AN1905 ST Microelectronics, Inc., AN1905 Datasheet - Page 64

• 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 45
shows the freewheeling demagnetization current during the step 4 to step 5 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 raising the M potential.
If the PWM is applied on high side, the M potential is either equal to HV/3 (PWM ON), or equal
to 0 (PWM OFF). The voltage applied on the winding B (potential difference between B and M)
switches from HV/3 to 0 (ON to OFF state). The demagnetization is effective only during the
"ON" state of the PWM.
If the PWM is applied on low side, the M potential is either equal to HV/3 (PWM ON), or equal
to 2 x HV/3 (PWM OFF). The voltage applied on the winding B is then doubled when the PWM
switches from ON to OFF state.
It is then better to apply the PWM on the low side during the step 5 demagnetization process
(C to D event).
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