Control circuit for brushless DC motor - incorporates resistance network for adjusting conducting angle and commutation without overlap

摘要

The control signals are obtained from the auxiliary windings (51, 52, 53), in which permanent magnets on the rotor induce a voltage. These voltages are applied to pairs of resistors connected in a ring. The centre point of each pair forms one input of an amplifier, the other being a reference voltage. The amplifiers control the switching transistors. If the mid point voltage exceeds the reference the associated transistor turns on and current flows in the main winding not associated in phase with the summed voltage in the resistor pair. If the voltage of the next auxiliary winding falls below that of the sum conduction is maintained, but if it falls below the reference conduction ceases.