To modern electronic systems, even the most simple by single chip microcomputer and a single I/O interface circuit composed of electronic system, the switching power supply voltage is usually made up of + 5 v, + 12 v, +15 v or + multiplex composition and so on, and for more complex electronic systems, more practical use of supply voltage. At present many voltage combination is mainly composed of the following:
+3.3v,+ 5v, + 12v, +15v,18v,24v,27v,60v,135v,300v etc...
(including a demand more than the same switching power supply voltage of the system), etc. Different electronic systems, not only for the above all kinds of voltage combination has strict requirements, but also to the switching power supply voltage of the electrical characteristics are more strict requirements, such as voltage accuracy, (current) output voltage of the load capacity, voltage ripple and noise, start delay, rise time, recovery time, voltage overshoot, the power delay time, step load response, step linear response, cross regulation, cross interference, etc.