Capacitively powered motor and constant speed control therefor

DETAILED DESCRIPTION It is an object of this invention to provide a low cost, low output capacitively powered motor which operates at a constant speed although its efficiency may vary.
It is another object of this invention to provide a capacitively powered motor which maintains a constant speed by advancing or retarding the commutation angle.
It is another object of this invention to provide a capacitively powered low output, low cost motor which operates at a selectable substantially constant speed.
It is another object of this invention to provide a capacitively powered motor which is low in cost and which may be employed as an evaporator fan motor for refrigeration.
In one form, the invention comprises a motor system for use with a power source.
A stationary assembly is in magnetic coupling relation to a rotating assembly and includes a winding.
A power switching circuit is adapted to be connected to the power source and is connected to the winding for selectively energizing the winding to generate a magnetic field which causes the rotating assembly to rotate.
A position sensing circuit provides a position signal representative of the position of the rotating assembly.
A commutating circuit controls the power switching circuit to commutate the power switching circuit at a commutating angle and at a substantially constant duty cycle to achieve a desired rotating speed of the rotating assembly.
The commutating circuit varies the commutating angle in response to the position signal to maintain a substantially constant rotating speed of the rotating assembly whereby the efficiency of the motor is varied to maintain the substantially constant rotating speed.
In another form, the invention comprises a control circuit for a motor for use with a power source and having a rotating assembly, and a stationary assembly in magnetic coupling relation to the rotating assembly and including a winding.
The circuit includes a power switching circuit, a position sensing circuit and a commutating circuit