59cd434f92921

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 29, 2018, 05:03:14 pm
content: If you need it, you can customize fold-back limiting with the 723. It's still a good part!

author: pelule
author_rank: Frequent Contributor
timestamp: June 29, 2018, 05:38:26 pm
content: QuoteObsolete?At least at TI the uA/LM723 is still active:http://www.ti.com/sitesearch/docs/universalsearch.tsp?searchTerm=LM723#linkId=1&src=tophttp://www.ti.com/sitesearch/docs/universalsearch.tsp?searchTerm=uA723#linkId=1&src=topCall me old fashioned, but I am still use the uA/LM723 in my designs, if I need a bit more sophisticates linear regulation (i.e current protection or precisely adjustable voltage. I also still use the 723 as a very cheap temp-stabelized reference voltage (an old Elektor circuit to temp-regulate the on-chip reference using the on-chip pwr transitor as heater and the on-chip current sense transistor as temp-sensore)./PeLuLe

author: Bassman59
author_rank: Super Contributor
timestamp: June 29, 2018, 05:48:48 pm
content: Quote from: Richard Crowley on June 29, 2018, 04:43:44 pmRead more of the service manual! It uses a 709 in the input stage and the quad 4741 elsewhere. An RC4558 is used in the oscillator.And zoom in on the schematic. It's dated 1976. So, no it's not modern, and it certainly wasn't designed in the 2000s.(This kinda silliness is why I don't bother with GearSlutz ... it's all idiots talking in a circle jerk about audio gear they don't understand and have never used.)

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 29, 2018, 05:53:08 pm
content: My very first project employing an IC that actually worked, was a variable regulated power supply using a uA723. Which I used for my personal experiments for about 10 years.So, I feel a lot of nostalgia for the uA723, and know that it is a very flexible building block which allows certain configurations like foldback current limiting.But I would not use it today, for a couple of reasons:The series pass transistor is not thermally protected.I prefer spending my limited time, board real state and components in something more meaningful than a power supply.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 29, 2018, 05:54:49 pm
content: Quote from: edavid on June 29, 2018, 05:46:31 pmDoh! You are right.From that perspective, it seems more reasonable to see uA723.I don't know where I got the notion that it was from the mid-2000s

author: chris_leyson
author_rank: Super Contributor
timestamp: June 29, 2018, 06:00:54 pm
content: As far as I know they're still available. Built a super low noise low power regulator a long long time ago, it performed much better that the low noise linear regs from TI, National etc. Can't remember the circuit but I think there was a big tantalum capacitor on the reference pin. They're very versatile regulator chips and like Conrad mentioned they're great for foldback current limiters. Even seen them used as switching regulators in the HP9825 power supply.

author: bd139
author_rank: Super Contributor
timestamp: June 29, 2018, 06:02:32 pm
content: Indeed. It’s a power supply construction kit not a voltage regulator. And each chunk of it has pretty good performance.

author: rdl
author_rank: Super Contributor
timestamp: June 29, 2018, 06:04:09 pm
content: Quote from: Hackadayhttps://hackaday.com/2016/12/02/get-to-know-voltage-regulators-with-a-723/I bought a handful of them years ago, and one of these days I'm actually going to use one for something.

author: DimitriP
author_rank: Super Contributor
timestamp: June 29, 2018, 06:12:02 pm
content: QuoteStellar noise performance (with very few- maybe 6 - expections) and you don't need magnifying glasses to see it.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 29, 2018, 06:13:21 pm
content: A SMPS using a 723!Now I remember a fascinating Unitrode app note describing a hysteretic regulator utilizing a 723.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 29, 2018, 06:41:16 pm
content: Still available in TO100-10 package but £8 or £9 each !

author: richard.cs
author_rank: Super Contributor
timestamp: June 29, 2018, 06:51:02 pm
content: I used one at work a few months ago. I needed low noise and there are very few options for that in the voltage range I required. It's versatile enough to have a lot of uses, if nothing else keep a few in the junk box for when you need to build a slightly unusual regulator.

author: pelule
author_rank: Frequent Contributor
timestamp: June 29, 2018, 08:55:44 pm
content: QuoteConrad, a German (not the cheapest) electronic seller offers:Texas Instruments UA723CDR, SOIC-14 for 1,12 EUR/pcsTexas Instruments UA723CN, PDIP-14 for 0,89 EUR/pcsTexas Instruments LM723H/NOPB, TO-100-10 for 11,70 EUR/pcsSo plenty options still active & available/PeLuLe

author: glarsson
author_rank: Frequent Contributor
timestamp: June 29, 2018, 09:15:40 pm
content: Quote from: Richard Crowley on June 29, 2018, 05:54:49 pmThe enclosure that other manufacturers might have designed in 2006?

author: rsjsouza
author_rank: Super Contributor
timestamp: June 29, 2018, 09:27:06 pm
content: I too agree the uA/LM723 is still a useful part.Funny how TI's product page for the LM723 shows an unwarranted comparison with the LM317L-N in the front page. (perhaps trying to steer people towards the other part).http://www.ti.com/product/LM723

author: Synthtech
author_rank: Regular Contributor
timestamp: June 29, 2018, 09:28:40 pm
content: I run a vintage synthesiser repair workshop, the uA723 is used in a lot of instruments and it is a part that rarely if ever fails. They are a workhorse that runs reliably for decades and it does it’s job very well. Three terminal regulators are also incredibly reliable of course but the 723 has advantages over them.

author: glarsson
author_rank: Frequent Contributor
timestamp: June 29, 2018, 09:53:21 pm
content: Quote from: schmitt trigger on June 29, 2018, 06:13:21 pmIn the early eighties I used a 723 as a heater element and heater controller for a crystal oven. The output driver transistor was the heater, a PN junction of the "free" transistor (normally used for current limiting) was the temperature sensor. Glue the crystal to the top of the DIP and pack with some insulating material.

author: KE5FX
author_rank: Super Contributor
timestamp: June 29, 2018, 10:13:47 pm
content: Only very recently have linear regulators been introduced that rival the ua723's noise performance. The ability to bypass the reference is a big deal in some applications, and for a long time it was either use a 723 or roll your own.

