This is a back EMF signal conditioning circuit that can be used to develop high-voltage sensorless motor drivers. When a sensorless algorithm is used to control the BLDC motor speed, the Back EMF (BEMF) signals are used. Based on zero crossing of BEMF signals, motor commutation is decided in the firmware. The signal conditioning circuit has mainly three blocks: the first is a low-pass filter for each phase voltage the second is a comparator circuit for determining the zero crosspoints and the third is a high-speed optocoupler. The optocoupler provides isolation between high-voltage motor driver circuitry and microcontroller.
Signal Conditioner for Sensorless BLDC Operations – [Link]
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