Switch-mode power supplies based on pulse-width modulation (PWM) have been in use since the early 1970s. One of their key circuit blocks has received relatively less attention, though: the second-order LC filter fed by the PWM wave. The role of this block is to extract the dc power embedded in the pulse train, and to suppress the undesirable harmonics to the extent possible. For the latter function, which is seen as a complex periodic ripple, it’s desirable to have a speedy approach capable of zeroing in on the steady-state ripple...
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