Discrete Regulated power supply

[techguru]

Hi to all,

I got this circuit from youtube , I cannot understand  current control action .

1) what are the transistor which will control the current because there is a preset in  collector of T7 transistor and potentiometer in base of T7?

2)correct me if i am wrong, T1,T2,T3 form single transistor compund configuration(sziklai pair).

3)what is the function of T4 transistor?

My answer is T4 transistor supplies current to the base of compund transistor.

4)how current limiting function is implemented?

Thank you all...

[ledtester]

FWIW, here's the youtube video about this supply:



The video says the circuit was published in Elektor Electronics around 20 years ago.

The explanation of how current limiting works begins at around 4:10 in the video.

[AG7CK]

T4 is a driver. As you say, based on the signal from the error amplifier T5-T6, it regulates the series element T1-T2-T3 by draining current from bias resistor R1.

T1-T2 is a pure PNP Sziklai pair. Add T3 to this, and it becomes a NPN compound transistor. D1 keeps T1 biased.

T7 is the current limiter. It acts by inhibiting the driver T4. It measures the voltage from base of T3 to output, and when the current is large enough, it turns on and raises the voltage on R2 which makes the driver drain current from R1, lowering the base of T3 and hence lowering the ouput voltage.

[schmitt trigger]

Many years ago, an electronics magazine had a section called "DANDY": Discretes are not dead yet.

There were many simple but clever discrete circuits, like this one, that would perform surprisingly well.

[cellularmitosis]

Hi to all,

I got this circuit from youtube , I cannot understand  current control action .

1) what are the transistor which will control the current because there is a preset in  collector of T7 transistor and potentiometer in base of T7?

2)correct me if i am wrong, T1,T2,T3 form single transistor compund configuration(sziklai pair).

3)what is the function of T4 transistor?

My answer is T4 transistor supplies current to the base of compund transistor.

4)how current limiting function is implemented?

Thank you all...

Thanks for starting a thread, I had seen that video recently and was quite curious to try this circuit out.

[james_s]

That does look cool, I might have to build a couple of those sometime.

[Cliff Matthews]

They posted an update with 2 series pass devices, but don't hunt for a 2.4v zener when TL431's are everywhere.

[techguru]

thank you all.

Still i am not clear, T7 does the operation of current limiting function. T7 is a PNP transistor where its emitter has to be at higher potential than collector. We see that schematic shows the base of T3 and emitter of T7 are connected together and we have series of resistances at the emitter of T7(as well as Base of T3).

what is the condition of for making T7 to switch on for Diverting T4 base current?
V_EB=V_E-V_B=should be 0.8V to swith it on to steel base current of T4.

Could any one explain me with some real time situation of with certain condition of current limiting function to occur?

[JS]

They posted an update with 2 series pass devices, but don't hunt for a 2.4v zener when TL431's are everywhere.

Be careful about those vids, I saw a couple and they have some mistakes. The CC video has quite a few wrong schematics.

JS

[Cliff Matthews]

@JS - Agreed. Eg: emiter resistors - open the zip and the PCB silkscreen has one at .1 and the other at .22 - Duh.. But if anyone wants to build one, they should be able to spot these sloppy errors (I'd hope..)

[JS]

@JS - Agreed. Eg: emiter resistors - open the zip and the PCB silkscreen has one at .1 and the other at .22 - Duh.. But if anyone wants to build one, they should be able to spot these sloppy errors (I'd hope..)

I saw "emmiter" resistors on the collectors on the simplified schematics from the video, she says open when transistor closes or enter in active operation, etc.

JS

Enviado desde mi LG-M250 mediante Tapatalk

[Cliff Matthews]

@JS - I didn't see that, are you referring to the output transistors?
BTW, "she" is only the voice of their English channel. FWIW, I have taken an interest in promoting good YT content, and have tried to help them out periodically with their literal translations. Eg: "power rails" she refers to as "shoulders" 

(Aunque los Rusos son como Cubano's agarrando cualquier recurso pa' inventar, son brutos (como yo) pa' charlar sobre el asunto)

[techguru]

Is the Schematic has error? If it is, Then how could be corrected?

