Patent ID: 8692491
Filing Date: 2014-04-08
Classification: H02P

Abstract:
1. A brushless motor driver that drives a three-phase brushless motor, the brushless motor driver comprising: a detection comparison circuit which compares a neutral point voltage at a neutral point of the three-phase brushless motor with a comparison voltage obtained by dividing a voltage between terminals of a power device, which is supplied with a power supply voltage to supply drive voltages to the three-phase brushless motor, respectively connected to a power supply and ground to halves, and outputs a first comparison signal depending upon a result of the comparison; 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; 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; 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 being discriminated on the basis of the second comparison signal; a first voltage division resistor that is connected at a first end thereof to a first terminal of the power device, the first terminal connected to the power supply; and a second voltage division resistor that is connected at a first end thereof to a second end of the first voltage division resistor, and connected at a second end thereof to a second terminal of the power device, the second terminal connected to the ground, wherein the comparison voltage is a voltage-divided voltage obtained by conducting voltage division on the voltage between the terminals of the power device which are respectively connected to the power supply and the ground with a ratio of 1:1, and wherein the comparison voltage is a voltage at a node between the first voltage division resistor and the second voltage division resistor.