1117 3.3 V Pdf. The lm1117 offers current limiting and thermal shutdown. Dropout of1.2 v at 800 ma load current.
AMS11173.3 DC StepDown Voltage Regulator Adapter
Additionally it is also available in adjustable version. Usb +5v is switched by a fet based on whether arduino vin/2 > 3.3 v. The ams1117 is available in six fixed voltage, 1.2, 1.8, 2.5, 3.3 and 5.0v.
AMS11173.3 DC StepDown Voltage Regulator Adapter
The lm1117 is available in an adjustable version, which can set the output voltage from 1.25 to 13.8 v with only two external resistors. You can see from this schematic that if the usb is plugged into the arduino, there is no voltage on vin, because vin is a connection from the external dc barreljack to the onboard 5v regulator input and the vin pin. The ams1117 is available in six fixed voltage, 1.2, 1.8, 2.5, 3.3 and 5.0v. The device is supplied in: