Linear lab power supply

[JuanGg]

Having a series connection of  a 10 V 2 A turn and a 15 V 1A transformer limits the current to 1 A AC and thus some 0.5-0.6 A DC.
It also needs the 3 transformers to be use together, as opposed to 2 totally separate units. ...

I know, I've been thinking about it. I don't really need much curent, 0.5 A would be plenty. Plus, I don't have much space in my 'lab', so I would  prefer a compact solution. And I am running out of power outlets! It seems that you can never have too many.

With a very large cap it would be closer to the lower value. Usually one has to accept a little more ripple, more like 5-10%.
I would consider on of the 6800 µF caps plenty for 1 A.

What do you mean "closer to the lower value", closer to 0.5 A than to 0.6 A ? I will use the 6800 uF ones I have.

The circuits could be still essentially the same (e.g. same board), just a higher possible current limit for the lower voltage one, or a lower maximum voltage if the 15 V transformers in parallel.

I can understand of wanting to build the supply without a kit. However the general type of circuit would be used as a starting point. It is a little odd in some aspects, but also has some good points.

Sure, just maybe a couple different component values between boards.  That one came from here : http://www.electronics-lab.com/project/0-30-vdc-stabilized-power-supply-with-current-control-0-002-3-a/ didn't it?

There certainly seem to be some naysayers!  Add me to the list...  Longer explanation deleted except to note that the probability of success likely decreases exponentially with parts count.

And give up the idea that it's easy to cut a fat hog and produce a $500 supply for a buck ninety-eight.

Constructive criticism is always welcome! I do understand that. I am not aiming for a high-end supply nor for building it for free.

JuanGg - I followed your first power supply project with interest and although I haven't commented on this one yet, I'm watching it as well. There are a lot of suggestions from posters with many different points of view and you've done a good job of evaluating the pros and cons of the suggestions to see how they would work for what parts you have to work with.

You're making good progress.

Thanks! Good to see you here. I have the other supply on hold, it works for what I need for now in its current state...

Attached is an outline schematic of your proposed three transformer, two power supply circuit. Could you check it to ensure that it reflects what you intend? Don't worry about the component values etc, just the architecture...

Yes, that is precisely what I thought. As I said, I have not much electronics knowledge, just what I have adquired as I had the need to implement into my rather simple projects. Any explanations are welcome.

I really appreciate you taking the time to do this. I am surprised at the help I am receiveing. Thank you.

[spec]

Attached is an outline schematic of your proposed three transformer, two power supply circuit. Could you check it to ensure that it reflects what you intend? Don't worry about the component values etc, just the architecture...

Yes, that is precisely what I thought. As I said, I have not much electronics knowledge, just what I have acquired as I had the need to implement into my projects. Any explanations are welcome.

I really appreciate you taking the time to do this. I am surprised at the help I am receiving. Thank you.

No sweat 

It is good that the circuit for the raw supply is now pretty much defined and that the overall architecture of the twin PSU is also defined. That is the first major milestone in the design.

It is also good that you respond quickly and intelligently to the various posts- it is not always the case on all threads 

There is one point that I forget to mention: heatsinks. I would suggest the lowest thermal resistance heatsink you can get. Also low thermal resistance insulating washers, with clamps on the power transistor/regulator case. I would also advise fan cooling.

The insulating washer has a surprisingly negative impact, so one approach is to mount directly to the heatsink. This does mean that the heatsink will be at the same voltage as the power component so the heatsink would need to be insulated from the other components and chassis/PSU case.

Another problem with a live heatsink is that it acts a huge capacitor and can cause parasitic oscillations by coupling to other components. With a bit of simple screening this is easy to fix though.

About the stabilizing circuit, here, as I see it, are the four options.
[1] LM723 based

[2] Three terminal regulator based

[3] Design available from books, internet etc

[4] Custom

LM723 BASED
The LM723 is a great PSU building block, but it has some limitations which mean that a LAB PSU using the LM723 gets complicated. Going down to 0V requires extra components. The voltage overhead is high, the absolute voltage is limited and the current limiting is basic, but probably adequate.

