Bypass Voltage Regulator

I am using the Arduino Mega with the ATMEGA1280. All of the peripherals using the hardware serial pins run off the supplied 5.5V on the Arduino board.

I was wondering where the voltage regulator was on the board and if it was possible to bypass the power hungry regulator and input a regulated 5.5V.

Thanks!

You can feed it with regulated 5.0 volts (not 5.5) by connecting it to the Gnd and 5V pins. The voltage regulator is next to the DC power socket.

I suggest you get a spare USB cable and cut of the computer connector end and use the two USB power wires to wire to your external +5vdc power supply. That way your +5vdc is going in at the correct place for the auto-voltage switching circuit on the Arduino board. Also that would prevent you from ever having the external +5vdc wired to the USB +5vdc when you are down loading new sketches.

Lefty

The point of seperating the USB power wires is to prevent supplying too much voltage when you are uploading code from both the usb power and the external +5vdc?

Does this bypass the regulator by using the auto-voltage switching circuit?

The point of seperating the USB power wires is to prevent supplying too much voltage when you are uploading code from both the usb power and the external +5vdc?

Does this bypass the regulator by using the auto-voltage switching circuit?

A USB cable has four conductors, data+, data-, +5vdc, ground. If you wish just to supply a +5vdc regulated external voltage source to a Arduino board, the best way is to use a hacked USB cable and just utilize the two power conductors wired to your external power supply and when you plug the cable into the Arduino it will power up just like it would if plugged into a PC.

USB power is one of the two sources of +5vdc on a Arduino board, the other being the on-board +5vdc regulator. There is a auto-voltage switch on the board that switches the board to the regulator's +5vdc output power if there is a power source plugged into the external power jack. If you have both the USB plugged into a PC and an external voltage source plugged into the Arduino, the external power (via the on-board regulator) takes precedence over the USB power.

So bottom line, any +5vdc source plugged into the USB jack does 'bypass' the on-board regulator. However if you then plug an external power source into the Arduino's external power jack the on-board regulator powers the board via the auto-voltage selector.

That make sense?

Edit: An added benifit of supplying +5vdc through the USB jack is that you gain the protection of the built in 500ma thermofuse on the board.

Lefty

Nice, thorough explanation. That makes complete sense. Thanks everyone!