I have came across a few documents regarding current mode control of resonant LLC converters (although it is applicable to all kinds of bridge type resonance converters). See image below:
It states the LLC CS pin is used for sensing the current in the resonant converter, and it is used to set the "on-time" of the switch. First question is: how exactly is it sensing the resonant current? It is dividing down the AC capacitor voltage and sensing that. How is this reflective of the current through the resonant stage at all?
Secondly: What does "on-time" modulation mean? Does it mean changing the frequency? To me it seems like that would mean changing the duty cycle? Maybe it changes the frequency AND the duty cycle? I don't know.
Any help is appreciated. Here is the entire document https://www.onsemi.com/pub/Collateral/NCP13992-D.PDF.
It states the LLC CS pin is used for sensing the current in the resonant converter, and it is used to set the "on-time" of the switch. First question is: how exactly is it sensing the resonant current? It is dividing down the AC capacitor voltage and sensing that. How is this reflective of the current through the resonant stage at all?
Secondly: What does "on-time" modulation mean? Does it mean changing the frequency? To me it seems like that would mean changing the duty cycle? Maybe it changes the frequency AND the duty cycle? I don't know.
Any help is appreciated. Here is the entire document https://www.onsemi.com/pub/Collateral/NCP13992-D.PDF.