Good quality LM723 LAB Power Supply

[2N3055]

Tesla, right? That brings back memories...

[blackdog]

Hi,

Every time I'm surprised at what I write and how it is interpreted by readers. 
That makes me think even more about how I put it here why I make certain choices.
And of course what I finally type into the translation machine "Deepl" and what it then makes of it.

Kleinstein
I use the Sziklai pair output stage with selected transistors to get the highest possible current gain.
This is to avoid using the emitter follower in the IC, it will give some delay according to my assumption.
Because of the very high Hfe ot the Sziklai pair, the differential amplifier in the LM723 will not be loaded too much and the loopgain will not drop too much.
And yes, I still have to test this to see if it really works well enough, also to see if the Sziklai pair is happy with the relativ high impedance on pin-13
That's why two connections are drawn in the schematic for controlling the Sziklai pair output stage, pin 10 (normal output) or pin-13 the compensation connection.


Sziklai pair
On the Internet it is often found that the Sziklai pair is unstable, I always think, designer then you have not set them up properly...
The 1.5 to 5.6 Ohm resistor in the emitter of the driver transistor is there for good reason.
Is a Ft of the transistors of around 10MHZ sufficient? I think these are also very useful.
But test if the combination you choose is stable!
Play with the emitor resistor of the driver transistor and ALWAYS directly at the base of the driver transistor a resistor between 22 and 150 Ohm, test this well!
A lower Ft of the power section makes room for longer wires if necessary, but.... test, test, test.

If you use fast transistors like I use them, spaghetti wiring is out of the question!
When using fast components, you will always need to use short twisted (low induction) wiring techniques.
And of course not only short wiring but also an low induction current measurement resistor.
If the builder for example thinks he gets a nice fast regulating / stable power supply with long wiring around the fast transistors, then the builder fools himself.

I learned a lot when I played with radio and stations on different high frequencies in my youth.
Then you learn that 5mm wire always has resistance and induction!

Current source
kleinstein I've already understood you the first time, what you say about the current source for current limitation control, I don't ignore you. 
For now I leave it as it is, I detest that I give the current limit a star value of 50ma.
Lower I don't think it makes much sense, because of the temperature sensitivity you already indicated.
But even when I replace the LED with a transistor, it still remains the case that there is not really a good coupling between this power source and the current sensor transistor in the LM723.
In my opinion, the "compensation" varies when varying the set maximum current.
I want to think more about this, and I would like to hear from you what you think about my comments on this.

negative rail
I'm still testing to find the best way to make the negative power supply rail, the schematic is not fixt about that.

For anyone who wants to know what kleinstein meant by supplying a small part of the reference voltage to the inverting input of the LM723,
search with Google for the schedule of the Philips PE1542A power supply.
This schematic also provides a way for better current limitation control.
This schematic has a high value for the compensation capacitor, this makes the dynamic behavior somewhat slow.
The tests in the schematic show a current variation for the dynamic tests from 80 to 100%.
I usually choose for 10 to 90 a 100% which is a lot more difficult for the power supply to be tested.
I will continue with my own design but find this solution certainly interesting.

Cliff Matthews
The negative supply rail can reach a value of -30V together with the 21V output voltage, gives slightly more than 50V over the LM317.
So a "normal" LM317 is not suitable here.

Hi SK_Caterpilar_SK
Thanks for the schematic, but I show here how to use a single transformer winding and a LM723 to create a pretty good power supply.

If I want a power supply with very good voltage and current control then I build one according to the Harrison concept and forget the LM723.
This topic is for fun and i hope people wil learn from it.


Kind regards,
Bram

[Wolfgang]

I have different schematic. Its a old lab powersupply for school purposes so basically idiot proof. No voltage spikes on startups no anything unwanted. Tested because I have the original unit which is performing great. The whole thing is nearly flawless. In its original config it uses the metal can variant of the 723 but I rewrote the shematic so that the pinout is compatible with the DIP version. Also uses some obsoltete transistors and zenners and diodes. I made a PCB layout for it so I can have another one to my desk. The original goes from true 0 to 20V. The only issue with it so far is that it requires a dual winding tranformer. I got the voltages and components so I can give you a list if youre interested to test it at all. It does 0 to 1A but I modified mine so it can do 30V max and 3 amps..

