> =E2=80=8B > On 7 June 2015 at 12:12, Harold Hallikainen > wrote: > >> I'm wondering what's in these things. I see them for something like $30 >> and rated for more than a kW. I don't think a 1kW 50Hz 240VAC to 120VAC >> transformer would meet airline baggage weight limits. So, anyone have a >> schematic of one of these? >> > > No schematic, but a 50% PWM of the mains waveform with filtering > appropriate to the PWM frequency should provide a half voltage sine wave. > > For other than pure resistive loads (which still need a bipolar switch) > you > probably need to consider it as a buck converter for the high frequency > variable amplitude "DC" input with the need to change the polarity of the > switch and catch (recirculating) diode every half cycle (or else). If > both > are implemented with eg back to back FETs and switched synchronously it > should be "easy enough" [tm]. > Switch (eg FET) in a bridge would look after bipolar switch. Catch diode > needs thought. > > > R Thanks! I wonder if that's what's really inside these things. The LPF for for the PWM seems like it'd have to be pretty big (expensive), and you need two, one for the incoming AC and one for the outgoing. I did try something like this years ago for a fluorescent light fixture for TV studios. The manufacturer claimed the ballast was not available for 230V. I blew up a lot of FETs trying to get this easy enough approach working (I don't have much good experience with high voltage FETs). I finally ended up putting the two ballasts in series and then having an autotransformer across the series pair to balance the load. I'm amazed I have not been able to find a teardown on these converters. Thanks! Harold --=20 FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available! Not sent from an iPhone. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .