In Figure 2-2, we see how the ac, dc, peak-to-peak, and peak values of the inductor current waveform are defined. In particular we note that the ac value of the current waveform is defined as

Figure 2-2: The AC, DC, Peak, and Peak-to-Peak Currents, and the Current Ripple Ratio 'r' Defined

We should also note from Figure 2-2 that I _L = I _DC. Therefore, sometimes in our discussions that follow, we may refer to the dc level of the inductor current as "I _DC ," and sometimes as the average inductor current "I _L ," but they are actually synonymous. In particular we should not get confused by the subscript "L" in "I _L." The "L" stands for inductor, not load. The load current is always designated as "I _O." Of course, we do realize that I _L = I _O for a buck, but that is just happenstance.

In Figure 2-2 we have also defined another key parameter called 'r,' or the 'current ripple ratio.' This connects the two independent current components I _DC and ? I. We will explore this particular parameter in much greater detail a little later. Here, it suffices to mention that r needs to be set to an "optimum" value in any converter usually around 0.3 to 0.5, irrespective of the specific application conditions, the switching frequency, and even the topology itself