The grounds are all connected together. So that is of no concern.
The highest voltage in front of a diode will provide the major current for 
the application.
The other diodes will be back biased if the highest voltage is a few tenths 
more than the rest.
You can soften each up by current limiting it with a resistor in series with 
each diode.

Voltage critical application will probably need voltage regulation down 
stream?

----- Original Message ----- 
From: "Vitaliy" <spam@maksimov.org>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Thursday, April 09, 2009 9:46 AM
Subject: Re: [EE] Diode ORing supplies


> alan smith wrote:
>> Typically if you have two power sources, you diode OR them, so they will
>> not backfeed to each other.  Application is battery backed systems, etc.
>>
>> If you have one supply, say the battery sitting on a trickle charger, and
>> aother wall supply, both feeding a power plane,and if one supply is at a
>> slightly higher potential,
>
> So you basically have THREE power supplies, all feeding the same circuit?
> Trickle charger, battery, and the wall supply?
>
> And the "ground" levels of the trickle charger and the wall supply, are
> slightly different? So like, the trickle charger's Gnd is at 0V, and the
> wall supply's Gnd is at +0.5V?
>
>
>> ..will it draw more current from the lower potential supply in order to
>> normalize the voltage on the plane?
>
> Either I don't understand the question, or the question is wrong. The 
> power
> supplies will be fighting each other, so they will both be supplying more
> current than is required by the circuit.
>
> Vitaliy
>
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