Good quality LM723 LAB Power Supply

[Wolfgang]

Hi Bram,

I would say well done. As usual, some rants from my side:

- Linear MOSFETs please. Advantages: Less saturation voltage, no SOAR issues.
- What would be useful is an undervoltage detector. Had the same with other load pulsers.
- Another nice trick would be a SOAR check (idea: multiply sampled current and load voltage via analog multiplier, then check limit)
  Jim Williams had this in an early appnote, IIRC
- You could measure the current on the source side of the MOSFETs, so you have less voltage drop because you need the current sampling resistors only once.

Neveretheless, congrats !
  Wolfgang

[blackdog]

Hi Wolfgang,

No problemo, good rants are always helpfull! 

I used the 30N06L because Jim specified a logic MOSFet because of the smaller voltage compliance for the LT1210.

The power problem with the Jim Williams active load was my own dumb fault.
This active load is not made for high dissipation, I have a heatsink which I mount against the bottom of the box when I measure longer with large pulse currents.
I had forgotten this heatsink... 

Your trick with the four-quadrant multiplier is nice, I have here some Burr-Brown IC's and some models of AD.
But there is not much space available in the box, and making something outside the box is so messy again.
I have some low temperature Clicksons, I think I can find a place for them.

The Jim Williams active load has the measuring resistor in its source and I used it for the measurements.

Back to the MOSFet, I have some linear models here, but not in a housing (TO220) that fit in this design.
These are from IXYS and are TO-247-3 models.
Later maybe it is better to make the version with a BJT, it has no trim points, and the bandwidth is enough for most applications.

Kind regards,
Bram

[blackdog]

Hi,

Due to work and a severe cold I can't work so much on this LM723 power supply.
Today I had some time to relax and paid some attention to the temperature drift of the current limitation.
So my starting point today was to use a BC550C as a sense transistor and to keep it at a fixed temperature.
I have already built many types of ovens because I like this work. 
I wanted to keep the oven simple and compact, this means that the "gain" is less than a "normal" oven I usually build.

Of a good single oven that is well insulated, the gain will be between 150 and 200.
With some simple insulation this oven achieved a gain of over 40x.
This means that the variation of the transistor temperature will also be about 40x lower than a transistor that is not kept at a fixt temperature.

This schematic is new but based on something I built 6 to 7 years ago.
The LM317 is the heat source and the BS170 increases the current from the current source built up by the LM317.
R1 of 1K provides the minimum current through the LM317 and the resistor R2 and Rds of the BS170 determine the maximum current at which the current source thus provides the maximum dissipation.
This oven must be fed from a stable power supply, because the set point of the BS170 is dependent on this, I have in this power supply a -12V available hence the value you see in the diagram.
R3 is setting the temperatuur and the temperature also depends on the point at which the BS170 will conduct, this is a bit different for every BS170,
so R3 will give a different temperature for every oven that is built with this schematic.

The temperature drift of the Gate Voltage of the BS170 is no longer important because it is also kept at the right temperature.
The temperature of this oven does not have to be exactly 46.5C, only stable at a temperature between say between 42C and 52C.




Some pictures to show how I built this oven, this is the beginning.



Of course I built the first version with the wrong resistors. 



Now the BS170 is glued to the LM317.



I use some pieces of teflon sleeving here.



The NTC next to the BS170 is a 10K type, the NTC with some wire against the LM317 is a 5K model that is connected to one of my 34461A DMMs.
The BC550C transistor will be mounted at the location of the 5K measure NTC.



The two resistors on the left side are now 1K and 10 Ohm.
The yellow capacitor is for decoupling.
The wiring is very thin, this is done to keep energy loss as low as possible, which again gives a better gain.



The oven was wrapped in this piece of foam for the last test I did tonight.
This foam is from a sample IC packed from Analog Devices and it is isolated heat very well.



Fully wrapped in the foam for a number of tests.



Almost 1 hour of measuring time and only about 0.02C drift, lying open on the table.



A big problem with ovens is always the loop stability, with this oven this is no problem at all.
This is the current through the oven just after switching it on, no instability is visible.



And this is the temperature behaviour after switching on, also here a very nice behaviour without abberations.



Later I glued the BC550C on the spot of the measure NTC and I lay a layer of special thermal glue over the electronics, to improve performance.
Of course I'll show some pictures of that, when I'm done with it.


Times up...

Kind regards,
Bram

[blackdog]

Hi,

I would like to say a bit more about the mini oven I showed yesterday which is meant for the current limitation transistor in the LM723 power supply.
The transistor that performs this function in the LM723 is then no longer used.
By keeping the temperature stable, a reasonably stable minimum of 30 to 50mA output current can be used.

