What is the difference between a negative linear regulator and a positive one?
I'm assuming you're asking why you can't just use a configuration like this?







simulate this circuit &ndash; Schematic created using CircuitLab

I used to wonder the same thing. The reason this doesn't work is that a positive linear voltage regulator does not like sinking current. If current ever goes into the out terminal of a voltage regulator, it will at best stop regulating and at worst completely break the regulator. As such, negative voltage regulators, which are designed to sink current at their output rather than source it, are used instead, like this:







simulate this circuit

(n.b.: I've left off the capacitors from these circuits just to keep them clean and to the point. Of course you would actually need input and output capacitors for each regulator.)