DIYbanter - View Single Post

On 16 Feb 2004 08:13:12 -0800, (Andy Wakefield) wrote:
Gary, as always I found your post to be most informative -- many
thanks. However, I did want to clarify one point. Can a switching
power supply really be fed a DC input? I was under the impression that
it required an alternating input -- not at any particular frequency,
but that it did use a step-down transformer to lower the voltage into
something closer to the required range. Of course, my impression is
based on what I vaguely remember from the schematics for an Apple II
power supply back in the early 80's, so it may be that my memory is at
fault, or that switching power supply design has evolved a wee bit
since then!

Not every switcher can operate from DC, but many of them can.
In particular, a PC power supply immediately rectifies the incoming
AC to DC before chopping it at high frequency and using a toroid
transformer to step it down to the working voltage.

Gary