Soo if  youre just interested at all in testing it. I will get you the infos so you can do science on it if you want. I will send you the full image if you want because the max filezise is tiny for this to work properly.

Hi,

good circuit, and expandable, too. In case you dont like the dual winding transformer you could use a small PCB transformer for the 723 and a larger one for the power part.

[SK_Caterpilar_SK]

Hi,

good circuit, and expandable, too. In case you dont like the dual winding transformer you could use a small PCB transformer for the 723 and a larger one for the power part.

Exactly. It doesnt have to be powerfull at all for the LM, the specified voltage for the LMs winding is 12VAC with like almost absolutely no current requirement except to drive the little transistor. You can stretch this circuit to anything realistic. I think I mentioned that the original design is meant for school application (20V 1A) and its idiot proof..no voltage spikes on startup nor anything. Some stuff on the schematic should be changed. The output capacitance should be just enough so that the supply is stable. Not so overdone as it is. In case youre testing zenners or something that 100uF charge will render the zenner into a smelly piece of a bridge. The transistors really do not matter. Keep in spec kind of stuff, the output transistor used originally is a 10A TO3 transistor. I bellieve one of the best packages to dissapate heat . The KF508 can be replaced by a BD 139. The KZ141 is a 4,8-5,1V zenner (very high tolerance components were used for maximum cheapness but still works great) 400mW..basically anything within that voltage range. The KA261 is a 50V silicon diode 500mA (anything will do really 50V diode or above almost all doing 1A these days). E16 E1-E8-E16 are alll just general purpose diodes rectifiers KY132/150 (voltage 150V and current I guess more than one amp.) I did replace the original ones with shottkys because I found them a bit out of comfort warm so I just replaced them with 5A shottkys because thats what I had but anything 5A will do. On my design I used a premade bridge rectifier so I dont have to solder a bilion diodes and its cheaper. On the right up side you see the volt/current meter. Its obsolete and unuseable so I just ignored it on my boards that I have designed based on that schematic. If you want I can send you the board files (either Eagle or GRBL). I only know this circuit by coencidence that I have the original PSU xD And I really like it because even tho its under specs for like regular standards. Only 20V instead of 30V that you would expect from a lab supply these days, and only 1A, But it does not really mater cause the supply is reallly stable electrically quiet, fits on the desk works no matter what and I just like nostalgic gear fight me  .

[SK_Caterpilar_SK]

Hi SK_Caterpilar_SK
Thanks for the schematic, but I show here how to use a single transformer winding and a LM723 to create a pretty good power supply.

If I want a power supply with very good voltage and current control then I build one according to the Harrison concept and forget the LM723.
This topic is for fun and i hope people wil learn from it.


Kind regards,
Bram

Yeah that I just toally forgot about 

[SK_Caterpilar_SK]

Tesla, right? That brings back memories...

Yeah it is. True nostalgy

[Kleinstein]

This thread started with intentionally not using the floating regulator type.

So the circuit with the auxiliary supply while still using the 723 is a little off topic.
The floating regulator has its good sides and it thus today kind of the standard for a lab-supply. The shown old implementation looks easy, but I am not so sure it behave that well under extreme conditions (e.g. with a larger low ESR cap at the output). It still has the classic old weakness of a set voltage dependent loop gain. So performance at the ends is not expected to be that good. New digitally set ones naturally adjust the reference input side and thus avoid this problem as a side effect. The auxiliary supply could also power a possible display.

The circuit chose from the start of the thread still has a few advantages:  even with a very slow compensation the load drops are not that large and the output capacitor can be small. In addition it does not need a second transformer winding. However it is kind of limited to some 25 V maybe 30 V.  At least with the crude current limit from the 723 I would not call it a lab-supply, at best a low end one.
The shown circuit with the shunt at the high side also makes it difficult to add a digital display of the current.

[blackdog]

Hi,

Kleinstein
It still has the classic old weakness of a set voltage dependent loop gain.
Did you not look at the last schematic?
It has now a fixt gain setting!


At the moment I am testing what the deviation is that occurs due to variation of the mains voltage of the -5V negative supply rail.
If I use an extra zener I can get the variation less than 10uV DC by large mains voltage variation of the -5V rail.
I use a LAB power supply to test this, I vary at the input of the LM337 from -22V to -32V.
22V is the minimum voor 20V output and 32V will be the if there is a very high net voltage.

