Switching Power Supplies A - Z

Feedback Loop Analysis and Stability

Criteria for Loop Stability

We should remember that phase angle can start changing gradually — starting at a

frequency even 10 times lower than where the pole or zero may actually reside. We have also

seen that a second-order double-pole (−2 slope with two reactive components) can cause a

very sudden phase shift of about 180° at the resonant frequency if the Q is very high.

Therefore, in practice, it is almost impossible to estimate the phase at a certain frequency,

with certainty — nor therefore the phase margin — unless a certain strategy is followed!

Therefore, one of the most popular (and simple) approaches