Brushless DC motor with multi-phase winding - has switching circuit with complementary drive and main emitter coupled transistors in each stage

摘要

The stationary motor windings are connected across the supply with one end common, and the other in series with a main switching transistor each. A complementary driver transistor is associated with each switching transistor. An RC circuit couples the main collector to the driver base on each transistor pair. The main collector is also connected to the next stage through a resistor. Three stages of a multivibrator are thus formed. By choice of RC circuit values the current is made to switch from one stage to the next one, as the rotor turns and induces a voltage in the windings during the non-conducting period. At a certain speed this induced voltage is sufficiently high to directly trigger the driver transistors and constant speed conditions are established.