4. What is trapezoidal back EMF?

The primary distinction between brushless DC (BLDC) motors and brushless AC (BLAC) motors is their back EMF waveform. BLDC motors typically have a trapezoidal back EMF, while BLAC motors (also referred to as permanent magnet synchronous motors, or PMSM) have a sinusoidal back EMF. The shape of a motor’s back EMF is important, because it determines what type of drive current and commutation method should be used.

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