This is a circuit that can generate dual plus/minus regulated voltages from a single unregulated floating supply, such as from a wall-wort or a single-winding transformer supply with no center-tap, and requires no additional virtual ground circuit. The trick is that the low drop-out regulators used can either sink or source current. Thus, for example, if the positive current drawn is more than the negative current, the bottom (negative) supply can sink the current difference to maintain regulation. A typical regulator can only source current, so would not regulate under those conditions.
Below is an LTspice simulation of the current, showing the two output voltages for a large step change in the plus output current, which generates no significant change in either output voltage. (V2, R9, Rld1, Rld2, and S1 are just for test purposes.)
The regulators can provide up to 400mA of current with proper heat sinking. Also along with the LT1118 adjustable output version, there are fixed voltage versions LT1118-2.5, LT1118-2.85, and LT1118-5.0.
Note: See the Updates for a variation using the LM317.
Dual Regulated Supply from Single Voltage
Dual +/- Regulated Supply from Single Floating Voltage source Using Two Identical Regulators
- Dual Supply Using Virtual Ground Circuit Jun 23, 2015