23 Dec 2003, 10:36, Tom Walker (1:202/1324), wrote to David Drummond:

Hi Tom.

 >> Does a switchmode supply not need an AC source (as in is it 
 >> somehow locked to the frequency of the mains)?

 TW>  Yes it does need the 60 Hertz line frequency to operate. One 
 TW> designed for operation from DC, be it 12/120/220 would need it's own 
 TW> internal Frequency reference.

How would it accomplish that?  There are NO internal taps or connections to
the AC input side.  Line in > Filter > Choke > Fuse > Rectifier
> Thermistor > Filter > Caps > Switcher transistor > Output
to Ferrite XFmr 
> Outputs.

The switching frequency of ~20KHz is controlled by the Ferrite saturation.


     Good luck...  M.

--- Msged/386 TE 06 (pre)