Digital Equipment Corporation

Thermal Dynamics Corporation

James M Gregorich

James A Daly

David A Tatham

Gerald J Brand

James F Mayrand

David M Morris

A pilot arc circuit for a plasma torch establishes a pilot arc current in the channel between the torch electrode and torch tip at a first target level which is greater than a predetermined minimum current sufficient to maintain a stable pilot arc. After a period of time following pilot arc initiation, the pilot arc current is reduced to a second target level which is greater than or equal to the predetermined minimum current so that damage to the torch is reduced by minimizing wear on the parts. The pilot arc current is established and maintained as a function of a pilot arc reference signal. Pulsing the pilot arc current assists in main arc transfer and enhances pilot arc stability.

Plasma torch pilot arc circuit

A high-power-factor power supply has a full-wave rectifier for rectifying an AC line voltage, a power regulator including switch means responsive to a control signal for controlling the application of the rectifier output to a load; and a control circuit for producing a switching control signal. The control signal includes a pair of AC line detectors: a first connected in a closed-loop automatic gain control arrangement, and the other connected in an open-loop arrangement. The control circuit initially produces a CURRENT DEMAND REFERENCE signal that is directly related to the difference between the power supply DC output voltage and a self-generated constant reference, and to the waveform shape of the AC line voltage, and is inversely related to magnitude changes of the AC line voltage. The control signal then produces the switching control signal in response to both the CURRENT DEMAND REFERENCE signal and the current flowing in the power supply. The invention avoids the square law dependency of prior art high-power-factor power supplies, can operate over a broad input dynamic range, and is 'self-biasing' in that the power supply itself generates any needed reference voltages.

High power factor switched DC power supply

A power converter, based on a modular architecture, in which a boost power factor correction circuit is provided as an input stage for both a primary power source and a battery power source. This arrangement permits the same power conversion stages which follow the boost power factor correction circuit to be used regardless of whether the primary or battery power source is in use. The power supply includes a controller for monitoring the primary power source voltage and the DC voltage produced at the output of the boost circuit and comparing each to a preselected reference. When a sufficiently large difference appears between each of those voltages and its respective reference, the controller connects the battery power source to the input of the boost circuit and simultaneously disconnects the primary power source therefrom. This switching of power sources is transparent to the load whose input voltage is maintained at a substantially constant level by the boost power factor correction circuit.

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Merrimack, NH, United States of America

James M Gregorich