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Author Topic: Adjustable DC Regulated Power Supply (0 - 30 V 2 mA - 3 A)With Digital Control  (Read 13138 times)
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sadman
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« on: March 11, 2019, 11:17:03 11:17 »

Hi

Although it is very famous design from electronics lab but recently Elektor launch it as kit, original design have some bug in it which was optimized by Audioguru at eevblog in this attachment i have added the schematic optimized by Audioguru and Elektor kit PDF document bonus added digital control of this power supply by a Russian forum and 10A version by the same forum. i like the digital control part of this power supply.

Regards
sadman

 
« Last Edit: March 11, 2019, 11:19:31 11:19 by sadman » Logged
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« Reply #1 on: March 11, 2019, 05:52:43 17:52 »

Elektor is selling same kit from banggood which is also have same bug as banggood and electronics lab circuit Audioguru modified the circuit which is much better and work as expected he did a great job complete discussion is here.

https://www.eevblog.com/forum/beginners/bangood-psu-enhancements/
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« Reply #2 on: March 12, 2019, 12:34:33 00:34 »

I built this PSU some years ago, Based on the same design as the links you posted. I did have some problems with it, If you read pages and pages over on the electronics lab forum, One topic is 94 pages long.

In my opinion the design is not very good or reliable, I found that it worked but after some testing I found that the current limit side did not work if I remember correctly, I was not really happy with it so I stopped using it and threw it in the bin in the end even tough I paid little extra for the TLE2141 op-amps and carried out all the mod's but still no joy.

Sorry don't mean to be negative, Good share for people who want to build it on a budget and some people may disagree with me. From reading through most of the comments there is lots of people having issues  and Audioguru has answered everyone or someone tries to change the design.


Makes you wonder if the Elektor are selling that supply with the TLE2141 op-amps with that kit as it only cost 11 euro's ?

Those op-amps cost me round about 6 GBP for the 3.
The digital readout looks ok, But I would rather build my own using a 16bit ADC with a TFT display or a GLD with bigger fonts .
One of the best power supplies I've built was based on the veleman K7200 which they discontinued  Sad

Well that's my 2 pennies worth  
« Last Edit: March 12, 2019, 12:37:33 00:37 by Wizpic » Logged

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« Reply #3 on: March 12, 2019, 04:22:43 04:22 »

I built this PSU some years ago, Based on the same design as the links you posted. I did have some problems with it, If you read pages and pages over on the electronics lab forum, One topic is 94 pages long.

In my opinion the design is not very good or reliable, I found that it worked but after some testing I found that the current limit side did not work if I remember correctly, I was not really happy with it so I stopped using it and threw it in the bin in the end even tough I paid little extra for the TLE2141 op-amps and carried out all the mod's but still no joy.

Sorry don't mean to be negative, Good share for people who want to build it on a budget and some people may disagree with me. From reading through most of the comments there is lots of people having issues  and Audioguru has answered everyone or someone tries to change the design.


Makes you wonder if the Elektor are selling that supply with the TLE2141 op-amps with that kit as it only cost 11 euro's ?

Those op-amps cost me round about 6 GBP for the 3.
The digital readout looks ok, But I would rather build my own using a 16bit ADC with a TFT display or a GLD with bigger fonts .
One of the best power supplies I've built was based on the veleman K7200 which they discontinued  Sad

Well that's my 2 pennies worth  

Hi Wizpic

I will never take your comment as negative as comments always open up new possibilities and ideas I have the whole design and build instruction of K7200 power supply based on LM723 using two pair one for current control and one for voltage.

I build that for 2 Amp current only as for hobby level you never need current over 2 amp personally I like mix mode power supply switching regulator for pre regulation and linear regulator for output Which will allow good control of heat dissipation (made that supply using LM2596 and LM338) with CC , CV function if member interested I will share K7200 build info here.

sadman
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« Reply #4 on: March 12, 2019, 03:56:00 15:56 »

Hi Wizpic

I will never take your comment as negative as comments always open up new possibilities and ideas I have the whole design and build instruction of K7200 power supply based on LM723 using two pair one for current control and one for voltage.
I think most of the newer K2700 projects are based on info from this book(link included not my own but checked out) But by all means start a new thread for a K2700 project
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Wizpic
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« Reply #5 on: March 12, 2019, 04:59:45 16:59 »

I think most of the newer K2700 projects are based on info from this book(link included not my own but checked out) But by all means start a new thread for a K2700 project
There is someone selling the bare PCB on e-bay and funny enough its my drawings and the one on 320v.com, years ago I copied and laid out the pcb for it,the one on 320volt.com is my case drawing too I know its mine because its got smart designs on pcb lol, its a good power supply
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« Reply #6 on: March 12, 2019, 09:32:16 21:32 »

Hi sadman

there is a relay control block diagram to select the secondary winding of the transformer,
do you have the sch for this block?

