I am building a circuit that uses a rechargeable battery and also has a USB port so it can be plugged in to charge the battery and power the system.
I am using a buck/boost converter to supply 3.3V for the circuit. I want the input for the converter to be the battery voltage when not connected to USB, but when plugged in, I want the input to be the USB.
One way I thought to do this was with a low forward voltage drop diode in series with each supply. Think it would work, but still some voltage drop, not the most efficient.
Another way I thought would be with a P channel FET that switches the battery voltage off when USB 5V is at the gate. Seems like the better method.
Would either of these solutions work? Thanks
Following the advice given, this solution seems like it should work: *Note the symbol for P channel Fet was re drawn from original image so that source is on top and drain on bottom