unconventional lab power supply - Page 1
Forum section: electronics / projects

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 05:08:26 pm
content: Hi all,Im new to the forum but been watching Dave's videos for some years.Im in the process of building my own power supply and was shopping for a design (there are some nice ones here in the forum). But searching on the interwebs I stumbled upon this design which seems very different to the rest (at least at the pass transistors):http://ludens.cl/Electron/Ps20/Ps20.htmlBeing a totally newbie to analog electronics, I lack the knowledge to understand the difference. Can some of the analog wizards tell me what the pro/cons of this design are ? Compared to something likehttps://www.eevblog.com/forum/chat/diy-power-supply-build/?Specially Im interested about how to imlpement current limiting on that design.thanks!Dardo.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 05, 2016, 06:22:00 pm
content: It's regulated on the low side. It's a design decision. A pretty good one, as it turns out. But this is for a *monster* power supply, why would a newbie be shopping for a35 amppower supply?You'd be a lot happier and richer with a nice simple 0 to 12V 1A supply, no?

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 06:41:15 pm
content: Quote from: dardosordi on September 05, 2016, 05:08:26 pmIt is being presented as a 13.8V 20 Amp power supply (original link).R5/R6/Q1 seem to be a crude 25 to 30 Amp, current limit circuit.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 07:00:30 pm
content: Quote from: Alex Eisenhut on September 05, 2016, 06:22:00 pmIm going for 0-24v 2 amps. I have winded the trafo myself, using the excellent guide this guy has on that website and then I stumbled o his PSU design. It struck me as pretty weird the position for the transistors. He claims its a pretty good one, but I didn't understand it.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 07:02:40 pm
content: Quote from: MK14 on September 05, 2016, 06:41:15 pmOk, so I should try to add a op-amp output to that transistor in order to implement a finer current limit.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 07:14:49 pm
content: Quote from: dardosordi on September 05, 2016, 07:02:40 pmIf it is only a 2 amp power supply, then you might want to completely re-think the design and/or use another design. It is meant to give out 20 Amps.I suspect trying to use it as a 2 Amp only supply may cause difficulties and/or waste components which are not needed.For 2 amps, I suspect you can get much better circuits.To answer your question, yes an op-amp can reduce the current limit, but the circuit configuration, is not ideal for doing it, as it was meant to give just one limit value.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 07:17:34 pm
content: QuoteThat's the answer I was looking for. I'll go for the other one. Thanks.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 05, 2016, 07:51:49 pm
content: Having the transistors at the low side is similar to the rather common version with a floating regulator. So it is not such a bad choice, though not very common.There are mainly the two versions of having the power device as an emitter follower or having it as a controlled current source, e.g. in emitter circuit. The two versions need a slightly different kind of compensation to make the feedback stable. The emitter follower version is usually considered slightly easier for voltage control, but more difficult for current control. The follower version also need the control circuit (e.g. OP) to have the full swing - so it gets complicated at more than about 30 V.The current controlled version is more like a low drop regulator and needs a little more thought to ensure stability at any load. Usually it is used with an floating regulator and auxiliary supply for the regulator part, but the version with the transistors on the low side is very similar, especially for the moderate voltage (e.g. 20 V). The good thing is that this version loosed little voltage, so higher maximum voltage from a given transformer.The lower current mainly means there is no need for so many transistors in parallel. At 20 V and 2 A, a single 2N3055 or TIP142 can be enough. So the current does not change much in choosing one or the other form, except that the lower drop is more attractive at higher current, especially for a fixed output voltage.The linked circuit still misses much of the compensation. So chances are it can oscillate with some loads. One might need to add a few caps / resistors to make it really stable.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 07:57:46 pm
content: Quote from: Kleinstein on September 05, 2016, 07:51:49 pmThat's what Im afraid of. I won't be able to test/tell/fix oscillations right now, so I'll stick to the the eevblog link. I might try the low-side deisgn and play with it once I convince the wife to let me buy a scope.I could try learning spice, but Im a software developer and Im doing this to get away from the computer. I like playing with knobs