Regards
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« Reply #7 on: March 15, 2019, 12:11:22 00:11 »

Not to be the bearer of bad news, but the russian "addition" does not do any Digital Control.

The so called "Digital Control" only reads the voltage and the current, displays it on a 16x2 LCD and probably (I cannot tell only by looking at the russian schematic) cuts the output if overload occurs.

There are options to do digitally controlled power supplies by implementing a DC/DC (like my PSU based on TL494 and 12 bit DACs), but also linear options may be implemented with digipots (careful on the max current that can pass through the digipot).
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« Reply #8 on: May 16, 2019, 07:08:52 19:08 »

I think it is not worth trying to do any digital control, because PID control is needed. But even so, the loop through the MCU takes time to regulate the output.

There are cheap alternatives in Banggood now that work very well, with lots of current and wide range of voltage output.

See here: https://www.banggood.com/RUIDENG-DPS5020-Constant-Voltage-Current-Step-Down-Communication-Digital-Power-Supply-Module-p-1181200.html?rmmds=detail-left-hotproducts__6&ID=514816&cur_warehouse=CN

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« Reply #9 on: May 17, 2019, 07:44:40 07:44 »

I have 3 of these, and I recommend them.


https://www.banggood.com/DP50V5A-Buck-Adjustable-DC-Power-Supply-Module-With-Integrated-Voltmeter-Ammeter-Color-Display-p-1050061.html?currency=USD&utm_source=rtbhouse&utm_medium=cpc_brand&utm_content=all&utm_campaign=rtb-electronics-all-en&cur_warehouse=CN


there are several versions, lower cost for the 30V, 3A version.

Bluetooth and serial interfaces work.

One of the DP50V5, I use a boost converter to up 12V to 50V.

https://www.banggood.com/DC-DC-8_5-48V-To-10-50V-10A-250W-Continuous-Adjustable-High-Power-Boost-Power-Module-Step-Up-Board-p-1248941.html?rmmds=search&cur_warehouse=CN

It works fine
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« Reply #10 on: May 17, 2019, 12:00:04 12:00 »

I've just ordered one of those after reading lots of opinions on them, a DPS5005. Should arrive next week. Now I'm deciding whether to power it from a linear PSU built around a 160W torroid I have lying around, or buy a 48V SMPS. I'm trying not to spend more than absolutely necessary though so I'll probably go for the linear since I have all the parts needed.

That boost converter is a good idea though... I have plenty of high current 12V PSUs... another option!
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« Reply #11 on: September 01, 2019, 10:30:29 10:30 »

an update to the schematic
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« Reply #12 on: September 01, 2019, 03:15:22 15:15 »

I don't think I will build something like this:
As the design is old ,full linear ,inefficient ,need tow power source ....
Today bench-top power supply designed as switching + tracking(LDO follow the switcher) in order to get low noise and high efficiency with computer control (digital control) and LCD (TFT) screen who can measure the resistance of the lead wire(cable) in order to compensate the loss, with far less weight in compare to linear unit due to the lake of heavy linear transformer

But whether you are looking for simple design Wurth Electronic has an evaluation board with schematic name : DNS002 MagI3C Power Supply
who can provide 0~15V and 0~2.5A from any switching 7~36V PSU the design is simple and can work with almost any switching regulator who provide [email protected] (test it with simulation) and no need for a heavy linear transformer.

https://www.we-online.com/web/en/electronic_components/news_pbs/News_Detail_Standard_Parts_111618.php


 

All the best

Bobi
     
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« Reply #13 on: September 01, 2019, 08:42:29 20:42 »

Things have changed and building a linear PS is too much power wasted as heat. Though, I have not found a good design with tracking LDO.

