Minimum off time of L6562 BCM PFC controller

[treez]

Hello,
In light load, BCM boosts go to high frequency. This should be limited by the controller.
Why does the L6562 datasheet not give the minimum off time?
(its a fixed off time controller)

L6562 datasheet
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00003316.pdf

 

[treez]

Page 16 of the L6562A BCM Boost PFC controller datasheet states that a bias winding is not necessary for the L6562A.....and a simple “RC method” can be used instead...........why does it say that the ‘RC method’ even works when the mains peak voltage is just below the output voltage?......why bothering stating this?, i mean, why wouldn’t it work in that situation?......and even if vout was lower than mains peak, ...so what?.......would that mean that the RC method would not work?...and that a bias winding would be needed?

L6562A
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00151385.pdf

 

[treez]

The following st.com application note shows an L6562A being operated in simple constant off time mode :clap: ..........This allows us to have a settable maximum operating frequency... :clap: ..so no matter how light the load goes, the operating frequency does not get ridiculously high. :clap: I cannot understand why they only offer this use of the L6562A as a sort of aside....i mean, its clearly better than the “usual” Critical conduction mode method of operation. Why is constant off time mode not the main method of control for the L6562A?

L6562A in constant off time mode App note.
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00195418.pdf

 

[treez]

https://shura.shu.ac.uk/14289/1/Al-...omparisons between CRM and CCM PFC (VoR).pdf

...the above is an article from a UK university on the difference between CRM and CCM PFC. What a waste of the 15 mins i just spent reading it. The article barely scrapes the surface.
Thank goodness for forums like this.
It concludes that ccm has two feedback loops, crm only one........yes, but the interesting point is what are the ramifications of this.....just stating it is pretty useless.
The missed point there is surely that in CRM PFC you can more easily get a fast-ish transient response whilst still being PFC'd. Also, it said nothing of the relationship of the bandwidth of the I AND v feedback loops in ccm pfc.
I am amazed that such an article has been allowed to be published from the post grad centre of a UK university.
The article failed to even mention the situation with CCM PFC going into DCM in lighter load.