Electronics > Beginners

Power supply | need help deciphering the schematic

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Wallace Gasiewicz:
wasadedoc and kim christensen have good points about the first "zener."   
But the voltage on the other side of the 120K resistor should be higher. Perhaps about the normal VCC of the op amp.   Perhaps the voltage thru the first transistor is brought up by the base resistor of 12K and then the op amp can take over control.
The two zeners setting the VCC of the second op amp are confusing. I would think that ONE 15 V op amp would be the correct voltage?    I looked at the original article, I do not speak German. Perhaps two smaller value zeners are used to get 15 V.     
Let us know if  it works!
Edit:
If your instructor wants you to build it, it is a good bet you will get a better grade if you do as he says!   
I do not think this is a great Lab PS but it is quite interesting
.

Pixelmarth:
It won't be "graded" but it's meant to be a learning experience :)

For now I'm gonna do some tests with a 741 instead of the 761 (which I don't have).
I might just build a PS with different components altogether  :-//



--- Quote ---There is only reason to build your own PSU - to learn how it works. After this you would throw it away and buy ready made.
--- End quote ---
Haha, you're right, it's for learning. I want to know what the first transistor does and also why zeners are used instead of just resistors.
I've been playing around with the second opamp in falstad https://tinyurl.com/2cdho3pa slowly grasping the concept.

Kim Christensen:

--- Quote from: Pixelmarth on April 12, 2024, 12:53:47 pm ---For now I'm gonna do some tests with a 741 instead of the 761 (which I don't have).
I might just build a PS with different components altogether  :-//
--- End quote ---

Try a LM321 instead of the LM741. Or a LM358 (It's a dual so you'd make a sight mod to the circuit. Or you could be wasteful and use 2) These will work OK, but will limit the upper output voltage as I explained before.
The problem with the LM741, is that it's inputs don't work all the way to ground like the LM358, 321, & 324, do. This will mean that you won't be able to adjust the supply output below apx 3V if you use a 741.
What other OpAmps do you have available to you besides the 741?

Pixelmarth:
T_T actually that the only one I've got, but I'll try to get my hand on the LM321 or 358 as you mentioned, there shouldn't be a problem. I bought the 741 without knowing too well what it could do  |O
It's my first time working with opamps so I'm learning by doing. can't hurt!
I'm looking at this: https://www.joretronik.de/Web_NT_Buch/Kap3/Kapitel3_2.html#3.2.6 Image below

Wallace Gasiewicz:
If you are going to solder things together on a board, use sockets for the op amps so you can switch them easily.

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