author: setq
author_rank: Frequent Contributor
timestamp: September 05, 2016, 08:44:11 pm
content: Also says "short circuit protected for as long as the heat sink can keep the transistors cool enough". Which unless you have some absolutely massive thing cooled with a blower may not be very long. I've blown up a couple of 2n3055's before quite easily. Better to use an LM723 than this with proper foldback current limiting.Art of Electronics 3rd edition, chapter 9 on power supplies is fortunately the free sample chapter. Have a read through this before deciding on a power supply build. It's better than random advice on the Internet:http://artofelectronics.net/wp-content/uploads/2016/02/AoE3_chapter9.pdfAs for stuff on ludens.cl, most of it is pretty damn good from a problem solving perspective and I've certainly been inspired by some of the designs, but I wouldn't build that supply.Software dev too by the way and doing this for exactly the same motivation.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 08:49:33 pm
content: Quote from: dardosordi on September 05, 2016, 07:57:46 pmHere is a simple one (I've not spent much time looking at it).It seems to be 0 to 24 volts, 0 to 1 amp, fully adjustable voltage and current controls.Made out of a modest number of simple, easy/cheap discrete parts.A much more complicated one is going to be better, in a number of respects. But this might make a simple one for you to start with.Starting with a very complicated one, with (what might be) difficult to obtain parts, is not necessarily the best way forward. Unless you like that sort of thing.http://www.electronicecircuits.com/wp-content/uploads/2009/09/Variable-Power-Supply-0-24V-circuit.jpgEDIT:Sorry, here is the original page, with much more information about it:http://www.electronicecircuits.com/electronic-circuits/variable-power-supply-0-24v

author: dannyf
author_rank: Super Contributor
timestamp: September 05, 2016, 08:51:11 pm
content: QuoteQ1 does that.it is not so unusual for low-side regulation.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 10:58:49 pm
content: Quote from: dannyf on September 05, 2016, 08:51:11 pmI get it now, so the drop across R7 drives Q1 and it pulls down the base of Q2. Thanks!I have another question, it seems to me that the op-amp does not have any feedback, but I guess it should have ? How its does it work ?

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:02:08 pm
content: Quote from: MK14 on September 05, 2016, 08:49:33 pmHow much current is it going to flow through the pot VR3 ?Could I use an TL431 instead of the zener ?

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:18:02 pm
content: Quote from: dardosordi on September 05, 2016, 11:02:08 pmIt seems to be meant for beginners, as an easy start power supply projects.It is not properly, closed loop regulated, so a TL431, is probably a waste.The designer is being very crafty with VR3, because he is relying on the fact that the reduction in current, as the control is moved, compensates for the increased voltage across it. Neat.I.e. the current drops off, at higher resistance values.If you want to mess with the circuit, you are probably going to be better off with a closed loop (op-amp) or IC regulator based design, as it will cope with the changes better. E.g. It needs to be exactly as it is, else VR3 is in danger of being overloaded, with excess current.Discrete transistor designs, are interesting, but can be harder to modify, compared to op-amp based circuits. Opinions may vary on this issue. But without enough knowledge of how the circuit really works, it can easily be messed up.VR3 (10 Ohms 1 Watt), is not so readily available in peoples parts boxes. So maybe the circuit is not as easy to obtain the parts, as I first thought.Current limits, do tend to be a bit tricky to design into power supplies, so I'm not that surprised.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:19:56 pm
content: Quote from: dardosordi on September 05, 2016, 10:58:49 pmIt HAS got feedback, because the output voltage, is being fed back through the resistors etc. R2 and pin 3 of the op-amp.EDIT:Sorry, I was a bit wrong here.It is the unregulated input voltage, with the ripple. So the ripple will act as a sort of control to the op-amp. But it may not have feedback as such. Let me look again at it.EDIT2:Actually I was sort of right in the first place. It has got the feedback, coming in via the GROUND, which is why I'm getting confused, SORRY!.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:24:55 pm
content: Quote from: MK14 on September 05, 2016, 11:19:56 pmThanks, if I remove the connection to pin 7 I can see the loop. Im not used to see it drawn that way.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:30:06 pm
content: Quote from: dardosordi on September 05, 2016, 11:24:55 pmDon't worry, it is confusing me as well. I'm too use to ground being a fixed/solid 0V reference point. But it does seem to create feedback.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:30:27 pm
content: QuoteHa! Now it makes sense, thanks now Im getting closer to understanding how it works. To me, this design is very unconventional.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:35:29 pm
content: Quote from: dardosordi on September 05, 2016, 11:30:27 pmThe circuit is both clever and got me admiring the designer, because in fairness they have got quite a lot of functionality, for few/cheap parts, and yet I also find it rather annoying and distracting at the same time.I normally don't like having many paralleled up bipolar transistors like that anyway, so I'm not surprised, that I don't fully approve of the circuit.Mosfets usually parallel up easier than that, but they are much less suited for the linear mode that this circuit needs.tl;drThe circuit is like trying to read something written upside down. But one gets use to it after a while.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:41:17 pm
content: QuoteI liked the low component count and the use of common parts. I guess I can replace the LM336Z-5.0 with a TL431 (and a divider) and use a dual op-amp to implement a current setting. The only thing left would be to know where it can oscillate, and that is out of my league for now.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:43:59 pm
content: QuoteI just need to drive 2 Amps, so I guess just one transistor would do for me. I don't have 2N3055 in my drawer so I'll try others (I don't mind letting the magic smoke escape while I learn and have fun).

