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PC power supply to lab power supply

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How are you planning to gey the +/-9V out?

Are you going to add a pair of LM317/337s or a switching regulator on the output?

Are you going to modify the internal circuit so it outputs +/-9V?


New Member
I plan to use a 7809 and 7909 with a SPDT switch on the +/-12V output, to produce 9/12 volt interchangably (but using different output sockets), and add a slow-blow 1A fuse to the 0v output.


Fusing the 0V line is never a good idea.

Suppose the +12V line shorts to the -12V line?

The fuse won't blow.

The 0V rail is internally bonded to earth ground in the power supply. If the output shorts to the metal case or another earthed object like a metal radiator the fuse won't blow.

Put fusses on all the outputs you intend to use. The power supply should be protected against short circuit anyway but you never can rely one it.


Well-Known Member
That is such a badly built power supply.

Twisting the wires then bunging a bit of insulating tape over them is just asking for trouble.

He doesn't appear to include any load on the 5v or 12v rails which could also lead to instability with PC power supplies under low current conditions.
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