Switching Power Supplies A - Z

Feedback Loop Analysis and Stability

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Unlike an RC filter, the output voltage in this case can be greater than the input

voltage (at around the break frequency). But for that to happen, Q must be greater

than 1.

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Instead of using Q, engineers often prefer to talk in terms of the damping factor

defined as

damping factor = ζ =

1

2Q

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So a high Q corresponds to a low ζ.

From the equations for Q and resonant frequency, we can conclude that if L is increased, Q

tends to decrease, and if C is increased, Q increases.

Note: One of the possible pitfalls of putting too much output capacitance in a power supply is that we may

be creating significant peaking (high Q)