Noise and offset parameters are what will determine how the psu will be and whether the general purpose opamps are suitable.
Is 0.01V offset or error good enough on the Voltgage output?
Is 0.005V noise ontop of the output good enough?
If the asnwer is yes to both these, then the general purpose opamps should be good enough.
thanks for your concern, but you dont get me when i said i'm a suck arse on this. so here it is:
0.1V offset is good enough.
0.05V noise is good enough. 0.01V is better.
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Maybe I miss something, but the circuit looks weird.
Can you explain what you are trying to do?
what i'm trying to do (and what you should help me) does not yet exist in the drawing. its a voltage reference for the next "linear regulator circuit", everybody who watch dave's video knows about it.
I can see the stepdown converter for both positive and negative voltage rails, but the drive input is connected to a comparator comparing the preregulated output voltage to some other voltage. I don't see an oscillator or other components for generating the PWM signal.
this is "novel" "PWM on demand" SMPS pre-regulator
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the PWM is generated by the 393 whenever the preregulated voltage goes below Vpc+ (and Vpc- for -ve rail). dont mind too much on it, i'll take full responsibility on this side.
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And I don't see where you need the 0-50V signal.
it goes from Vrc+ and Vrc- to way beyond the boundary of the schematics drawing, page 2, does not yet exist.
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You already have a highside mosfet driver with a level shifter. By the way: You mosfet driver needs some improvement, because it drives the mosfet with 60V on the gate! Most mosfets only tolerate 20V.
you are right! i missed that thanks. i will ammend the drawing, maybe i'll shift the driver side to 15V rail. the note there: whats not shown is, i tested with 30V rail on IRF4905 on breadboard, my main concern was about the bjt driver (Hero999 setup). but i guess i've abused it with 30Vgs for no good reason, i think its still alive i hope. thanks.
A 50VA(50W) transformer will nowadays not be able give 50VA, they skimp on the magenetic which means as you get to the top limit, the magnetic core saturates and you cannot get the rated output. You need to over rate the spec of the taransformer to get the performance you want.
If a 50VA transformer is not able to supply 50VA into a resistive load, it is simply not a 50VA transformer.
Saturation has nothing to do with output current, it only depends on the voltage applied to the winding: The core gets only saturated if the input voltage is too high (for a fixed frequency with no dc bias). If you draw more current, there will be a larger voltage drop on the primary, reducing the voltage seen by the inductive part, so it satures less than at no load condition.
If you add a rectifier the transformer needs to be overrated, because of the high peak currents generated when rectifying the voltage. Those peaks generate a higher rms current than the avarage output current, so you have higher losses in the transformer compared to a resistive load. So for 50V 1A dc you need a transformer rated for at least 50V 75VA. 50Vac will give probably 75Vdc at no load.
thanks for the info. my transformer put ±63.2V on capacitors after rectification. but as i said, i will change the spec if the transformer or PSU performance cant take it, i'm no transformer expert anyway, only what i've tested empirically.