And I also tested the attenuation with a modular power supply (HP 6823A) to measure the attenuation of the 50, 100, 150 and 200Hz frequencies.
This is from -60 to -75dB depending on the measurement frequency, this is sufficient for my setup if i chose the buffer capacitor.

But...
This does not provide the results I would like to have for this power supply.
That is low noise and the best possible DC stability power supply without using expensive parts and extra transformers or windings.
I took out the zener and resistor and tested with a -15V LM7915 which I had available, BINGO clean!
I'm probably going to replace it with an LM7912 to reduce the dissipation in the LM337 a bit more to reduce the DC drift of this voltage regular.
Later today I will put this morning's testing into the last schematic.

kleinstein, later today I wil make soms remarkt about the stability of large capacitor on the output en maybe also BIG inductors. :-)

Kind regards,
Bram

[Kleinstein]

I saw the voltage setting was changed in the 723 circuit.

The remark on the variable loop gain was for the floating regulator circuit that SK_Caterpilar_SK  brought up. The same with the stability.

[blackdog]

Hi 

Here is the last schematic with adjustments I did after some measurements and thinking about the schematic.

I had already explained in the beginning that one of the characteristics I like to see in a power supply is good DC stability and few interference signals.
These interference signals can be noise from the LM723 itself and the extra -5V rail, but also interference signals from the 230V grid here in Amsterdam.

The tests I did this week showed that the sensitivity to voltage variations due to the 230V mains voltage variations and the load variations at the output of the power supply, I found the variations too large.
This means that I will have to use more parts than I had intended.
But the parts used are just like the LM723 "Old School" and I allow myself to use these parts. 
What I have done now is not so much different than that you see more in well designed power supplies, the LM723 itself is powered by "clean" power lines.

The -5V power supply line.
I have done extensive tests on the LM337 to see how good the hum suppression is and what the sensitivity is for variation of the DC level at the input of the LM337.
The output of the LM337 which is about -5V is in series with the reference voltage of the LM723, so you see every deviation of this -5V as variation in the output voltage.
After some tests with zener diodes I switched to a LM7912, it costs almost nothing and has a much better performance than a resistor and zener diode.
Now there is no hum or DC variation at the output of the LM337 that is present at the input of the LM7912.
The ripple on C3 is suppressed by more than 120dB if you do the wiring properly.

For a power supply with good properties, the wiring technique is important!
If you look at the diagram below, you can see that the ground (which is on J2 output bus) is split into multiple connections to this node.
There is a thick horizontal line in the diagram to J2 connection, which is the return connection of the energy coming from the transformer and the rectifiers and capacitors.
The same DC level of the -5V power rail (The GND connection of the LM7912 and this has a thick green line) must be connected directly to the J2 socket, as I drew in the schematic.
A third important connection to J2 is the resistor R21 in the diagram below, this is the negative "sense" connection.
Ignoring this wiring technique means that you end up with a worse power supply than is possible with the used circuit.

+23.5V power rail
Also the DC level on the Vs and the Vc connections of the LM723 are sensitive to variation.
When loading the power supply from 100mA to 1.9-Ampere, the voltage at C8 can drop 1V. (This is due to the Ri of the transformer)
This drop in the voltage at C8 is then seen as an extra drop in the output voltage, making the DC Ri lower than necessary.

The level of 23.5V will probably still change, as it depends on the Power output section.
I'm going to make two connections on my test print as shown in the schematic, the normal output which is pin-10 and pin-13 which is the direct connection of the difference amplifier in the LM723.
This direct connection goes beyond the Darlington in the LM723 IC.
I hope that with my high gain of the Sziklai pair I will have both a low DC Ri and a better phase margin, but the test wil show if this use of pin-13 is usefull.

The DC level of 23.5V therefore depends on the Power stage configuration and whether it is possible with the used transformer to reach 20V at 2-Ampere,
if it becomes 1.8-Ampere at a low mains voltage, then I will settle for that, no problemo.
Because this power supply is for fun and teaching. 

