This example shows you how to make a selectable output voltage (3.3V / 5V / 12V) switching voltage regulator using the AP63200WU (2A current capability – but the approach works with any adjustable voltage regulator). The voltage can be selected using a three-way jumper.
The main trick here is to change the feedback network when selecting the output voltage.
One major mistake is to design the regulator so it doesn’t operate safely when the jumper is removed (for example, the output voltage goes to 12V or even up to the input voltage when no jumper is connected). In our circuit, when no jumper is used, the output voltage is 3.3V. We achieve this by using selectable (& optional) resistors in parallel to the bottom feedback resistor. The 3.3V feedback resistor is fixed.
Using a selectable-in-parallel-to-bottom-FB-resistor topology will always guarantee that the lowest output voltage will be selected when none of the optional parallel resistors are active.
