I am designing a system that has 2 power inputs and has to be working as long as these power supplies are fine. I mean, the system starts working with power supply #1 but if it fails, switches to power supply #2.

I've read some threads and noticed of LTC4417 CI, that does exactly what I want.

The circuits I've found in many threads (as done too in eval board DC1717A) suggests to connect all grounds lines together (http://cds.linear.com/docs/en/demo-board-manual/dc1717af.pdf page 6).

Knowing that every power supply has a ground reference (in essence, a ground line has an electric potential lower to positive terminal), is there any risk connecting all ground terminals together?

Do I have to put any kind of filter between this physical lines?

Thanks in advance.

PD: as an example of a circuit that does this function: Switching between power supplies - USB dominant.


1 Answer 1


There could be a risk from ground "fault" currents. You haven't mentioned how far apart these power supplies are and what else their individual grounds may be connected to. In an industrial environment, for instance, a ground fault current on machine X may cause excessive currents to pass thru the grounds of other pieces of equipment. This may give rise to secondary failure of connected devices. It may also give rise to intermittent or faulty operation of other devices too.

On the other hand, if you have AC powered supplies and they are isolated on their respective outputs, there is little chance of problems when connecting grounds.

  • \$\begingroup\$ Oh, I forgot to mention that both power supplies are DC batteries mounted in a ground vehicle, and they provide the same voltage (24V). They are just installed to provide redundant power supply so the different systems (as a GPS or a camera) can be working uninterruptedly. \$\endgroup\$
    – jaym
    Aug 24, 2015 at 11:24

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