I am familiar with BLDC drivers and know how to drive the motor with 6 MOSFETs (at least I think so).
So to keep it easy lets say we use rectangular signals which can be +Vcc, GND or -Vcc. This would work like shown in the AN5423 from ST:
(1) So first of all do I understand it right that if you don’t have a negative power supply (which is the case most of the time) you reverse the current flow through the individual coils by commutating the direction of the voltage supply?
(2) To drive the motor the way mentioned in (1) you always need to either drive each mosfet individually (like in “6PWM”) or to only drive each H-bridge by having negated low side driver inputs like in the picture of “3PWM”. Is that also correct? That means for the second type you also need enable inputs for the H-bridge to get a tristate output?
(3) So, is it possible to drive the BLDC motor by only using the H-bridges without driving the individual MOSFETs or having an enable input? I think about offsetting the voltage to have the zero crossing at VCC/2 by using 3 sinusoidal signals (e.g. sinus signal with V_max/2 DC offset).
And when using that kind of offseted signal on each phase (by means of PWM) you can keep the neutral point of the coils at zero by superpose.
(4) As mentioned here, the enable input is optional. If not using the technique from (3), how can you drive the BLDC motor with just 1 enable pin or with even no enable pin by just using the H-bridge without HighZ state?
Thanks for any help in advance!