I have chosen for the 23.5V regulator to use a TL431 shunt controller.
The measurements I did on my test setup, which supplies the voltage to LM723 and the current that supplies the reference output of the LM723 to P-1 and R11 is between 5 and 6mA.
This is not the only current, also the current source made with Q3 which is about 1mA together with the current through the red LED are about 2mA total,
which should be added to the current consumed by the LM723, in total this is about 8 to 9mA.
C8 is now also enlarged to 2200uF to make the ripple as small as possible, this gives some more space for the TL431 controller.
later I can replace D3 with a Schottky version for about 300mV extra margin.
How to calculate the resistors arroud the TL431b?
I use a TI speadsheet which you can download via the link below.

www.bramcam.nl/NA/NA-723-PSU/TL431-Calculator.xlsm

Resistor R9 and R10 are setting the voltage voor de LM723 IC.
R6 determines the current that can be drawn that still falls within the control range of the TL431b.
Don't forget that you don't exceed the maximum dissipation of the TL431b!

I'm going to test the resistor R6 which is now listed as 120 Ohm in the schematic with the power supply connected to a 2-Ampere load
and 20V output voltage, to see if it still works at 220V mains voltage, at the two Power section configurations.


LM723 output voltage and sensor lines
To keep the phase marging stable on the output voltage between "0" and +20V, I decided to test the regulating the +input of the LM723 after a remark of kleinstein.
The bottom side of the potentiometer P-1 has a DC level of "0V" compared to J2.
The reference voltage(pin-6 LM723) is also with respect to J2 about 2.1V.
Note, I am not saying that the reference output of the LM723 is now suddenly 2.1V instead of 7.1V!
This 2.1V is due to the reference shift of the -5V regulator relative to J2, this because pin-7 of the LM723 is connected to the -5V regulator.
The trim-1 potentiometer in the -5V regulator ensures that the output voltage can be adjusted to "0V" when P-1 is turned all the way counterclockwise.

It is not that important that the -5V rail is exactly 5.0000V.
Noise, hum and stability are important here for this power supply rail.
It can also be -4.2V, -4.85V or even 3.765V or as kleinstein suggested 2.5V.
2.5V I found a bit on the low side by some testing I did at this low commonmode voltages for the inputs.
It's no problem to sit in the "sweet spot" of the input commonmode range for the best performance.
By using two regulated supply lines in this diagram, the LM723 can never get too high a supply voltage again.

As shown in the diagram, P-1 controls between 0V and +2.1V, this value will have to be amplified by the differential amplifier in the LM723.
As with a normal opamp, the gain is controlled by two resistors connected to the -input.
In the schematic these are R17 of 10K and R21 of 1K, I have a small trim range applied so I can set the maximum output voltage, this is done with Trim-2 potentiometer.

A few remarks about the values of the resistors and potentiometers that are attached to the + and - inputs of the LM723.
With the chosen schematic it is not possible to precisely equalize the impedances.
The impedance at the -input is fixed but that of the +input depends on the position of the potmater P-1.
At the +input there is always a 1K resistor present that together with C12 of 4u7 form a low pass filter, witch filters the reference noise and when changing the output voltage.
At this 1K, in the worst case with the potentiometer on "0V" the parallel resistance of P-1 and R11 must be added up which is around 700 Ohm.
At this low value of impedances, the bias currents and noise are less important.

Schematic version 0.7



Resume
So what has changed in the schematic:

1e
The output voltage is now controlled by variation of the + input, phase marging remains stable over the entire output voltage range.

2e
The LM723 is powered by two clean power supplies that are much more stable and cleaner than the first setup.
This makes the final performance a lot better, I love to design clean power supplies, which is one of my abberations. 

3e
That there is now the possibility to choose the output to which the power section can be connected with D7 and capacitor C16
which give a DC shift for the output commonmode without adding phase margin.


Still to be done
Testing of the Power section connected to the compentation connection.
Select the current limitation components well, it involves R20 and R24 and perhaps replace the current source version as proposed by kleinstein.
If the phase margin and dynamic behavior are good, the timing of the Power On/Off circuits should be further tuned so that no abberations occur.

And some more explanation why I made certain decisions for this power supply.
But, to say it again, this is a power supply for me, and not meant to be a building project.
And the second reason I started this topic is that I learn to express myself better.

