Driving a 4-wire Hard Drive Motor

Question

After reading many contradictory accounts of the "proper" method, I would like to clear it up: what is the correct method for driving a 4-wire, star configuration hard drive motor?

What I have observed people/companies doing:

1. Driving the motor using 3 wires and not connecting anything to the Common wire.
2. Putting half-bridge drivers on all 4 wires.
3. Setting Common to GND and driving the other 3.
4. Setting Common to V+ and driving the other 3 open-drain.

Now, I recognize that there may be multiple ways to drive it, but what is the intended method? How are they SUPPOSED to be driven?

For your reference, I am planning to use the HDD motor to build a variable-speed precision driver, which will have optical feedback (i.e. optical tick marks on the platter rim) for the speed control.

Answer 1

You could rotate them in any mode you suggested 3 phase Delta or WYE but each is sub-optimal

If you want to run it quietly with optimum torque speed control using synchronous V/F PWM sine wave Voltage control for optimal torque, current and speed control, then you would use them with the HDD spindle driver hardware made for them and drive 3 full bridges in PWM sine voltage.

Feedback consists of;

• a common current sense resistor for all low side driver ground currents to control acceleration

• the common wire for BEMF sensing the balancing of the 3 phases to null any offsets per cycle.

Answer 2

the hard disk I have in my hands measures high resistance from all four motor terminals to all four supply terminals

meaning that unipolar drive is unlikely.

the driver chip STMicro "L6283 1.3" connects to all 4 pins, but I can't find a data-sheet for this TQFP-60

attaching a scope the drive seems to be PWM three-phase and the common is not driven, I suspect that is is used to sense the time to commutate,