There are plenty PCBs ready made SMPS with a lot of ampere capacity and digital control in the usual Chinese sites if one wants an almost ready made solution.
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« Reply #14 on: September 01, 2019, 11:04:56 23:04 »

Things have changed and building a linear PS is too much power wasted as heat. Though, I have not found a good design with tracking LDO.

There are plenty PCBs ready made SMPS with a lot of ampere capacity and digital control in the usual Chinese sites if one wants an almost ready made solution.

Keep in mind switching power supplies tend to be noisy (electrically) so may not be ideal for some applications such as those dealing with very small voltages.
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« Reply #15 on: September 02, 2019, 08:36:32 08:36 »

That is why (in good designs) they are followed by a tracking LDO.
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« Reply #16 on: September 02, 2019, 07:01:14 19:01 »

That is why (in good designs) they are followed by a tracking LDO.

I will share a good design with tracking LDO
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« Reply #17 on: September 03, 2019, 02:48:24 02:48 »

Are there any lab power supplies that have a switching topology with an LDO or other method of reducing noise on the output?  

I've been using these old HP linear variable power supplies that are rated at 0.35 mV (rms) ripple/noise.  I wish I could finish a switching version with noise characteristics that are within an order of magnitude of that.  

https://www.keysight.com/us/en/products/dc-power-supplies/bench-power-supplies/e3630-series-bench-power-supply-80-200w.html

Some switching models such as this one claim 0.5 mV (rms) noise/ripple, but that seems hard to believe:

https://www.amazon.com/Variable-Precision-Adjustable-Regulated-Alligator/dp/B077GVMP5X
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« Reply #18 on: September 05, 2019, 01:49:34 13:49 »

That is why (in good designs) they are followed by a tracking LDO.

here is design with LDO and tracking
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« Reply #19 on: September 08, 2019, 03:43:44 15:43 »

here is design with LDO and tracking

One limit this power supply output limited to less then 20V

All the best

Bobi
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« Reply #20 on: September 08, 2019, 05:40:52 17:40 »

One limit this power supply output limited to less then 20V

All the best

Bobi

share design is for reference it can be easily modified up-to 30 volts in those days i am working on good LAB power supply with CC/CV mode and microcontroller controlled

sadman
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« Reply #21 on: September 09, 2019, 10:34:47 10:34 »

The point of sadman was to show how to use tracking regulator. The rest is up to the experienced designer.
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« Reply #22 on: April 11, 2020, 10:41:40 10:41 »

if u have a password for zip file sir.
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« Reply #23 on: April 11, 2020, 10:54:50 10:54 »

if u have a password for zip file sir.
For you and all the new members. An universal way to unlock files in this forum. Is the forum name in lower case. The name only, not the full internet adress
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« Reply #24 on: April 11, 2020, 12:04:59 12:04 »

another adjustable regulated psu circuit link.

if help full plz give me a thank you.

Posted on: April 11, 2020, 11:55:23 11:55 - Automerged

For you and all the new members. An universal way to unlock files in this forum. Is the forum name in lower case. The name only, not the full internet adress

sir i can't understand how to unlock password protected zip file
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« Reply #25 on: April 11, 2020, 01:37:27 13:37 »

sir i can't understand how to unlock password protected zip file
The name of this forum is sonsivri. Try that Smiley
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« Reply #26 on: April 12, 2020, 08:03:24 08:03 »

 
The name of this forum is sonsivri. Try that Smiley


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« Reply #27 on: April 23, 2020, 02:56:43 02:56 »

I purchased a few of these power supplies recently and found they were surprisingly good, especially for the price.  They also include the unusual capability of limiting power output.  The 0-30V 5A version was US$60 and the 10A version was $100 (but 10A version is sold out).  I haven't tried the USB software remote control features yet. 

