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What circuit do you have that needs a negative supply?
An opamp or an audio power amplifier has its output at half the total supply voltage so that the signal can swing equally up and down. If the total supply is positive one plus a negative one then half is 0V so the input is also biased at 0V.
If the total supply is only positive then the output should idle at half the supply voltage so the input must be biased at half the supply voltage and an input capacitor, output capacitor and feedback capacitor couples the AC but blocks the DC.
These schematics show the difference: