Switching Power Supplies A - Z

Chapter 2

How Inductance and Inductor Size Depend on Frequency

The following discussion applies to all the topologies.

If keeping everything else fixed (including D) we double the frequency, the voltseconds will

halve, because the durations t

ON

and t

OFF

have halved. But since ∆I is “voltseconds per unit

inductance,” this too will halve. Further, since I

DC

has not changed, r = ∆I/I

DC

will also

halve. So if we started off with r = 0.4, we now have r = 0.2.

If we want to return the converter to the optimum value of r = 0.4, we will now need to

somehow double the ∆I we were left with at the end of the last step. The way to do that is to

halve the inductance