US 4,734,627 A · Brushless D.C. motor having two conductors per phase energized alternately by complementary-conductivity-type semiconductors controlled by the same rotor-position signal, at times modified by a compensating technique

Abstract

A one-phase motor has two conductors energized alternately via respective pnp and npn transistors and from the same output of a Hall-IC, without polarity inversion. When the Hall signal goes high the first transistor goes conductive and the second non-conductive, or vice versa. Capacitive delay elements slow down the switching-ON and -OFF of the two transistors. The capacitive delay elements have the undesired effect that, in response to the self-same change in the value of the Hall signal, the signal at the base of the OFF transistor changes comparatively quickly to switch the same ON, whereas the signal at the base of the ON transistor changes comparatively slowly to switch the latter off, which can lead to both being briefly conductive simultaneously, leading to voltage spikes and precluding safe dissipation of inductive energy in the transistors themselves. A coupling capacitor connects the transistors at their bases and has a capacitance value such that it develops and maintains a substantially fixed potential difference between the two bases. This causes the change in base potential at the ON-going transistor to be retarded in dependence upon the otherwise slower change occurring in the base potential of the OFF-going transistor, and furthermore causes the OFF-going transistor to become non-conductive before the ON-going transistor becomes conductive. This too helps to make it safe to dissipate in the OFF-going transistor the stored energy of the associated wound conductor.

A brushless d.c. motor having a permanent-magnet rotor and a wound stator, the stator being provided with a stator winding comprising first conductor and second conductor means which are to be energized in alternation to each other to establish, alternately, a stator flux of a respective first and a stator flux of a respective second polarity at the part of the stator associated with that stator-winding phase,

first and second power-supply lines connectable to a D.C. power source,
first and second semiconductor control means for each such stator-winding phase and being of opposite respective conductivity types and each having a respective main current path with two end terminals and a respective control input,
the main current path of the first semiconductor control means and the first conductor means of the respective stator-winding phase being connected together between the first and second power-supply lines such that the first semiconductor control means when conductive or ON carries current of the first conductor means,
the main current path of the second semiconductor control means and the second conductor means of the respective stator-winding phase being connected together between the first and second power-supply lines such that the second semiconductor control means when conductive or ON carries current of the second conductor means,
rotor-position sensing means operative for producing at a single output a rotor-position signal that assumes a first value when the turning rotor reaches a predetermined first angular position and a second value when the turning rotor reaches a predetermined second angular position, one of said values being a relatively high value and the other being a relatively low value,
connecting means connecting said single output of said rotor-position senisng means to said first and second control inputs
such that, when the rotor-position signal changes from the low to the high value thereof, first and second control-input signals respectively present at said first and second control inputs both assume in response thereto predetermined relatively high values causing the first semiconductor control means to be rendered conductive or ON and the second non-conductive or OFF
and such that, when the rotor-position signal changes from the high to the low value thereof, the first and second control-input signals both assume in response thereto predetermined relatively low values causing the first semiconductor control means to be rendered non-conductive or OFF and the second conductive or ON,
and wherein, in the absence of compensating means recited below,
said first signal exhibits a tendency to reach said predetermined relatively high value thereof more quickly than does said second signal,
and likewise said second signal exhibits a tendency to reach said predetermined relatively low value thereof more quickly than does said first signal,
as a result of which each of the two semiconductor control means exhibits a tendency to be rendered conductive or ON more quickly than the other semiconductor control means is being rendered non-conductive or OFF,
and compensating means connected to the control inputs of said first and second semiconductor control means and
upon a change of said rotor-position signal from said low to said high value thereof, operative for slowing the rate at which said first signal reaches said predetermined relatively high value in dependence upon the speed at which the second signal reaches said predetermined relatively high value,
and upon a change of said rotor-position signal from said high to said low value thereof, operative for slowing the rate at which said second signal reaches said predetermined relatively low value in dependence upon the speed at which the first signal reaches said predetermined relatively low value,
whereby to counteract said tendency of each semiconductor control means to be rendered conductive or ON more quickly than the other semiconductor control means is being rendered non-conductive or OFF.

13 more elements

Brushless D.C. motor having two conductors per phase energized alternately by complementary-conductivity-type semiconductors controlled by the same rotor-position signal, at times modified by a compensating technique

Life of this patent

Brushless D.C. motor having two conductors per phase energized alternately by complementary-conductivity-type semiconductors controlled by the same rotor-position signal, at times modified by a compensating technique

Life of this patent

Abstract

Claims27