AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 27

• Manufacturer Part Number: AN1857
• Description: A 3-Phase ac Induction Motor Control System Based on the MC68HC908MR32
• Manufacturer: Freescale Semiconductor / Motorola

AN1857
MOTOROLA
BEMF_sense_A
Phase_A
Figure 18. Back-EMF and Zero Cross Detection Schematic
V_sense_DCB_half_15
GNDA
comparator is set by a reference from the dc bus divider
(V_sense_DCB_half_15). Using the dc bus divider as a reference, when
phase A,B or C phase voltages reach 50 percent of the dc bus signal,
corresponding to the phase zero cross point, the output of the
comparator will transition from a logic 0 to a logic 1. That transition is
used for distortion correction information to the IS1–IS3 inputs of the
PWM generator and as an input to the zero cross widow logic for zero
cross interrupt generation.
In the case of an ac induction motor, this zero cross circuit provides the
phase current polarity signals needed as inputs for use by the dead-time
compensation algorithm.
R501
324 k –1%
R502
274 k –1%
R504
215 k –1%
R507
21.0 k –1%
R508
6.81 k –1%
Freescale Semiconductor, Inc.
For More Information On This Product,
GNDA
Go to: www.freescale.com
R506
0
C505
22 pF
9
8
+
–
U501C
LM339D
14
R505
10 k
Zero_cros_A
Application Note
Power Stage
27