Why not put the whole LM723 in an oven, yes you can, but I had already decided not to do this.

This mini oven can also be used to keep other components at the right temperature.
Think of a TL431, LM329, LT1009, LM385, 1N829 series zener diode.
These parts made in a plastic housing and are the easiest to apply.
then there is no galvanic coupling with the oven electronics.

I have also checked whether if I use a more modern LDO or the number of parts will be reduced, this is not the case for what I have investigated.
I have looked at the LDO's of Linear, but then I miss the extra gain of the BS170 and more decoupling capacitors are needed, so that is not a good option.
It is possible to use one resistor less, that is the 10 Ohm resistor in the Drain of the BS170.
The peak current through the LM317 is then entirely dependent on the Rds of the BS170 and the current limiter in the LM317.

I have also looked at a larger housing for the LM317 or the LM338. The TO3 version is getting more and more difficult to buy and has a hefty price.
A TO3 housing does give some more building space if you're not used to building small electronics.

Some remark about ovens.
Use good isolation material.
Use when posible thin wiring (heat loss)
Use a tight coupling between the heat source and the NTC
Work neatly, ovens require the same way of working precisely as with voltage or current references.
Also build up your test circuits neatly, spaghetti wiring is absolutely undesirable.

The version of the oven that I showed here, uses at 12V supply voltage around 20mA.
That is about 250-mW, at 22C LAB temperature and about 45.5C oven temperature.

For those who would like to try this oven for their project, keep in mind the maximum LAB temperature.
In the very warm places on this world it is better to adjust R3 so that the oven temperature is above 50C.
If you lower R3 in value, the temperature of the oven will be higher.
It is also possible to take another value for the NTC, e.g. on ebay I bought glass  NTC's of 100K, which were very cheap.
Adjust the value of R3, with a 100K NTC you will use approximately 10 times as high a value for this resistance.

If a TO3 version of the regulator is used, then the larger surface area also increases the power required for the same oven temperature.

I hope you like this mini oven!

Kind regards,
Bram

[blackdog]

Hi, 

I have not forgotten you guys...

Work and the flu consumed all my spare time and energy.

But is is better now.
I emptied my workbench to do dynamic measurements on the LM723 circuits.
So a little patience please, it's coming!

Kind regards,
Bram

[blackdog]

Hi,

This is just the start of some measurements and how i do it to not fool myself or the readers of this topic.

Lets start whit the schematic/design i wil test first.
It is better to ignore the current limitation in this diagram, I'm going to solve this in a different way.

The two extra capacitors over the output are Ceramic and therefore have a low ESR and I chose this one especially here together with the Rubycon 100uF YXG capacitor.
This gave good results in the dynamic tests.
What I am now showing here is what is possible with the uA723 and a fast Power Stage regarding the dynamic behavior.

This is the starting point for me, the voltage loop should be good, before I continue with the other parts of the design.



And now some info about the current pulse I use for the dynamic tests.
I had already shown my Jim Williams Fast Current Source that I repaired.
This has now also been used in the tests below.

This is the voltage measured with a battery scope over the current measurement sensor in the Jimwilliams Current Source.
I use a battery scope for these measurements because of commonmode errors that often occur during these measurements.

This is the pulse measured at the maximum bandwidth and largest sample memory settings.
I show this to indicate that the used pulse is very clean and no signal will be masked if I filter this pulse in the scope to get rid of some noise.
The yellow line at the bottom represents the "0" current.
I modulate the Jim Williams Current Source with a 500Hz pulse from one of my generators and this pulse has a 10% Duty Cycle.
The level I use is from 200mA to peak 1.6-Ampere.
This pulse already has a much greater variation than most manufacturers use in their specifications.
And I also specify the edge steepness of the pulse, which here is 5uSec.

This is the pulse measured over the current measurement sensor in the Jim Williams Current Source at maximum bandwidth (200MHz) and memory depth.
Incredibly clean in my eyes.



And this is the pulse when I make the memory depth 1K and 16x average.
Now that the noise is gone, there are still no abberations to be seen.
I am now sure that what I measure is not influenced by a pulse current that would have abberations itself.



And this is the result, some of you might think, Bram that's not good at all...
And then I say, look at the scale settings of the scope, 2mV/Div. the pulse is about 7mV!!



