Hi everyone, I want to start by saying that i'm at the first year of Electronics engineering and so i'm more or less a beginner in the field.
I wanted to start an ambitious project by building a variable power supply using stuff i have already laying around for the most expensive components. My goal is more or less a 0-40v 4/5A power supply with reasonable efficency and output ripple, and with 0.1V 50/100mA precision.
I was thinking to build a minimalistic syncronous buck converter on the rectified output of a 48v transformer by using two N-ch mosfets, an half bridge driver ic (like the IR2111) and controlled by a microcontroller pwm output. I really don't know a whole lot about switching converters, so please correct me if i'm saying something stupid, but it seems that managing the output ripple is a quite a challenge if you want to have a wide range of output currents, because since it is basically an amplified pwm signal with an LC low pass filter, if you want a small precise output current the output capacitance should be low or you risk to blow up stuff, and on the contrary if you want a big current the output capacitance should be higher to avoid an huge ripple to occur.
I searched for different solutions to this problem:
-"Big" output capacitor and a switchable dummy load on the output that automatically turn on if a small current is required in order to provide always a minimum current draw for the buck converter.
I rejected this idea because i would most likely using the power supply for 5v at low currents a lot of the times and so the dummy load would be on causing a terrible efficency.
-Linear regulator built around an LM317HV or a NPN darlington power transistor + an op-amp, controlled trough DAC by the microcontroller, and connect it in on the output of the transformer with a relay to switch between it and the buck converter. The idea being using the linear regulator for small currents and the buck converter for high ones. I also rejected this idea for pretty much the same reason as before since the linear regulator would pretty much always have to drop 43v to produce 5v.
I recently started to investigate more elegant solutions: like building only a fixed linear regulator and regulate the voltage on the primary side of the transformer with a triac, with the possible downside of producing huge noise electrically and even acoustically, or just building a variable linear power supply with a big heatsink and screw the efficency. Even if this last option was tempting, as there are already plenty of designs online, I really wanted to use a microcontroller in order to use rotary encoders,big led displays and dedicated ADC with hall effect sensor for precise current sensing, instead of potentiometers and chinese volt/ampmeter with crappy displays.So since i'm already using it I might just use one of the pwm output that it has and build for a more efficent switching regulator.
I found yet another design solution that has the potential to be the perfect answer to my needs but has little to none documentation online. I saw a tear-down of the MDP-XP power supply by Miniware, wich uses a buck converter to step the input voltage down to a little bit higher of the requested output voltage, and then a linear regulator to regulate the voltage precisely for the last bit. I think this design is very clever as it combines the efficency and high power rating of a switching power supply with the low ripple of a linear regulator, and so i would like to build something similar even if I admit the complexity of such a design scare me a bit.
I want to share those ideas to someone more skilled than me to get an advice on what to do, what do you think it's a good challenging design to replicate for a semi-beginner as I am?
thank you in advance for the answers, and sorry for the long post filled with bad english

(I forgot to add it before but yes,I know i need a negative voltage rail in order to get the linear regulator output down to 0v, when I settle on a design I will probably swap the big 48v transformer with something with a center tap, or maybe add another transformer).