3kW SMPS

[artem_bond]

Hello all.

I'm a newbe in powerful SMPS design and I need a some help.

The first.
In example I have a IRF640 transistors 18A, 200V, RDS=0.18Om. It's
mean that using this transistors in full-bridge I's easy to make a 3kW
power supply? And static losses on Rds was 12*0.18=2.6 Watt. How big
was a switching losses? In case non-resonance SMPS at 50kHz? (I'm
using low-impedance isolated transformer for transistors)

The second.
Transformer. If course is much better is wending secondary directly on
the primary. But I will not do this because I need a 3kVolt and I
afraid discharge between primary and ans secondary coils. So, I have a
too choses. The first is wending primary in a one size of UU core and
secondary at another size. But I have a no idea about inductive losses
(proximity effect?). One people told me that losses was nearby a few
percent. Other people told me about 60%. Before I work only with EI
and toroids cores and I wending primary directly on the secondary. If
course I can make a bobbin with section and make a something like
this:
------------------------------------
Primary
------------------------------------
secondary
------------------------------------
Primary
------------------------------------
secondary
------------------------------------
Primary
------------------------------------
secondary
------------------------------------
Primary
------------------------------------
secondary
------------------------------------
but If losses was a not big I will make a separated bobbin with
secondary and primary coils.

************
**************
** **
** **
** ** S
P ** ** E
R ** ** C
I ** ** O
M N
A ** ** D
R ** ** A
Y ** ** R
** ** Y
** **
** **
**************
************



And also.
If I need a make 20kW power supply, I was read that the best choice is
using few small power supplies working synhronus. But I think is
possibly is using a few bridges working at one big transformer. Like
this
------------------------------------
Primary coil bridge 1
------------------------------------
secondary
------------------------------------
Primary coil bridge 2
------------------------------------
secondary
------------------------------------
Primary coil bridge 3
------------------------------------
secondary
------------------------------------
Primary coil bridge 4
------------------------------------
secondary
........
IMHO in this case parasitics losses can help spread equal power at all
bridges.

Thank for help, sorry for English.