RE 28v swither psu
 

budgie wrote:
On Sun, 17 Aug 2003 03:54:19 +0100, "zindazenda"
wrote:

thanks for info peoples.....

2x12v computer psu is interesting but takes up too much space....
now i have more info i will try using the parts from a computer psu but with
modified/own stepdown transformer...going this way as it will be cheap..ie
ex psu costs 3gbp so if i kill it then so what!!

I assume the transformer will be similar just with twice (ish) the amount of
windings on the sec.and that i will have to add some R in the feedback crt
so that the pwm chip still sees 2.5v(ish) and prehaps remove the scr
overvoltage protection..OR i will make it unregulated.

Find out which winding is used for feedback/regulation, and leave it
alone - or consider replacing it with lighter gauge wire to obtain
more core cross-section for your 28V winding.

Now that's a good idea!

Also, if an AT type, usually the +5V winding requires a base load.

But it's less than 1A so the new wire could be quite thin, and the rest
of the core window is all yours to play in... thanks mate, that's set me
thinking...

Simon, there's also an interesting Australian radio club site that has
lots of in-depth information on modifying computer PSUs (sorry, I
thought I'd saved the URL, but can't find it - can anyone post the URL
please?).


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek