[rescue] Power supply load balancing

[nick at snowman.net]

So how hard is this to PCB for 3 supplies providing +12 +5 and (in
theory) +3.3 as well?  (I may pull as much as .5a of +3.3)
	Nick

On Thu, 28 Feb 2002, George Adkins wrote:

> On Thursday 28 February 2002 05:05 pm, you wrote:
> > That's what I've been designing & working on.  What I need right now is a
> > sure fire way to load share across three ATX power supplies, with the
> > ability to loose one.  I've got a few ideas, but most of them are UGLY.
> > 	Nick
> >
> 
> The best way to do this is to build a network of comparators and wire them to 
> a feedback type control and adjust the incoming voltages from each supply, 
> this will insure an even current draw and proper load balancing.  
> 
> If you just hook them up in parallel, variations in output voltages between 
> different supplies mean the highest one will get maxed out on current (until 
> the extreme load causes it's voltage to fall below the next highest one and 
> then it begins to pull a portion of the load, etc...)  With switching 
> supplies, this results in one of the supplies running at max load all the 
> time (unless the load is less than one supply, in which case it works for 
> hot-failover, but you need steering diodes and a dummy load before they come 
> together, to keep the un-loaded supply "live").
> Running at 'Maximum Load' is unhealthy for switchers.  They burn out.
> 
> So, working back from the common bus, you have steering diodes to prevent 
> voltage from other supplies from affecting the comparator, then the voltage 
> comparator (output voltage of the supply is compared to the main bus 
> voltage), then the output of this drives a voltage regulator which adjusts 
> the output voltage of the individual supply to match the main bus voltage, 
> then you have the power supply plugged in and supplying power.
> 
> Multiply this times the number of supplies you need to handle the load, and 
> add one for redundancy.  Voilla! you have N+1 reduntant load-balancing power 
> supplies.
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