Driving a BLDC Motor

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This BLDC driver was originally built around the dsPIC33FJ12MC201 breakout board designed as a quadrature encoder decoder to SPI. For this version the chip was upgraded to the dsPIC33FJ12MC202 which has more pins.

The circuit uses the HIP4086 80V, 500mA, 3-Phase MOSFET Driver to drive 3 N-channel MOSFET H-bridges. The gate driver chip solves two issues with driving an N-channel MOSFET H-bridge using 3.3V logic level outputs. It amplifies the output voltage from 3.3V to 12V to fully saturate the gates of the MOSFETs. It also drives the High Side N-channel MOSFET gate to Vmot + 12V. To drive the MOSFETs the Gate-to-Source Voltage must be above the threshold voltage. This is easy on the low side MOSFETs because the source is tied to ground. For the high side MOSFET source is tied to the output voltage of the H-bridge. This means that in order to turn the high side MOSFET fully on it is necessary to pull the gate voltage level to Vmot + 12V, where Vmot is the motor drive voltage. The HIP4086 accomplishes this through the use of bootstrap capacitors.

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