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.