Hi David.

15-Dec-03 22:26:36, David Drummond wrote to Jasen Betts


 DD> Al salaam a'alaykum Jasen

 DD> 14 Dec 03 09:35, Jasen Betts wrote to David Drummond:

 DD>>> How do you achieve the -12V? You'd have to set up your 12
 DD>>> volters to produce 24V overall, with the centre tap as zero...

 JB>> nah, get ten of them in series and feed 120V DC into the power
 JB>> socket of the powersupply.

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

on the input end of a SMPSU, typically after a RFI filter (radio frequency
interferance filter often built into the socket) and maybe a fuse there's a
great big rectifier and a large capacitor  the remainder of the PSU runs
off the DC in that capacitor.

in 115/230v selectable powersupplies the capacitor is actually two
capacitors in series and
the "115V" switch connects the middle point to one of the AC legs of the
regulator configuring it as a doubler in 115V mode and as a bridge in
230V mode

anyway all the powersuupply  needs is about 260V DC in that capacitor
and in "230V" mode the bridge will pass DC just fine.

the only problem that could occur is if there's a fault and that fuse isn't
rated for the DC voltage present...

 -=> Bye <=-

---