Brushless motor drive circuit

Abstract

A brushless motor drive circuit supplies power to a brushless motor by soft switching and prevents saturation of power supply transistors under any conditions. The brushless motor drive circuit includes, for respective phases, a first set of transistors for driving output transistors connected to the side of a DC power supply; a second set of transistors which constitute current mirror circuits in combination with the first set, respectively; a reference voltage generating device is connected to the second set of transistors respectively, for generating voltages proportional to currents flowing in the second set. A current feedback circuit, which, when potential differences between the inputs and outputs of the first set of transistors reach values close to the voltages generated by the reference voltage device, are turned on, causing voltage drops nearly equal to voltages generated by the second set of transistors, so as to partly feed back output currents of the first set of transistors to stages preceding the reference voltage generating device so that input currents to the first transistor are reduced. This results in an avoidance of saturation of the output transistors and also avoids the adverse reliance on circuit values.

Dependencies are inferred from the claim text.