>
> Hi Byron,

Hi. Glad you got back to me.

>     I started building my PSU before I got an inductance meter, I just
> guessed, wired it up and tried to pull lots of amps (this was just for a 5v
> rail at first), I got 10 Amps ok but the coil got a little warm (using 1mm
> wire) so I re-did it using 1.2 mm  and a bit less turns and it was fine.  At
> this stage I forked out the money for a good meter.  Instead of my 300uH I
> expected, I had wound 15mH !!  The circuit did not care.  Here is my new
> rule of thumb (or should it be little finger?) - find a torroid you can just
> stick your little finger through and each turn is about 15 to 20uH.
> Depending on your finger size and the composition of your torroid YMMV .

Well I tested with a 300uH coil. Got so hot it started to burn the cloth
cover. I decided to try a coil with the right amperage, so I bought a 50 uH
9.5 Amp coil. Works like a champ.

>
>     Because I am using external switching transistors rather than just using
> the LM2576 on its own as only a small proportion of  the total switching
> current is provided by it, because the transistor sees the acition it looks
> like you can do lots of 'bad things' like sloppy wiring guesswork caps,
> almost anything and get away with it.  My only real comment is to use a good
> diode (schotkey 16A 45V in my case) and fast transistor (2N5038).  I tried
> using a slow (mje2955) with an LM2577, and that killed the LM2577 :(

I used a schotkey 8A and couldn't locate a 2N5038, so I substituted a
Motorola 15003 instead. Works like a champ.

In fact I've finished the supply. I didn't cheat like you did and actually
put two more switchers for the negative voltages. I also ended up wiring
the 15V supply and regulating it with a 7812 regulator.

The machine boots and works fine. The only problem is that the sound really
bites. I may end up installing a better sound card using a horizontal
socket.

My next task is to get a keyboard and display working. This is where the
PIC comes in. I have a LED board that uses National DL1416 smart Alpha
displays (24 characters). Plan to hook it up to a PIC along with switches
and a MAX232, using the serial port as my connector.

Thanks for all the help.

BAJ