THREE TERMINAL REGULATOR BASED
This is the simplest and quickest approach, if the standard non-adjustable current/temperature limiting is acceptable. As you can only dissipate about 12W in a LM317 or LM337 (with a good thermal washer, case clamp, and high performance heatsink + fan cooling), before the current limiting kicks in. The PSU would produce around 1A with an input/output voltage difference (IOD) of about 12V, but as the IOD increased the current output would limit proportionally reducing to 400mA at 0V output. I can probably post a schematic of this approach if you like.

Of course you could select a 10A regulator which would give a touch more current but not that much more because of the same thermal factors.

DESIGN AVAILABLE FROM INTERNET ETC
There are 100s of designs available, but I have not been able to find one that is well proven or simple. Maybe the other EEC members could advise here.

CUSTOM
This approach has been suggested in other EEV threads about PSU construction. I think I have read them all. The general feeling is that this approach has the potential for the best performance with the simplest circuit. It promises precise voltage control, precise current control, and a simple technique to allow the output voltage range to include 0V. Overall it is probably the cheapest approach too.

Out of interest, I outlined a circuit which should do the job (famous last words). If you are at all interested in this approach I could post the schematic for you to consider. One big factor to take into account with new designs, that have not been prototyped and tested is that they may not work at first and may need some development work.

So there it is. Could you give the approach some thought and post what you think?

And finally a lecture about protection. Many of the circuits that you see around have no protection and are not worst case designs. There is often no reverse voltage protection, no protection for the emitter/base junction of the output transistor, and no over-current or over-voltage protection on the input. How do you feel about protection? Some protection can be bolted on later, but some needs to be incorporated at the architecture stage.

[ArthurDent]

Quite often the simplest circuits work well enough to cover almost all your needs. Here is a 0-30VDC/1A uA723 circuit I found that looks pretty good. You could scale it for other voltages or just use it as a starting point for your own design. They use a fairly simple circuit to generate the necessary negative voltage the uA723 needs to allow the output to go down to zero volts.

As has been pointed out trying to use common grounding points is a good idea but if you are using adequate size wire at 1A any voltage errors caused by drops along a lead probably won't be significant compared to temperature drift, etc.. If you are using an adjustable current limit where you have sub-ohm sensing resistors with higher currents that's where you really have to be careful about adding stray lead resistance that could have a large effect on your readings. Some of the better power supplies use 4-terminal resistors to get higher precision current adjustments. 

I might use a larger filter capacitor than the 1000/63 shown in the attached schematic but one of the previous circuits showed 4x4700 used which I believe to be overkill. All regulators also acts as capacitance multipliers by a factor of the combined hfe of the series transistors and that allow you to use smaller capacitors.

[Wolfgang]

Quite often the simplest circuits work well enough to cover almost all your needs. Here is a 0-30VDC/1A uA723 circuit I found that looks pretty good. You could scale it for other voltages or just use it as a starting point for your own design. They use a fairly simple circuit to generate the necessary negative voltage the uA723 needs to allow the output to go down to zero volts.

As has been pointed out trying to use common grounding points is a good idea but if you are using adequate size wire at 1A any voltage errors caused by drops along a lead probably won't be significant compared to temperature drift, etc.. If you are using an adjustable current limit where you have sub-ohm sensing resistors with higher currents that's where you really have to be careful about adding stray lead resistance that will could have a large effect on your readings. Some of the better power supplies use 4-terminal resistors to get higher precision current adjustments.   

.. you could further simplify this by using an 7905 regulator for the negative rail. It would also improve stability.

[JuanGg]

No sweat 

It is good that the circuit for the raw supply is now pretty much defined and that the overall architecture of the twin PSU is also defined. That is the first major milestone in the design.

It is also good that you respond quickly and intelligently to the various posts- it is not always the case on all threads 

There is one point that I forget to mention: heatsinks. I would suggest the lowest thermal resistance heatsink you can get. Also low thermal resistance insulating washers, with clamps on the power transistor/regulator case. I would also advise fan cooling. ...

