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Author Topic: ATX Power Supply HELP  (Read 310 times)
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Hi guys

I am new to Arduino and thus need a bit of help.

I have made my own power supply for my projects from an ATX power supply I had as a spare.

The power supply works fine when powering my Mega 2560 and the projects. I use the +5V and Ground from the Power Supply. I have always used either the USB power source or the Power Supply via the DC input, never both at the same time( Only one plugged in at a time )

I decided I want to keep the power to the Mega on via the DC input while using the USB (Serial Interface). I decided to make sure there was no voltage across the two Power Supplies (Computer and ATX ) and was shocked to see 120V AC between the ground on the Mega and the Ground on my Power Supply  smiley-eek-blue. I checked the DC voltage differance and it was 30mV.

Will it be safe to use the USB from my computer and the power via the DC supply from my Power Supply?

I am from South Africa and we use 220V

Thanks in advance
« Last Edit: June 15, 2013, 09:42:31 am by Xproximity » Logged

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...was shocked to see 120V AC between the ground on the Mega and the Ground on my Power Supply  smiley-eek-blue.

This is why you always connect all grounds together - voltages need to have a common reference point.

So... connect them both together before you do anything else!
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Will it be safe to use the USB from my computer and the power via the DC supply from my Power Supply?
Yes.As long you have power in the DC supply connector the arduino will use that source as Power Supply.This is because there is a fet T1 FD340P that  turns off when the comparator IC7B detects Voltage in the DC connector.If then you remove the Power from the jack then the fet will switch the supply to the USB 5V powering the arduino from there now.
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Thanks a lot guys  smiley

Looks to be all sorted now. I have used the 12V output on the Power Supply for the Mega and the 5V for my projects(All the Grounds are connected together inside the power supply).
All seems to be working.

Thanks once again.
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