Bi-level electronic switch in a brushless motor

Claim 1

A brushless d.c. motor of the type having a plurality of stator windings arranged around the periphery of the motor; a permanently magnetized rotor rotatable therebetween; and commutating means for successively energizing said stator windings from a d.c. source in synchronism with rotation of the rotor, said commutating means including individual rotor position sensing means corresponding to each stator winding; individual amplifying means for producing command signals having a specified amplitude in response to output signals from said sensing means; and individual switching means coupled to each sensing means for switching energizing current to the associated stator winding in response to a command signal; each of said switching means including a diode, and input and output transistors each having base, collector, and emitter electrodes, both of said transistors having their base and emitter electrodes coupled to one side of said source and their collector electrodes coupled to the associated stator winding; the emitter electrode of said input transistor being further coupled to the base electrode of said output transistor, said input transistor being coupled to the stator winding through the diode; said diode being oriented to permit current flow from said winding to the input transistor; said output transistor being selected to saturate in response to a command signal when the motor is running at its normal speed, said specified amplitude being larger than the saturation voltage of said output transistor whereby the diode is backbiased in response to a command signal when the output transistor is saturated.