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4.4.2
Feedback Circuit
Inverter Leg Shunt Resistor Feedback, a shunt resistor is located between the emitter of
the low side switches U, V, W and the "-DC bus". A simple differential amplifier circuit is used
as shown in Appendix A. The operation of the circuit used for the U-phase leg is described
below:
The current is measured using the shunt resistor R43 and the operational amplifier L224D
(U6C); R50, R51, R53, R54 and R55 set the gain. The output of the TL431 (U7) shifts the
voltage of the shunt resistor with 2.5V DC offset level. Hence the voltage applied to the
ADC of MCU channel varies within 2.5~4.75V. R52 and C27 filter out the high-frequency
noise. The same topology is used for the phase V,W.
Quadrature Position/Revolution Counter (
provides exact rotor position to the MCU. There are two
contains three channels A, B and Z. They are pulled up to the +5V by resisters respectively.
J7, J8 are used as the feedback signal input ports. The boards can supply + 5V to the
optical-electric encoder which is fixed in the motor through the port.
4.4.3
Fault Circuitry
Phase Over- current Protection, an operational amplifier (U6D) acts as a comparator to
compare the amplified voltages on shunt resistors with the regulated 2.5V. One channel of
voltage is higher than 4.75V DC. The U6D will output a high level up to 13.5V to the power
module. This fault signal can turn the low side IGBTs off.
The threshold of the phase over-current protection can set 15A as default value.
QPRC
) Feedback, this feedback signal
QPRCs
25
AN706-00042-1v0-E
in the MCU. Each counter
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