A battery charging, discharging, and protection switch circuit with enhanced
reverse
voltage protection is achieved. The circuit comprises, first, field effect transistor
(FET) switches having gate, source, drain, and bulk. The FET switches may comprise
either NMOS devices or PMOS devices. Second, means of controlling the FET switch's
gate and bulk are included. The FET switch gate voltage determines the OFF and
ON state of said FET switches. The bulk is switchable coupled between the battery
terminal and the load terminal. To achieve high voltage breakdown limits the FET
switch is realized with cascaded MOSFETs, where as a novelty here under certain
operating conditions, i.e. the battery charger coupled in reverse condition—one
FET is working as a source follower. All the necessary MOSFET switches are integrated
onto a single chip, together with its controller logic. To form these MOSFETs within
a single IC together with the other circuit elements is much less expensive. The
circuit of the invention is manufactured with CMOS deep well technology.