What happens when we connect two different gorunds?

[seyyah]

My µcontroller was operating normally. There was only one supply at that moment. Than i plugged out the power cables to connect two different supplys grounds. One of them is 5VDC and the other is 33VDC. I made the connections of the grounds with the supplies are offline. But the main capacitors of the supplies were charged i think. After this µcontroller didn't work. I think it burnt. What may cause this? A negative transient? What should we do to prevent this kind of damages?

 

[_i386sx25_]

If both supply is not isolated , there could be ground current leakage. In that case there would be potential difference between both grounds which causes a current flow. That could destroy your circuit. Check the isolation and potential difference between two power supply.