author: dardosordi
author_rank: Regular Contributor
timestamp: June 30, 2018, 03:26:35 am
content: Just recently stumbled upon this guy, he likes the lm723 so much that it had made me appreciate it a lot:https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/Also check out lm723 self heated reference:https://electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/

author: edpalmer42
author_rank: Super Contributor
timestamp: June 30, 2018, 04:24:09 am
content: FYI, the elektor version of the self-heated reference was in the 1978 July/Aug. issue on page 7-89 which is page 94 of this pdf.https://archive.org/download/ElektorMagazine/Elektor%5Bnonlinear.ir%5D%201978-07_08_text.pdf

author: texaspyro
author_rank: Super Contributor
timestamp: June 30, 2018, 05:47:33 am
content: Quote from: KE5FX on June 29, 2018, 10:13:47 pmYep, and that new fangled stuff can cost 10x-100x what you can get 723's for... I recently bought 100 of them for $5.00.

author: BravoV
author_rank: Super Contributor
timestamp: June 30, 2018, 10:49:18 am
content: Quote from: edpalmer42 on June 30, 2018, 04:24:09 amThanks for the link, also extracted that page and attached below.About the uA723 used as TC voltage reference, any idea what is the realistic performance ?

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 10:52:37 am
content: Hi,I think they chose this old chip because it has much less noise than a LM317, LM78XX and many others, even much more modern chips.For low level audio, measurement and other sensitive app like low phase noise oscillators this can be important.I learned a lot from a german paper about regulator noise (just looking at the graphs tells you everything you need):https://www.bartelsos.de/dk7jb.php/rauschen-von-spannungsreglernAnother aspect is a datasheet value for long time drift and tempco. The cheap 3-legged regulators can be off by 5%, have up to 10mV of noise, a bad PSRR at higher frequencies, and no long term drift specs, plus a bad tempco in comparison. I agree that a 723 is more effort, but it can make sense.The question for me is not if a chip is old or new, but if it does the job I need. Electronic design should not be based on what is fashionable, but on specs.There must be a reason why TI, ST and others still sell this methusalem ...For prototyping, the availability of a DIP or TO-99 is also a plus.RegardsWolfgangPS: If you want to see some 732 designs for all kings of projects:https://electronicprojectsforfun.wordpress.com/power-supplies/and something a bit off-center:https://electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/

author: blackdog
author_rank: Frequent Contributor
timestamp: June 30, 2018, 11:29:54 am
content: Hi,And do not forget my uA723 Oven designshttps://www.eevblog.com/forum/metrology/small-oven-controler-for-voltage-reference/Kind regards,Bram

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 11:37:23 am
content: Hi,thanks for the tip. I will try this one out !Wolfgang

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 12:06:33 pm
content: Hi,apart from being in cents range for 100pcs, the LM723 has survived a lot of competitors that provided better data.One of these was the SG3532 regulator, which offered the following advantages:- lower voltage due to a 2.5V reference- high error amp gain- precision current limiting- overtemp protection- better tempco...There were some others, too, like the LAS1000 and LAS1100. The funny thing is that all of them have been discontinued. The key point wasthat the LM723 price/performance was hard to beat, and the LM723 was good enough for most applications, so the niche for the competitorswas not large enough.Today, there (supposedly) are chips that outperform the 723, but they do not even come close to the price.BTW: Which chips today can compete and who builds them ? Just curious ...So - maybe its lasts for some more decades to come. The 723 has already survived its inventor by 27 years now !RegardsWolfgang

author: bd139
author_rank: Super Contributor
timestamp: June 30, 2018, 12:56:57 pm
content: Quote from: Wolfgang on June 30, 2018, 12:06:33 pmOnly because he drank so much

author: David Hess
author_rank: Super Contributor
timestamp: June 30, 2018, 01:44:35 pm
content: There are a couple of things which I think the 723 should have included like thermal protection and a second transconductance amplifier for precision current limiting but its price for performance cannot be beat.The 709 on the other hand was a terrible operational amplifier but contrast it to devices like the 301A and 741 which are still excellent.

author: CopperCone
author_rank: Super Contributor
timestamp: June 30, 2018, 01:47:28 pm
content: What kind if noise performance can you get with uVrms with 100KHz bandwidth limit and 10Hz bandwidth limit?OK, I found it on some audio forumIt says the 723 is roughly 2uV RMSMost linear regulators out there that are considered low noise will be between 100-0.5uV RMS, with the LT3042 being 0.8uV rms or so, which is the lowest noise manufactured part I found with a rating.As for negative rails, for precision parts you will get between like 100uV rms to 20uV rms I think. They don't do quite so well.I like LT3080 and LT3015 (neg), which have 20uVrms/60uV rms respectively.************Can the uA723 be used to make a negative rail by any chance? If it's only 2.5uV rms for a negative rail that would be an order of magnitude improvement over other devices.And how are it's specifications for PSRR and tempco compared to modern references? If they are particularly bad it would require its own temperature stabilization as not to effect a system. The tempco should not have much effect on AC circuits though.150ppm/C - 723 (worse case), ripple rejection not bad either. Best case is 30ppm.For comparison, the LT3080 -0.5% change in bias current over 75C,0.006%/C, 60ppm. Unknown if this is typical, max, random sample, etc. Just extrapolated from a graph. Has a curve around 0 so if you freeze it then it will reverse.I think I ignored this part because it is old. It seems decent. For home made instrumentation I'm not sure I give a shit if a linear regulator melts or has current limiting. Maybe hard to make use of it for powering modern op-amps.It is only 100mA though.****I think that parts like the LT3042 which have a lower noise are more designed for PSRR at MHz then low noise, for use in biasing an RF transistor or MMIC directly from a rail. Modern op-amps have typically a high PSRR so you can kinda get away with feeding them garbage, so I am not sure how much benefit lowering the rail noise has... This I think changes if you use them to bias transistors (i.e. differential matched transistor input stage for op-amp). Not sure how PSRR works out for something like a MMIC, usually I just see the voltage connected to the output by a resistor, but it does have VDD pins I think.I would like to hear an explanation about the corporate decisions and market demands that lead to the current product market that we have today when it comes to precision linear regulators.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 03:03:34 pm
content: Hi,just for curiosity, please give me a few examples of the new linear regulators than can rival 723 performance.ThanksWolfgang

