Answer 2—If you look carefully, the only difference between them is which side of the output capacitor is grounded. You can use the same circuitry to create positive or negative voltages by simply providing a switch, as shown below.

Of course, this diagram ignores the issues related to measuring the output voltage in order to provide feedback to the circuitry that controls the switching element. This is addressed in the next question.

Contributor: David Tweed