It would be unwise not to reply quickly, as I am the first one interested in getting this thing working

I was thinking of using CPU cooling heatsinks, which usually have a fan attached to. I think the easisest approach is no thermal washers and mount them inside the case. I can esily make some plastic brackets for that purpose. (abs, so they won't melt, even if the heatsink is at 100 ºC, which it shouldn't be...). Insulating washers can be added later on if needed. I will hopefully have news about the heatsinks in a couple days time.

On the stabilizing circuit, as you present it, the "Custom" option seems the best, if it delivers good performance on a simple circuit, and thus more likely for me to better understand what is going on. I don't mind prototyping and testing. Going through the whole design process is something I would like to do.

Regarding protection, it being a lab psu it should be a litle bit foolproof (to use). If adding some is a matter of including a couple diodes here and there, a fuse or an SCR, then for sure.

Quite often the simplest circuits work well enough to cover almost all your needs. Here is a 0-30VDC/1A uA723 circuit I found that looks pretty good. You could scale it for other voltages or just use it as a starting point for your own design. They use a fairly simple circuit to generate the necessary negative voltage the uA723 needs to allow the output to go down to zero volts.  ...

That looks simple enough and it will fit my purpose just by changin a couple resitors for the 0.5 A current. About capacitors I have two salvaged 6800uF /50V and another couple 10000 uf / 50V on the way.

Regarding components, could you guys propose some common ones that will likely be used in any circuit I will end up building? I have 5x 3055 transistors, some op-amps, assorted resistors, diodes and so on, but nothing about zeners or other things. This is so I can order stuff now so it arrives when I need it. Anything I don't use can go the the parts bin, and else I can resort to the local elcetronics shop.

Juan

[ArthurDent]

"Regarding protection, it being a lab psu it should be a litle bit foolproof (to use). If adding some is a matter of including a couple diodes here and there, a fuse or an SCR, then for sure."

One problem with power supplies with crowbar protection circuits is that some people use their power supplies for battery charging. I've seen spikes on the output lines or limit adjustment errors cause the crowbar to trigger causing the output leads to short. The battery will then deliver a large amount of current into the supply blowing the SCR circuitry and quite often burning runs on circuit boards.

I have mixed feelings about having crowbar circuits in adjustable bench type power supplies, I have some with and most without. If I were using a fixed supply built into a piece of equipment where I was not changing the load then I'd be comfortable using a crowbar but probably not in an adjustable bench supply I was building.

A lot of the newer supplies have MOSFETs for the pass elements and sense if the output is over a set point and turn the output off rather than shorting the output and this is much nicer. Here is how two of my supplies allow you to set OVP/OCP points.

[JuanGg]

One problem with power supplies with crowbar protection circuits is that some people use their power supplies for battery charging. I've seen spikes on the output lines or limit adjustment errors cause the crowbar to trigger causing the output leads to short. The battery will then deliver a large amount of current into the supply blowing the SCR circuitry and quite often burning runs on circuit boards.
...

Given that, we can rule crowbar protection out for now. It is something that can be added later, and it will only prevent the output from going ,say, + 25 V. If the series pass transistor fails short, and I am powering something at 5 or 12 V, it will kill it anyway...

[spec]

Quite often the simplest circuits work well enough to cover almost all your needs. Here is a 0-30VDC/1A uA723 circuit I found that looks pretty good. You could scale it for other voltages or just use it as a starting point for your own design. They use a fairly simple circuit to generate the necessary negative voltage the uA723 needs to allow the output to go down to zero volts.

Brilliant 

As has been pointed out trying to use common grounding points is a good idea but if you are using adequate size wire at 1A any voltage errors caused by drops along a lead probably won't be significant compared to temperature drift, etc.. If you are using an adjustable current limit where you have sub-ohm sensing resistors with higher currents that's where you really have to be careful about adding stray lead resistance that could have a large effect on your readings. Some of the better power supplies use 4-terminal resistors to get higher precision current adjustments.

That is true about the voltage drops to an extent, but there is also frequency stability to consider. Using star points costs nothing so why not do it? (don't forget the huge gulps of current flowing into the reservoir capacitor)

I might use a larger filter capacitor than the 1000/63 shown in the attached schematic.