[JS]

@JS - I didn't see that, are you referring to the output transistors?
BTW, "she" is only the voice of their English channel. FWIW, I have taken an interest in promoting good YT content, and have tried to help them out periodically with their literal translations. Eg: "power rails" she refers to as "shoulders" 

(Aunque los Rusos son como Cubano's agarrando cualquier recurso pa' inventar, son brutos (como yo) pa' charlar sobre el asunto)

Those things connected to the resistors looks like collectors to me!
Second pict, more like 1.5A to infinity and beyond (current limit or thermal shout down, more likely).
Third, kind of the same, but no specs, this time till smoke.

I figured wasn't a girl, I didn't intended to mention she as such but it seems I did it anyway. Translation mistakes might be happening to me as well, but also from english to Spanish as I do most of my electronics in english, many times I don't know how things are called in spanish.

Is the Schematic has error? If it is, Then how could be corrected?

I don't see any obvious errors in the schematic you posted, in any case not the best lab PS out there, while it has all the parts I wonder about stability and regulation, among others. Really nice circuit to understand BJT transistors working in different ways and interacting with each other, much better than your first emitter follower, applaud for being interested in analyzing it. If you are aiming to build something there are many other projects out there, maybe not as simple but might also be better.

I'm with a project for designing such thing, I started with a CC and CV dummy load, which behaves quite nice in the simulator by now. I builded and tested the first version and it was ok. Now I'm in the process to convert it to a power supply, or doing something similar to that circuit but optimized for PSU, which needs different characteristics as it's interacting with the DUT in a different way. If you look at the schematic you'll see many different feedback paths, tweaking all of them for a fast response with little overshoot and without stability issues under various loads is tricky, I think I got it. That's why LAB PSU are quite complex devices. I intend to finish this project and make it as flexible and well documented as possible, and being able to use cheap and easy to get components is one of my goals. While I'm also thinking for precision, swapping some opamps and compensation networks should improve things quite a bit, so I'm probably going to roll a few boards with different options. I leave you a link if interested.
https://www.eevblog.com/forum/projects/cccv-dummy-load/

JS

[techguru]

thank you all..


If any body is having discrete regulated power supply with variable current and voltage control, please share here. so that i will construct the one.
once again thank you.

[Zero999]

They posted an update with 2 series pass devices, but don't hunt for a 2.4v zener when TL431's are everywhere.

If you're going to use the TL431, you might as well connect the pass transistor in the feedback loop, so the IC is performing the regulation.


http://www.tij.co.jp/product/jp/TL431/datasheet/applications_and_implementation#SLVS5434039

[schmitt trigger]

BTW, "she" is only the voice of their English channel. FWIW, I have taken an interest in promoting good YT content, and have tried to help them out periodically with their literal translations. Eg: "power rails" she refers to as "shoulders" 

(Aunque los Rusos son como Cubano's agarrando cualquier recurso pa' inventar, son brutos (como yo) pa' charlar sobre el asunto)

If you want to have a good laugh, read some Chinglish translations. Or for that matter, some early Japanglish ones.

Your Spanish phrase is very good...including the slang use of pa' instead of para. However, Cubano's should go without the apostrophe: Cubanos.

[HoracioDos]

If any body is having discrete regulated power supply with variable current and voltage control, please share here. so that i will construct the one.
once again thank you.

Please keep us informed. As I don't have the knowledge to spot errors in schematics I would prefer to invest my time in circuits that work. I don't trust internet anymore.

[schmitt trigger]

Since the circuit is so simple and all-discrete, you may want to give it a try on LTSpice, and read the .DC operating points.

Before actually building it.

[HoracioDos]

Since the circuit is so simple and all-discrete, you may want to give it a try on LTSpice, and read the .DC operating points.
Before actually building it.

You are right  .

[IanMacdonald]

As in other thread, problem with variable resistor P4 in -ve feedback line is that if it goes O/C even momentarily, your device under test gets BLAM! from max output voltage. Since this may be very short duration -a tiny bad spot on the track- you might not know why things are being blown.

