Low cost and efficient control for brushless DC motors

A control circuit for three-phase voltage source inverters is described in this paper. The high side FETs are controlled by PWM, while the low side FETs are controlled each by a comparator. The comparator output turns high, when the voltage between source and drain is positive, due to the induced voltage during current free-wheeling operation. The voltage at the comparator input automatically prohibits switching on the corresponding FET while the complementary FET is still conducting. This short-circuit protection is also given in fault cases, such as microcontroller or driver defect, where the gate signals can be all high. The power stage applies to brushless DC motors with low voltage supply.