If you leave the buck transistor on, it becomes a plain boost converter. If you leave the boost transistor off, it becomes a plain buck converter.
Use hysteresis current mode control with the buck operating on a slightly higher threshold than the boost.
As for the SCR-based charger, it may actually be cheaper to operate.
a quiz about AC power - diyAudio
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Does the utility wattmeter register the DC component of the power used? (probably not) Someone will have to turn off everything in their house to measure the meter rotation speed with the diode in and out.
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No!
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Take the extreme example: If our diode-equipped soldering iron was one of 1000 in a large factory, all connected in the same way, the facility would be consuming a considerable current which could not be registered by the eddy-current motor driving a standard consumer meter, which responds only to the in-phase AC component).
To put it another way: as you say, high I/V phase angle decreases the work done by, in this case, the meter, but the unregistered power is still available for space-heating or whatever, free of charge.
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