I used to wire two 12VDC 1A power adaptors in series to produce a split supply with center "ground".
Now that it's all switch mode, there seems to be a problem with this.
Is there any way around it? Apart from builidng one from scratch, or running 120VAC into the box.
Ken Rockwell
Perhaps the "negative" supply can't sink current? How about load resistors on the negative side so it's supplying current?
** You'll have to detail this alleged "problem". ** Around what ?
.... Phil
What's not working?
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com
Is one end (of the output) grounded to a safety ground?
I'm with most of the rest of the group: if you can't tell us what symptoms you're seeing, we can't diagnose your problems.
If the outputs are isolated from the plugs (which they should be if it's North American two-bladed plugs), then at first blush I don't see what the problem might be.
-- Tim Wescott Control system and signal processing consulting
You can't use a virtual ground IC ?
Jamie
"Tim Wescott"
** If one of the SMPS adaptors is not powered - what happens ?If one strips the PCBs out of their boxes and wires them to the AC supply - this cannot happen
Also, you must add reverse polarity diodes to both DC outputs so overloads ( from + to -) will not result in one output being forced 12V in reverse when that PSU current limits or shuts down.
Might be *very bad* for the curcuit being supplied IF both DC rails are ever the same polarity too.
.... Phil
** So have I won your guessing competition ??
Old school DC adaptors with iron transformers, rectifiers & filter caps did not have the same issue - the rectifier diodes would alway act to effectively short the output if sufficient reverse current were applied.
If you just add 3A diodes ( ie 1N5401s etc ) to each SMPS adaptor's output you will probably be OK.
Good practice anytime with split DC rails.
... Phil
A Schottky rectifier from each rail to common will usually save the load from dying due to supply reversal. Otherwise, if the outputs are isolated, there should be no issue at +-12V. I'd do it myself in a heartbeat.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
** What planet are you on ??
FFS, with split DC supplies the load is from one rail to the other.
So BOTH have to be able to supply the same current OR or bad things can happen.
If one is not powered OR one shuts down and the other does not ????
Get real wanker.
The OP is smarter than you.
.... Phil
If you're only building audio amps, maybe. Other things typically load the positive supply harder than the negative one.
You have to size the power supply properly, so what?
The diode prevents damage. You posted something similar yourself. Using Schottkys will protect against the ground going open as well, assuming that the diodes are on the load side of the break.
I'm not too interested in who's smarter than whom. This is a discussion group, so try to discuss rather than disgust. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
** The diodes must be reverse biased in normal operation.
... Phil
I don't know why everyone is posting nonsense. It works fine and you don't need to add any diodes. Crack one open and you can see what a simple circuit it is.
You can also buy a nice center tapped SMPS online.
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