LLC resonant converter overcome high frequency at light load

Thread Starter


Joined Mar 4, 2022

I'm currently studying the LLC resonant converter.

The frequency range depends on the minimum and maximum required gain factor. This is dependent on the necessary input voltage.
The frequency of the converter is dependent on the input voltage (therefore the needed gain) and the connected load. The lighter the load, the shallower the gain factor curve. Meaning that for light load we need a high switching frequency, when a gain factor is required:

To overcome this high switching frequency problem, can't one just use a high transformer turn ratio (ratio=primary windings/secondary windings)? This would result in a need of a higher gain factor. Therefore the frequency range would be in the area where the gain response is steeper and the frequency range narrower:
The higher gain factor results in a better efficiency, but also makes the system more unstable. This is because a small change of frequency results in this setup in a large change of the gain.

When now using the Hybrid Hysteresis Control we should get a system witch is suitable for dynamic load.

Please let me know if my approach is flawed or not.

Best regards
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