Author Topic: Very Low Noise Preregulator for Benchtop Power Supply  (Read 46771 times)

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Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #50 on: April 03, 2015, 09:38:17 pm »
If you simulate the circuit from this branch, we can see that the capacitor at Base-Collector is able to slow down the turning off of the transistor and reduce the voltage overshoot. But the power dissipation in the transistor is too big.

Changing the transistor control when turning on in the middle of the half-period and turning off at zero crossing, to reduce the capacity of the B-C without the risk of spike. In this case power dissipation in the MOSFET is much lower.

What about importing the PCB design to KiCad and modify it in Github (open hardware? Please, I would love to see Open Hardware high qiality design of a linear adjustable bench lab power supply) I can try it, but not sure about my fails.

If you mean my project of linear power supply PSL-3604, it is a little different from the discussion here, since it does not have a pre-regulator. Instead, it has a multilevel supply. Unfortunately, neither KiCad nor Github not know.

PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline timofonic

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #51 on: April 03, 2015, 09:51:51 pm »


If you simulate the circuit from this branch, we can see that the capacitor at Base-Collector is able to slow down the turning off of the transistor and reduce the voltage overshoot. But the power dissipation in the transistor is too big.

Changing the transistor control when turning on in the middle of the half-period and turning off at zero crossing, to reduce the capacity of the B-C without the risk of spike. In this case power dissipation in the MOSFET is much lower.

What about importing the PCB design to KiCad and modify it in Github (open hardware? Please, I would love to see Open Hardware high qiality design of a linear adjustable bench lab power supply) I can try it, but not sure about my fails.

If you mean my project of linear power supply PSL-3604, it is a little different from the discussion here, since it does not have a pre-regulator. Instead, it has a multilevel supply. Unfortunately, neither KiCad nor Github not know.

KiCad is an open source EDA for PCB and schematic capture. These days CERN is investing on it and it's progressing faster than ever. It may be an Eagle killer in one year or less.

What software do you use? Are those SPICE simulations? Maybe it can be imported to KiCad.

GitHub is used commonly for Open Hardware and projects modified by a team with branches and final designs, similar to open software development methodology. Some propietary EDAs use a similar approach integrated in their software package, Open Hardware commonly uses Git for it and Github is the defacto standard.
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #52 on: April 03, 2015, 10:05:09 pm »
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline cellularmitosis

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #53 on: April 04, 2015, 05:45:03 am »
I've been interested in this topic lately (using a sine wave approach for low noise).

I just wanted to point out the TI SN6501 chip, which does exactly what you are proposing.  However, it is only good for a few hundred milliamps.

I've ordered a few and I'll throw them in my Dutch oven faraday cage and report back with some measurements.  Hopefully the results will be better than my ICL7660 efforts :). https://www.eevblog.com/forum/projects/an-evening-with-the-icl7660/
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #54 on: April 04, 2015, 07:47:38 am »
sorry i just have to ask, how does the LM317 work for this arrangement?

LM317 works here as a current source and provides a constant current load. Not a good idea, it is better to use the output of the voltage error amplifier and turn on the load current only when the output voltage must be reduced.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline blackdog

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #55 on: April 04, 2015, 07:48:31 am »
Hi 3roomlab,

The rectifier for the negative power supply will be changed, also the transformer in this schematic wil change.
This because i wil use the Fet pre-reg.
I need a negatif supply for the LM317, so that if the uitputvoltage is say 2V, the LM317 current source is stil working.
I will NOT use a swiching unit to maken a negatif voltage, its a low noise powersupply (at 5 amps, I was measuring less than 5uV noise at 20Khz bandwidth, yes Micro Volts)

The circuit with the LM317 current source remains in the circuit, these help to improve the dynamic behavior.
It always draws 57mA from the output and helpt at light loads to quickly settle the ouput voltage.


Kind regarts,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 
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Offline blackdog

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #56 on: April 04, 2015, 07:52:22 am »
Hi Liv,

LM317 works here as a current source and provides a constant current load. Not a good idea, it is better to use the output of the voltage error amplifier and turn on the load current only when the output voltage must be reduced.

I disagree, my extensive measurements show that this is a good way to get the response time to very low values.
The only negative thing I can say is this, it takes some power.


