Importance

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Abstract

A semiconductive power unit for controlling drive motor speed by controlling the power applied to the motor through a variable or switchable semiconductive control element, such as a Darlington transistor. Electrical power is supplied from a power supply to the variable speed drive motor via the controllable semiconductive device connected to provide a variable impedance branch path between the power supply and the variable speed drive motor. A power dissipation characteristic for the variable impedance branch path is established, wherein current flow therethrough decreases monotonically with increasing voltage across the variable impedance branch path. The circuit establishing the characteristic also provides a feedback signal to the controllable semiconductive device to maintain its operation at the established power dissipation characteristic. The method involves determining a maximum permissible power dissipation for the impedance of the controllable semiconductive device, establishing a power dissipation limit characteristic including the step of calculating the constants A, B, and C for the relationship AV+BI-C=0 where the relationship represents a line segment starting from the value of V for which I is zero and proceeding to, and past, a tangent point with a curve of a constant product of V and I, where the constant product is the maximum permissible power dissipation.

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First Claim