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:47:32 pm
content: Quote from: dardosordi on September 05, 2016, 11:41:17 pmSo your adjustable current control scheme would be something on the lines of the second op-amp, amplifying R7, and putting the output into R6. With the op-amps gain (x1 .. x100 or something), being adjusted by the current control potentiometer.

author: MK14
author_rank: Super Contributor
timestamp: September 05, 2016, 11:50:24 pm
content: Quote from: dardosordi on September 05, 2016, 11:43:59 pmMany transistors would easily be similar enough to the 2N3055. NPN power transistor type.But be careful of the heat dissipation. It will produce huge amounts of heat especially at low output voltages. Possibly too much, even with a massive heatsink, at 2 Amps.Something like 50 watts or so (assuming that it is a 24 volt incoming supply, after rectification, voltage will be more than this), at 2 amps and low voltage out. Which is a lot for most heatsinks.Maybe don't rule out keeping at least a pair of output transistors, to help with the huge heat dissipation.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:54:56 pm
content: QuoteNot sure if I understood that correctly, I'm was planning on feeding the drop in R7 into the negative op-amp input and a voltage divider of the reference into the positive. The output going into the base of Q1 through R6. Not completely sure if my approach would work.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:00:04 am
content: Quote from: MK14 on September 05, 2016, 11:50:24 pmThat's the reason I winded my own trafo (using the core of an old autotransformer), I has 4 outputs in steps of 6 V. I plan to switch them on using relays, but that's after Im done with the regulator.Im going to do some thermal calculations based on the excellent video from Dave (thanks Dave!).And thank you MK14 for helping me understand the regulator.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 12:00:24 am
content: Quote from: dardosordi on September 05, 2016, 11:54:56 pmIf you are still talking about the current limit control, then I don't think that would work. You need to amplify the small current sense signal, so that adjustable smaller currents, can turn the Q1 on, and hence reduce the output voltage, until the current limit, is no longer being exceeded.EDIT: Correction, actual it may be fine, I was misunderstanding it. Sorry.The ideal thing is if you could sketch your entire new schematic and post it here. Then we can look it over if you want. You can even photograph your pencil sketches, if you don't want to bother doing them via a CAD program.Or accuse me of being too lazy to post what I described above as a schematic.There are many ways of doing it, feel free to come up with a different way.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 12:06:52 am
content: Correction:Actually what you said may be fine and work out fine. I was misunderstanding it.Best if I see a sketch of it. It is very easy to get mixed up when it is described in words.Where you are confusing me, is how and where is your current control potentiometer, going to be connected up ?(If it is how I now think, it should/may be fine).But you may find that the voltage reference, is wrong. In that you want something that is accurate between ground and its voltage. But the voltage reference is connected to the positive line. There are many ways round this.Quote from: dardosordi on September 06, 2016, 12:00:04 amGood idea. That will save a lot of the heat dissipation. That relay technique was used, sometimes in linear power supplies, when they use to be more commonplace. It is interesting to hear the relay clicks, with some power supplies.You have to make sure that it can always supply the right voltages, and doesn't get confused when the current limit, steps in.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:22:53 am
content: This is my plan.

author: Dave
author_rank: Super Contributor
timestamp: September 06, 2016, 12:27:01 am
content: No good. The voltage across your potentiometer is pretty much arbitrary, the original circuit itself is most likely unstable and now you just added another control loop that is most definitely going to oscillate.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:27:51 am
content: Quote from: MK14 on September 06, 2016, 12:06:52 amGood point, I guess I would have to use the voltage set and not the voltage output for that. Problem is that if I change the supply rail, it will change the voltage set. I could use a fixed divider and use the pot to divide the reference into the op-amp.Im planning on using an arduino to control the relays (not 'cause I have to but cause I have a relay shield with 4 relays that is accumulating dust in my drawer).

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:29:46 am
content: Quote from: Dave on September 06, 2016, 12:27:01 amCrap, I would not know how to fix that yet.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 12:41:25 am
content: Quote from: dardosordi on September 06, 2016, 12:29:46 amWhere you connect to R1 and the voltage reference. You need to create another voltage reference, because it is not relative to ground.You could use a zener and resistors to divide it down for the pot or use a diode as a voltage reference, since it is only the current limit, and you may not be expecting that to be so accurate.But oscillations/stability is another possible issue, I agree.

author: Dave
author_rank: Super Contributor
timestamp: September 06, 2016, 12:42:44 am
content: I would suggest you just take a known good design and copy it completely.You can't go wrong with something like a good old HP.E361xA service manual. Scroll to the bottom for the schematics and BOM.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 12:44:03 am
content: Quote from: Dave on September 06, 2016, 12:42:44 amI have to agree (with the concept of using a good circuit design, that already exists), especially if you are not planing on getting an oscilloscope yet. But there may be better/easier circuits you can get hold of.There are so many ways in which you can get a power supply design wrong.Also some of these circuits we have posted (including me), from the internet, are not really that good. When you get to the finer details. They are ok for some quick messing about and learning experiences. But not so much for making a good, solid and reliable power supply.If you are REALLY determined to do it. How about using the rather old, LM723 voltage power supply IC. It has a built in reference and other features, and is potentially suitable for beginners (and beyond) to design with. If you can still get hold of one.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:49:38 am
content: Quote from: Dave on September 06, 2016, 12:42:44 amThe lInk is broken.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 12:51:16 am
content: Quote from: dardosordi on September 06, 2016, 12:49:38 amTry here:http://sites.fas.harvard.edu/~phys191r/Bench_Notes/A1/agilent_e3610a.pdf

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 01:29:43 am
content: The LM723 is a rather precise device, amazingly cheap (or use to be), and has a lot of stuff built into it. It is specially designed to be somewhat stable for power supply circuits, and tends to minimize the components you will need. You can probably get/see design application notes, to help you, if you want to partly/fully do it yourself.Example:

author: Dave
author_rank: Super Contributor
timestamp: September 06, 2016, 01:45:32 am
content: Quote from: MK14 on September 06, 2016, 12:51:16 amI went full retard there. I had this exact URL copied in the clipboard and I forgot to paste it in.Anyhow, I fixed the original post now.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 01:49:20 am
content: Quote from: Dave on September 06, 2016, 01:45:32 amA very easy mistake to make. I've sometimes created a long post, then quickly googled a page in another tab/window to check something. Then closed that tab/window, but by mistake close the one with the post in it, losing the post foreverFortunately this forum, seems to allow going back to a briefly closed post, via history.

author: dardosordi
author_rank: Regular Contributor
timestamp: September 06, 2016, 02:53:05 am
content: Quote from: MK14 on September 06, 2016, 01:29:43 amI like it and I have an LM723 in my drawer. I'll look into it, thanks!

author: setq
author_rank: Frequent Contributor
timestamp: September 06, 2016, 08:52:52 am
content: Section on LM723 in here as well:http://artofelectronics.net/wp-content/uploads/2016/02/AoE3_chapter9.pdfIt's one of those ICs that is probably never going to die. 50 years old next year!