author: CopperCone
author_rank: Super Contributor
timestamp: June 30, 2018, 03:07:12 pm
content: I don't know the real specs of the 723. I just found 2.5uV RMS for unknown bandwidth in some audio forum.The LT3042 has graphs and stuff and it is rated at 0.8uV RMS for a wider bandwidth I think.Everything else is at least 10uV rms IIRC. But thats just noise.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 03:48:24 pm
content: The noise specsof the LT chip are not bad, but its not a replaceable part because it has much less voltage tolerance and dissipation.What I would be looking for is a 40V part with better specs than the 723. The SG3532, LAS1000 and LAS1100 are gone, ist there something else I missed ?Best regards, thanksWolfgang

author: David Hess
author_rank: Super Contributor
timestamp: June 30, 2018, 04:08:19 pm
content: Quote from: Wolfgang on June 30, 2018, 03:48:24 pmIf you want better specifications then use an external buffered reference and precision low noise operational amplifier to drive the pass element of your choice.The idea of buffering the reference is to low pass filter it. A 723 by itself incidentally makes a pretty good buffered reference except for its tolerance. Zener references have lower inherent noise than bandgap references when their higher output voltage is taken into account; multiplying a bandgap reference up to the working voltage multiplies its noise as well.The pass element can be a three terminal voltage regulator to take advantage of its integrated protection. Placing it inside the feedback loop of a low noise operational amplifier lowers its noise.Noise measurements of different parts and circuits really need to be made under controlled and specified conditions. There is more to it than just noise bandwidth.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 30, 2018, 04:39:46 pm
content: One of Ulrich Rohdes books gave me the idea of using an LM723 as a low noise regulator. I'm pretty sure it was "Communications Receivers, principles and design" 2nd Edition but I could be wrong. Found something similar in Microwave and Wireless Synthesizers: Theory and Design, fig. 2-20. Got a copy somewhere I will have to go dig it out. Found the original harware for 20 years ago and I didn't bypass the non-inverting input or use an external PNP pass transistor and the noise spectral density was still better than any of the othe "low noise" regulators at the time. I think that when I measured the output noise spectral density I used a pair of AD797's AC coupled to give me 40dB gain and an HP3585. Sadly don't have the 3585 anymore.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 04:53:24 pm
content: Hi.I agree that regulator noise is a difficult topic. The german paper I mentioned in one of my last posts did a very comprehensive study on several regulator chipsplus different loading and filtering environments.IMHO, the critical points for standard chip regulators are:- the reference must be filtered- If a pass transistor needs to be used, it should be a PNP bipolar type (this adds less noise due to the fact that the base spreading resistance of a PNP is less than an NPN,causing less noise there).- in case the regulator has no spectacular PSRR (as the LM723), its own supply should be cleaned up (preregulator)- To clean up rests of noise and ripple, active noise killer circuits (like the shunt designs by Charles Wenzel) can help.When observing all this, sub-millivolt RMS noise levels are possible up to more than 100kHz.If you need definetely more than that, there are no single-chip possibilities anymore. Then the way to go would be:- An ultra low noise heated reference (LM399, LTZ1000).- No mechanical stress on the reference, buffer and error amp. Make PCB cuts to make sure.- No sockets- An ultra low noise reference buffer (LT1028)- Only ultra stable and low noise metal FOIL resistors- No electrolytic caps in the control path (due to leakage currents causing noise)- A super high gain error amp (LT1028), with almost no power dissipated inside the chip- A PNP bipolar driver and pass transistor with low noise specs (very good audio types)- No ceramic caps due to piezoelectricity, nonlinearity and noise. Only NP0 or good quality foil allowed !- No current limiting inside the control loop. Do this outside, by a dedicated circuit.- Use a preregulator (this could be well an LM723) for the sensitive part of the circuit.- No unshielded connections to the load. Use shielded, coaxial, low thermal EMF and low triboelectricity cables to the load and for sensing.- In extreme cases, do not use a PCB, but single ceramic standoffs.- Stalinistic packaging and shielding is a must.If you make no mistakes, microvolt noise levels are possible. The number of pitfalls is enormous, however.And an 8 1/2 digit Fluke or Keysight multimeter is neccessary, too ...RegardsWolfgang

author: CopperCone
author_rank: Super Contributor
timestamp: June 30, 2018, 04:58:51 pm
content: i am debating if stalin would produce a good package or not.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 05:03:09 pm
content: Stalinistic is probably a European term for "Paranoic", leaving no room to electricity to escape ...

author: CopperCone
author_rank: Super Contributor
timestamp: June 30, 2018, 05:40:50 pm
content: im still debating if stalin would make a good package, i think his solution would be marginal because he would be afraid that he might be misusing precious party resources that could be better used to crush capitalism.maybe he would slowly scrape away the walls till he got to a level thats acceptable. not sure.

author: bd139
author_rank: Super Contributor
timestamp: June 30, 2018, 05:54:46 pm
content: Stalin would tell everyone the manufacture of packages would empower the proletariat in the name of Lenin yet at the same time Siberian gulag workers would be grinding the packages out of rocks with their finger nails under threat of execution to meet the package quota.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 06:00:06 pm
content: ... well, he considered himself an expert of fencing in people (it was called "Iron Curtain" at the time), so the term is sometimes misused for a watertight packaging style. From an economical or rational point, his actions never made a lot of sense ...What is serious, however, is the importance of perfect EMI shielding for extreme performance power supply circuitry. Shielded transformers, a lot of space between stray fields and possible receptive circuitry, enclosures with feed-thru caps, ... are a must. Even fans must be viewed with caution ! Another issue is mechanical vibration.So, whatever term you prefer, make sure that nothing you dont want can get into your circuitry. Have you ever tried placing your mobile close to a DUT when it just receives a call or is dialling out ? You might be surprised ...Best regardsWolfgang