This is mainly intended as a learning project for those who do not yet have much experience in building or designing power supplies.
Many who start with electronics want to build/design a power supply without sufficient electronic knowledge. (buy The Art of Electronic)
I am no exception, I made many mistakes and have read very many hours in the first versions than The Art Of Electronic

Power supply are difficult circuits, and yes I know the Internet is full of "simple" schematics.
This almost always means that the "designer" himself does not know what he or she is working with at that moment.
A common mistake is that the person who is going to rebuild a schematic will replace parts without much thought because they have them in stock.
Please do this in you want to have a poorly functioning circuit. 

For your information.
This piece of text with the adjustment of the schematic took me almost 6 hours today.
Gaining knowledge and transferring it takes a lot of time and effort, if you want to learn you will have to make a real effort
and this effort for good learning can not only consist of just looking up something quickly via Google.
I see more and more that people want to know everything at the push of a button.
And I think, who are you fooling?

Like Louis Rossmann I want to say now, I hope you learned something from, I dit.

Kind regards,
Bram

[Cliff Matthews]

R7 and Trim-1 seem hard to get, for the avg. bloke with just e24 series, why not use 390 and 100 ohm trim?

Also, can I use 2SA1695 I mentioned as the final output? (another big PNP I have is TIP147..)

[Kleinstein]

The 2SA1695 should be OK. The TIP147 is a Darlingtion transistor and would thus behave different. AFIAK the PNP does not have to be super fast, its more like the NPN in the Sizlaki pair should be considerably faster to ease stability. Otherwise one might artificially slow down the PNP with an extra cap.

The circuit still has the weakness of using 2 references in a kind of difference mode. In the last plan the adjustment range for the the pot is only around 0-2V for the input. This is set as a fraction of the 7 V reference inside the 723 minus the 5 V from the LM337. I don't think this a really good idea.  I would expect it to get better if the negative voltage from the LM377 is reduced, e.g. by having the adjust pin directly at ground. With a higher reference level there could be less divider in the feedback and thus better DC precision.

7 V - 1.3 V sound a lot less odd than 7 V -5 V for the reference. It should also work having the pot directly towards the ground (= negative output) instead of the resistor towards the -5 V (negative supply of the 723).

[blackdog]

Hi,

I already showed that I want to keep the impedances around the inputs of the LM723 low.
That results in some more gain needed to reach 20V.
I also indicated that with earlier measurements the open loop gain became lower, when the inputs have to work at low commonmode voltages.
I do think there is still room to bring the -5V to e.g. -3V, this without too much performance loss.

Wait.... let's just say that I'll run the new test print setup with -3V power rail.
Tonight I will have change the resistance values for that in the schematic.
But.... Keep in mind that this is a schematic that is in the design phase.
If it suits me or the measurements dictate this, I will adjust the value again.

In the weekend I decided to bring the maximum output voltage of the power supply to 20.1V.
The reason is that I have analog meters on my order list of 20V and 2 or 3-Ampere.

2SA1695
I prefer the 2SA1943, the reason for this is that this transistor is cheap, and the most important reason is the large size of the housing.
This almost always results in a better (lower) thermal resistance.
And this, please, please, please, please, do not buy the cheap transistor junk on ebay!

Cliff
Even if you only think of the TIP147, your punishment is that you have to read this whole topic 5 times. 
Yes now I am joking!
As kleinstein indicates, the PNP Darlington is a PNP that you don't want to have in this circuit.
This Darlington can also be used in power supply's, but not in this one without the properties I want to be affected too much.

Resistance values and trimpots.
I calculate the values I find necessary for the best results.
As you can see here already in this topic quite a lot changes in the schematic by insight and measurement results.
If you would like to build this design, it is best to wait until the schematic is in its final stage.

I use values from the E96 series, but if possible I choose nice round values like I did with R17 which sets the gain of the LM723 and also R8 of the -5V regulator.

Trim-1 I choose in the final schematic so that this trimpotmeter has only a small range to compensate for the inaccuracy of the LM721 reference voltage,
Potmeter P-1 resistance deviation, the resistors R7 and R8 and the accuracy of the LM337 reference voltage.
Trim-2 will be chosen so that I can eventually set the max. output voltage to 2.1V.
This trimpot will also have a small range, to be determined when I have the schematic ready.
The trimpotmeter will therefore have as small a range as possible, so that they will only have a small part in terms of DC stability.

