SLLSFH8A August 2021 – December 2021 MCT8316A
Figure 8-38 shows the operation of active demagnetization during the BLDC motor commutation. As shown in Figure 8-38 (a), the current is flowing from HA to LC in one commutation state. During the commutation change over as shown in Figure 8-38 (b), the HB FET is turned ON (and HA FET is turned OFF), and the commutation current (due to motor inductance) in OUTA flows through the body diode of LA. This results in a higher diode loss depending on the commutation current. This commutation loss is reduced by turning on the LA FET for the commutation time as shown in Figure 8-38 (c).
Similarly, the active demagnetization operation of a high-side FET is realized in Figure 8-38 (d), (e) and (f).
Figure 8-39 (a) shows the BLDC motor phase current waveforms with Active Demagnetization with trapezoidal commutation. This figure shows the operation of various switches in a single commutation cycle.
Figure 8-39 (b) shows the zoomed waveform of commutation cycle.