Model: HM305P/HM310P

Output Voltage: 0-30V four digit display

Output Current: 0-5A four digit display

Power Effect:

--Voltage:≤ 0.1%+5mV

--Current: ≤ 0.03%+3mA

Load Effect:

--Voltage:≤ 0.1%+5mV

--Current: ≤ 0.01%+10mA
 Ripple:

--Voltage:≤ 20mVrms

--Current:≤ 100mArms

Display Resolution:

--Voltage: 10mV

--Current: 1mA

https://www.amazon.com/gp/product/B07SPYF8ZW/
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« Reply #28 on: August 21, 2021, 01:20:04 13:20 »

I found on a Russian forum very well optimized design he also added voltage and current regulation through voltage reference  based on TL 431 the author of the power supply also publish a article in Russian magazine prakticka elektronika scan copy of article attach a youtuber made this supply and shared his experience link given.

https://www.youtube.com/watch?v=M36MDYnTRRw
  
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« Reply #29 on: August 22, 2021, 08:31:52 20:31 »

HI All

Here is analog device latest 75 Watt, Single-Output Bench-top tracking Power Supply design!!!!

you can buy the board , add a micro , or just use a potentiometer to adjust current and voltage

https://www.analog.com/en/design-center/reference-designs/circuits-from-the-lab/cn0508.html?ADICID=some_NA_P328165_LinkedIn_IMG_CN0508

All the best

bobi


 
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« Reply #30 on: November 20, 2021, 03:18:46 15:18 »

I have built a couple of the RIDEN RD6006 power supply kits using their box and my choice of switching supply to put in the box. They work as advertised for the application I wanted. (Initially as a current controlled supply for anodizing aluminum.) I havent actually looked at the ripple output, but I suspect it is mostly determined by the SMPS I selected.

The price on BG is ~$67USD,  so after a case & SMPS, Im not sure the cost matches those complete supplies in earlier posts from Amazon. I think I paid a good deal less a year or so ago.

The RD6006 is here:
https://www.banggood.com/RIDEN-RD6006-or-RD6006-W-Digital-Control-Switch-Adjustable-Power-Supply-DC-Stabilized-Power-Adapter-Buck-Module-Monitoring-Power-Supply-p-1587151.html?rmmds=detail-left-hotproducts&cur_warehouse=USA&ID=6279943

One thing I always ask myself before starting a project like this is.
Do I want to design power supplies or do I want to use power supplies? An honest self-answer can save a lot of time. This also applies in many other areas. Some years ago I had a need for a CNC mill to do a paying project. I spent some time evaluating all of the kit stuff available for various bare bed mills. In the end I bought a complete mill from Tormach for the job. Paid off the mill with work in < 6 months and never looked back. Im glad I realized early that I was a user not a builder of mills!
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« Reply #31 on: April 26, 2022, 06:22:25 18:22 »

I found on a Russian forum very well optimized design he also added voltage and current regulation through voltage reference  based on TL 431 the author of the power supply also publish a article in Russian magazine prakticka elektronika scan copy of article attach a youtuber made this supply and shared his experience link given.

https://www.youtube.com/watch?v=M36MDYnTRRw
  

The main problem of this design and derivatives, including similar power supplies with 723 ic, is the negative auxiliary summing voltage ( used to achieve a 0 volts output). The zener diode determines the whole temperature coefficient of the output voltage.
 
An improved option would be to use a low-dropout regulator 3.3volt or 5 Volts IC instead of that zener.

Regards,

kreutz
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« Reply #32 on: April 27, 2022, 07:59:20 07:59 »

The main problem of this design and derivatives, including similar power supplies with 723 ic, is the negative auxiliary summing voltage ( used to achieve a 0 volts output). The zener diode determines the whole temperature coefficient of the output voltage.
 
An improved option would be to use a low-dropout regulator 3.3volt or 5 Volts IC instead of that zener.

Regards,

kreutz
During the worst Covid boredom I did make a discrete LM723 type power supply.
http://www.sonsivri.to/forum/index.php?topic=68701.msg199426#msg199426
However I did not come around to build a working model of it. But the simulation show that I at least was on the correct track (perhaps)
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« Reply #33 on: April 27, 2022, 05:23:57 17:23 »

During the worst Covid boredom I did make a discrete LM723 type power supply.
http://www.sonsivri.to/forum/index.php?topic=68701.msg199426#msg199426
However I did not come around to build a working model of it. But the simulation show that I at least was on the correct track (perhaps)
I did play with your design and like you say it works well in simulation, The last time I worked on mine I have it all working laid out all the PCBS got all parts here just need to get back into it and order the PCBs For it and finish off the software for it. If I get time I may have ago at building and playing around with your design in the link you posted. Need to give myself a kick up the back side and get motivated
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« Reply #34 on: April 27, 2022, 11:30:05 23:30 »

