[jjoonathan]

How does switching current behave in the limit of power transistors? I know that it's significant in high-performance ASICs but I could certainly imagine the junction capacitance of a power-MOSFET being small enough that kHz or even low MHz switching would cost a miniscule fraction of the power being switched. I mean, I've been able to switch the floating gates of sizable MOSFETs by waving my hand at them, I'd be surprised if the power usage at tens to hundreds of kHz was more than a few mW.

[zAy0LfpBZLC8mAC]

There are at least three different ways switching a transistor consumes energy, the power for charging the gate is only one of them and tends to not be the limiting factor in small power bricks. The other two are current spikes in the channel during the switch in logic circuits (because you normally cannot let the output float, which means that during the switch you have to switch on both transistors at the same time, but that's not a problem when driving some inductor/transformer), and energy loss due to voltage drop while the transistor is moving between on and off states (that's where all the heat tends to come from - apart from the heat from the rectifying/free-wheeling diodes).

[jjoonathan]

Ah, ok. That makes sense.