As far as I'm concerned, Trim-2 may also be in series with R17 if the right ratio is chosen.
Trim-2 may also be parallel to R21 with a series of resistors, which is even nicer.
Of course I calculated it in such a way that it only has the necessary control range.
Then there is this, a trimpotmeter is usually placed on the side, which is the least sensitive, so the lowest impedance possible.

In my next schematic I will apply that too.
So the trimpot can be placed at the top of R17 or at the bottom of R21.
In schematic version 0.7 Trim-2 and R21 have to change places.
Where the trimpot Trim-2 will be depends on the values I will calculate.
So later this evening I place version 0.8 of the schematic in this topic.

But now first I go to my mothers house, to reset her TV, because the cable company has changed some settings.
And then I am expected to participate in the evening meal with the lady of the house. 

Kind regards,
Bram

[blackdog]

Hi,

The schematic has been modified, so I get a slightly higher value over the voltage potentiometer, this one is now 4V instead of the 2.1V it was.
The gain of the LM723 now only needs to be 5x to get 20V output voltage.

Schematic version 0.8


I have made sure that where I can I use default values.
I have made R10 equal to R18 so there is no need to buy 10.5 and 10K in a 1% E96 value.
Furthermore, it is no longer possible to use a 1K type for P1, this gives a too high a current that has to come from the reference connection.
This results in a larger dissipation in the LM723 IC and a larger startup drift.

So the next logical step for the ones who want to build the schematic is a 5K potmeter.
A 2K potentiometer can also be applied when the value of R9 is adjusted.
The current through the P-1 potentiometer is then 2mA which I consider to be maximum, I know this may be 15mA, but that doesn't mean it's good.

25mA current source
Dissipation VR3, the LM317HV, the dissipation of this controller can be limited a bit by recording a 560 Ohm 2-Watt resistor.
This is then 14 a 15V voltage, and there remains enough voltage for a good control, even at a low output voltage of the power supply.
Keep in mind when applying this resistor and maybe a small capacitor of 1uF should come after the resistor to keep the LM317HV stable.
At 680 Ohm you could even use a "normal" LM317, but then I would put a 36V zener over it for protection.
I'll test that and if I'm okay, include it in the schematic later.
All in all, a single LM317HV is easier.

Testprint
I had already started rebuilding the test print, but due to the other value of the reference voltage I will now have to change it again in part., live sucks 



At the far left top you can see three parallel connected bridge rectifiers (BY164) These are replaced when the schematic is finished by a GBJ-1506U .
The top three capacitors is C5 in the schematic, only here the total value is 6700uF.
The two large capacitors on the row below are 2x1500uF and that are C1 and C3.
These are 1500uF on the PCB and 1000uF on the Schematic, the 1000uF will be on the later PCB when I finish measuring on it.
And the last capacitor, the black small one is C8 in the schematic.
The small blue trimpotmeter and two resistors on the right side of the LM723 will be changed in value because the reference voltage has changed.

It will probably be the end of the week before I can show measurement results from the last scheme.
My work doesn't allow me to spend more time there, no matter how much I like it.
Please be patient, I will certainly read your comments because I appreciate that.

Kind regards,
Bram

[iMo]

The TL431 as the shunt regulator for the 723 - hmm, would not be better to use a 7824 instead?
Also, what happens if the wiper of the potentiometer P-1 5K loses its contact?

[blackdog]

Hi imo,

Of course I thought of a 7824 or a LM317.
But also think about the noise, I would like a power supply as clean as possible for the LM723.
These are all considerations that go a bit further than just looking at e.g. the dropout voltage of a regulator.
The suppression of e.g. the ripple voltages present at the input of the regulator.
This suppression often gets less the closer you get to the dropout voltage.

If the input voltage of the TL431 becomes too low to regulate properly, there is still good extra ripple attenuation by R6 and C14.
But these are now the decisions you will have to take when you are designing a circuit.
If I had some more voltage from the transformer like a 22V model instead of the 20V, there would be a LM317 in that place. 
But i am designing with my 20V transformer and the minimum of 220V mains voltage. (230V is here nominal)

What wil happen if R17 or R18 break lose...
And I can think of even more disasters, you have to live with it.

