At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Wing K Eng

Robert E Schroeder

William F Slack

A power converter is operative to reduce harmonics at an AC input by controlling its power switching so that a current waveform in a switched inductor is substantially identical to a rectified version of the input AC voltage waveform. The voltage spikes induced by the switching of the inductor into circuitry that includes the leakage inductance of a power transformer are subdued by circuitry that absorbs the initial voltage spike temporarily and then delivers that energy to the output load of the converter.

Single stage power factor corrected converter having isolated output

An off-line switcher includes an auxiliary winding on the secondary side of the power transformer coupled by a power switch to a secondary voltage source in order to provide uninterruptible power to the output from either a primary AC or a secondary DC source. The power switches coupling both primary and secondary source voltages to the power transformers are driven at identical duty cycles by a common regulation control. Differing transformation ratios between primary and secondary sources of power define different operational ranges and determine flow of power based on the magnitude of the primary source of power.

Off-line switcher with battery reserve

A converter circuit that derives its bias power from voltage supplied by a tertiary winding including a tertiary winding voltage level responsive circuit with a hysteretic characteristic to selectively enable and disable the drive circuitry controlling the converter's power switching transistor. Should the bias voltage drop due to an output fault, the converter is operated at a subfrequency of its normal operating frequency in order to prevent operating the power switching transistor in its active region during high current conduction.

Bias power source energized by tertiary winding including hysteresis

A power converter circuit, which is voltage-regulated and current-limited by a peak current control circuit, significantly reduces the current tailout effect by decreasing the frequency of operation of the converter during low voltage output current-limited operation by increasing the nonconduction interval of the power switch while maintaining a fixed conduction interval. The peak current control circuit periodically initiates current conduction in the power switch in response to a clock pulse, and terminates conduction when a peak current level is attained. The peak current control includes circuitry to compare decaying current in the filter circuit during nonconducting intervals with a preset current tailout threshold level. The periodic triggering of the power switch into conduction is inhibited until current has decayed to this current tailout threshold level.

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Stanhope, NJ, United States of America

Wing K Eng