Yeah, 1mF is too small and will give a large ripple voltage. 4.7mF upwards would be better and give a peak to peak ripple of 2v rather than 10V which is not workable. Reservoir capacitors normally have a tolerance of -40% +100% so you would need to factor that in. So 6.8mF upwards would be good. 10mF would be ideal, giving a ripple voltage of 1V peak to peak.

one of the previous circuits showed 4x4700 used which I believe to be overkill. All regulators also acts as capacitance multipliers by a factor of the combined hfe of the series transistors and that allow you to use smaller capacitors.

I would say that 10mF would be ideal: low ripple voltage, giving more voltage overhead margin and less ripple voltage on the output.

Just one point about the PSU circuit- there is no decoupling.

[spec]

Quite often the simplest circuits work well enough to cover almost all your needs. Here is a 0-30VDC/1A uA723 circuit I found that looks pretty good. You could scale it for other voltages or just use it as a starting point for your own design. They use a fairly simple circuit to generate the necessary negative voltage the uA723 needs to allow the output to go down to zero volts.

As has been pointed out trying to use common grounding points is a good idea but if you are using adequate size wire at 1A any voltage errors caused by drops along a lead probably won't be significant compared to temperature drift, etc.. If you are using an adjustable current limit where you have sub-ohm sensing resistors with higher currents that's where you really have to be careful about adding stray lead resistance that will could have a large effect on your readings. Some of the better power supplies use 4-terminal resistors to get higher precision current adjustments.   

.. you could further simplify this by using an 7905 regulator for the negative rail. It would also improve stability.

There is a bit more to starpoints than just voltage drops. Bad wiring can also lead to frequency instability, just like in audio amps. And there is no reason not to do a proper job - it costs nothing

Good suggestion about using a three terminal regulator for the -5V reference supply.

[Kleinstein]

One can protect the crowbar circuit with an extra fuse. So there would be a fuse between the crowbar and the output terminal. Someone adding a strong external supply would only blow the fuse. This type of fuse might be a good idea anyway to avoid a "short" through the diode across the output - in case the battery is the other way around.
Well set the crowbar can be closer to the actually set voltage and actually protect the circuit, if no too sensitive.

The LM723 circuit with the negative supply shown below has 2 slight problems:
There is a supply voltage limit for the 723 - so with 30 V output voltage this would likely cause too much voltage at least under no load conditions. With an output level above about 25 V it might be a good idea to have some voltage limitation / regulation for the LM723. Often an extra filter cap is also a good idea, as this allows some extra 2 V more ripply on the main supply current and thus maybe half the capacitor there.

The 723 only needs a rather low negative voltage, if at all. So something like -2 V should be enough.

In that circuit the negative voltage is part of the reference. One of the good points of the 723 is it's usually low noise reference.

The simpler way to use the 723 in a supply that goes all the way down to 0 V (or at least very close) is to have the feedback divider no towards 0 V but towards a small fraction (e.g. around 1.5 V) of the reference level and no extra negative supply.  The little current flowing back from the divider might limit the lowest voltage to get open circuit to some 50 mV, depending on the minimum internal load.

It is also better to adjust the reference level and keep the feedback divider constant. I know many old supplies do it the other way round, but it's not that clever, because it changes the loop gain. Adjusting the reference side is also more convenient if a digital control is used.

[spec]

I was thinking of using CPU cooling heatsinks, which usually have a fan attached to. I think the easiest approach is no thermal washers and mount them inside the case. I can esily make some plastic brackets for that purpose. (abs, so they won't melt, even if the heatsink is at 100 ºC, which it shouldn't be...). Insulating washers can be added later on if needed. I will hopefully have news about the heatsinks in a couple days time.

Using a CPU heatsink and fan is a good idea but it will limit your PSU. I am thinking that you should be able to make a 0V to 20V supply (x2) with the transformers and reservoir capacitors that you have already.

On the stabilizing circuit, as you present it, the "Custom" option seems the best, if it delivers good performance on a simple circuit, and thus more likely for me to better understand what is going on. I don't mind prototyping and testing. Going through the whole design process is something I would like to do.

