You want 600 va ? But that means 90% effeciency !
That means you must use switch mode .

You must choose an ungapped ferrite core with 2000 or more MU ,

it will need litz wire on output ( simply use smaller wire and mo
strands ) .
Tiny cores will easy do 600 watts .
MJE13005's are the most popular but the Cxxxx ( 2SCxxxx)
equivalents are seen more cause all are built in China .

You will see all switch mode pow supplies changing to single
drive , for they are just as eff as push pull , and cheaper .
Thery self oscillate ! Control circuit simply pulls down the Base
of bipolar Xisistor to adj output voltage .
It is a myth that more power can be sent to output using push pull !
All low end switch mode PS are using single transistor and if you
measure
the Xformer and other parts , SURPRISE , it is same size and cheaper
to build and its also an easier circuit to control ! Simpler parts .
You still need a volt ref and Opto and a LM393 to sense current .

The myth started when they said the dead time would waste time
but as we EE's know the dead time dont exist ! And we dont have to
control it as LM494 crowd must do !

Its a simplification made in heaven , no compromises al all .
You simply dbl up the Primary winding transistors !
Remember ! Transistors in class D dont worry about balancing !
If standard PCPS has push pull using 2 each C2335/or MJE13005
i simply put them in parallel ! Same power output !
Of course in dumpster diving , you will need to be clever on the
2ndaries to get same voltages

Dont be put off , this is so simple it should be used in school
to teach . You will be amased at how many parts are tossed out !


BTW Free OpSys for PDA . I'll buy a ARM Eval board (
www.littlechips.com)
and create a Forth like integrated OpSys , call it NewForth for now .
Wanna learn to do top System software ? Follow me .....



Mark Fortune wrote:
Greetings to the collective.

For my next project I want to build a bench power supply and do away
with this old switch mode AT computer PSU that i'm currently using.

The design I have in mind will be pretty beefy, giving a wide range of
fixed and variable output voltages (i'm thinking from -50v up to +50)
and deliver up to 5amps of current. if my estimates are right i'll need
a 600va+ (100v * 5a + overhead) transformer to do the job well. Now i've
had a look at some transformers in this range, and they're a little out
of my price range. so now i'm considering building my own.

The specifications I need are as follows:

primary: 0-230v @ 50Hz
Secondary: 60v-0-60v
secondary output current max: 5A

I have an intermediate understanding of transformers, but have never
actually built one, hence I am seeking advice from those with experience
in this field.
So where do I start? what type of core is best for this application? - I
have a friend who's blasting off that toroids are best, but i'd like a
second opinion, and what kind of wire to use for the primary and
secondaries? what are good safety practices regarding insulation? Is
this even a feasable project to undertake (moreso on the money side than
timewise). Any other advice also greatly appreciated.

regards,
Mark