LLC resonant converter has too high V and I RMS?

For a LCD television power supply of 240W....

I think that an interleaved, non-resonant , half bridge converter would be more efficient than an LLC resonant converter.

All resonant converters suffer from exceptionally high RMS currents or voltages.

They are not practical for most equipment, and only have use in a very narrow range of areas.


Is this true?

...the point is that LLC resonant converters seem to be getting used everywhere now, and i think its a waste of time.

LLC do have higher rms currents in the mosfets - true, but there are a number of other advantages:

They can have an output higher or lower than nominal output, or you can have a wide input range for a fixed o/p,

due to the soft switching, there are only conduction losses in the mosfets, no switching losses, also the gate drive is much easier,

They create a lot less RFI due to the soft switching, making it a lot easier to comply with EMC requirements.

They do not require an output choke - but need good caps on the output to handle the ripple current.

The transformer design does not need to be low leakage, so a simple pri over secondary geometry can be used,

The components can be quite small, low on resistance fets are quite cheap these days,

The voltage stress is no worse (mosfets) and somewhat better for the o/p diodes in an LLC,

The diodes suffer no voltage spikes - helping with EMC.

Regards, Orson Cart.

surely the fets have switch-off losses?

Hi,

I don't know much about LLC resonant converters. I have little experience on Flyback Resonant converters.

Resonant converters can reach high efficiency only at high loads.

They were invented by Philips for their monitors that, indeed, are a high load for the power supply.

Enrico Migliore

The fet turn off losses are very small, < 0.2 watt for a good fast gate turn off (<30nS)