The feedback arrangement of typical switching regulators doesn’t allow the regulated outputs to go lower than the reference voltage. If you try to lower the output by modifying the feedback network, the compensation components the manufacturer recommends may no longer stabilize the regulator’s error amplifier. An external reference voltage helps overcome this problem. source

This document is an engineering report giving performance characteristics of a 24 W Flyback converter – 8 V @ 3 A. This design uses TOPSwitch-GX – an integrated IC comprising a high voltage MOSFET, and PWM controller.This document contains power supply specification, schematic, bill-of-materials, transformer documentation, printed circuit layout, and performance data. A photo of the power supply prototype is shown in Figure above.source

This is 3V/3A switching regulator by using LM2576-ADJ which is an adjustable output version of 3A Step-Down Voltage switching Regulator and capable of driving 3A load with excellent line and load regulation.You can change R1 and R2 for your desired output voltage.source