How to isolate cabinet of a desktop SMPS unit from earth?

[debasisswan]

Hi,
I am trying to build a flasher to switch a load of 12V DC 2Amps in a variable cycle using a 555 basic circuit and a TIP 127 attached to its output as the switch. I am taking 12V DC from a ATX SMPS taken out of my old Desktop computer and trying to house the whole, flasher unit inside the SMPS cabinet.

The problem is, whole cabinet of the SMPS is not connected to 0V. DC but, some other line to go to earth point of mains supply. On connecting the earth line and 0V DC of the SMPS output is showing some kind of SHORT , switching stops working and the switching transistor of the 555 board gets too hot within no time.

Please help-
Regards-
Debasisswan



Is there any way to isolate the cabinet from the earth line and put the whole body of the cabinet to 0V Dc of the SMPS output? Please help.

[I_Daniel]

I hibernated for 17 years so my knowledge of abbreviations is not so good.
SMPS does this refer to a standard PC (Personal Computer) power supply?
If so to earth the board to the power supply earth is playing with fire. Using a PC power supply the O or negatrive line is any one of the black leads. Yellow is 12 volt + and red is 5 volt +

Incidentally the old L-shaped power supplies from old XT's make excellent five and twelve volt power supplies for charging batteries etc.

[debasisswan]

Hi,
Thanks. The issue is resolved. The body of SMPS is in floating ground fashion. So, I got 0V on the body and no need to isolate it from power line ground point. The fault was in my assembled board, not in SMPS.

Thanks again-
Regards-
Debasisswan