[JS]

As in other thread, problem with variable resistor P4 in -ve feedback line is that if it goes O/C even momentarily, your device under test gets BLAM! from max output voltage. Since this may be very short duration -a tiny bad spot on the track- you might not know why things are being blown.

It's not supposed to be moved around a lot, just to fix the max value, so an internal trimmer, much less likely to fail. Also it could be replaced with a fixed resistor. The every day voltage adjustment should be done by moving P1.

JS

[HoracioDos]

Hello!
I tried to model the circuit with component's original names and I changed a few things. I'm sure there are some mistakes, please be kind.
Thanks!

[techguru]

Thanks a lot.

If any one has a current control circuit with discrete circuit,Do post here. If it explains the operation well and good. Thanks you all

[HoracioDos]

This version has a TL431 and a pass transistor. I adapted the TL431 model from Eugene Dvoskin to match SCR symbol pins and I avoided to import an .asy file. I'm as dangerous as a thornbush brandished by a drunkard. I don't know if that part of the circuit is correct. R6,R10,R11 are not calculated. Output seems to be correct but perhaps it's just a coincidence.

[HoracioDos]

While looking for PSU circuits with passive components I found this one.

from
https://www.homemade-circuits.com/how-to-make-versatile-variable-voltage/
It's a simplified version of a previous one. I liked this site very much.

PS: I guess it can be mirrored like this one to get positive and negative voltage.
https://www.homemade-circuits.com/0-to-50v-0-to10amp-variable-dual-power/
Is there any policy about linking content between sites?

[HoracioDos]

Here is Ltspice model for Nuno PSU. Voltage output raises very slow and there's no ripple. It will take me a while to understand how the BJT network works in both circuits and how to choose different kind of loads in ltspice. I found Kicad schematics and PCB for this one.

PS: if someone arrives to an improved and working version, please post it here.

[not1xor1]

While looking for PSU circuits with passive components I found this one.

from
https://www.homemade-circuits.com/how-to-make-versatile-variable-voltage/
It's a simplified version of a previous one. I liked this site very much.

PS: I guess it can be mirrored like this one to get positive and negative voltage.
https://www.homemade-circuits.com/0-to-50v-0-to10amp-variable-dual-power/
Is there any policy about linking content between sites?

ROTFL
"Ripple free, with less than 1Vpp" 
and 0-100V  with a 2N3055? 
and just Vbe as V reference...   

that would have been a really bad project even 50-60 years ago
now there are no excuse for such rubbish 

just forget it

[HoracioDos]

ROTFL
"Ripple free, with less than 1Vpp" 
and 0-100V  with a 2N3055? 
and just Vbe as V reference...   
that would have been a really bad project even 50-60 years ago
now there are no excuse for such rubbish 
just forget it

I see. I still don't have the skills to spot these things. Internet fooled me again, but it makes me wonder what I did wrong because I didn't see the ripple. I will check it again.

[blackdog]

Hi,

All i see is schematics who do not care about phase marging...
Like the schematic with 1000uF at the output, this must be a joke... 

Power supply's are not simpel!
Can you build a good powersupply with discrete components, yes!, but you need to follow the same rules as with a opamp power supply.

Anyone who wants to build power supply will have to learn what phase margin and gain margin is.
And do dynamic testing. :-)

Kind regard,
Blackdog

[HoracioDos]

Lol. Where can i hide? I was playing with some silly values to see if they make any difference. I should have fixed it before posting.
PS: When I read your comment for the first time about 1000uf cap on the output I thought it was the 10000uf cap in the input after the bridge rectifier. That's the one I ment. Output capacitor is not mine.....

[Cliff Matthews]

Elecktor had something basic back in '82 - should make you feel better.
http://www.retro.co.za/zs1ke/projects/PrecisionPowerSupply/PrecisionPSU-Elektor-Dec-1982.pdf

[not1xor1]

Hi,

All i see is schematics who do not care about phase marging...
Like the schematic with 1000uF at the output, this must be a joke... 

Power supply's are not simpel!
Can you build a good powersupply with discrete components, yes!, but you need to follow the same rules as with a opamp power supply.

Anyone who wants to build power supply will have to learn what phase margin and gain margin is.
And do dynamic testing. :-)

Kind regard,
Blackdog

I think the 220µF capacitor connected to the collector of Q2 is even worst than the output capacitor.

[not1xor1]

I see. I still don't have the skills to spot these things. Internet fooled me again, but it makes me wonder what I did wrong because I didn't see the ripple. I will check it again.

I guess you did not see any ripple because you were testing with no load or little current load and the 1mF output capacitor can easily take care of that.

I think the first circuit showed at the start of the thread is much better although I would change it a bit with a couple of current sources and check better the open loop response. It is probably overcompensated.
But there is no way a single 2N3055 can provide 0-38V/0-3A.
It looks like somebody just do not have any idea about power dissipation, SOA, etc..

Another good source of discrete components PSU schematics could be the service manuals of of old (50-60 years ago) bench PSUs.

[blackdog]

Hi not1xor1,

Yes, its and, and bad   
First short circuits and gone is the 2N3055 

The 220uF capacitor has a good funtion, and that is to keep the current trough R3 (Basis Q1) free of hum.
A extra resistor between C3 and Q2 would resolf a big part of the extra pole.

But... it is still bad! 

The Elektuur design from december 1982 is a bit slow but a good design to start.
It is not to difficult to make it better, but won't advise this for this beginners section.

Kind regards
Bram

[not1xor1]

Hi not1xor1,

Yes, its and, and bad   
First short circuits and gone is the 2N3055 

The 220uF capacitor has a good funtion, and that is to keep the current trough R3 (Basis Q1) free of hum.
A extra resistor between C3 and Q2 would resolf a big part of the extra pole.

But... it is still bad! 

The Elektuur design from december 1982 is a bit slow but a good design to start.
It is not to difficult to make it better, but won't advise this for this beginners section.

Kind regards
Bram

I do not agree about the 220µF capacitor. It affects the transient response much more than the output capacitor.

The right way to reduce the ripple in that kind of circuit is to use two resistors instead of just one (i.e. R1).
For instance a 1.5k resistor plus the 220µF capacitor would reduce by a fair amount the ripple, while another 1.8k resistor would improve the transient response.

Besides that ugly circuit, the Elektor circuit diagram, is affected by the same problem. Even just 4.7µF is enough to produce a really ugly transient response.
That capacitor was probably added as an afterthought because that circuit oscillates badly without it.
It is just a matter of ignorance. The BJTs composing that sort of sziklay configuration are badly polarized and do not work at their best.

Just a couple of resistors between the base and emitter of T1 and T2 make the circuit behave properly and the 4.7µF (C2) capacitor is no longer necessary to avoid oscillations while the transient response is greatly improved.

There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.


Elektor schematic LTspice circuit simulation (current limit removed)


Output ripple at 2.5A load


The ugly transient response from 100mA up to 2.5A


The current through the 3 output BJTs


Better BJTs polarization and a little improvement in transient response


Modification of the compensation network and better transient response

[HoracioDos]

It's very interesting to see how analysis and improvement is done.
Could you please tell transient and load parameters.
Thank you very much.

There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.

I'm interested but I don't want to take advantage of your generosity

[techguru]

thank you  not1xor1 sir,

                      As a student give me the path by which you have acquired this knowledge. No text book worries about gain and phase margin.

[not1xor1]

It's very interesting to see how analysis and improvement is done.
Could you please tell transient and load parameters.
Thank you very much.

There are other bad design choices and other possible improvements in that Elektor circuit, but I'll leave that to another future post, if anybody is interested.

I'm interested but I don't want to take advantage of your generosity

I do not have much time at the moment.
Anyway I found a good solution to make a simple yet better current limitation circuit. I also replaced the two zeners with a TL431.

According to LTspice the circuit even behaves nicely at turn-on and turn-off with the output voltage increasing/decreasing slowly.