But back to P-1, and there is a capacitor of 4.7uf parallel to the + input, this capacitor does not only filter the reference noise but also helps with dendering of the rider of the potentiometer.
And again, the same as my comment about the transistors, don't buy rubbish on ebay!
Order the good Vishay type model 534, 10 turn pots.
I have hardly ever had any problems with this type.

Kind regards,
Bram

[Wolfgang]

Bram,

if you are concerned to supply a cleaner voltage to the LM723 you could try to preregulate the V+ pin. This pin goes to the error amp, and this error amp inside the LM723 has a limited CMRR only. So filtering this improves output ripple. What you could also do is filter the reference voltage. This reduces output noise, too.

If interested

https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/

[blackdog]

Hi Wolfgang, 


I am filtering the reference voltage, but only on a different point.
C12 in the last schematic has also this function.

Kind regards,
Bram

[Wolfgang]

Hi Wolfgang, 


I am filtering the reference voltage, but only on a different point.
C12 in the last schematic has also this function.

Kind regards,
Bram

Hi Bram,

I've seen C12, but you could add another C directly at the reference output too, thats what I wanted to say. Pedantry ? Yes. 
Your solution for current control works from low currents on, but its still dependent on the Vbe of the 723s CS/CL pins. So its temp  dependent and not very accurate. 723 current limiting is more for the prevention of desasters than for fine and accurate current regulation. What you could do is to keep the idea of the current source, but then use an op amp to compare the drop across the current sensing resistor. The op amp could then (via a diode voter circuit) pull down the base of your pass darlington.

Have fun
  Wolfgang

[blackdog]

Hi Wolfgang, 

I know that the current limitation is not optimal....
I don't need that for this power supply.
As you already explain it, it is this kind of simple solution only meant for "calamities".
I am fully aware of the control properties and their temperature sensitivity.

A large part of my life (> 50 years) I often use the current limitation differently than many other people do.
When I connect a D.U.T. to a Power Supply, I first think about the current that will or may be consumed.
Then I set this current and whether this is 50mA or 55mA does not matter so much to me, even if the current drifts from 48 to 53mA, so what...
When I need a very precise current I almost never use a power supply but a current source.

And I'll repeat it again, I won't charge a battery with power supplies and certainly not without using a diode.
I think it doesn't happen more than twice a year that a battery is charged from a power supply in my LAB, I use battery chargers for that. 
And a LED is always tested here via a series resistor, or via one of my multimeters (TEK DMM4050)
I have 15 power supplies here in my LAB and if I need precision current limitation then I do so with a power supply type that is suitable for that.

This design I show here puts more emphasis on the smallest possible abberations and as little noise as possible and a reasonable DC drift.
It is not a "One size fits all" power supply.
And again, every user of measuring equipment must know the characteristics of this equipment if you want to make as few mistakes as possible.

If I want a more precise current setting, I can always choose at least two power supply's that are on my workbench, that is the Rigol DP832 and the Agilent 6632B.
But as I said, that almost never happens especially for that purpose.

I Love/Hate my Rigol DP832, this has a high resolution for both current and voltage and this together with the power display.
But the 470uF over the output terminals don't make much sense if it is for example set to 24V and 20mA maximum current.
The charge of the 470uF capacitor is dumped into the DUT when something goes wrong.
What is the point of a precise 20mA current limit then? so... the user must know the characteristics of this equipment if you want to make as few mistakes as possible. 

But I would like to hear more good comments, we learn from that.

Kind regards,
Bram

[Wolfgang]

Hi Bram,

I never intended to keep somebody from experimenting. So having fun is most important, its clear that your
PSU is not an academic endevour. In my view it should work and is worth to be tried out.

Some comments about output caps. Output caps have two functions:
- to reduce output impedance at higher frequencies where the regulator gain goes down
- for LDOs, together with a suitable ESR, to ensure stability.

Its clear, as you write, that all current limiting is useless if you have a large output cap and the limiting happens *before* the cap, as it does in all power supplies I know (DP832 included). If you need precision limiting in nanoseconds *plus* a stiff regulator, then stability with arbitrary loads becomes a challenge. So, the solution most PSU manufacturers offer is a medium size output cap with no further limiting, but an all load stability and a reasonable PSU output impedance.