author: CopperCone
author_rank: Super Contributor
timestamp: June 30, 2018, 08:15:30 pm
content: people like to use plastic lolThe only PSU I have seen with RF feedthroughs is the small power supply from my 1980's spectrum analyzer. Each of the rails had a RF feedthrough, and the unit fan had a big series torrodial inductor on it.For what you want, you either need to build it with a special chassis that has air cooled heat sinks that go to the outside, formed as part of the shield (like some microwave amplifiers I have) or you want to put RF-Honeycomb on your air ventsExample:http://www.raymondemc.ca/products/products6a.htmThe fan itself may be a problem because they are made of plastic typically and have their own circuitry. You might have to get a metal shielded motor, figure out its proper grounding and isolation, then use a belt to drive a fan, this way you can control variables, or figure out how to turn it into a fan yourself.I have absolutely no clue as to the status of some kind of low electrical noise and emission fans.

author: Wolfgang
author_rank: Super Contributor
timestamp: June 30, 2018, 09:11:50 pm
content: Agreed.Probably the best way is a "no holes" design with a milled chassis where the cooling fins on the outer side of the RF-tight enclosure. Fans are a problem; if you want to be sure they dont create hassle you cold detach them from the fooling fins via an air duct loosely filled with iron wool of a few cm AND use a honeycomb against RFI. I have seen techniques like this in Rohde and Schwarz equipment from the 80ies.This shielding and precision instrument business is a bag of tricks more than science ...

author: CopperCone
author_rank: Super Contributor
timestamp: July 02, 2018, 07:47:25 pm
content: its not really a bag of tricks as much as you may need to do complex time consuming RF/parasitic simulation to really optimize it, and most people don't know howBut your gonna get a good baseline using certain design techniques. You still need to know how to do relevant calculations on filters, shielding thickness, impedances, etcI don't like the term 'bag of tricks' because then some wise ass is going to get the idea that its not really engineering effort that goes into it, then some ones boss is going to be acting like it should be easy, fast and that you don't need a good understanding of electronics to do it right. You can still do rough calculations to guide a design using first order models of parasitics and stuff, and its not super popular so you probably want to test along side of designing to make sure your going in the right direction.

author: BravoV
author_rank: Super Contributor
timestamp: July 04, 2018, 11:42:29 am
content: Just found my LM723 stash, almost 3 decades old, given by my mentor many-many moons ago.

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 04, 2018, 02:09:17 pm
content: Produced in 1989! Almost 30 years old.Because of their metal can and frit seal, I am sure they are as good as new.You are sitting in a stash of 24 karat gold, my friend.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 04, 2018, 10:19:07 pm
content: What I experienced is that there is a limit to what can be successfully simulated. The higher the precision gets, the larger the number of dirt effects will get that do play a role in your design. It is very instructive to see how really precise (7 1/2 and 8 1/2) digit multimeters are built.Just have a look there at component selection, PCB design , thermal management, aging, drift, shielding, EMF, thermoelectricity, triboelectric effects, hysteresis, ...I have never seen a model that takes all these effects into account. For certain effects, only heuristic models are available (Arrhenius, ...).It is probably fruitless to build a complete, successful model of a very high accuracy ultra high precision circuitry taking ALL relevant effects into account. Some effects can be handled heuristically, without a complete theory behind it, and the heuristics can still be useful.Conclusion: A well handled bag of tricks can make your precision elecectronics design life a lot more easy. If a consistent theory is available, you dont need the tricks anymore, but at cutting edge technology we are quite far from this situation.So, the search for exact models and deep understanding is fine, but pragmatic solutions are OK too, as long no established and general theory is available.It is like the old Aristotelian saying : The Perfect prevents the Possible.Enough of philosophy, get back to your benches, measure, research, model and create better a better understanding. In the meantime, some (plausible) tricks are OK. The final result is what counts.RegardsWolfgang

author: Zero999
author_rank: Super Contributor
timestamp: July 05, 2018, 08:01:22 am
content: Quote from: David Hess on June 30, 2018, 01:44:35 pmA lower reference voltage and an error amplifier with a common mode range down to 0V, would also be nice, but probably would have pushed the price up too high back then.

author: David Hess
author_rank: Super Contributor
timestamp: July 05, 2018, 12:46:00 pm
content: Quote from: Hero999 on July 05, 2018, 08:01:22 amA lower reference voltage would have meant a more complex bandgap reference.A PNP input gain cell with transconductance reduction like the 324/358 would have been nice not only for operation down to ground but because PNP transistors on an NPN process support a high differential input voltage but that had not been invented yet. It was common in later switching and linear voltage regulator controllers. An NPN version would have allowed high side current sensing but adding these sorts of features can get out of hand quickly.It would be nice if there was a standard precision operational transconductance amplifier for these types of applications.

author: Giuss
author_rank: Contributor
timestamp: July 05, 2018, 01:27:30 pm
content: I think it is a very good chip: stable, reliable, easy to use and cheap.I have used it in some projects and I have no reasons to search modern chips to replace it

author: Wolfgang
author_rank: Super Contributor
timestamp: July 05, 2018, 01:57:00 pm
content: 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 gainI would appreciate to see better chips again, but with 40V/150mA capabilities. All the hyped new regulators are low voltage only.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: July 05, 2018, 03:14:32 pm
content: " 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

author: Wolfgang
author_rank: Super Contributor
timestamp: July 05, 2018, 08:17:00 pm
content: 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 05, 2018, 08:25:37 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: July 05, 2018, 10:51:53 pm
content: Quote from: Wolfgang on July 05, 2018, 08:17:00 pmIt 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 06, 2018, 09:07:59 am
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: July 06, 2018, 10:26:33 am
content: Re-reading the datasheet, just realized as I spotted that the TO-100-10 package doesn't have the VZpin as other packages.

author: precaud
author_rank: Frequent Contributor
timestamp: July 06, 2018, 01:27:50 pm
content: Quote from: Giuss on July 05, 2018, 01:27:30 pmIn all the instruments I've serviced/repaired, I've never seen a bad 723...