Kind regarts,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #57 on: April 04, 2015, 08:23:24 am »
Yes, additional power dissipation - a disadvantage. And yet - when you turn off the output necessary to turn off the current source, otherwise the output will be a negative voltage. In his scheme, I use MOSFET current source, which eliminates the need for a negative supply. And it turned on only when needed. Problems with the dynamics is not observed, it looks like a 2-quadrant PSU.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline Electroplated

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #58 on: April 04, 2015, 10:50:10 am »
HI,

I played around with the design trying different mosfets then changed the design to use npn transistors to explore the possibilities of using alternative pass transistors for my own reasons and is only at this stage a proof of concept, the design needs more work. I also had n channel mosfets in place of the npn darlingtons, only because I needed the two used in the original circuit on another project and will have to wait to restock.

I had this circuit feeding a LM317 regulator and it preformed reasonably good inside the constraints of the 317.

Attached diagram and scope shot, lower yellow trace, drive to Q3/Q4 upper blue trace, Thyristor gate waveform, neither are perfect but the waveforms are spike and aberration free across the full range of the LM317.

--
EP
 

Offline JohnnyBerg

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #59 on: April 04, 2015, 11:23:40 am »
the load is no longer there, there is some "window" of hysteresis there. maybe a more active "pull" circuit?

Well, a good PSU has a current source on the output, that forces a minimum current through the series element, to ensure that the output is quickly going down when needed.

With a large capacitve load that is still not good enough, so my PSU has some other neat stuff to do that :)
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #60 on: April 04, 2015, 12:35:35 pm »
i am starting to think the output side not only needs a push, it also needs a pull

True, the PSU must not only source a current, but sink it. In the simplest case this is current source, which is able to sink a certain current (e.g., 1/10 of the maximum output current). Such a scheme Agilent calls "Down Programmer". The next step - is to control both source and sink current. It may, for example, Agilent 6633A which has a push-pull output stage and two current control loops - both positive and negative.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline T3sl4co1l

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #61 on: April 04, 2015, 05:16:32 pm »
Last bench supply I built, I just made a beef-ass audio amplifier.  The 2N6059(?) outputs (so, it's quasi-complementary) are capable of dumping over 40A.  It would be a fine (sub)woofer amp in the 1-2 ohm range, and has a BNC input for analog use.  Most of the time, it's set to an internal TL431 reference and 10 turn pot, for 0-20V DC operation.  A consequence of the bidirectional output stage is, if you plug in a bypass capacitor to your breadboard, and it was still charged from a previous use, whether above or below the supply voltage, it will be charged or discharged in just the same manner.  Quickly. ;)

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Offline prasimix

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Blackdog's pre-regulator model...
« Reply #62 on: April 07, 2015, 04:33:47 pm »
If someone is willing to play with blackdog pre-regulator presented in this thread, here is the LTspice model...

« Last Edit: April 07, 2015, 04:35:48 pm by prasimix »
 
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Offline Thor-Arne

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #63 on: April 07, 2015, 05:24:23 pm »
Thanks, was planning to play with this in LTspice.  :-+
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #64 on: April 07, 2015, 05:40:37 pm »
The main advantage of this preregulator is simple control. I do not understand what interest to do simple design today. PSU can not be imagined without an integrated microcontroller which can implement the software control of preregulator, for example, using the PI-algorithm.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline Thor-Arne

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #65 on: April 07, 2015, 06:16:27 pm »
The reason for using a pre-regulator like this one is that it is not under software control.

IMO, microcontrollers is fine for it's use, but it should be limited to providing a set point for the regulator. All control loops should be analog to ensure that it's not affected by software lock-ups.
 

Offline blackdog

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #66 on: April 07, 2015, 06:27:10 pm »
Hi Liv


Que! >>  I do not understand what interest to do simple design today...

One thing i learnt is this, do not make things more complex than necessary!
CPU controled Power Supply's, almost never i use them for developement.
I use most the Dutch DELTA Linear power supply's (some 40 years old), and multiple power supplies of HP/Agilent.
And multiple power supplies of my own design.
All linear, no switchers and no CPU control, give me two multiturn potmeters for U and i, and i'am happy  :D
All are analog, and there is one exception, and that is the "DELTA ES-30-5", a nice low noise switcher.

