switch between battery and usb power no microcontroller Following an earlier question about how to switch between battery and USB power, I would love to implement the TC2014 LDO as suggested by Russell McMahon. That way I could switch between 4AA batteries (1*4 or 1*4) and USB power. The battery voltage would nicely be regulated to 5V too. Switching Between Battery and External Power Sources Portable equipment that can operate from a battery pack or an external power source (such as a wall-adapter or external supply) needs to be able to smoothly switch between the two power sources. This application note describes a circuit (Figure 1) that switches power sources with good efficiency and without switching noise. Figure 1.