The IRF9640 is a 200V 11A Fifth Generation P-Channel HEXFETs from International Rectifier utilize advanced processing techniques to achieve extremely low on-resistance per silicon area. This benefit, combined with the fast switching speed and ruggedized.
This device is designed as a general−purpose amplifier and switch. The useful dynamic range extends to 60V 200mA 625mW as a switch and to 100MHz as an amplifier.
The BC548 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin.