Microchip Technology dsPICDEM MCHV-3, Руководство пользователя, Страница: 41 / 68

Hardware

2016 Microchip Technology Inc. DS50002505A-page 41
3.2.4 Feedback Circuitry
The power module stage provides three different methods to sense the motor position.
These signals are also useful to determine the speed, torque, current consumption and
applied voltage.
Hall Sensors:
The Hall sensor circuitry is designed to attach open-collector configured
sensors. It has a pull-up resistor at the Hall sensor inputs (R23, R24 and R25) and a
voltage divider (R26-R29, R27-R30, R28-R31) in order to scale the input waveforms to
the PIC MCU or dsPIC DSC logic levels. C25-C27 and R26-R28 form a low-pass RC
filter for each Hall sensor signal.
Phase Voltage Feedback:
For each phase, this circuitry is compounded by a voltage
divider, a current limiter and a low-pass RC filter. R79, R84 and R92 scale the
Phase M1 voltage in order to match the PIC MCU or dsPIC
DSC logic levels. R85 limits
the current going to the ADC pin (<6 mA). C51, R79 and R84 form the low-pass filter.
The Phase M2 and M3 have the exact same circuitry as shown in the schematic.
DC Bus Voltage Feedback:
This voltage feedback is compounded by a voltage divider
and a low-pass RC filter. R75, R76 and R81 scale the DC bus voltage in order to match
the PIC MCU or dsPIC DSC logic levels. C47, R75 and R76 form the low-pass filter.
Inverter Leg Shunt Resistor Feedback:
A shunt resistor is located between the
emitter of the low-side switches, M1 and M2, and the “-DC bus”. A simple differential
amplifier circuit is used, as shown in
Appendix A. “Board Layout and Schematics”
.
The operation of the circuit used for the Phase M1 leg is described in the following
paragraph.
The current is measured using the shunt resistor, R86, and the operational amplifier,
MCP6024 (U13A); R32, R33, R34, R36 and R37 set the gain. R38 shifts the voltage
present at the shunt resistor to a 1.65V DC level. Hence, the voltage applied to the PIC
MCU or dsPIC DSC ADC channel varies within 0V to 3.3V. The offset is controlled by
R59, R60, R38 and U13D. R35 and C34 filter out the high-frequency noise.
The same topology is used for the Phase M2.
DC Bus Current Feedback:
A shunt resistor is located between the shunt resistors of
side switches, M1 and M2, and the “-DC bus”. A simple differential amplifier circuit is
used, as shown in the schematic. The operation of the circuit used for sensing the DC
bus current is described in the following paragraph.
The current is sensed using the shunt resistor, R95, and the operational amplifier,
MCP6024 (U13C); R49, R51, R52, R56 and R57 set the gain. R58 shifts the voltage
present at the shunt resistor to a 1.65V DC level. Hence, the voltage applied to the PIC
MCU or dsPIC DSC ADC channel varies within 0V to 3.3V. The offset is controlled by
R59, R60, R58 and U13D. R54 and C42 filter out the high-frequency noise.
Note:
It is possible to select any of these feedback signals using jumpers, J12,
J13 and J14. Please refer to
Section 3.2.9 “User Interfaces”
for more
information.