Power Sources and Supplies: World Class Designs

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Chapter 3

3.6 The Current Ripple Ratio r

In Figure 3.2 we fi rst introduced the most basic yet far-reaching design parameter of the

power supply itself—its current ripple ratio r . This is a geometrical ratio that compares

and connects the AC value of the inductor current to its associated DC value. So

r

I

I

I

I





L

AC

DC

 2

(3-10)

Here we have used  I  2  I

AC

, as defi ned earlier in Figure 3.2 . Once r is set by the

designer (at maximum load current and worst-case input), almost everything else is

pre-ordained — like the currents in the input and output capacitors, the RMS (root mean

square) current in the switch, ...