AN1627 Freescale Semiconductor / Motorola, AN1627 Datasheet - Page 2

• Manufacturer Part Number: AN1627
• Description: Low Cost High Efficiency Sensorless Drive for Brushless dc Motor Using MC68HC (7)05MC4
• Manufacturer: Freescale Semiconductor / Motorola

a rotational field. This easy to create shape of applied voltage ensures the simplicity of control and drive.
The rotor position must be known at certain angles in order to align the applied voltage with the
Back-EMF, which is induced in the stator winding due to the movement of the permanent magnets on
the rotor. The alignment between Back-EMF and commutation events is very important. At this condition
the motor behaves as a DC motor and runs at the best working point. The simplicity of control and good
performance makes this motor a natural choice in low-cost and high-efficiency applications.
1.2
As explained in the previous section, the rotor position must be known in order to drive a Brushless
DC motor. If any sensors are used to detect rotor position, then sensed information must be transferred
to a control unit (see Figure 1-2.). Therefore additional connections to the motor are necessary. This
may not be acceptable for some kind of applications. There are at least two reasons why you might want
to eliminate the position sensors:
1. Real impossibility to make additional connections between position sensors and the control unit
2. Cost of the position sensors & wiring
The first point might be solved by integration of the driver within the motor body. However a significant
number of applications requiring a sensorless solution still remain.
MOTOROLA
2
Why Sensorless?
~
Figure 1-1.
=
Three Phase Voltage System
M
electrical
angle
REV 0.2
AN1627