Buck Converter Feedback Loop - Stability Criteria

Question 1 :

I am having some trouble understanding the Stability criteria of the Buck Converter Loop Stability which says, "The cross over frequency should be less than 1/8th or 1/10th of the switching frequency ".

Can someone tell me with the switching frequency pulse waveform and the cross over frequency waveform - on why the cross over frequency should be less than 1/8th or 1/10th of the switching frequency.

I think it would be clear if someone shows me the waveforms of the switching frequency and the crossover frequency and explain with the above criteria.

• The Switching Frequency is the PWM frequency. You get the cross-over from the open loop bode plot (google it). Good answer for the frequency ratio here: electronics.stackexchange.com/questions/126568/… Commented Oct 30, 2020 at 8:07
– user220456
Commented Oct 30, 2020 at 8:21
• Sorry there are no waveforms to compare, the PWM plot would be in the time domain and the loop gain is in the frequency domain. I can't explain it any better than the answer in the link I provided. Realize that you must have a good understanding of loop stability criteria to understand the answer to the frequency ratio question. Commented Oct 30, 2020 at 8:41
• You asked this same question a while ago. What's the difference with this newer question? Commented Oct 30, 2020 at 9:13
• In the earlier question, I didn't ask for waveforms. In this question, I am asking how the switch frequency waveform will appear and how the cross over frequency waveform will appear. Because the stability criteria says,"Cross over frequency must be less than 1/8th or 1/10th of the switching frequency". Since, switching frequency can be visually seen as a PWM waveform, I'd also like to visualize how the cross-over frequency waveform would look like. And from where is this cross over frequency waveform generated?
– user220456
Commented Oct 30, 2020 at 9:56