On Sat, 8 Dec 2001, Dave Dilatush wrote:

> Alexandre Guimar=E3es wrote...
>=20
> >    No getting back to the SMPS. I will have an application where I will
> >have to make a supply with 74 volts DC input and 24 v at 300 ma and 5 v =
at
> >30 ma. I am thinking about using 2 of your 2 transistor designs modified=
 to
> >the my specific needs. When I finish it I will let you and the list know=
 how
> >it goes and what modifications are needed.
>=20
> With those voltages and currents, why not use Russell's design to step
> the 74 volts down to 24, then Roman's circuit to step the 24 volts down
> to 5?  Russell's circuit is probably more suited to the high-voltage
> part of this thing, especially if you need 300 milliamps out of it.
>=20
  I wouldn't do it like this. For me sounds like a standard switching
supply using a driver ( tl494, UC3842 ), a mosfet or bipolar switch and a
transformer, then a good rectifying diode pair and finally a filtering
stage.
To increase the efficiency the driver could be supplied directly from
output voltage after the oscillation has begun.=20
I know that many piclisters are afraid about designing feritte core
transformers for switching supplys. So why many of you are using standard
coils. However for dedicated applications we need dedicated solutions.

Regards, Vasile

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