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OR-ing voltages together

stuart sutherland

Jul 6, 2015
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Does anyone know most accurate way to calculate the output volatge when or-ing voltages together.
I really want to know what would happen if one of the voltages was greater than the other?

Thanks.

Stuart
 

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Harald Kapp

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You "can't" do that. Well, you can, but you risk destroying your voltage sources as current will flow from the higher voltage into the lower voltage and many voltage sources are not meant to sink current.

The standard way of using multiple power supplies on one line is decoupling via diodes or equivalently controlled switches (typically MOSFETs) acting as controlled "ideal diodes".
A useful description is given e.g. in this datasheet.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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You can also use resistors connects to a virtual ground and measure the current which will be related to the sum of the voltages.

Herald's solution with diodes will give you either the max or min voltage (depending on how you arrange the diodes).
 
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