The most common type of inverter is an analog inverter. Inverters are used in a wide range of applications, from small power supplies for a computer to large industrial applications to transport bulk power. An inverter can have one or two switched-mode power supplies (SMPS).
Simple inverters consist of an oscillator driving a transistor that is used to interrupt the incoming direct current to create a square wave. This is then fed through a transformer to produce the required output voltage.
More efficient inverters use various tricks to try to get a reasonable sine wave at the transformer input, rather than relying on the transformer to smooth it. Capacitors and inductors can be used with the inverter to smooth the flow of current into and out of the transistor. This method results in an output that is called a "modified-sine wave". Modified-sine inverters may cause some loads, such as motors, to operate less efficiently.
More expensive power inverters use Pulse Width Modulation (PWM) with a high frequency carrier to more closely approximate a sine function. The quality of an inverter is described by its pulse-rating: a 3-pulse is a very simple arrangement, utilizing only 3 transistors, whereas a more complex 12-pulse inverter system will give an almost exact sine wave. In remote areas where a utility generated power is subject to significant external, distorting influences such as inductive loads or semiconductor-rectifier loads, a 12-pulse inverter may even offer a sport ter, "cleaner" output than the utility-supplied power grid.