The Adapter Interface Circuit (AIC) is used to sense the presence of an external power source for a portable computer. It notifies the computer if a source is present and indicates if the source is appropriate for charging battery packs inside the computer. The AIC also senses an adapter current and its direction. AIC isolates the adapter and signals the computer when peak current threshold is exceeded. LM2601 drives P-channel FETs. No high current rated Schottky diode is required to implement an adapter switchover circuit. This significantly decreases additional heat dissipation during simultaneous fast battery charging while running a computer, particularly in Maximum Performance mode of operation