I have tested the DP832A output impedances. Results can be seen here:

https://electronicprojectsforfun.wordpress.com/power-supply-impedance-measurements-for-various-power-supplies/

and here:

https://electronicprojectsforfun.wordpress.com/power-supply-impedance-measurements-using-the-bode100-lf-vna/

regards
  Wolfgang

A last comment: did you know that the (obsolete) SG3532 did implement your current limiting idea ?
This chip made by SGS ATES was meant to be an improved LM723 with a lower voltage reference, better current
limiting, overtemp protection, ... Only it failed on the market because the LM723 was often "good enough"
plus it soon became dirt cheap.

Have fun
  Wolfgang

[blackdog]

Hi Wolfgang,

Maybe I even have an SG3532, but as you said it makes little sense to develop anything with it because it is no longer for sale.

Are you the owner of the measuring instrument, because this device is quite expensive.
A few years ago I already looked up how much it cost, I fell off my chair...

Rigol tests
This is the left channel, the yellow trace is the current pulses from 50 to 0.8mA.
The measuring cables are optimally connected to measure as precisely as possible with as few abberations as possible.
The blue trace is the deviation at the output of the power supply caused by the current pulse.



This is the middle channel with the same conditions as the left channel.
It is visible that this channel is not quite the same as the left channel, but the differences are small.
This may be because the 470uF over the output is slightly different, and the sense wiring in the power supply is different.



And this is the right channel, which goes up to 5.5V but tested under the same conditions.



You want more? 

OK
The analogue DELTA E 030V 1-Ampere power supply, famous here in the Netherlands for its very good quality.



And this is also a DELTA Power supply and the type is ES 030-5 and this is a fully digital power supply.
The blue output pulse shows that this power supply is not suitable for precision applications.
An advantage of this power supply is that although it is a digital model, it has little EMF.
I use this power supply regularly when I need higher powers and the pulse response and EMF are not that important.


The power supply I made according to the Harrison concept
is much better than the pictures I show here of the Rigol and the DELTA power supply's.
That's because I use modern parts with fast power sections.
Does everyone need that? No, of course not, many can use an average power supply.
But I also think that many people don't know how their power supply behaves when switching it on or off or sudden large load variations.

I don't need this power supply with the LM723 at all, I do this because I like to get the most performance out of the LM723 without using expensive parts, adding opamps and extra transformers.
Furthermore, I hope that readers who don't have so much experience with designing will learn something from it.

Kind regards,
Bram

[Wolfgang]

Hi Bram,

your curves look quite reasonable, you would expect something like that. It proves that the DP832 is lethargic and the control loop has enough phase margin. The deltas dont look good, and weakly damped oscillations should never appear in a lab PSU.

When injecting current its important that leads are kept short to minimize inductance. Some tests of commercial current injectors I have done can be found here:

https://electronicprojectsforfun.wordpress.com/measuring-a-picotest-j2111a-current-injector/

or you use injection transformers (not so practical for a commercial PSU where you cannot open the regulator loop):

https://electronicprojectsforfun.wordpress.com/injection-transformers/

The equipment I have is in my EEVBlog profile, if you are interested. In fact I have a VNA, but not for low frequency stability work (E5071C 8.5GHz). It starts at 9kHz so its not too useful. I agree that LF VNAs are surprisingly expensive. The absolute record holder is the Keysight E5061-3L5 which can do sweeps from 5Hz to 3GHz in one go and a 120dB dynamic range for a whopping 35K€ list price. Keysight did not want to give me reasonable discounts because they claim that the market is very small and they have no competitors. A Bode100 does 1Hz to 50MHz with a little less dynamic range for about 5K€. I might get my hands on a Bode100 again soon, maybe Omicron and myself team up and I can have a test unit.

Have fun
  Wolfgang

[IconicPCB]

Bram,

What is this Harrison concept You refer to?
I know Harrison were bought ou by HP i guess in the sixties may be seventies, but i do not know what this concept is You refer to.

[Cliff Matthews]

Bram,

What is this Harrison concept You refer to?
I know Harrison were bought ou by HP i guess in the sixties may be seventies, but i do not know what this concept is You refer to.

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1962-07.pdf