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2016, 11:52:33 am
content: When doing your own supply design, it might be a good idea to do a simulation. This can be very helpful to check for stability.Most of the HP supplies and many of the cheap Chinese one you can buy today use a floating regulator and thus are similar to the idea with the transistors on the low side. If you can add another winding (e.g. 10 V, low power) for the regulator, one could use one of those circuits.The LM723 is a possible starting point, but it gets difficult when you need fine current limiting. It is more a chip for a limited current supply inside a unit, not so much to build a lab power supply.

author: CJay
author_rank: Super Contributor
timestamp: September 06, 2016, 02:55:51 pm
content: Quote from: MK14 on September 05, 2016, 06:41:15 pmThought it looked familiar, it looks very much like a circuit used by Kenwood I think, as an external PSU for one of their *old* ham radio transceivers

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 03:06:22 pm
content: Quote from: CJay on September 06, 2016, 02:55:51 pmI find that easy to believe, because it does seem to have been cleverly designed, especially to be low cost and yet functional/good. It also seems to have various bits of similarities to other available circuits. So I guess that these things tend to be copied and modified, as well as part copied.They just want to make lots of them at the lowest possible cost, before the days of widespread switched mode power supplies.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2016, 06:37:20 pm
content: The initially shown circuit is Ok in principle, but it missed compensation. I doubt one can get away just with the speed of the 741 OP. However this is not a big deal money wise: something like a resistor between the zener and the OP and an RC series combination in direct feedback at the OPs should be all it takes to make it stable. The output might also want an extra low ESR /ESL cap parallel to the 1000µF electrolytic one. To get fast and stable even with critical load, one might also want a cap in parallel to R2 and maybe some extra protection for the OP than.The plan has another error: you don't want a 18 V transformer and 25 V filter cap. It's more like a 12 -15 V transformer for a 13 V output.Also the actual construction might get important - at 25 A wire resistance can be important. Also parasitic inductance can make things tricky.

author: MK14
author_rank: Super Contributor
timestamp: September 06, 2016, 08:05:21 pm
content: Quote from: Kleinstein on September 06, 2016, 06:37:20 pmThe 18V transformer seems to be about right, but I agree the 25V capacitor (C1), is too small, and needs to be larger/higher. At least 35V, but probably 40V if not more, to play safe and give it a reasonably long life.18V AC transformer * root 2= 25.45VAllowing for a 10% mains voltage drop and still be reliable and work ok.25.45V - 10% = 22.9VThe text says that for the pair of active at any time, silicon diodes, the voltage drop is about 2.4V, because of the relatively high currents.22.9V - 2.4V = 20.5VThen there is ripple voltage, which the text (saving me the effort of calculating it), is given as 3.3V at 20 Amps load.20.5V - 3.3V = 17.2VThen there is about or at least a 2 volt drop across the voltage regulator = 17.2V - 2V = 15.2VThe output is suppose to be 13.8VSo we have a safety margin (excess) of about 15.2V - 13.8V = 1.4VThe author/designer states that he wants a bit of safety margin to make it nice and reliable, and 1.4V is not too bad. (He wants to avoid any chance of dropout).So 18V transformer AC, seems perfectly reasonably (unless you go for a switching  design).

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2016, 06:19:33 am
content: One of the virtues of that monster design is that the collectors of the paralleled 2N3055s are at ground potential so they need not be electrically insulated from the heat sink simplifying construction and improving thermal performance.For technical work I prefer to use fully floating tracking dual supplies except where current levels are high. For pass elements I like to use integrated linear regulators for their built in short circuit, safe operating area, and thermal protection but they are not suitable for high current, high voltage, or high power designs.

author: dannyf
author_rank: Super Contributor
timestamp: September 08, 2016, 06:51:46 am
content: QuoteWhat would it do that a typical 3-terminal reference / regulator + buffer doesn't do?

author: MK14
author_rank: Super Contributor
timestamp: September 08, 2016, 07:57:19 am
content: Quote from: dannyf on September 08, 2016, 06:51:46 am3 terminal regulators, such as the LM317, can make nice, quick and easy beginners power supplies.But 3 terminal regulators usually/often don't come with current limit control options (easy/simple and readily adjustable ones), don't easily allow the addition of external pass transistors as easily as the LM723 does and the LM723 allows potentially even beginners (with some help), the ability to partially/fully design their own, variable bench power supply.I suspect the LM723's extra abilities and extra pin connections, allows a more precise and better/versatile power supply to be made with it. E.g. It can even make (showing its huge versatility and flexibility) switch mode power supplies (although these days, there are probably many better SMPS IC's available, I would expect).But there are many ways of creating a bench power supplies, and the LM723 is only one of them.

