BLDC does not run on either direct AC or Direct DC supply. Its required to energized appropriate phase according to rotor position. So hall sensors are used to sense the rotor position so appropriate phase can be energized. Hall sensor convert magnetic filed to voltage and thus produce voltage at specific rotor position. So voltage output gives rotor position and utilized energizing appropriate phase. Hall sensor is three terminal device. Do not forget to watch easiest testing procedure for hall sensor explained below. Thank You Write your comment.