(1) Field of the Invention
The present invention relates to a three phase brushless D.C. motor mounted in a fuel supply pump for an automobile, for example. More particularly, it relates to an abnormal driving current cut-off circuit which interrupts current to the brushless D.C. motor, in the event that more than two stator coils are simultaneously energized.
(2) Description of the Prior Art
FIG. 3 shows a conventional drive control circuit for a three-phase brushless D.C. motor. As may be seen, three position sensors MP for detecting a magnetic pole position of a rotor RO magnetized by a permanent magnet are arranged adjacent the outer periphery of the rotor RO at the intervals of 120 degrees, and output signals from the position sensors MP are fed into a position detecting circuit MPC. The position detecting circuit MPC converts the output signals from the position sensors MP to logic "1" signals, for example, and supplies the logic signals to a three-phase logic LC. In accordance with the magnetic pole position signals generated from the position detecting circuit MPC, the three-phase logic LC supplies driving signals DS from a first-phase output terminal .phi.1, a second-phase output terminal .phi.2 and a third-phase output terminal .phi.3 through resistors R1, R2 and R3 to transistors TR1, TR2 and TR3, respectively, at the output timing of each phase as shown in FIG. 4. The transistors TR1, TR2 and TR3 are turned on every time the driving signals DS generated from the three-phase logic LC are supplied to each base of the transistors. As a result, driving current for the brushless D.C. motor is sequentially supplied from a power supply +B to each of three stator coils SC to thereby rotate the rotor RO.
Diodes D1, D2 and D3 are connected to each of the stator coils SC in parallel, so as to absorb surge of the stator coils SC.
In the conventional drive control circuit for the brushless D.C. motor, when the three-phase logic LC is affected by an external noise or the like, the driving signals DS are sometimes generated quite randomly without following the regular output timing shown in FIG. 4. As a result, there is a possibility of the driving signals DS being generated simultaneously from the first-phase output terminal .phi.1 and the second-phase output terminal +2 of the three-phase logic LC, for example. In this case, as the transistors TR1 and TR2 simultaneously turn on, driving current is simultaneously supplied to the first-phase stator coil and the second-phase stator coil.
When the driving current is simultaneously supplied to the plural stator coils, the stator coil of such a phase as should originally not be supplied with the driving current acts as a load to cause a reduction in rotational speed of the rotor RO and undue power consumption.