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Help me design a PSU

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Efe_114:
schematic at attachment. I couldnt figure out how can i convert kicad to pdf and didnt see the attachment button down there and  converted it to jpg and tried with add image function and it didnt work and i finally figured out attachment button. first time sending something as attachment. so it took quite a while

fsr:
Well, you can capture the screen and save it to a PNG file, probably easier than exporting to PDF.

Why is that capacitor there? It doesn't seems like it can do much as it's connected. The voltage at the (-) input will be 2 Vbe below the opamp's output, no matter what.

Your circuit will buffer whatever voltage you have on the potentiometer's wiper, but if Vcc has noise, or ripple, or goes up or down, so is your output voltage. So, your output can only be regulated if Vcc is well regulated already.

At this point, you may want to take a look at how national made it with the LM317. I attached and image with the functional schematic. That's how they did a variable voltage regulator.
To get how the LM317 works, just remember that an opamp with negative feedback will try to set it's output voltage to a value that causes it's two inputs to match.

Kleinstein:

--- Quote from: Efe_114 on December 22, 2018, 06:52:24 pm ---schematic at attachment. I couldnt figure out how can i convert kicad to pdf and didnt see the attachment button down there and  converted it to jpg and tried with add image function and it didnt work and i finally figured out attachment button. first time sending something as attachment. so it took quite a while

--- End quote ---

The minimal circuit would need at least an extra resistor in the connection between the output and the OPs inverting input.

Efe_114:

--- Quote from: fsr on December 22, 2018, 10:58:55 pm ---Well, you can capture the screen and save it to a PNG file, probably easier than exporting to PDF.

Why is that capacitor there? It doesn't seems like it can do much as it's connected. The voltage at the (-) input will be 2 Vbe below the opamp's output, no matter what.

Your circuit will buffer whatever voltage you have on the potentiometer's wiper, but if Vcc has noise, or ripple, or goes up or down, so is your output voltage. So, your output can only be regulated if Vcc is well regulated already.

At this point, you may want to take a look at how national made it with the LM317. I attached and image with the functional schematic. That's how they did a variable voltage regulator.
To get how the LM317 works, just remember that an opamp with negative feedback will try to set it's output voltage to a value that causes it's two inputs to match.

--- End quote ---
but im not measuring referance voltage im measuring output voltage and i power a load output voltage rises up i dont mean the ripple, the ouput voltage rises.


--- Quote from: Kleinstein on December 22, 2018, 11:28:02 pm ---
--- Quote from: Efe_114 on December 22, 2018, 06:52:24 pm ---schematic at attachment. I couldnt figure out how can i convert kicad to pdf and didnt see the attachment button down there and  converted it to jpg and tried with add image function and it didnt work and i finally figured out attachment button. first time sending something as attachment. so it took quite a while

--- End quote ---

The minimal circuit would need at least an extra resistor in the connection between the output and the OPs inverting input.

--- End quote ---
i didnt know a resistor is needed. it says only a capacitor in art of electronics. not speccifically "ONLY" but it says a capacitor

Efe_114:
Whatever i tried i wasnt able to fix it  :-// |O. Any help?

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