Brushless motor driver and brushless motor system

摘要

The brushless motor driver includes a sample and hold circuit which samples and holds a first value of the first comparison signal in a first case in which a current is forced to flow from a first phase coil of the three-phase brushless motor to a second phase coil and no current is forced to flow to a third phase coil in a first period having a preset setting time and a second value of the first comparison signal in a second case in which a current is forced to flow from the second phase coil to the first phase coil and no current is forced to flow to the third phase coil in a second period having the preset setting time subsequent to the first period. The brushless motor driver includes an addition circuit which adds up the first value and the second value sampled and held by the sample and hold circuit and outputs an addition signal depending upon a result of the addition. The brushless motor driver includes a comparison output circuit which compares a value of the addition signal with a reference voltage and outputs a second comparison signal depending upon a result of the comparison. A position of a rotor in the three-phase brushless motor is discriminated on the basis of the second comparison signal.