Resonant converter with trapezoidal power currents.

[cupoftea]

Hi,
Please confirm that a resonant converter (not "quasi resonant"), would always have sinusoidal power currents, eg, as in an LLC.....there is no example of a resonant converter with trapezoidal power currents?

 

[BradtheRad]

Efficiency is better when sines go through a transformer, so they are the desirable waveform. Of course that's when operated properly.

However it's our human tendency to push a transformer in an attempt to get greater performance from it. Then the generating stage of the cycle (flux collapsing) departs from the sine-shape while flux was building.
Examples:
* exceed current saturation rating.
* apply slower frequency than transformer is designed for.
* output circuitry has an effect on waveform entering primary.