But let's zoom in a bit to get a better picture of the pulse.
First I want to let you know, that when measuring with the Hameg scope I first looked again with a large bandwidth without averaging,
to see if there is something to generate at a high frequency, just to be save!
Yes, this power supply is FAST and stable. 
Of course the negative pulse is a bit faster than the positive pulse.
This is a 1 quadrant design that can only supply current and not draw current from the load or the output capacitors.


And now the scope is at 1mV/Div. to better measure the voltage drop in the middle of the picture.
The cursor measurement indicates that the voltage in this piece has dropped 720uV.
My Delta-i is 1600mA -200mA = 1400mA and that gives an Ri of about 0.5 mOhm of this power supply.


The attentive reader might think, He Bram, your scoop clips! that wil gives measurements errors!
Because of that, I also measured on the 2mV/Div. mode, this gave the same results only a bit worse to read.

Setup on the bench.


The grey wire in the foreground is the "0" sense wire.
The yellow thin wire is the +Sense wire.
The BNC connector is located at the points where the sense wires are.
The BNC cable is placed at right angles to the current-carrying wiring, this is done to minimize measurement errors through the magnetic field of the current-carrying wiring.



The measurements are done at the point where the sense wires are mounted on the output terminals.
Why not measured at the output terminals themselves?
Because I will measure the induction and resistance of the output terminals and not the properties of the circuit itself.

And what happens then when I connect 1M cables to my D.U.T. to provide energy.
Go and measure that, but prepare yourself for some horror.

You always need decoupling of the D.U.T. of sufficient size, so that the connection cables do not receive fast signals to process.
It can also help to use a power supply with external sense wires.
But really fast power supplus with sense wires are difficult to make, the wiring acts like inductors, and the compensation can become rather complex.
The first step for all currents larger than 1-Ampere, is the wiring twisting between the power supply and the D.U.T.

Now is the time to enjoy the first spring sun!

Kind regards,
Bram

[iMo]

The dynamic params of that 723 PSU - compared to various 2xopapms based PSUs people elaborate here today - should be better, indeed, as the opamp inside the 723 is with much lower gain, probably higher BW and consists of maybe 6 transistors..

Your SlowCC comparator consists of a single npn transistor.

Compared to 2xLM324/LM358/TLC072 the 723 is a pretty "empty box"

[blackdog]

Hi imo,

I do not onderstand your remarks...

Kind regards,
Bram

[iMo]

"Dynamic parameters of the above 723 based PSU will always be much better than the dynamic parameters of PSUs based on 2xopamps".

[blackdog]

Hi imo, :-)

"Dynamic parameters of the above 723 based PSU will always be much better than the dynamic parameters of PSUs based on 2xopamps".

This is only correct if you use slow opamps and slow power stages...

My "big" power supply design is even faster than this uA723 design.
But that design is equipped with fast opamps and the best result I had with opamps in that circuit that were 1000V/uSec.
That resulted in only a few mV variations and within a few uSec corrected again at a 10A pulse.
It was not possible to measure the Ri of that power supply in the same way as I did with this uA723 design, this is because the Ri was very low.

Back to this design, I had forgotten to mention that the hum and noise level at 2-Ampere output current is around 10uV RMS, yes uV... in a 22Hz to 22KHz bandwith.

Do these values make this a good design? It's a start...
Power On/Off may not create abberation that can hurt the load.
Current limiting must be fast enough.

I will say it again, current limitation is for me a function of a power supply that protects the power supply and the load.
I have a digital power supply where I can set the current per mA, I have never needed this in three years of use.
Of course the current was set but whether it was 50, 53, 46 or 60mA was never important.
I choose when I power a device the current slightly above the expected current that will be used, so with me a power supply is a voltage source with a current limiter on it for protection.
When I need a current source, I do use a current source device for that.
Power supply's are generally bad current sources with a very low AC impedance and often also a high hum current.

However, everyone can use their measuring equipment as they like it.
I have known for a long time that I regularly look at this in a different way 

The next measurements I will do are the ones that show how the switch on and switch off behaviour is of this circuit.
And if the behavior of the circuit is good enough for me, then I will do the measurement to the current limitation part.
And yes, the current limitation will be done with 1 transistor and this transistor will have an oven to reduce the temperature sensitivity of the current setting a lot.

Stay tuned 

Kind regards,
Bram

[m3vuv]

so where are these supposed schematics?,nothing showing here!!!!.

[m3vuv]

What schematics?,none show up for me,did they vanish in the server fire?,can you repost,im following this but all the op attachments have dissapeared from  this thread,73 m3vuv.

[Kartika]

Hi I  looking for Dual power supply with lm723?