Why do you need two linear regulators for split supply?
When wired up this effectively shorts the output of the virtual rail to the negative terminals. As such you need to be sure things are correctly isolated in your circuit and internal to the supply.
Can a split supply be used in an op-amp circuit?
They need a split supply. The output terminal has positive, negative, and ground. But most power supplies have only a single output (positive and negative). So, you cannot use them to power op-amp circuits.
How to make a split supply from a single supply?
Adding some load to the negative rail to ensure that it draws more current than the positive rail does is required to ensure regulation as the 7812 will not sink current. As Janka points out the positive rail will be unregulated. Here is a solution which uses two adjustable linear regulators (LM317/LM337) to form a virtual ground.
What are the values of a split power supply?
Most analog designers know how to use op amps with a split power supply. As shown in the left half of Figure 1, a split power supply consists of a positive supply and an equal and opposite negative supply. The most common values are ±15 V, but ±12 V and ±5 V are also used.
Which is the voltage reference for splitting a rail?
Splitting a rail using the voltage reference will often mean compromising a bit on the symmetry of the split, for example, if a 3V3 rail is to be split then the closest would be to use the 1.8V output reference, which gives a +1.8/- 1.5V asymmetrical supply.
How are power supplies isolated from each other?
RE ISOLATION Note the drawing below, both power supplies have their negative outputs ties to mains ground. When wired up this effectively shorts the output of the virtual rail to the negative terminals. As such you need to be sure things are correctly isolated in your circuit and internal to the supply.