Undervoltage detector with the LM3900 (CB25172E)

The figure shows how to implement an undervoltage detector using a Norton amplifier and a zener diode as the main elements.

DTMOS V Super Junction MOSFETs
August 2017 - New DTMOS Super Junction MOSFETS from Toshiba are in stock at Mouser Electronics....
Analog Capacmeter (CB3930E)
This circuit has been found in an old American documentation, but can be easily implemented with common...
SAW Filters and Duplexers - Taiyo Yuden
Taiyo Yudem SAW filters can be ordered from Mouser Electronics for UMST (W-DMA), GSM, CDMA, LTE,...