The ProMini is connected to a RFID reader and SD card reader and is powered for 10 secs for every reading. I am planning to power up the setup using a Lithium cell. ( Range 3.7 to 4.2V)
While the ProMini can with stand the Lithium full range, I am afraid the RFID / SD Card reader cannot tolerate beyond 3.3V.
So what options are there to regulate the voltage and which LDO regulator will fit this application.
Incidentally in a simple LDO regulator what happens to the Output when the Input falls below the recommended minimum ? Does it become a pass through element with no regulation or shuts down ?