USB Power Source Circuit for Arduino

Here’s is a circuit that used for the USB source, power will enter through the USBVCC section into a P-channel MOSFET FDN340P. Explaining briefly, MOSFETS are transistors that are normally closed (connected) until a certain amount of voltage triggers the gate. Consequently, triggering the MOSFET opens the transistor (disconnected). Using this characteristic, a comparator is connected to the gate terminal of the MOSFET to function as a switch mechanism. If you use the USB source, it will just power up the 3.3V regulator since the MOSFET is normally connected. If you plug a dc supply, the LMV358 op-amp will produce a high output triggering the gate of the MOSFET, disconnecting the USB source from the 3.3V regulator. So if both are plugged, the board will use the DC power supply. This is the figure of the circuit.

 

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