Actually, Phil, the low wattage type uses a real two-winding transformer, and the high-wattage type uses a single high-current diode (rectifier) that changes the normal, full-wave sine wave into a half-wave 'half-a-sine wave' that puts out 220V, but as a half wave, the normal heater-element type of appliance "averages out" the wave form to be 110V over time. This is also how a dimmer works, by supplying line voltage at a smaller 'duty'cycle', or a percentage of time.

Larry
www.fineelectricco.com