[msandford]

> A transistor generates no loss if it is in the full on or full off state (saturated)

Not entirely true. They make a lot LESS loss when fully on than when linear, but there's still some loss.

Even with a highly efficient transistor you can still get losses while in the linear region if your gate drive circuit can't push enough current. When designing a switching power supply you don't just hook the microcontroller output to the gate of the transistor. To do it right you might need one or two or three intermediate stages of power amplification so that you can switch the main transistor's gate very quickly.