Please, see: https://www.youtube.com/watch?v=2w4cR8D8WJ4
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« Reply #35 on: April 28, 2022, 04:10:33 16:10 »

I agree with the author in this video. The idea is kind of correct. But poorly implement. I have built and used many LM723 based adjustable power supplies. The fact that have not been able to go lower than two volt has not bothered me at all. 
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« Reply #36 on: April 28, 2022, 07:07:23 19:07 »

I am sure this problem can easily be fixed by dropping in a standard voltage (2.5 V) TL431 in place of the zener. Alternatively, using a low-voltage  regulator as mentioned. As long as the 431 shunts at least 1 mA, it will regulate very well.
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« Reply #37 on: April 28, 2022, 07:43:06 19:43 »

I am sure this problem can easily be fixed by dropping in a standard voltage (2.5 V) TL431 in place of the zener. Alternatively, using a low-voltage  regulator as mentioned. As long as the 431 shunts at least 1 mA, it will regulate very well.
Not that the LM723 is a bad regulator. But you can find a lot modern linear regulators that can go down to zero volt
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« Reply #38 on: April 28, 2022, 07:53:16 19:53 »

In its time, we used the 723 frequently in RF VCO designs because of its very low noise properties, which can help reduce phase and amplitude noise. The noise output of the chip is just a few uV's (100 - 10 kHz BW) with the recommended Cref capacitor. This noise can be reduced even more by using an external PNP pass transistor with the 723. The idea is that the noise of the PNP will be lower than the internal NPN follower.
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« Reply #39 on: April 29, 2022, 05:22:21 17:22 »

One way to get a zero volt output. Use a ICL7662 or LT1054 negative charge pump to get the negative reference voltage to feed your zener or negative regulator. A ICL7660 would work but does not like more than +10v
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« Reply #40 on: April 29, 2022, 07:41:42 19:41 »

Eh no...with that approach you will ending up injecting high frequency noise into your setup. The high frequency noise will be spawn from the internal oscillator charge pump. What you could do is to use a second low ampere transformer to create a the negative voltage and use a proper low noise voltage reference. For the negative bias. In a hobbyist setup this will be perfectly fine. Or just jeez realize that the LM723 although not a bad regulator ( it make even me feel young). It is outdated if you really need need power supply that need to go below 2 volt. Just use a more modern approach. It is plenty of ICs that can do the job job.
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« Reply #41 on: May 01, 2022, 03:17:09 15:17 »

............ Just use a more modern approach. It is plenty of ICs that can do the job job.

Some examples, please.
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« Reply #42 on: May 03, 2022, 06:06:47 06:06 »

Some examples, please.
Here are some suggestions. You should be able to insert a pass transistor(s) in all of these I think. They do not go down to zero volt except one I think. But They are able to go down to in the range of 0.6 to 0.4 volt. Do you really need to have lower output than that? Non of them are super expensive either
https://www.analog.com/en/parametricsearch/11459#/p5576=Output%20Current%20Monitor&p5574=36|45
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« Reply #43 on: May 03, 2022, 01:09:05 13:09 »

The one attached can be easily improved providing the right Vin with the right Current and the right heatsink.

Based on 2N3055 or TIP3055 can arrive at 7A and I suggest 35V as VMax.

I suggest to add 10K load on the output.

Just for info: From ST the TIP3055 is easier to be found.

'njoy & take care,

X!



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« Reply #44 on: May 03, 2022, 07:36:03 19:36 »

The one attached can be easily improved providing the right Vin with the right Current and the right heatsink.

Based on 2N3055 or TIP3055 can arrive at 7A and I suggest 35V as VMax.
Dude it is because of the shortcomings of this kind of voltage "regulator" . That they come up with the monolithic, or integrated, linear voltage regulator ICs eons ago. 
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« Reply #45 on: May 04, 2022, 07:01:33 19:01 »

One way is to use the higher current LM338T and combine it with some op-amps to form a current feedback control loop.
The circuit below show one possibility of implementing this idea. The current scaling gives 1V/Amp so the current limit setting can be  monitored on TP1 and the instantaneous current feedback on TP2. The scope traces shows the transient response with a 3 Amp current pulse load on the output.

