Variable threshold starting circuit for induction motor

Abstract

A circuit for the automatic starting of an induction motor of the type having a sensing means for producing a signal proportional to the main winding current and control means for allowing current flow through a start winding only when energized by a start winding control signal. The starting circuit includes means for continuously producing a variable threshold level which is proportional to a condition capable of affecting the current level in the main winding and which defines an adjustable threshold switching level. A comparison means continuously compares the adjustable threshold switching level to the signal proportional to the main winding current and, whenever the latter signal exceeds the former, the comparison means generates a start winding control signal which activates the start winding control means thereby establishing current flow through the start winding. When the main winding current decreases to a sufficient extent, the comparison means is characterized by the absence of a start winding control signal whereby the start winding control means will block the flow of current through the start winding.

Dependencies are inferred from the claim text.