In a couple of days I hope I'll be able to post a zip with the various models and test circuits.

[blackdog]

Hi,

No Spice for me, just solder. 

I hackt the schematic and below you can see the result for now.


Selecting and measuring the transitors with a cheap China meter, handy!.



Testing the current source and the zener with a variable power supply to see how mutch the zener voltage wil change.



I am now about half of building the circuit, the transistors 1 and 2 in the schematic are tight together for better thermal behavior.



I have adapted this version so that I can supply 22V and 2-Ampere.
If the circuit works, I will test the dynamic behaviour of this circuit.
The reason for using a modern power transistor is that it will then be easier to keep the circuit stable.
I have to confess that I have never built a Power Supply with a Darlington that has three transitors.
Probably there will be another HF stop resistor around this transitor.

Because I would like to have a reasonable noise / hum free design, the number of parts used is increasing rapidly.
And also three extra diodes for safety.

But be aware that with two opamps and a TL431 you can make a better power supply! 
Why then all that effort to even build it, because I like to keep everything discreet and also just to play with it...
Depending on my work in the coming week, I will show the outcome of the above schematic.

Kind regards,
Bram

[blackdog]

Hi!


Yes i had some spare time today, to hot to go outside here in Amsterdam 

Schematic update:



And this is the Power Section, build on a CPU heatsink, everything short wired.



Almost done, only the ground and de +bar on the bottum side.



Not yet cleaned and missing two wires like i expland, row-01 (ground) and row-18 (+)



Shoot @ It!

Regards,
Bram

[Cliff Matthews]

@Blackdog - I've seen 2SC5200 in audio amps.. OK you twisted my arm  Digikey has them at $2 ea. if I buy 10.

Thanks, I am looking forward to see your perfections on this design sir - great work as usual!

[blackdog]

Hi Cliff,

Do not order or buy anything, let me first do some tests...

Circuitboard cleant with IPA and a old toothbrush, i hope is stays this way 


Heathsink mounted with a Ty-Wrap.



Frontview of the testsetup.



Backside.



And now its time to doe some work!
Later more.

Kind regards,
Bram

[Cliff Matthews]

Looking good!  (Q6 needs a label correction though, details details..)

[HoracioDos]

For those who might be interested. I hope I didn't make any mistake while copying the schematic.

PS: I've fixed the schematic around 6.2V zener as it will be seen next

[blackdog]

Hi HoracioDos, 

Of course you made at least 1 mistake! 
Back to the drawing board, the parts around the 6.2V zener are wrongly drawn.

Thank you for showing this spice setup!

Kind regards,
Bram

[HoracioDos]

Of course you made at least 1 mistake! 
Back to the drawing board, the parts around the 6.2V zener are wrongly drawn.

Thanks Bram! I'll try to fix it and I'll upload it again in the same post.
PS: Done!

[HoracioDos]

Hello.
This is the model for the elektor 1982 PSU. Simulation lasts forever. I can't find the problem (I'm pretty tired right now). I wanted to see if the LM741 can be changed to a TL071. Model and the LM723 part are inside the zip file. I'll be grateful if someone makes it work.

[not1xor1]

Hello.
This is the model for the elektor 1982 PSU. Simulation lasts forever. I can't find the problem (I'm pretty tired right now). I wanted to see if the LM741 can be changed to a TL071. Model and the LM723 part are inside the zip file. I'll be grateful if someone makes it work.

that is the classical Harrison schematic:
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1962-07.pdf
The LM723 is used just as voltage reference. You might use any other reference in the simulation.

BTW you can find many useful informations about power supplies in this really interesting application note of HP/Agilent
http://literature.cdn.keysight.com/litweb/pdf/5952-4020.pdf

[Cliff Matthews]

Hi Cliff,

Do not order or buy anything, let me first do some tests...

Circuitboard cleant with IPA and a old toothbrush, i hope is stays this way 


Heathsink mounted with a Ty-Wrap.



Frontview of the testsetup.



Backside.



And now its time to doe some work!
Later more.