R14 is not needed, but Proteus kept crashing without this in place. Something with the TL431 model.
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« Reply #46 on: May 05, 2022, 12:48:33 12:48 »

One way is to use the higher current LM338T and combine it with some op-amps to form a current feedback control loop.
The circuit below show one possibility of implementing this idea. The current scaling gives 1V/Amp so the current limit setting can be  monitored on TP1 and the instantaneous current feedback on TP2. The scope traces shows the transient response with a 3 Amp current pulse load on the output.

R14 is not needed, but Proteus kept crashing without this in place. Something with the TL431 model.
Have you made this in real world or just simulated it. I have only taken a sort look at it. But I have problems with your current sense setup. Mainly that that the voltage on the current sense resistor seems to have lower potential than the LM358 opamp grund point
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« Reply #47 on: May 05, 2022, 05:00:30 17:00 »

At this stage, it is just a design suggestion. The latest LM358's have been upgraded from the older design. You may improve the low end more by using the LMV358 (rail-rail), but it only works with 5.5 V rail, so it needs additional 5 V regulator.  With differential input configuration using the LM358, it will just limit the low current sensing to about 100 mA. Below that it becomes non-linear with about 70 mV error at zero. Naturally, using a negative supply of a few volts, will correct this error.

The diff amp needs well matched resistors of at least 1% tolerance or better for good performance. Alternatively, one of the feedback resistors should be adjustable.
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« Reply #48 on: May 08, 2022, 06:11:15 06:11 »

As a follow-up for those interested, I tested the current sense, and read-back function using a standard LM358. The circuit actually performed much better than predicted by the simulator, and I could get accurate readings down to as low as 13 mA through the 0.1 ohm sense resistor.  
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« Reply #49 on: May 08, 2022, 10:30:29 10:30 »

in my opinion there is a flaw in your design:
you are measuring the total current with R3, including the currents that are used by the LM358 / LM393 und the current through Q1.
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« Reply #50 on: May 08, 2022, 11:12:53 11:12 »

in my opinion there is a flaw in your design:
you are measuring the total current with R3, including the currents that are used by the LM358 / LM393 und the current through Q1.

Yeah it would be better to move R3 on the high side. It can be inserted between  LM338 pin 2 and and R1. This way the regulator will compensate for any voltage drop in the current sense resistor. However also this will introduce some errors. As it will pick up the current that flow into LM338 pin 1 and R13//RV1
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« Reply #51 on: May 08, 2022, 11:32:59 11:32 »

you can keep R3 on the low side, you just have to move it to the output so that it is only measuring the output current.
Of course you have to change the circuitry for the voltage regulation to compensate for the voltage drop.
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« Reply #52 on: May 08, 2022, 03:44:29 15:44 »

Yes, there will be an error offset current of about 11 mA coming mainly from the regulator idling current. I don't see this as a problem since most of the time such a 5 A capable power supply will be used and operated at higher currents where the 10 mA error can be ignored. The 120R (R1) min load resistor value can be increased to 220R, and that will drop the error current by 6 mA.  It is usually recommended to use a value that will ensure the 10 mA (worst-case) loading current (data sheet) for the LM338. If you use the higher spec LM138, it will have a worst-case of only 5 mA. It is meant to be a simple and cheap power supply, not precision type. The error can easily be subtracted with a little more effort and complexity.

Other changes to reduce the error current:
1) R1 - 220R
2) R2 -27k (need 1 mA min)
3) R10/11 - 10k or more
4) RV2 - 10k or more
5) R8 - 6.8k
6) LM138 ( 5 mA )
7) Use TLV431 (0.1 mA) with R2 =270k, but need to scale R10/R11 ~ 3; 33k/11k

Alternative to LM358 (LM7332 with R-R output)
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« Reply #53 on: May 08, 2022, 10:44:05 22:44 »

Makes sense but ideally, a device must be versatile enough to operate in a broad range of conditions. For example, many DC-to-DC converters cannot be stable if the load current is under a certain limit. We need to add a resistor to let them always face a tiny amount of current. Without these little tricks here and there they would not last very long.
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« Reply #54 on: May 09, 2022, 09:44:42 21:44 »

By adding a separate negative regulated voltage source of -5 V @ 20 mA, we can make it adjust down to zero. It also fixes the near-zero error of the opamp, and compensates out the steady error reading (adjusting P2) caused by the idling current of the regulator and other parts. Now the read-back of the true load current is linear down to zero.

