Sgs-thomson Microelectronics Limited

Stmicroelectronics Gmbh

Li-Hsin D Lu

Karl M Schlager

Francesco Carobolante

Chinh D Nguyen

Francis Yu

A circuit for determining an initial winding combination for motor startup of a polyphase dc motor having a transistor driver circuit comprising a plurality of high side winding drivers and low side winding drivers operably connected to first and second voltage sources comprises a current mirror circuit and a plurality of sense FETs each operably connected between one of the voltage sources and the gate of one of the winding driver transistors in each phase combination. The sense FETs are operably connected to one side of the current mirror circuit. The mirror circuit compares the current through the sense FET with a current threshold provided on the other side of the current mirror and produces an output signal when the threshold is reached. At the same time, the time to reach the threshold is measured and the phase combination having the longest time is stored. Also when the threshold is reached, the sequencer advances to the next phase combination for measurement until all phase combination have been sequenced. The motor is then started with the phase combination having the longest time measurement energized first.

Circuit and method for determining optimal phase combination for startup

A motor drive system, and method for operating the same, which includes current mirror load current sensing, is disclosed. Sensed current is used in the well known manner to control the low side drive of the motor. The disclosed motor system operates in a bipolar mode on startup, and in a unipolar mode during full speed operation. In unipolar mode, a current mirror transistor is provided to sense the load current through the center tap drive transistor in a continuous manner. Ripple in the sensed current is avoided, as the center tap drive transistor is not commutated during motor operation in unipolar mode. In bipolar mode, current mirrors are provided for both of the high side and low side drive transistors in each leg, with the currents summed for each coil at a sum node, and with the summed current applied to a cumulative sum node; the summed current never drops to zero, as only one drive transistor changes in each phase change in the commutation sequence.

Current sensing and control in brushless DC motors

A method and apparatus for switching a motor between bipolar and unipolar mode. During each phase of the bipolar mode, one of the coils floats and has a back emf. In the method, first, a mode change signal requesting a change between the bipolar mode and the unipolar mode is received. Second, the back emf across the floating coil is monitored. Third, a point in time when the back emf equals the center tap voltage is detected. Last, the motor is switched between the bipolar mode and the unipolar mode at a point away from point in time when the back emf across the floating coil equals the center tap voltage. Various circuitry is also disclosed for switching a motor between a bipolar mode and a unipolar mode.

Method and apparatus for switching a motor between bipolar and unipolar

A method and circuit for providing a dual slew rate to a driver transistor. The method includes turning off a driver transistor at a programmable slew rate until a BEMF voltage spike is sensed, and then switching in a slower clamping slew rate. The slew rates are controlled by discharging a capacitor through a programmable discharge path until a voltage spike is detected and then through a clamping discharge path. The discharge paths include several transistors connected in series and control by digital logic.

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San Jose, CA, United States of America

Li-Hsin D Lu