author: setq
author_rank: Frequent Contributor
timestamp: September 08, 2016, 08:21:27 am
content: Another option is find an old HP discrete power supply service manual and clone it, replacing some of the parts with jellybeans.

author: CJay
author_rank: Super Contributor
timestamp: September 08, 2016, 08:41:06 am
content: Quote from: MK14 on September 08, 2016, 07:57:19 amThere most definitely are but the LM723 is a pretty good solution, it needs a little bit of 'fiddling' to get it to 0V but it's got a reputation for being reliable, RF quiet and RF immune, as a simple bench supply it can be put to good use.

author: MK14
author_rank: Super Contributor
timestamp: September 08, 2016, 09:29:51 am
content: Quote from: CJay on September 08, 2016, 08:41:06 amI've made lots of stuff with the LM723, including bench power supply(s), and been very pleased with the results. For someone who is not that experienced with designing/building power supplies (which I think applies to the OP), I think it is a very good solution.It was VERY popular, in the old days of the Electronics Magazines, (a number of decades ago), and hence with home hobbyist constructors, appearing in numerous designs (if I remember correctly).They were particularly impressed with its combination of really low prices for the IC, readily available, relatively few parts, no exotic parts needed and its very good precision, with a nice in built very accurate (at the time) reference and capabilities.If you want a very high performing (which these days probably means SMPS, possibly with a final linear regulator output section), and top notch power supply, then really your best option is probably going to be to buy a really good power supply, or classic good used one, on ebay or somewhere. Making top end ones is not that easy. It is all too easy to mistakenly believe that you can readily make such a thing, but in practice there are so many subtleties and issues, that you may well find that you can't, really. N.B. I am talking about really high end stuff here, NOT typical hobbyist level bench power supplies, which the LM723 is rather good for (Linear power supplies).

author: setq
author_rank: Frequent Contributor
timestamp: September 08, 2016, 10:17:30 am
content: This. I've got a CC/CV design that worked for an LM723 somewhere as well. The thing is a power supply kit, not a regulator! Used an external op amp to do CC and let the LM723 handle the CV. External diode OR gate was used.LM723 finds itself in all sorts of professional products. There were three in the Philips PE1542 bench supply and I've seen one as a switching regulator in military grade kit. Usually CA723 metal canned ones there. Philips info here:http://www.analogdesign.be/files/gear/Philips_PE1535-PE1545_Operating_Manual.pdfIt's really the 555 of power supplies.I'm even using one as a crude but effective voltage cal source for meter spot checks.

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2016, 03:06:19 pm
content: I have never been a big fan of the 723 but one reason I would consider it is that its buried zener reference provides better noise and drift characteristics than the typical bandgap reference found in an integrated regulator. For a discrete design, I would consider using it just for the reference.It would be interesting to use the 723's built in error amplifier, output transistor, and current limit transistor to build a thermal regulator to hold the buried zener reference at a constant temperature which would make it the lowest cost ovenized reference and the 723 is already cheaper than a LM329 which is the lowest cost buried zener reference.

author: setq
author_rank: Frequent Contributor
timestamp: September 08, 2016, 03:35:47 pm
content: I'm actually using an LM723 for that but not ovenized in any way. It keeps within 1mV between about 15-45oC which is good enough for spot checking DMMs against.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 08, 2016, 04:16:41 pm
content: Not all of the 723 use a buried zener - many can be just a conventional zener. With the typical DIP case stability is not that good, even if it is one. The metal can versions are rare today, but could be an option if high stability is needed. But thus is more for a reference, not so much as a regulator.

author: David Hess
author_rank: Super Contributor
timestamp: September 08, 2016, 08:20:31 pm
content: Hmm, I just assumed the 723 used a buried zener reference but even if it does not, it still makes for a lower noise reference or regulator than most.The ovenizing idea is to use the output transistor as a heater and the current limit transistor as a sensor to hold the reference at a constant temperature but I do not know of any cases where this was done. The old LM389 audio amplifier could be used this way (National Semiconductor application note 264) to make a temperature stable log or antilog circuit without temperature compensation but unfortunately they were discontinued a long time ago. Linear Technology application note 5 shows how to do the same thing with a CA3096 transistor array.

author: setq
author_rank: Frequent Contributor
timestamp: September 08, 2016, 08:38:00 pm
content: That's interesting. Have a few CA3096's lying around.