Arthur Dent's circuit is really neat and with a few mods: 6.8mF reservoir capacitor, three terminal -5V regulator, decoupling, a low thermal resistance heatsink, and to say it yet again, star point wiring, you will have a pretty good power supply that will be a useful piece of lab equipment  for the future.

But, as you are still interested in a custom approach, I will post an outline schematic to give you a feel for the custom PSU design mentioned in reply #26. As well as an adjustable precision voltage output, it also has adjustable precision current limiting. The OV output point is pretty accurate too.

[iMo]

I like 723 but I think you can do the same with discrete parts easily (and maybe better). Also from my experience the important things your PSU should manage well are:
. it has to sustain a time unlimited short at its output, and,
. produce 0V (or close to zero) when your output voltage potentiomer's wiper looses its contact.

For example a cheapo LM358 (or similar) with 78L05/8/9 as the ref source will do the same. And the over-current protection is done by a single NPN in 723, you may do it better with the second opamp in the package. And you may "filter" the ref source with RC in the same manner as with 723, in case you require uV noise

[spec]

NOTE: In the attached PSU schematic, D8 is the wrong way around. Thanks to Arthur Dent for spotting (2018_11_18).

The circuit is not ready for prototyping and may have some errors- but it is the principle that matters at this stage. The known shortcomings are:

[1] Too much loop gain

[2} No optimization

[3] Inadequate decoupling

[4] Frequency compensation components not shown

[5] Resistor values not normalised

[spec]

Wow, this thread is attracting a lot of interest, as is normally the case with PSUs. 39 posts so far, and a lot more to come, no doubt

[JuanGg]

One can protect the crowbar circuit with an extra fuse. So there would be a fuse between the crowbar and the output terminal. Someone adding a strong external supply would only blow the fuse. This type of fuse might be a good idea anyway to avoid a "short" through the diode across the output - in case the battery is the other way around.
Well set the crowbar can be closer to the actually set voltage and actually protect the circuit, if no too sensitive.

That would do it then. I had no idea the crowbar voltage could be adjusted to the set voltage. I am not planing on using the supply to charge batteries or anything like it, but better safe than sorry.

The simpler way to use the 723 in a supply that goes all the way down to 0 V (or at least very close) is to have the feedback divider no towards 0 V but towards a small fraction (e.g. around 1.5 V) of the reference level and no extra negative supply.  The little current flowing back from the divider might limit the lowest voltage to get open circuit to some 50 mV, depending on the minimum internal load.

It is also better to adjust the reference level and keep the feedback divider constant. I know many old supplies do it the other way round, but it's not that clever, because it changes the loop gain. Adjusting the reference side is also more convenient if a digital control is used.

Going close enough to 0 V should be fine. My original intent was to also be able to controll it from a micro, as I am going to use one for the displays. That would do.

Using a CPU heatsink and fan is a good idea but it will limit your PSU. I am thinking that you should be able to make a 0V to 20V supply (x2) with the transformers and reservoir capacitors that you have already.

I just got hold of the heatsinks! (photo attached). Two identical ones with a 12 V 0.28 A fan each. They look pretty substantial, don't know if it would be enough. No markings or anything, so no idea about thermal resistance.

Arthur Dent's circuit is really neat and with a few mods: 6.8mF reservoir capacitor, three terminal -5V regulator, decoupling, a low thermal resistance heatsink, and to say it yet again, star point wiring, you will have a pretty good power supply that will be a useful piece of lab equipment  for the future.

But, as you are still interested in a custom approach, I will post an outline schematic to give you a feel for the custom PSU design mentioned in reply #26. As well as an adjustable precision voltage output, it also has adjustable precision current limiting. The OV output point is pretty accurate too.

It surely will do, plus the modifications proposed by Kleinstein for it to be digitally controlled and removing the negative rail. I am doubt which way to go. I can maybe have a go at both approaches...

Attached, below, is an outline schematic for the custom PSU mentioned in reply #26. ...

