"Current mode" regulation of LLC Resonant Converter

Thread Starter

SiCEngineer

Joined May 22, 2019
238
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:

1601394703940.png
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.
 

Delta prime

Joined Nov 15, 2019
490
What does "on-time" modulation mean?
Hello there :) The ratio of ON time to the switching period time is the duty cycle. If I had a pulse width modulation power supply set to 60% then it will be off for 30% of the time current flows in the on time. Slow down! the answers to your questions will only cause further confusion. take smaller bites.
 

Thread Starter

SiCEngineer

Joined May 22, 2019
238
Hello there :) The ratio of ON time to the switching period time is the duty cycle. If I had a pulse width modulation power supply set to 60% then it will be off for 30% of the time current flows in the on time. Slow down! the answers to your questions will only cause further confusion. take smaller bites.
I understand, that was my assumption as well. But I do not believe it too common-place to have a duty-cycle controlled resonant converter in industry, sometimes it is seen in research papers as a fixed frequency approach. But I assume then, if they perform duty cycle control (limit 50%, min. 5% or so?) then they would also have frequency modulation alongside this - since it is a resonant converter after all - hope I am making sense!
 

Delta prime

Joined Nov 15, 2019
490
The questions you ask are far too common scroll down to similar threads they're in lies your answers. It's a good read and you get to learn the personalities of my superiors.
 

Thread Starter

SiCEngineer

Joined May 22, 2019
238
The questions you ask are far too common scroll down to similar threads they're in lies your answers. It's a good read and you get to learn the personalities of my superiors.
I do not see any topics that address what I am asking. If you can point me to a single similar thread that would be appreciated. I have been on this forum a while and do appreciate the sheer knowledge of the people that help less experienced engineers such as myself.
 

sparky 1

Joined Nov 3, 2018
332
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.
Historical approach 1959 Argonne national labratory.
The capacitor current. uses peak detection both maximum and minimum for each respectively I_C T1,T2 and I_C1 T3,T4
injection timing using capacitor bank current called acceleration and reset
Something like a duty cycle? No forget that. Timing cycle T1,T2 ... T3,T4 18.2 kA
Derived from man named Praeg at Argonne , He introduced a procedure on a synchrotron , He simplified it using laplace transform.
 
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Thread Starter

SiCEngineer

Joined May 22, 2019
238
Historical approach 1959 Argonne national labratory.
The capacitor current. uses peak detection both maximum and minimum for each respectively I_C T1,T2 and I_C1 T3,T4
injection timing using capacitor bank current called acceleration and reset
Something like a duty cycle? No forget that. Timing cycle T1,T2 ... T3,T4 18.2 kA
Derived from man named Praeg at Argonne , He introduced a procedure on a synchrotron , He simplified it using laplace transform.
hello, thanks so much for your comment. Is it possible that you could reword what you mean? I can’t quite understand what you are trying to say. Apologies!
 

sparky 1

Joined Nov 3, 2018
332
No apologies necessary very few can follow me.
A resonant power supply was made and published in 1960.
When you read it will make more sense, likewise easier to follow than me.
In 2020 after many revisions along with assorted BS engineering and consultation fees
companies can purchase resonant systems therefore reverse engineering is the most difficult approach.

I_C see figure 4 also see references
https://accelconf.web.cern.ch/p91/pdf/pac1991_0949.pdf
 

Thread Starter

SiCEngineer

Joined May 22, 2019
238
Here you go! :)
I have seen this before. And I have seen hybrid hysteretic control and know how it works. However the paper I have sent in this thread is NOT the same method. The block diagram states "on-time processing and current limitation". The TI paper uses the voltage on the resonant capacitor to create a triangle waveform and modulates the frequency accordingly. There is no mention of current limitation and there is definitely no mention of on-time processing, aka duty-cycle control. Where in the TI paper does it say the duty cycle is controlled in the converter?
 
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