power supply circuit analysis

[Gaber Mohamed Boraey]

hello everybody, greeting for all

I've attached a power supply circuit which i am interested in , i have found in a book, the authors didn't say much about it, and i'm thinking to modify and make if possible, and if components available in market,
what i need help with, is how this circuit work?, on which principle of electronics engineering the designer rely on?
can you explain how it work?, how the transistors work?

regards

 

[barry]

Q1, Q2, Q3 form a triple darlington (a very high gain ‘super transistor’) pass transistor. Q5, Q6 form a ‘normal‘ darlington that provide negative feedback; as the output voltage goes higher, they pull current away from the pass transistor, keeping the output voltage constant.

I’m not quite sure how it works (too lazy to figure it out) but i think Q4 provides some kind of current limiting.

 

[Easy peasy]

Q4 is in parallel with Q3, ideally base resistors and emitter resistors needed for good sharing.

The overall ckt is not that flash, as the temp goes up the Vout will go down, there is no current limiting - so a short = bang.

For 10A out at low o/p voltages - real heat-sinking is needed - else => bang.

 

[BigBoss]

It's an expensive and inefficient circuit.
LM317+Pass transistor will work much better.

 

[barry]

The overall ckt is not that flash, as the temp goes up the Vout will go down, there is no current limiting - so a short = bang.

I do believe a fuse is a current limiting device

 

[KlausST]

Hi,

This circuit maybe is from the 1970ies.
It's output will drift with temperature. No electronic current limiting, may generate a lot of heat.
Heavy (4kg toroid transformer, so maybe total 6kg including heatsink and metal case), big, expensive (about 150€ only the transformer) and not good.

Now we have 50 years of experience, new techniques, new parts that make the circuit more precise, lightweight, useful.

What's the idea behind building such a device?

 

[betwixt]

I agree with Klaus's comments. The circuit is a linear adjustable voltage dropper which could under some settings dissipate 300W of heat so it needs big heat sinks and possibly a cooling fan. It has no voltage reference so will be prone to drift and it's voltage regulation is not only poor but varies with the voltage setting. Note that it requires 5W rated power resistors just to function, hardly efficient.

A simple LM317 with a similar 'loop around' current booster will cost less, use fewer components, be far more stable and if constructed properly will provide over-temperature shut down as well. It can even incorporate over-current protection while still not being more complicated than the original design.

Brian.

 

[danadakk]

A series of designs :

Hackaday

Fresh hacks every day

hackaday.com

Quite a few designs over here, but index searching is manual as the index is image :

POPULAR ELECTRONICS: Consumer Electronics and Experimenter magazine

Popular Electronics Magazine: 1954 through 1982 Consumer electronics and experimenter publication. All issues available for reading or searching.

www.worldradiohistory.com

https://www.worldradiohistory.com/Archive-Poptronics/Index-Popular-Electronics-1954-2003.pdf

Search for text in image : https://apps.microsoft.com/detail/9NJNV7SH2413?hl=en-us&gl=US

Microsoft OneNote can search for text in pdf image....


Regards, Dana.

--- Updated Oct 7, 2023 ---

Adobe cans search in pdf images, other utilities on web.

 

[Easy peasy]

@barry, " I do believe a fuse is a current limiting device "

your mastery of the English language lets you down a bit here - to what current level does a fuse limit current to ?

nope a fuse is either low R compared to the load, or open circuit compared to a fault level load

it does not and cannot limit the current to any specific level until after it has blown - when that level is zero - which is the trivial and unhelpful answer.

When it blows the current transcribes an arc of very high current, before falling to ( hopefully ) zero - so no limiting there either.

Per my earlier comment - a short = bang ( either of the fuse or the semi's or both )

Current limiting, and perhaps foldback, are extremely useful on a bench supply to prevent hours of circuit fixing for new circuits under run-up / test.

 

[barry]

@barry, " I do believe a fuse is a current limiting device "

your mastery of the English language lets you down a bit here - to what current level does a fuse limit current to ?

nope a fuse is either low R compared to the load, or open circuit compared to a fault level load

it does not and cannot limit the current to any specific level until after it has blown - when that level is zero - which is the trivial and unhelpful answer.

When it blows the current transcribes an arc of very high current, before falling to ( hopefully ) zero - so no limiting there either.

Per my earlier comment - a short = bang ( either of the fuse or the semi's or both )

Current limiting, and perhaps foldback, are extremely useful on a bench supply to prevent hours of circuit fixing for new circuits under run-up / test.

Um, my mastery of English is quite good, thank you very much. Perhaps you should open your dictionary and look up the meaning of "limit". Here, I'll do it for you:

Limit
2 of 2
verb
1
: to assign certain limits to
2
: to restrict the bounds or limits of

What do YOU think limit means?

 

[KlausST]

Hi,

Wikipedia says ( https://en.m.wikipedia.org/wiki/Current_limiting )
" Current limiting is the practice of imposing a limit on the current that may be delivered to a load to protect the circuit generating or transmitting the current from harmful effects due to a short-circuit or overload. The term "current limiting" is also used to define a type of overcurrent protective device. According to the 2020 NEC/NFPA 70, a current-limiting overcurrent protective device is defined as, "A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having compatible impedance."

Klaus

 

[barry]

Hi,

Wikipedia says ( https://en.m.wikipedia.org/wiki/Current_limiting )
" Current limiting is the practice of imposing a limit on the current that may be delivered to a load to protect the circuit generating or transmitting the current from harmful effects due to a short-circuit or overload. The term "current limiting" is also used to define a type of overcurrent protective device. According to the 2020 NEC/NFPA 70, a current-limiting overcurrent protective device is defined as, "A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having compatible impedance."

Klaus

This is confusing. You can’t “interrupt” current and also “reduce the current” (although interrupting it does reduce it to zero).

Look up “current limiting devices” and you’ll find FUSE in the list.

But this is just a stupid argument over semantics. I’m moving on.

 

[KlausST]

You can’t “interrupt” current and also “reduce the current”

I don´t know either.

Maybe something like this:
When a (usual) fuse trips .. it interrupts the current.
When a polyfuse trips ... it reduces the current.

Klaus

 

[Easy peasy]

The problem here is - a raw fuse as shown in the ckt diagram will not protect the semi's, unless the I^2T of the fuse is less than half that of the semi's

A 10A fuse will sit at 20A for quite some time before it goes open - there is no hard limit at all.

 

[Easy peasy]

@barry:

or: current - limit.