DC-DC Ground connections

[haggisbasher]

Hi all,

I'm using a DC-DC to drive a logic circuit from 12V, trouble is I need to make the ground of both the logic and power circuit common as they interface and power the same unit, this unit runs off of the 12V that I use to feed the DC-DC but the logic circuit also drives parts of this unit hence the ground connections needing to be common between logic and power.

Any help or ideas appreciated.

DC-DC is traco power 9-36VDC I/P; +/- 5VDC O/P.


Regards


Andrew

 

[itsmoked]

There is generally no problem with the 12V and the logic sharing a common ground.

So...

Your question is not clear... Please try again.

 

[fsmyth]

Generally, small switching supplies benefit from the
input and output lows common (noise reduction).
As long as the common (ground) is negative on both,
there should be no problems. I do it routinely
when driving steppers. There are methods to add/
subtract the input voltage to the output, but I
doubt that that would be desirable in your case.
Onr thing you do need to do: make the common
ground connections at one point only, preferably
as close to the logic ground as possible.
Otherwise, noise in the driver section could
affect the function of the logic board.
Bypass everything liberally.
<als>

 

[haggisbasher]

Thanks for info guys. Just wasn't sure whether it was OK to do this as i'm just a junior at the moment....yes I did ask the engineers but I still wanted to check it was OK.


Regards


Andrew

 

[dinkelja]

We always put a zero-ohm resistor between the logic and power ground planes on our CB's. Can't explain exactly why though, sorry.

 

[haggisbasher]

Fsmyth wrote: Generally, small switching supplies benefit from the
input and output lows common (noise reduction).
As long as the common (ground) is negative on both,
there should be no problems. I do it routinely
when driving steppers. There are methods to add/
subtract the input voltage to the output, but I
doubt that that would be desirable in your case.
Onr thing you do need to do: make the common
ground connections at one point only, preferably
as close to the logic ground as possible.
Otherwise, noise in the driver section could
affect the function of the logic board.
Bypass everything liberally.
<als>



The I/P is 12VDC (2 pin) and O/P is +/- 5VDC with a common connection (3 pin).

 

[itsmoked]

dinkelja we always do that for a few reasons. One is you really only want the two systms sharing their ground at one point and it is just easier to put a zero ohm resistor into the schematic and then flow through the layout tool with it. Secondly sometimes it can help in trouble shooting an unhappy board. Third you can stick a low value resistor in their and measure for any current that shouldn't be there.

 

[walker1]

Controlling 12V or higher voltage circuitry from logic is quite common.
Usually it is done, as intended here, with a common ground potential.

However, at times controlling through opto-couplers can make things easier.

It could depend on things like number of controls, wanted max. delays of the controls, noise sensitivity in the analog circuitry, cost budget for the project, final production costs etc.