An integrated circuit for driving a VR step motor as a brushless DC motor

Reports the successful development of a CMOS integrated circuit which enables a variable reluctance step motor to operate with a torque-speed characteristic similar to that of a brushless DC motor. A key feature of the integrated circuit/step motor system is that it does not require a position encoder to directly sense rotor position, and thus should prove very attractive in applications where system costs have to be minimised. The position encoder is eliminated by using input current waveform to the motor phase winding to obtain a measure of rotor position. This method is based on using a chopper drive circuit and monitoring the variation in the chop current rise time