Sithambaram Palaniappan
Avago Technologies

Brushless Direct Current (BLDC) motors are gaining popularity and larger market acceptance. They are used in industries such as Industrial Automation Equipments, Medical, Automotive, and Aerospace.

Commutation — the process of activating current flow through the appropriate stator phase windings to produce an output torque — is achieved electrically in BLDC motors. It is essential to have feedback devices attached to the motor shaft to indicate the current rotor position to the controller. With various forms of feedback devices available, magnetic hall sensors and optical commutation encoders are the preferred feedback devices in today's industry. Hall sensors detect movement of the commutation magnet, while the optical commutation encoder senses the movement of the codewheel. The commutation magnet pole pair and codewheel track patterns are fixed and matched to BLDC rotor pole pairs. This disables the end user from configuring the commutation magnet or codewheel pattern when they have to match up a different pole pair BLDC motor.

This white paper explains how Avago's AEAS-7000 (16-bit) Absolute Encoder overcomes this problem of configuration by feeding back the absolute counts, where the absolute counts will be compared with the pre-programmed counts in the controller, to activate the correct commutation sequence.