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I am using a DB9 to provide voltage(Vcc and GND) to a board. Now, the supply is given a long cable(the length of which is not known). Now, the power supplied is DC(about 30V or so).

Now, I believ that the longer the wire, the more radiation it will leak due to the antenna like property of the cable. Now, when plugged in there might be spikes that can cause damage to the board. How can I protect my board from such spikes? Would using TVS diode help me ?

The problem is that even though the supply is 30V , it can go as low as approx 18V. I was thinking of placing capacitors very close to the connector that can filter out any spikes or transients. What are the other precautions or design mechanisms I can take to protect my circuit from damage ?

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    \$\begingroup\$ Don't worry about the wire acting as an antenna. As long as the signals are DC and/or low frequency (< 10 MHz) there's not much to worry about. I would suggest to protect the inputs with a zener diode if that's not too expensive. The DC lines will probably have a decoupling capacitor elsewhere on the board. That should provide enough decoupling. \$\endgroup\$ Oct 27, 2015 at 14:54

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What are the other precautions or design mechanisms I can take to protect my circuit from damage ?

Plenty of things you can do - you might consider using a bridge rectifier so that if the wires got swapped over, the device would still work. Depending on the application and the environment some people would use a DC-DC converter to provide high isolation levels between power in and actual PCB supply. This can help when your PCB is meant to be locally functionally earthed because, without isolation, your circuit might be subject to an earth fault current from some other piece of equipment - to obtain a single earth point means you should isolate your incoming supply.

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