Thank you. I kind of understand what everything does in the circuit. Not sure about micro control with the negative 12V rail though. Again, don't know wich way to go, the LM723 one or something more like this one. I may as well try both. For now, I will model the transformers and the heatsinks on the computer so I can start designing the case. I hope the AC mains connector and the bridge rectifier arrive soon (a week or two...) so I can assemble the raw supply.

Wow, this thread is attracting a lot of interest, as is normally the case with PSUs. 39 posts so far, and a lot more to come, no doubt

It certainly is. Thank you to anyone that is taking part.

[Kleinstein]

The circuit in #38 has still quite a few weak points. So it is a starting point at best. It's still in between the 2 main circuit types.

With a lab supply designed essentially from scratch it is a good idea to use a simulation (e.g. LTspice) to do the first tests and adjustment if the loop. It is a really powerful tool for this.

Starting from 25 V AC is just at the border, where one can still use the LM723 or an OP as voltage mode controller and emitter follower. One might still need to limit the supply for the LM723 or the OP, but the voltage swing to some 25 V is sufficient. The LM723 is not that bad: it has a reasonable good reference and the difference amplifier with access to the transconductance part can also be handy. The main drawback it the limited voltage and crude current limit - so not really a lab supply in this respect.

The other circuit type uses an output stage that is more current controlling. However this usually needs an extra auxiliary supply for the control part and thus another transformer. This type of circuit is commonly used in many commercial supplies, as it is very flexible. However it usually needs a larger capacitor at the output. 

[spec]

The circuit in #38 has still quite a few weak points. So it is a starting point at best. It's still in between the 2 main circuit types.

There is no circuit in answer #38. I take it that you mean answer #37. I really cannot see that your general  and sweeping statements from on high are of any help. And your negative statements are unwarranted. In fact, they are disruptive.

What are these weak points- please be specific. If you are thinking about the points I have already listed, what is the objective of mentioning them again. Besides that circuit, as clearly stated, is not complete. It is an outline circuit posted at this stage to show the architecture and scope. Just for the record, that architecture, which has been recommended a number of times on EEV and elsewhere has a lot going for it in terms of flexibility, cost and, most of all, performance. The other thing about it is that it can easily be built in a negative version, which is usefull when you need plus and minus supplies in one PSU, using a single transformer.

What does the statement "It's still between the 2 main circuit types mean". What 2 main circuit types? Anyway, this sounds like another instance of opinion being stated as fact. Besides which, it is up to the OP to decide which circuit to go for.

"So it is a starting point at best"  I cannot see the point of this statement.

Finally, I take it from your tone that you are an expert in PSU design and construction. So if you can post a schematic for a PSU, that is complete, practical, and meets your own undefined criteria? That would be a big help. Perhaps include a simulation too.

[xavier60]

What does the statement "It's still between the 2 main circuit types mean". What 2 main circuit types?

Too me the two types are whether the voltage control op-amp has to tolerate the full unregulated supply voltage or not.
With the type often referred to as the "floating type" , everything is referenced to the positive output terminal including the +/- control power supply rails. The op-amps see only the control rail voltages regardless of what the unregulated and output voltages are. 

[xavier60]

I see that the circuit in #37 is the exception. The op-amps have there own supply rail that is independent of the unregulated voltage.

[spec]

… Not sure about micro control with the negative 12V rail though. Again, don't know which way to go, the LM723 one or something more like this one. I may as well try both.

I would not worry about controlling a PSU with a negative supply- it is dead easy and not an issue.

All linear stabilized PSUs are essentially voltage feedback power amplifiers in their normal mode and you can alter the voltage feedback arrangements to suit your requirements. But when the PSU goes into the constant current mode you need to consider the frequency stability in that mode too. There is a quite difficult situation when both voltage feedback and current feedback are operating at the same time (there are techniques to sort this), especially with the LM723 single transistor approach.

