" Vu Nhu Khanh wrote:
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Hi El.
It depends on how high an out put you want. If it’s a jump to 24 v then you will have to rewind the out put transformer. If it’s say about 7 or 8 volts most PC smps will give you a voltage adj pot. But remember the rectifiers especialy the ones for 5v line has very low piv(that’s peak inverse voltage,in case you’ve forgotten) in the region of 12 volts only, and the ones for 12v line couldn’t stand 24 volt level.Now if you have to have a,say 24 v supply and 12 and 5 too ! then do like I did on an CNC plastic molding machine. Choose a discarded PC supply which uses bridged switching pair. you can tell by confirming it uses TL494 power control IC since it’s not a flyback power s type rewinding the transformer should be no problem, refit it with higher power,high speed switching transistors (they operated at 40 Khz),leave the rest intact because you need a high power, REGULATED power supply right ?  .Now prepare another transformer (same size) wind 70 turn of 0,5 m/m for primary and 22/22 turns 0.8m/m for the sec.Locate the 105 to 225/250vac capacitor usually orange colored, one end should go to E/C junction of the power pair the other end goes to the transformer on board that’s the coupling capacitor ,duplicate the rectifier from there. If you want to just send me an email and I’ll send you detailed schematic in Protel format. The converted power supply I did still working after three years on round shift basis.
Good luck "

Hi all,
Do you have any e-mail address from Vu Nhu Khanh Registered Member ?
Any one know please tell me (khootk@pc.jaring.my) I need the detailed schematic for 8051 system.