Kind regards,
Bram

Will we be privileged to see your finished product? (and maybe any final schematic/asc corrections?) 

[blackdog]

Hi Cliff Matthews,

I am currently busy with the work and administration involved.
Some measurements have already been made and of course it generates. 
But not at a frequency you would expect.

The power supply is easy to set up and to load with 1 or 2 Ampere, so that works.

But debugging takes a lot of time, and I don't have that available now, probably next week.
A bit of patience please 

Kind regards,
Bram

[schmitt trigger]

Blackdog;
I really like your prototype assembly techniques. They show you took the time to lay out things properly.

I specially like your "copper clad chassis". Very ingenious! And it makes a good ground plane too.

[GigaJoe]

So what the goal ? mediocrity PSU on 2 transistors ?  I may sound sarcastic , but really it not 80x  when find some opamp like to find a precious gemstone
for a zener need const curr, and diff amp need  const curr as well - to minimize pulsation

[blackdog]

Hi GigaJoe, 

I have already explained in this topic that with two opamps you can make a much better power supply.
But also that I like to work occasionally with discrete's, just for fun.

And not to forget, I am still learning from it!

I've already placed some extra "stopping" resistors here and there to avoid oscillations.
At a certain load and output voltage, oscillation occurs around 45 MHz! 
Touching the collector who is grounded from the differential amplifier, changed the frequency and level, total length of this wire 1.5cm!
Welcome in the world of small fast modern transistors...

A good reason to not do it this way 

Some pictures
Testing with a Heatkit dummy load.


The red circels are ground wires, all change the oscillation frequency.
Blue circle, wextra power decoupling off the board, can be removed again.
Small pink circle, collector is now connected via en small 100 Ohm resistor to ground.


Later more.

Kind regards,
Bram

[GigaJoe]

OK, got it, even pay attention on circuit, that i missed ...
does osculation happens when current limiter involved ?  That usually a problem with all compensating VR, current pushing regulated signal down, when in the same time a second half trying to compensate it ... that when oscillation happens.
so need to change signal on input of diff ampl.


 

[GigaJoe]

silly ideas:  dif amp - darlington,   output from a zener going to another zener - that would be a vref;

[mike_mike]

Hello,
Is there any way to add more than 2 power transistors in the attached schematic ?
I don't need more output current, just more power transistors in parallel. It is enough to add more transistors with emitter resistors in parallel or I need to make other modification ?
The maximum output current set by P3 will be 5A and maximum output voltage set by P4 will be 27-28V.

[not1xor1]

Hello,
Is there any way to add more than 2 power transistors in the attached schematic ?
I don't need more output current, just more power transistors in parallel. It is enough to add more transistors with emitter resistors in parallel or I need to make other modification ?
The maximum output current set by P3 will be 5A and maximum output voltage set by P4 will be 27-28V.

yes, you can 
that PSU is already so bad that there is no chance you can make it worse 

[Cliff Matthews]

@not1xor1 - If he adds one or 2 more, shouldn't he at least upgrade the PNP driver to a TIP42c or similar?? (Ic = 6a)

[IanMacdonald]

Yes, I would advise a TIP42C as a more substantial driver. You could also look at using 2N3773's instead of the 2N3055s. They are not much more expensive and are quite a bit higher rated.  Especially in voltage. (Which matters more than it might seem because the current handling of a transistor drops off quite rapidly as you approach its voltage rating - known as secondary breakdown.)

Other useful mod is that you can make P1 and P2 'bad wiper safe' by adding a high value resistor from the wiper to the minimum volts/current end. Say 220k. This will ensure that the supply goes to min output instead of max if the wiper goes open circuit.

[not1xor1]

@not1xor1 - If he adds one or 2 more, shouldn't he at least upgrade the PNP driver to a TIP42c or similar?? (Ic = 6a)

  NO because mike_mike wrote:

I don't need more output current, just more power transistors in parallel.

so the current required by the PNP driver would be approximately the same
the same because the maximum output current doesn't change, is just split among more BJTs
approximately because h_FE vs. I_C is not flat