Transient response of LLC converter

[cupoftea]

Hi,
Do you know why the shown HHC method of LLC control never took off (brought out 7 years ago)

https://www.ti.com/lit/an/slua834b/slua834b.pdf?ts=1709817023812&ref_url=https%253A%252F%252Fwww.ti.com%252Fsolution%252Fpc-psu-game-console-power-unit

It has no downsides, makes control easier, and can make transient response faster, and is cheap (UCC25640), and reduces BOM cost since smaller output caps are needed.
...But nobody uses it..why?

One problem that i can think of with LLC + HHC is that if the PFC output voltage falls, then the LLC has problems because LLC's are not conducive to operating with a wide input voltage range....so it seems a waste of time improving the transient response when the transient is likely to also result in the PFC output voltage (the LLC's input voltage) getting pulled down so low that the TTF cannot properly operate anyway.

 

[Easy peasy]

Charge control ( now widely used for LLC ) is essentially the same - and provides near optimum control.

 

[D.A.(Tony)Stewart]

24 AUG 2023

Digital hybrid hysteretic controlled (HHC) LLC converter based on C2000 real-time MCUs | Video | TI.com

Looking for a good candidate to meet high transient response requirements in power supplies? This digitally controlled LLC converter design will show you how.

www.ti.com

C2000WARE-DIGITALPOWER-SDK Software development kit (SDK) | TI.com

View the TI C2000WARE-DIGITALPOWER-SDK Software development kit (SDK) downloads, description, features and supporting documentation and start designing.

www.ti.com

 

[cupoftea]

Thanks, i am seekign a fuller report of the charge controlled LLC or the HHC LLC.

Its hard to believe that LLC can be operated any other way than just kind of voltage mode control, where the frequency is adjusted in correspondance with the Vout.
LLC has a big LC power stage, and any other control method seems likely to instigate dreadful oscillations.

The LLC cannot compete with the 2 tran forward for fast transient response hysteretic mode control.....the attached shows the 2 tran forward in burst mode.......no LLC can compete with this for excellent transient response....resonant converters are just not capable of this kind of sharp on/off control....they would ring like mad.

LTspice and PNG shown

 

[Easy peasy]

correct - LLC and similar resonant converters need a few cycles to move up to full output ( or the reverse )

any type of forward converter, can have better dynamics - as long as Vin is high enough - pure hysteretic control is the fastest form of control for forward based converters.