author: Wolfgang
author_rank: Super Contributor
timestamp: July 06, 2018, 07:40:26 pm
content: 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).

author: David Hess
author_rank: Super Contributor
timestamp: July 06, 2018, 08:12:32 pm
content: Quote from: BravoV on July 06, 2018, 10:26:33 amThe VZpin is used where the output compliance of the error amplifier is not sufficiently low. The minimum output voltage at the Voutpin is 2 volts.

author: iMo
author_rank: Super Contributor
timestamp: July 07, 2018, 10:14:49 am
content: I wonder if the 723 could "ovenize" its own chip die - for example:1. the current sense transistor (B-E) as the temperature sensor, and2. the output transistor as the heater.... and then you may find the zero tempco of the zener (if any)..

author: David Hess
author_rank: Super Contributor
timestamp: July 07, 2018, 11:03:59 am
content: Quote from: imo on July 07, 2018, 10:14:49 amApparently 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:

author: Wolfgang
author_rank: Super Contributor
timestamp: July 08, 2018, 06:58:42 pm
content: 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

author: leonababy
author_rank: Regular Contributor
timestamp: July 08, 2018, 09:16:34 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: July 09, 2018, 12:21:44 am
content: Quote from: Wolfgang on July 08, 2018, 06:58:42 pmThere 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 09, 2018, 08:55:13 am
content: In Germany you can still buy this one for 67€Cent at Reichelt and other distributors. Its a smart part, I like it too.

author: dardosordi
author_rank: Regular Contributor
timestamp: July 10, 2018, 09:33:53 pm
content: Quote from: Wolfgang on July 08, 2018, 06:58:42 pmI contacted the author of this articlehttp://www.cappels.org/dproj/1.024voltreference/portvoltref.htmland asked for the schematics. Hopefully he can reveal the mystery since Im really curious about it.Edit, relevant quote from the article:Quote

author: Wolfgang
author_rank: Super Contributor
timestamp: July 10, 2018, 11:00:38 pm
content: 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

author: EmmanuelFaure
author_rank: Regular Contributor
timestamp: July 11, 2018, 12:11:43 am
content: 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. 74-6If 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.

author: dardosordi
author_rank: Regular Contributor
timestamp: July 11, 2018, 04:53:28 am
content: Quote from: EmmanuelFaure on July 11, 2018, 12:11:43 amThis seems to be the 1974 article and it doesn’t use a LM723http://www.seekic.com/circuit_diagram/Basic_Circuit/10_V_TEMPERATURE_STABILIZED.htmlAnd here’s the 1973 one using the lm723 with the ca3046.http://sigmambient.blogspot.com/2017/01/lm723-heater-circuit.htmlBut none is a standalone 723 heated reference. I guess the one in elector is the only one.

author: markce
author_rank: Regular Contributor
timestamp: July 11, 2018, 09:25:51 am
content: 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/

author: DimitriP
author_rank: Super Contributor
timestamp: July 26, 2018, 05:21:31 pm
content: Quote from: Wolfgang on July 09, 2018, 08:55:13 amStock up before prices magically go up.(it may already be too late)

author: Kleinstein
author_rank: Super Contributor
timestamp: July 27, 2018, 12:07:54 pm
content: There are still quite a few LM723 and µC723 to get. The µA 723 (DIP) even for under 40 cents.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 27, 2018, 06:25:36 pm
content: ... 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 ...

author: iMo
author_rank: Super Contributor
timestamp: August 23, 2018, 09:48:30 pm
content: Interesting reading for 723 fanshttps://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-

author: rsjsouza
author_rank: Super Contributor
timestamp: August 24, 2018, 12:41:00 am
content: 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...

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 24, 2018, 02:01:40 am
content: Quote from: rsjsouza on August 24, 2018, 12:41:00 amI 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.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 24, 2018, 02:17:56 am
content: Quote from: Richard Crowley on August 24, 2018, 02:01:40 amHah... It was on the thread linked by the post just above mine.

author: mike_mike
author_rank: Super Contributor
timestamp: October 24, 2018, 11:05:06 am
content: 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 24, 2018, 12:44:43 pm
content: Quote from: mike_mike on October 24, 2018, 11:05:06 amHi 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 funWolfgang

author: not1xor1
author_rank: Frequent Contributor
timestamp: October 25, 2018, 10:11:43 am
content: Quote from: Wolfgang on October 24, 2018, 12:44:43 pmI started to read "a collection... etc" but...1) there is no buried zener in 723s2) what they call minimum drop-out voltage (10V) is just the minimum supply voltageI did not read any furtherthat is a case of fake EE

author: Wolfgang
author_rank: Super Contributor
timestamp: October 25, 2018, 03:03:40 pm
content: Quote from: not1xor1 on October 25, 2018, 10:11:43 amWell, 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 wasHere is one of the first datasheets of the LM723 I found, found 1968:https://electronicprojectsforfun.files.wordpress.com/2018/08/ua723_application_note.pdf

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 25, 2018, 03:12:56 pm
content: What an extraordinary app note!No one writes such a thorough and detailed app note anymore.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 25, 2018, 03:18:54 pm
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 25, 2018, 04:17:47 pm
content: Quote from: Wolfgang on July 27, 2018, 06:25:36 pmBoth 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?

author: Wolfgang
author_rank: Super Contributor
timestamp: October 25, 2018, 04:51:10 pm
content: Quote from: Richard Crowley on October 25, 2018, 04:17:47 pmI 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

author: not1xor1
author_rank: Frequent Contributor
timestamp: October 25, 2018, 05:53:36 pm
content: Quote from: Wolfgang on October 25, 2018, 03:03:40 pmI 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 25, 2018, 06:33:03 pm
content: 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.

author: not1xor1
author_rank: Frequent Contributor
timestamp: October 27, 2018, 07:24:58 am
content: Quote from: Wolfgang on October 25, 2018, 06:33:03 pmIt 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 datasheetsBTW 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 27, 2018, 09:10:39 am
content: 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.

author: iMo
author_rank: Super Contributor
timestamp: October 27, 2018, 06:22:56 pm
content: Where the 2mVpp noise comes from? (ie. your mil 723j).

