AN1905 ST Microelectronics, Inc., AN1905 Datasheet - Page 62

• Manufacturer Part Number: AN1905
• Description: St7mc Three-phase BLDC Motor Control Software Library
• Manufacturer: ST Microelectronics, Inc.

ST7MC THREE-PHASE BLDC MOTOR CONTROL SOFTWARE LIBRARY
Figure 44
shows the freewheeling demagnetization current during the step 1 to step 2 transi-
tion. In order to minimize the demagnetization time in the freewheeling diode, it is easy to
verify that the shortest time is achieved while lowering the M potential.
If the PWM is applied on high side, the M potential is either equal to 2 x HV/3 (PWM ON), or
equal to HV/3 (PWM OFF). The voltage applied on the winding B (potential difference be-
tween B and M) is then doubled when the PWM switches from ON to OFF state.
If the PWM is applied on the low side, the M potential is either equal to 2 x HV/3 (PWM ON),
or equal to HV (PWM OFF). The voltage applied on winding B switches from HV/3 to 0 (ON to
OFF state). The demagnetization is effective only during the "ON" state of the PWM.
It is then better to apply the PWM on the high side during the step 2 demagnetization process
(C to D event).
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