i have successful build a system to drive a LED Panell (4Ampere) with external Power and two MosFet circuit board .
The Power of 6V comes from a switching power supply an goes to the MosFet circuit board and also to the Arduino at Vin.
Everything is working well if the power supply is switched on.
If i connect the USB, i am able to programm the Ardoino.
But one Situation is bad: If i forget to switch the power supply on and connect the USB then the Power comes from the USB and went over Vin to the MosFet circuits and then to the LEDs. The Power of 4Amps are to much to go throu the Ardoino.
I now put a Diode in the wire that goes to Vin to prevent backward Power.
Is this enough to protect the Arduino and die USB Port?
In the schematic, you can see that the USB power is turned off at 6.6V.
And there is a diode from the DC barrel jack to VIN.
That means that the DC barrel jack should be at least 7.3V (7.5V with safety margin) and VIN should be at least 6.6V (7.0 with safety margin).
If you are below that, the USB power is still connected.
The USB power going through the voltage regulator to VIN and to your circuit is not good.
Yes, the diode prevents backward current.
However, there might be current flowing from VIN to the USB power, because VIN is too low.
That should not damage something. I think that diode is enough to protect the Arduino.
There is a polyfuse of 500mA to the USB power for extra protection. I think nothing is damaged.
