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Abstract

Instabilities in the output voltage provided from an AC power supply system connected to a power factor correcting load are suppressed by a stabilizer which is connected across the output lines from the power supply system to the load. The stabilizing apparatus includes a rectifier having AC input nodes connected to the power supply system output lines, and DC output nodes at which DC voltage appears. A capacitor and resistor are connected in parallel across the output nodes of the rectifier. During normal operation, where the peak AC voltage from the power supply system is substantially constant, the capacitor charges up to a voltage level near the zero to peak value of the AC voltage waveform, with the charge on the capacitor slowly dissipated through the parallel resistor at a rate that does not substantially dissipate the charge between peaks of the AC voltage waveform. When changes in the peak value of the AC voltage waveform from steady state occur, the capacitor clamps the voltage across the output lines at a value near the steady state peak value to damp out oscillations in voltage level and reduce the effect of positive feedback caused, for example, by interaction between the power factor correcting load and the leakage inductance of the output winding of a transformer in the power supply system. A damping resistor may be connected in parallel with the capacitor during start-up of the load, or whenever excessive voltage changes occur, to provide more rapid damping of the voltage oscillations.

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