How to assemble a homemade constant voltage source?

Question

Batteries

Hello. I really want to assemble an adjustable constant voltage source, and so constant that the oscilloscope produces a straight line parallel to the horizontal axis. Of course, no matter how my perfectionist soul resists, you can’t get an ideal straight line, but still I want the frequency and amplitude to be extremely small.
My knowledge in the field of electrical and radio engineering is not extensive enough and a lot of explanations from Google are not very clear to me, no matter how hard I try.
What I understand:
1) a diode bridge is needed to reflect the negative part of the sinusoid to the positive region;
2) a smoothing capacitor is needed
3) voltage regulation can be implemented through an ordinary voltage divider.
What I don’t understand (or what confuses me):
1) The smoothing capacitor will still not allow the curve to be completely straightened, and the infinite increase in capacitance will not work as a result, since the capacitor will not have time to charge. To what extent does it make sense to increase the capacity?
2) I saw a circuit in which there was a two-stage transistor amplifier of an already rectified signal, but, as I understand it, the transistor thereby causes voltage fluctuations, which I do not need. Am I right? Or maybe this circuit is what I need?
3) The resistance of the voltage divider should be an order of magnitude less than the load resistance, but how to achieve this, because when installing low-resistance resistors, the current through them will be huge and they will burn out. And from this source, I planned, among other things, to check the LEDs, in which the resistance is extremely low.
4) Is it possible to apply any filters here to solve the problem?
If there are ready-made solutions, throw them in, but it’s still much more interesting to read the principle of operation of this scheme, and indeed the theory. Therefore, I will take links to good educational material only for joy.
PS Why do I need such an ideal source? No need. I'm just a perfectionist and I love everything perfect :)

Answer 1

the circuit
and in general the theory of circuitry is good at Horowitz Hill

Answer 2

Collect charging for li-ion for two cans, while one is on charge - the load is powered from the second, then the switching is reversed with a relay, something like this. Only one can is charged at a time

Answer 3

2) In the circuit, this is not a transistor amplifier, rather more in key mode. The transistor does not cause oscillation, but oscillates with it: the amplitude is greater, the transistor closes slightly, the amplitude is less - the transistor opens slightly.
the ideal line will be if the transistor is introduced by adjusting the variable resistor to a point where the output voltage is below the ripple voltage. then you get the perfect straight line.

Answer 4

Your circuit is correct, the key thing in it is actually a zener diode. Exactly a circuit with a pair of resistors and a zener diode gives a source of more or less exactly constant voltage (at low load currents and correctly selected resistors. Why is it so - see Horwitz and Hill, volume one). On transistors, a current amplifier (emitter follower) is assembled there. If you really want to suffer from perfectionism, you can also solder the third transistor there, but something tells me that with your measurement method (with a look at the oscilloscope) two will be enough for your eyes.

Answer 5

For maximum immersion in perfectionism, I recommend taking linear stabilizers with ultra-low noise. These are used to power the ADC and DAC, for example. Manufacturer, for example, TI. If you're interested, I'll find a brand. In this case, your perfectionism will be satisfied and you will get such an ideal straight line, the noise on which you will need to make out a very ugly oscill, which you need to look for.
In short, your perfectionist soul will be pleased! More straight lines give only, perhaps, batteries and batteries.