so here i am. Searching for a suitable power supply for my lab....i stumbled upon the desing of peter oakes and i watched the videos that explain the working principles but there are some things that bothers me.. but before here it's the link and the schematics.
https://www.element14.com/community/groups/test-and-measurement/blog/2014/09/15/the-modular-bench-power-system-the-essential-diy-build-for-every-ee-student-and-old-timer-alike so from what i've understood we are sensing the current through the shunt resistor and the voltage at the outputs with 2 op amps, comparing them with a setpoint (voltage from a pot or something else)...
and making the difference, then the integrators are going to ramp up or .....here it comes the tricky part....
1)the op amps can only draw current from the gate of the mosfet (but the mosfet is a voltage controlled device )because of the diode....and then what is supposed to to the zener there??
2)give a reference voltage to the gate and then the op amps drawing currrent are going to pull down also the voltage at the gate of the mosfet...??
3)nope thats not it because if we are putting a load that requires lets say 3 amps the voltage on the gate or VGS has to be bigger than when whe have lets say a 100ma load... how are the op amps able to feed voltage with that diode in betweeen?
so could someone explain this to me... anyways when putting the circuit on the breadboard ,... at the first attempt tyhe circuit didn't worked .. the voltage dropped around 4V even if it was set to 22V so i figured out that since the op amps can only draw current (am i right ?) the voltage should have benn provided by the zener
so i swapped out the 10K resistor of the zener with a 1K resistor and the circuit started working.
4) why did peter used a 10K resistor?if there are some kind of calculations behind the zener and all the stuff that are going on onto the gate of the zener could someone explain them to me or give me some hints ,, surely i don't want the dish already served.
5) why the output dosen't go all the way down to zero it is something related to the opamps?
then there is all the part about the mosfet..i will open another post... currently using a IRFP240 as opposed to a IRFP064 ..and for the ones wondering the op amps that i'm using are NE5532
for the reference a 7805(it will be replaced by something better) for the supply of the op amps 2 lead acid 12V batteries and for the main supply a 27V 11A meanwell psu (it will be replaced by a transformer diode bridge and caps)
tested with the 22ohm resisto thet you see on the fotho and the voltage is rock solid , checked with the oscilloscope and it didnt't overshoot, 220uF cap on the out opposed to the 1000uF
aiming for a lower capacitance around 50uF?
so that's all if there are something that i didn't explained well fell free to ask and yes english isn't my main language