It shows using the LM317 with current bypass transistor, but will work the same with the original LM338 without any bypass.

This auxiliary supply can be obtained from a small isolated DC-DC converter, connected to the 12 V rail, or from the usual capacitor coupled, charge pump used by other designs.  https://www.mouser.com/datasheet/2/670/pyse1_d-2821163.pdf

The DC-DC modules are not that tightly regulated (10% - load dependent), so you will need something with a 9V output and then add a small 5 V regulator, (LM78L05 or LM79L05).  
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« Reply #55 on: May 10, 2022, 12:12:38 00:12 »

Charge pump devices will fall short of satisfying any sort of current requirement other than that of a buffer stage anyway. With DC-DC converters there are regulated and unregulated ones. TI raves about one of theirs like this:

It is increasingly difficult for DC/DC converters to achieve tight output voltage tolerances driven by smaller
process geometries for new FPGAs, DSPs, and ASICs. As process technology advances, the performance
processors require tighter voltage accuracy and lower core voltages. Multiple factors need to be taken into
consideration when determining the output accuracy of a DC/DC converter. Most engineers stop at the
initial accuracy on the front page of the datasheet of the DC/DC converter. However, designers must
consider the tolerance of the voltage feedback resistors used by the following:
DC/DC converter
The ratio of the resistor divider
Routing distance and trace losses of the circuit board
Input voltage variations
Voltage ripple
Temperature swings
Load transients
Additionally, many designers will want headroom or margin to make sure the solution is always within the
tolerance expectation of the processor. The TPS546D24A was developed to help designers achieve
higher output voltage accuracy by actually specifying the output voltage accuracy, rather than the initial,
reference, or VFB accuracy.
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« Reply #56 on: May 10, 2022, 04:16:13 04:16 »

I don't think that the 20 mA requirement is too much for a charge pump. You will need at least 100 uF caps to do the job and 5 V regulator.

One important requirement of this type of charge pump connection, is that you need to have some load current on the output of the bridge, in excess of the maximum aux load current needed. It is a good practice to make this min current at least twice (40 mA in this case) of what the pump output should provide. Below it can be seen that if we sweep the load current (IG1) up from zero, you only get proper operation around 40 mA. With 0 mA load current, there is insufficient output.

Using dual diode full wave, with center-tap transformer you won't have this min current limitation. 
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« Reply #57 on: May 10, 2022, 04:39:08 16:39 »

here is some idea's from my side on LM317 CV/CC power supply

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« Reply #58 on: May 10, 2022, 05:59:27 17:59 »

Using the cheap LM358 at high gain (x100) will be a problem because of the input offset voltage spec of this part. This figure can be between 0.3 - 3 mV. So you may get a part giving an output error voltage between 30 - 300 mV. To help cancel this out, you may need one of the more expensive zero-drift opamps that is available. This particular model from National comes with about 1.7 mV programmed in.
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« Reply #59 on: May 10, 2022, 06:58:24 18:58 »

Using the cheap LM358 at high gain (x100) will be a problem because of the input offset voltage spec of this part. This figure can be between 0.3 - 3 mV. So you may get a part giving an output error voltage between 30 - 300 mV. To help cancel this out, you may need one of the more expensive zero-drift opamps that is available. This particular model from National comes with about 1.7 mV programmed in.
How often do you need your lab power supply to deliver below say .3 volt?
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« Reply #60 on: May 10, 2022, 07:08:29 19:08 »

The problem is with the current sensing circuit, not the power-supply  output voltage. With no load current, it may sense it as 172 mA. This reading can be as low as 30 mA or as high as 300 mA depending on the manufacturing spread on the part you get.
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« Reply #61 on: May 11, 2022, 05:31:44 05:31 »

Using the cheap LM358 at high gain (x100) will be a problem because of the input offset voltage spec of this part. This figure can be between 0.3 - 3 mV. So you may get a part giving an output error voltage between 30 - 300 mV. To help cancel this out, you may need one of the more expensive zero-drift opamps that is available. This particular model from National comes with about 1.7 mV programmed in.

there is well optimized LM317 power supply schematic in side the power board zip file also look at that
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« Reply #62 on: May 11, 2022, 05:54:51 17:54 »


here is Elektor answer to this video

https://www.elektormagazine.com/news/0-30v-ua723-based-regulated-power-supply
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