A cpu controled Power Supply can be usefull, i know, but fore development only sometimes necessary. (i know, i know there are exceptions)

These characteristics I expect from a Power Supply
Simple to use, all my attention should go to test the circuit and not with the operation of the Power Supply.
The power supply may not have power On or Power Off aberrations.
The power supply must have a mute without On/Off aberrations.
The power supply must be kind to itself and the load.
Low Noise under all conditions <0.1mV 200Khz BW.
Fast acting no oscilation current limiting.

I can make the list longer, but i think you understand my point :-)

Just 2 cent's of low noise remaks  :-DD

Kind regarts,
Blackdog
« Last Edit: April 07, 2015, 06:58:52 pm by blackdog »
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #67 on: April 07, 2015, 10:20:39 pm »
One thing i learnt is this, do not make things more complex than necessary!

Amateurs make devices for fun. What a pleasure from simple circuits?
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline blackdog

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #68 on: April 07, 2015, 10:43:36 pm »
Hi Liv,

Thank you that you cal me a amateur...
You are intelligent enough to know that your comment is not true.
I like this one from Einstein: Make everything as simple as possible but not simpler
Som time's design's wil by complex, but complexity should not be a starting point in my point of view.

I have no problems with it, if you make your design's as complex as possible, because it give's you pleasure.


Kind regarts,
Blackdog
“Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe.”
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #69 on: April 08, 2015, 02:28:44 pm »
your comment is not true

This is not true for commercial projects where the cost should be minimal. But I do not understand why for fun for the hundredth time doing primitive PSUs using LM317. Modern PSU contains a microcontroller, has an informative display, advanced control functions. Even better - Intelligent Power Supply (IPS), where the feedback is closed software. Such projects are interesting to implement.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline schopi68

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #70 on: April 08, 2015, 03:17:20 pm »
Well... it is always easy to make things complex up to the boundary of human comprehension.
But really genious work is to make these complex things simple without sacrifying the result.  ;)

On the other side in my opinion a microcontroller-controlled PSU is a comprehensive, but not a complicated design.

Do you think of building just the preregulator or the whole PSU microcontroller based?
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #71 on: April 08, 2015, 03:46:17 pm »
I already gave the link here on DIY PSU (schematic) where preregulator controlled by a microcontroller, and it simplifies the circuit. The same microcontroller controls the entire PSU, although feedback in the analogue. This is an example of modern DIY PSU.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline schopi68

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #72 on: April 08, 2015, 09:24:35 pm »
Do you have any measurement values for this PSU?
I could not find information about items like Load regulation, rippe, noise, drift, transient recovery times, accuracy. Will a best of it's class "modern" PSU be able to compete in this parameters with a "classical" one?
 

Offline Liv

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #73 on: April 09, 2015, 10:07:21 am »
Will a best of it's class "modern" PSU be able to compete in this parameters with a "classical" one?

These parameters are determined exclusively by analog circuitry and "modern" PSUs are the same as for the "classical". There is no need to improve them, in the older PSU generations has been reached a sufficient level. Development goes the other way - easy control, enhanced display and advanced feature set. As an example - Rigol DP 800 series. Analog circuits are the same as in the old series. But there was a beautiful high-resolution display, which is served by a powerful processor. This is the current trend until DIY PSU, unfortunately, still behind.
PSU PSL-3604 Pulse gen. PG-872 Freq. cnt. FC-510
 

Offline schopi68

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Re: Very Low Noise Preregulator for Benchtop Power Supply
« Reply #74 on: April 09, 2015, 10:33:50 am »
These parameters are determined exclusively by analog circuitry and "modern" PSUs are the same as for the "classical". There is no need to improve them, in the older PSU generations has been reached a sufficient level. Development goes the other way - easy control, enhanced display and advanced feature set. As an example - Rigol DP 800 series. Analog circuits are the same as in the old series. But there was a beautiful high-resolution display, which is served by a powerful processor. This is the current trend until DIY PSU, unfortunately, still behind.

Maybe we are not talking about the same. :) I am interested in the possibilities of PSUs controlled completely by an microcontroller. This would also include the regulation path. If it is just about programming the output voltage i could easily use the remote programming feature of an 30 year old HP PSU and connect it to a microcontroller with a fancy front-end (resulting in a PSU with better data than most of todays devices).
 


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