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two power supplys on the same board question

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firegod88

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Hi I have a design that needs a 12v DC from an ATX PSU on the board running to everything that needs 12v, I have a serial device that needs 24v but it's logic tx and rx are derived from the 12v part of the circuit. I have a header on the board that goes off to the serial device with the tx and rx lines plus a +24v from a seperate switched mode PSU.

My question is the serial devices need a ground, do I send the ground from the 24v supply or the 12v supply? Does it even mater? Can I link the 24v switchmode supplies ground to the ATX 12v supplies ground?

Thank guys, I need to know what to do with the 2 grounds?
 

IanP

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If circuits are totally independent you may leave separate grounds, if they, however, need common reference - "star grounding" is the most recommended option .. see attached picture ..

.... I need to know what to do with the 2 grounds?
Connecting them together wouldn't heart ..

Rgards,
IanP
 

firegod88

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IanP said:
If circuits are totally independent you may leave separate grounds, if they, however, need common reference - "star grounding" is the most recommended option .. see attached picture ..

.... I need to know what to do with the 2 grounds?
Connecting them together wouldn't heart ..

Rgards,
IanP
Thanks for the fast reply. Just to make sure, it's ok to connect the ground from (not earth) from an ATX 12v supply to the ground of a switched mode 24v supply?
Even though the 2 grounds are effectively comming off the terminals of two seperate transformers?
 

IanP

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There is nothng wrong, or strange, in connecting grounds of two (12V and 24v) power supplies together ..
Once connected, you have 0-12V and 0-24V, both sharing common "0V" reference ..

Regards,
IanP
 

    firegod88

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firegod88

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IanP said:
There is nothng wrong, or strange, in connecting grounds of two (12V and 24v) power supplies together ..
Once connected, you have 0-12V and 0-24V, both sharing common "0V" reference ..

Regards,
IanP
Great....Thank....I can send my board to the fabs now cheers.
 

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