I would like to convert a voltage of 230VAC in a variable voltage between 140VDC and 380VDC (0.6A max.)
I assume 230VAC to a bridge (with capacitor) that comes into a DC voltage of 325VDC. Then it goes in a buck delivers 140V output and everything is in a boost assembly 140VDC variable (at a current of 0.25A) 380 VDC (at a current of 0.6A).
Is this feasible with these simple editing Buck / Boost?
How to drive the gate of the mosfet? (VG input is 325V ...).
380*0.6 = 228W, ..I would do an LLC converter as you can get the fet drivers on integrated control chip....I wouldn't do a split section bobbin, but just do a tight coupled trafo , and a "separate" external "leakage inductor"
There isa good fairchilsemi.com app note...AN4151 or something similar https://www.fairchildsemi.com/an/AN/AN-4151.pdf
otherwise, do a 2 tran forward.
The LLC is best of you can put a boost pfc in front of it.
At 228W, if you don't have a pfc stage, then you will need a big cap bank after the mains rectifier, and your mains harmonics (3rd 5th etc) will be very high which is bad.
I'll try to change the switching frequency (100KHz at least see 500KHz) to reduce the value of the inductance.
For the N-channel mosfet, I just need to be careful VDS maximum (about 600 volts) and low RDSon.
The filter capacitor is calculated I guess (you set a default value?).
If I do not succeed I will look to the SEPIC configuration.
right, I see, floating load, yes that's a very good way.
Your fet will need rating to more than 600v as you know.
At 500khz, you will get massive switching losses in that fet.
So you do opto feedback?
SEPIC notes:
Remember sepic cap voltage need be greater than vin....so that's a big cap......or several in series. Remember with sepic and uncoupled inductos.....calculate the L-L-C resonant freq...then you do rc snub across sepic cap.
Rsnub = SQRT((L+L)/C), then Csnub = calc'd to be 1/(2.pi.Rsnub.Fres)
Also, remember current mode sepic above 50% duty need slope comp.....unless you do constant off time converter.
Make sure that your crossover frequency is either 3x greater than , or 3x less than, the L-L-C ringing frequency.
Make sure also that delta V on the sepic cap is no more than 5% of its steady state voltage.
Also beware start-up overshoot on sepic cap voltage.