author: Wolfgang
author_rank: Super Contributor
timestamp: October 27, 2018, 07:47:45 pm
content: Hi Imo,what exactly are you referring to ?

author: iMo
author_rank: Super Contributor
timestamp: October 28, 2018, 07:00:49 am
content: 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.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 28, 2018, 10:55:52 am
content: 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. Accuracyis 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/

author: iMo
author_rank: Super Contributor
timestamp: October 28, 2018, 12:50:06 pm
content: @Wolfgang: try to measure an 1.5V AA battery with your logger, I bet you will see no noise like the above one..

author: Wolfgang
author_rank: Super Contributor
timestamp: October 28, 2018, 05:37:27 pm
content: 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.

author: mike_mike
author_rank: Super Contributor
timestamp: October 29, 2018, 06:48:47 pm
content: Hello,I asked TI about UA/LM723 and I got the answers from the attached images.

author: glarsson
author_rank: Frequent Contributor
timestamp: October 29, 2018, 07:20:45 pm
content: 723, 555, 2N3055, 1N4148,... will live forever. :-)

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 29, 2018, 07:29:09 pm
content: 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?

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 29, 2018, 08:12:49 pm
content: Quote from: glarsson on October 29, 2018, 07:20:45 pmAlso the 7805. And the 1N400x diodes.

author: glarsson
author_rank: Frequent Contributor
timestamp: October 29, 2018, 08:29:33 pm
content: Yes. They were included in the ellipsis.It is weird that the components I used when I started with electronics, ca 1975, are still manufactured and used in new designs.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 29, 2018, 09:33:03 pm
content: Quote from: Richard Crowley on October 29, 2018, 07:29:09 pmI have a box of all kinds of 723s at home, from different manufacturers. I have some from- National Semiconductor with LM Prefix- Fairchild with uA Prefix- SGS ATES with SG prefix- ST with LM prefix- RCA with CA prefix- Harris with CA prefix- Texas Instruments, some with LM and some with uA- Siemens with TDB prefix- Tesla with MAA prefix- plus some more exotic stuff where I could not derive the manufacturer.I simply dont know which ones were- just relabellled- built as a second source in a chip factory owned by the company- clonedIn the last years, the major producers were National, ST and TI.The spec sheet look almost identical among all 723 manufacturers.Hope that helps. As said, I hope these chips wont survive me.

author: iMo
author_rank: Super Contributor
timestamp: October 30, 2018, 08:08:26 am
content: FYI - Tesla company produced "hybrid" ICs with the 723 die. Interesting to see how they mimicked the 723's function in the negative rail with discrete components - here is a +/-15V linear voltage regulator (in metal DIL24 package, you may click on the hybrid IC in the mid text):http://www.mlab.cz/Articles/PodKapotou/HybridIC_WSH913/DOC/HTML/HybridniObvody_WSH913.cs.html

author: Wolfgang
author_rank: Super Contributor
timestamp: October 30, 2018, 09:02:42 am
content: Quote from: imo on October 30, 2018, 08:08:26 amCool ! I never saw one of those ! Highly exotic, but why not !

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 30, 2018, 09:26:05 am
content: Quote from: imo on October 30, 2018, 08:08:26 amNote: there is at least one error in the schematics on that web page, top end of R12 goes to pin 22, not to pin 19.CheersAlex

author: bd139
author_rank: Super Contributor
timestamp: October 30, 2018, 09:40:44 am
content: Quote from: Wolfgang on October 30, 2018, 09:02:42 amYes very interesting indeed.I really like looking at some of Tesla's old stuff, and most of Eastern Bloc tech. It was amazing progress for the times and I have nothing but respect for the engineers. Thanks to COCOM etc it wasn't easy but they did good.Also their DIP packages were 2.5mm not 2.54mm which makes much more sense for us metric lot!

author: iMo
author_rank: Super Contributor
timestamp: October 30, 2018, 11:22:49 am
content: The Tesla's pitch was 2.54mm with all the DIL/DIP ICs they ever produced..http://www.tesla-ic.com/cat/

author: bd139
author_rank: Super Contributor
timestamp: October 30, 2018, 12:07:06 pm
content: Who produced 2.5mm then?

author: iMo
author_rank: Super Contributor
timestamp: October 30, 2018, 12:12:27 pm
content: Soviets.. And "VEB Kombinates" in East Germany..Usually with larger packages. The smaller one (DIL14-16) were all 2.54mm, afaik.PS: I've spent a while browsing the beautiful sitehttps://zeptobars.com/en/but no 723 die-shot there, a pity..

author: not1xor1
author_rank: Frequent Contributor
timestamp: October 31, 2018, 08:19:19 am
content: Quote from: Alex Nikitin on October 30, 2018, 09:26:05 amYes, the positive rail is the master and the negative "slave" is just inverting the positive output.I wonder if that might cause any problem when the master BJT limiter switches on as negative rail BJTs might get reverse biased in case of short on the positive one.

author: iMo
author_rank: Super Contributor
timestamp: October 31, 2018, 11:40:18 am
content: Here is a model of the WSH913 Negative rail:1. it gives -14.99V/-50mA out (-14.97V/-75mA),2. max current -87mA with shorted output.With positive rail=0V you get:1. max -12..-13mV out (for 100-300ohm load) and2. max -70mA with shorted output.PS: the negative output voltage is referenced by the positive rail voltage. The 723's Vref plays almost no role with the negative rail voltage level here (ie. with 723's Vref= 6..10V you get the same output voltage)..PPS: below the mod - now the negative output is referenced by the 723's Vref. Otherwise it works the same, except it does not sense a short on the positive rail.

author: not1xor1
author_rank: Frequent Contributor
timestamp: November 01, 2018, 07:45:20 am
content: Quote from: imo on October 31, 2018, 11:40:18 amwell but if the positive rail output is brought to 0V by a sudden short, then Q6 emitter is connected to -15V of the charged output capacitor (just for a short time) while the base of the Q5-Q6 darlington is a bit above 0V (Q2 is saturated).Given just 15V of output voltage it is unlikely that the voltage gets above Q5+Q6 Vbe breakdown.Anyway, since somebody might be tempted to use this design for higher voltages, I think it might be useful to remark the need for a reverse bias protection diode.