I would not be put off by the general statements about circuit design, which sound very learned but often do not take in the whole picture. A circuit needs to be analyzed in it's entirety to reach a proper conclusion.  One example is K's treatise where he warns of the danger of varying the feed back voltage rather than the reference voltage. Well, perhaps the millions of three terminal regulators in use ought to be withdrawn and redesigned. You simply cannot design by platitudes,

As to the lecture about referencing the feedback on an LM723 back to the reference voltage, that has already been shown in the schematic in the original post. Besides which it is a well known technique in general.

K has also voiced some undefined warnings about your three transformer approach, which is difficult to fathom.

There seems to be a lot of fear and loathing about having a negative supply, but a negative supply is a low technical risk and costs little in money and complexity terms. A negative supply has a lot of advantages, especially as it allows the PSU to go to exactly to 0V which is a big issues for some lab testing. It can also be used (as in PSU #37) to keep the temperature of the control electronics more constant as they will not be exposed to all the fire and brimstone going on above them with the raw supply and the power transistors heating up and cooling down.

Don’t forget that the output transistors will have quite a high leakage current, especially when the junction heats up and you need to get rid of that current.

Another advantage of a negative supply is that it allows you to have some current sinking which is useful.

Some PSUs without a method of draining off the various standing currents get into an unhappy state around zero volts output.

Having said all this, I am not advocating the answer #37 PSU. I leave that up to you? But, as mentioned before, the Arthur Dent circuit #27 (with modifications) has a lot going for it in my book.

[spec]

What does the statement "It's still between the 2 main circuit types mean". What 2 main circuit types?

Too me the two types are whether the voltage control op-amp has to tolerate the full unregulated supply voltage or not.
With the type often referred to as the "floating type" , everything is referenced to the positive output terminal including the +/- control power supply rails. The op-amps see only the control rail voltages regardless of what the unregulated and output voltages are.

Yes, that is a good general categorization.

[spec]

I see that the circuit in #37 is the exception. The op-amps have there own supply rail that is independent of the unregulated voltage.

Yes again That is one of the major advantages of that architecture and it brings huge performance benefits, as I mention in answer #44

Interestingly, with a few mods here and there, that architecture can be turned into a high precision calibration type PSU/voltage source. 

[spec]

JuanGg

The PSU in answer #36 may be suitable for your needs: https://www.eevblog.com/forum/beginners/help-me-design-a-psu/msg1971227/#msg1971227

It is certainly the cheapest and simplest approach.

Once you complete the chassis and raw power supply you could quickly build this circuit. Then, as you go along, you could enhance the performance in a number of ways which we could discuss on EEV.

One enhancement would be to fit a bypass power transistor to improve the current output at PSU low output voltages.

Another enhancement would be to replace the LM317 with a better three terminal regulator.

[spec]

There is a topic which I have been meaning to mention.

With the transformers arrangement you have with 10V and 15V windings it may be an advantage to have a range switch which selects just one of the windings for PSU low output voltages and both windings for high output voltages. This is common practice on many linear supplies, either manually or automatically. On my linear lab PSUs the switching is automatic by a relay.

The reason for this switching is to reduce the power dissipation in the output power transistors.

[not1xor1]

I would not be put off by the general statements about circuit design, which sound very learned but often do not take in the whole picture. A circuit needs to be analyzed in it's entirety to reach a proper conclusion.  One example is K's treatise where he warns of the danger of varying the feed back voltage rather than the reference voltage. Well, perhaps the millions of three terminal regulators in use ought to be withdrawn and redesigned. You simply cannot design by platitudes,

Hi
Are you referring to Kleinstein's message? 
Sorry... but he is right and you are wrong.
Platitudes???
It doesn't matter if a theory is fancy of fashionable, but if it is confirmed by the facts.
And if you change the loop gain the phase margin does change while it generally doesn't if you just change the input signal level (in this case the voltage reference).

Regarding 3 terminal regulators I guess you are referring to the ubiquitous LM317 ?!?!
Well its feedback is fixed, not variable.
You just program a fixed current via the resistor between output and adjust which sets the output voltage via the resistor between adjust and the ground reference (just the plain, old, boring and unfashionable Ohm Law  ).

For that reason you can add a 10µF or even greater capacitor in parallel to that resistor (adj-ground) without affecting stability, while the output capacitance may cause ringing or oscillations.