So far, we have been implicitly assuming a fixed input voltage. In reality, in most practical applications, the input voltage is a certain range, say from 'V _INMIN' to 'V _INMAX'. We therefore also need to know how the ac, dc, and peak current components change as we vary the input voltage. Most importantly, we need to know at what specific voltage within this range we get the maximum peak current. As mentioned, the peak is critical from the standpoint of ensuring there is no inductor saturation. Therefore, defining the "worst-case" voltage (for inductor design) as the point of the input voltage range where the peak current is at its maximum, we need to design/select our inductor at this particular point always. This is in fact the underlying basis of the " general inductor design procedure" that we will be presenting soon.

We will now try to understand where and why we get the highest peak currents for each topology. In Figure 2-3, we have drawn various inductor current waveforms to help us better visualize what really happens as the input is varied. We have chosen two topologies here, the buck and the buck-boost, for which we display two waveforms each, corresponding to two different input voltages. Finally, in Figure 2-4 we have plotted out the ac, dc, and peak values. Note that these plots are based on the actual design equations, which are...