# 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/… Oct 30, 2020 at 8:07
• Thank you for the comment, I already saw that question and answer. Could you please provide an answer with the waveform explaining your answer? It would help a lot for my understanding
– user220456
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. Oct 30, 2020 at 8:41
• You asked this same question a while ago. What's the difference with this newer question? 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
Oct 30, 2020 at 9:56

## 1 Answer

Please check out this article which will explain in detail Designing Compensator Networks to Improve Switching Regulator Frequency Response.

I felt this link is useful.

• This answer currently seems to fully rely on a link to answer OP's questions. Consider adding some minimum, important details from the link which will answer the question. This way, the answer will still remain useful even if the link becomes dead later. Also consider quoting the page number or chapter / section / figure number in the link which will answer OP's question. In its current form, a reader will not know if the linked resource is a very large document and where to look for the answer to this specific question.
– AJN
Nov 1, 2020 at 6:02