31 Jan
2011
31 Jan
'11
12:39 p.m.
Many switch mode power supplies will work happliy with
both 230V and
110V. The 110/230 switch only ever seemed to switch in a secondary
capacitor after the bridge rectifier for the HV DC supply to the
switching circuitry. I guess it was difficult to get 300VDC+
capacitors for a while. Adding a second capacitor (in series) meant
that each capacitor only ever saw about 1/2 the DC voltage, and hence
kept the smoke in.
Not at all!. The adjustable SMPUS are designed so that the chopper
cirucit works correctly with a DC inpout of around 350V. This can be
obtained in 2 ways :
a) By full0-wave rectifiying a 230V mains supply
b) By voltage-doubling a 115V mains supply
The first uses a bridge rectifier (normally) and a smoothing capacitor.
The second uses a pair of diodes and a pair of capacitors. It turns out
you can use 4 diodes (in a normal bridge configuration) and 2 capacitors,
along with a couple of resistors to get the 2 capacitors to charge to
approximatle the same voltage if you want to use the series combination
as a single cacpaitror) to make a cirucit that can aci as either of those
simply by adding a link for (b).
That;s what happens in every dual-voltage SMPUS I've worked on.
-tony