author: orolo
author_rank: Frequent Contributor
timestamp: November 01, 2018, 01:10:10 pm
content: Quote from: imo on October 30, 2018, 12:12:27 pmI've been decapping some suspect (beta > 400) BD139s from ebay lately and figured it couldn't hurt to throw some 723s into the acid pot. My microscope is barely good enough for discretes, so please excuse the Frankenstein composition.The chip is a genuine, very old, uA723 from TI, marked: TI LOGO, 2020Z7T UA723CN. Images attached below.I've also decapped a very suspect NS LM723 from ebay, but the acid was quite diluted, and the quality of the images is much poorer. I can upload it, if someone is interested.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 01, 2018, 01:28:18 pm
content: Hi,I am curious about the other NS723 as well. Which acid did you use ?Wolfgang

author: iMo
author_rank: Super Contributor
timestamp: November 01, 2018, 02:23:56 pm
content: It seems the MAA723 is of a simpler design. And the Vref noisier than the original, imo. Below the die-shot from the above .cz link.

author: orolo
author_rank: Frequent Contributor
timestamp: November 01, 2018, 03:18:39 pm
content: Quote from: Wolfgang on November 01, 2018, 01:28:18 pmHi. Some time ago I opened athread about decapping, and BarsMonster helped me to refine the technique. Essentially, I use 98% sulfuric acid very carefully heated in a test tube. The tube is held in a fixed rig, with a perforated stopper degassing into an alkaline solution, with a buffer in between to avoid catastrophic reflow of the solution into the acid when cooling.I'll post the NS723 later. It's a lot uglier, though.Edit: NS chip attached below. With direct light at low mag. it looks nice, at higher magnification didn't manage to capture much detail. At least I can see the NS logo, a copyright symbol, something like UK, and 723D below. I guess the chip is legit, if maybe a reject.BTW, in all the examples there seems to be a big diode next to the output stage, connected to a pin. Could it be the zener pin?

author: iMo
author_rank: Super Contributor
timestamp: November 01, 2018, 06:00:31 pm
content: That is the output zener. Not connected in MAA723 (metal package).

author: orolo
author_rank: Frequent Contributor
timestamp: November 01, 2018, 06:36:06 pm
content: I agree, that one is easy. Following the same schematic, do you think the Zener D1 is where I put it? I'm not sure at all about R2, D1 and Q1. As a real addict to silicon porn, I watch all the pics, but know nothing of the real thing.

author: iMo
author_rank: Super Contributor
timestamp: November 01, 2018, 06:57:39 pm
content: The Vref zener is the D2, afaik..PS: the internal schematics from 1968 differs from TI's latest.. Most probably the vendors did changes in the original design..PPS: I think there is a bug in TI's schematics - the D2's anode should not be grounded..

author: iMo
author_rank: Super Contributor
timestamp: November 02, 2018, 10:49:19 am
content: Quote from: orolo on November 01, 2018, 06:36:06 pmIt seems it matches the '68 schematics well..

author: orolo
author_rank: Frequent Contributor
timestamp: November 02, 2018, 11:37:01 am
content: I like the 723 for the low noise. I doubt the comercial versions use buried zeners, because a discrete buried zener as the LM329 is about 90 cents a piece, last time I bought them. It would be great checking where the D2 zener is in the dies, but it seems hard to find. D3 stands out, and D1 is connected to V+, which is easy to locate and follow.Anyway, IMO the NS die seems easier to understand. The current limit transistor Q16 is in the upper left corner, the differential amp Q11-12 at the middle of the left side, Q13 at the lower left corner, and I think D1 and D3 are rather easy to place. Placing D2 should be easy, since the Vref pad must be the one at the bottom left, but I get lost in all the things happening in at the center of the die. I really hope there isn't a bandgap circuit there.

author: m3vuv
author_rank: Super Contributor
timestamp: August 31, 2021, 11:24:25 am
content: its funny but the infinion sg1532 is still available on ebay but quite expensive,i just brought one,but looking for a good schematic to build a 3-30volt 30 amp psu,may use one for a 723 with mods.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 31, 2021, 02:36:10 pm
content: Well people like thier comfort zone and IC names they can remember. I've never used a 723 becaue the're are better components. Of you can afford lundahl transformers then your not building down to a cost, go luxury. My pet hate is the 555! I dont see what its good for except flashing LEDs and making crap monostables. Its a teaching aid but jack of all trades but master of none. Put them in the crusher with the 741s!Sorry guys....

author: David Hess
author_rank: Super Contributor
timestamp: August 31, 2021, 04:37:24 pm
content: Quote from: Terry Bites on August 31, 2021, 02:36:10 pmBut those better components are either less versatile than the 723 or much more expensive. For instance the inexpensive regulators which commonly replace the 723 do not support a current limit below their design current without external circuitry.QuoteI do not like the 555 either, but as I became a better designer, I found more virtue in older parts like the 301A operational amplifier because they could do things that newer but easier to use parts could not. The 301A for instance has a common mode range which includes the positive supply, and external compensation allows for clamping and higher performance.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 04:49:21 pm
content: Quote from: David Hess on August 31, 2021, 04:37:24 pmThe discussions about 723 obsolescence have the tendency to repeat themselves. Fact is thatthere is no equivalent or better part for the range of specs (40V, 150mA, ...). There *are* better parts for less voltage and current, but thats like apples and oranges. The reason why it still sold after 50 years is that there is *no* direct replacement, obviously.

author: David Hess
author_rank: Super Contributor
timestamp: August 31, 2021, 05:20:31 pm
content: Quote from: Wolfgang on August 31, 2021, 04:49:21 pmThere have been improved functional replacements like the Motorola MC1466L which includes a second differential pair for current regulation, but they never became popular enough to replace the 723 or even continue production.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 06:50:29 pm
content: Quote from: David Hess on August 31, 2021, 05:20:31 pmMC1466 has spec advantages over LM723, but it is less flexible because it only works in a floating architecture. Moreover, its not made anymore since many years, along with SG3532 and L146 and other competitors.I am prepared to donate a cask of the finest bavarian beer for anyone who points to a *real* improved LM723 equivalent (no crippled low voltage, current or power versions, please) that is in volume production *today*.

author: DC1MC
author_rank: Super Contributor
timestamp: August 31, 2021, 08:29:44 pm
content: Quote from: Wolfgang on August 31, 2021, 06:50:29 pmI'm entering the contest with TPS7B7701-Q1https://www.ti.com/product/TPS7B7701-Q1Cheers,DC1MC

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 08:36:01 pm
content: Only 20V maximum output voltage ? Another try, please.

author: bd139
author_rank: Super Contributor
timestamp: August 31, 2021, 08:57:04 pm
content: LT3081

author: KE5FX
author_rank: Super Contributor
timestamp: August 31, 2021, 09:35:52 pm
content: I'd say the LT3042/LT3045 would be good candidates. They are much quieter than the LT3080 series, and requiring >15V output seems like an unnecessary constraint for 95% of use cases.If you need 40V, dunno what to suggest other than a discrete component solution.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 09:36:07 pm
content: Quote from: bd139 on August 31, 2021, 08:57:04 pmMuch more noise, no long term drift spec, ... This part is for heavy lifting, rather than precision.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 09:38:29 pm
content: Quote from: KE5FX on August 31, 2021, 09:35:52 pmI agree that there good low noise regulators for 15 to 20V, some better than 723. But again, the comparison is not fair because good high voltage analog is much harder to make than low voltage only. So - still waiting for the 723 replacement part.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 09:42:03 pm
content: Quote from: KE5FX on August 31, 2021, 09:35:52 pm"Real" precision stuff uses precision references (LM399,LTZ1000), precision ultra low noise op amps and discrete power components. Its probably too hard to integrate power transistors *and* precision circuitry in a single chip. Not seen any of those, they always try to keep heat generation and precision regulating circuits apart.

author: KE5FX
author_rank: Super Contributor
timestamp: August 31, 2021, 09:44:56 pm
content: How about an LT3042 or LT3045 with an external pass transistor? You would probably have needed that with the 723 anyway. It might be feasible to use a Sziklai pair with a 2:1 resistive divider to return the emitter (collector) voltage to the OUTS pin.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 31, 2021, 09:49:07 pm
content: Quote from: Terry Bites on August 31, 2021, 02:36:10 pmWhat?! No. 555 is for making AM radio.http://tubetime.us/index.php/2011/02/23/555-contest-entry/

author: rsjsouza
author_rank: Super Contributor
timestamp: August 31, 2021, 10:25:14 pm
content: Things that people do for a case of beer...I would throw a few that might be a replacement with very near characteristics, such as theTPS7A39,TPS7A47,TPS7B4254, etc.A parametric table at:https://www.ti.com/power-management/linear-regulators-ldo/products.html#p238max=30.01;200

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 10:37:49 pm
content: Quote from: KE5FX on August 31, 2021, 09:44:56 pmPossible, but again an unfair comparison due to only half the LM723 voltage range.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 31, 2021, 10:45:28 pm
content: Quote from: rsjsouza on August 31, 2021, 10:25:14 pm... getting better, but the parts have either- not enough voltage- too much noise- not very well defined current limitingbut I will have a closer look.

author: profdc9
author_rank: Frequent Contributor
timestamp: September 01, 2021, 04:18:12 am
content: As an alternative to uA723, which is not common anymore, you can use an op-amp based power supply. I made one based on a two op-amp design I found which has been floating around.https://github.com/profdc9/LinearPSA linear regulator is basically a slow unipolar amplifier with feedback, and so I added external inputs so that the voltage and current limits could be regulated by an external analog input (for example using an arduino output PWM).

author: David Hess
author_rank: Super Contributor
timestamp: September 01, 2021, 04:36:09 am
content: Discrete designs using operational amplifiers work but are not very practical now compared to integrated regulators, and operational amplifiers have a performance disadvantage in dual loop designs because of integrator windup.The reason I mentioned the MC1466L as an improvement is that it has the same operational transconductance amplifier as the 723, but has two of them with parallel outputs so switching between voltage and current limiting is seamless. There are modern switching regulator controllers with the same arrangement.The same thing might be accomplished with an externally compensated operational amplifier like the 301A or 308 but that is hardly a modern solution. I have seen a couple of power supply designs now which used two 723s with the error amplifiers paralleled to do it. A general purpose single/dual/quad precision OTA as a universal building block would be ideal but the closest thing is the LM13700. Tektronix used a lot of dual transistors in their regulators to do this.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 01, 2021, 08:47:41 am
content: Quote from: profdc9 on September 01, 2021, 04:18:12 amI would not say your approach is uncommon. Most lab supplies with adjustable voltage and current work this way, with some op amps and a reference. The weakness of the LM723 is the low precision, temperature dependent current limiting. It can be used to avoid desasters and shorts, but it is not elegantly adjustable and always needs a diode voltage drop to work.

author: iMo
author_rank: Super Contributor
timestamp: September 01, 2021, 10:17:49 am
content: @Wolfgang: I can see a nice picture on your 723 site - "Proper design practices.." - with a 7815 pre-regulator for the 723 itself. Did you make any measurements how the output ripple improved?

author: Wolfgang
author_rank: Super Contributor
timestamp: September 01, 2021, 06:23:58 pm
content: @imo:I dont remember it but the gain in ripple rejection is considerable. My guess is around +30dB.When you look at the 723 internals the error amp is a single long tailed pair, so this can profitfrom a quieter internal supply. 723 collector voltage can be supplied by a less filtered supply, no problem.

author: DimitriP
author_rank: Super Contributor
timestamp: October 04, 2021, 05:37:11 pm
content: In short, the viability of the uA723 in the 21st century depends on having hoarded as many as you think you might need.For some reason there seems to be no "replacement" with "ultra low noise" specs and the voltage range of the uA723; Progress!