Power depends on the RMS voltage, not average voltage, so it's only
2 times less. (Another way to look at it - you're switching the load
off for 50% of the time, so the power dissipated will be halved.)
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I did not bother reading much of the original article because it
probably covers the topic well and straightforwardly.
What Andrew Gabriel does not realize is that this kind of application
most likely uses an inductive input ripple filter. This filter smooths
the pulses into a dc output with low ripple. sufficient load current
flowing so that current in the inductor never goes to zero. Look up
"inductor input ripple filter critical current."
Under such circumstances, power during the too high pulse voltage is
stored in the inductor. when the pulse is turned off, current continues
to flow through the inductor through a free-wheeling diode (or bridge
rectifier). That allows the energy stored in the inductor to provide
power to the load while the pulse is off. The result is that except for
power lost in the semiconductors from switching transients and diode
drops, the efficiency is going to be close to unity. There are a few
other losses from residual resistance, or magnetic losses.
The higher frequency you can chop, the smaller you can make the filter
components, although other losses may go up.
To sum up, dc to dc converters of this nature can be made highly
efficient. The efficiency will be limited by how large you are willing
to make the components.
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