During the on-time of the switching cycle, the inductor (L1) is charged by applying the supply voltage across the inductor. During this time the output capacitors (C2 and C3) are supplying the load. During the off-time of the switching cycle, the energy stored in the inductor is transferred to the output capacitors and the loads. The LM2595 is regulated off of the negative output. The positive output is regulated because of the coupling between the windings of the inductor. The diode D4 prevents the ?12V output from the going positive above a diode drop during the turn-on of the circuit. The diode D1 is used for providing isolation between the output and the input. LM2595 operates at a switching frequency of 150 kHz resulting in small inductor and capacitor sizes.