usb to serial

I made a breadboard with an arduino atmel 328p chip that is behind a LM7805 voltage regulator. To upload the software or to download the data stored in the project I use the FTDI usb to serial converter from Arduino. Up to now I remove the external voltage before I connect the FTDI to the 6 pinned connector on my breadboard.

My question is, do I damage the FTDI breakout board by also applying my external voltage via the LM7805? In other words, do I need to include an N channel MOSFET with a voltage comparator as on the arduino uno board to prevent possible damage or, is the FTDI breakout board able to handle this issue?

Up to now I remove the external voltage before I connect the FTDI to the 6 pinned connector on my breadboard.

A wise thing to do, keep on doing it.

My question is, do I damage the FTDI breakout board by also applying my external voltage via the LM7805?

You should never connect the source of two voltage regulators together.

There is no need to connect the 5V from the FTDI adapter to your circuit itself if you are providing another supply for the 5 volts.