Resonant converters not so needed now like in the 1980's?

treez · Nov 8, 2013

is the following true about resonant converters?

Resonant SMPS’s saw great service in the 1980’s when Power Transistors were not so suited to fast switching operation in SMPS’s. Due to this, in the 1980’s , SMPS’s which were operated at relatively high switching frequencies suffered rather high switching losses. –Resonant SMPS’s went some way toward reducing these switching losses.

However, in Modern Times, Power Transistors are far more amenable to fast switching operation, and so resonant SMPS’s are not always needed like they were in the past. (Another thing is that Modern Transistors in 2013 can have high voltage ratings, and yet relatively low on-state resistance.)

FvM · Nov 8, 2013

I think, this sentence is true

resonant SMPS’s are not always needed like they were in the past

But in fact it says nothing against todays advantages of resonant converters, isn't it?

Secondly, saying they have been needed in the past doesn't state that many engineers would have known how.

dick_freebird · Nov 8, 2013

Resonant (or quasi-resonant) styles can be much better
at low power (PFM control mode is happy to downrange
fSW / switching losses, better than pulse skipping a PWM
in my book. They make the most of whatever transistor
you've got, the place where that matters has simply moved
up in frequency. A resonant converter tends to have less
EMI initially generated so can reduce filtering bulk.

What is "fast"? That's the question. GaN buck converters
running over 20MHz are out there. But your resonant
converter also has taken on new life as your Class E
RF power amplifier, running at 1.9GHz.

treez · Nov 8, 2013

OK thanks you're talking of some high end stuff there.

As a general rule in SMPS's....resonant converters are used to reduce switching losses.
However, the FETs of a resonant converter can often experience higher off-state voltages, and so these fets tend to have higher rdson...therefore, ones conduction losses can end up being higher with resonant converters.

Certainly I agree your point about the filters......however, often its as if the filter components have just moved into the power stage, eg with LLC.

mtwieg · Nov 8, 2013

The thing is the switching FETs are getting faster, which mitigates the need for resonant converters in order to get high efficiency at high frequency.

edit: of course you could just use the better technology to make even higher frequency resonant converters (>10MHz), but I think at that point inductor and transformer limitations become dominant...

Resonant converters not so needed now like in the 1980's?

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