At&t Bell Laboratories

Operating Technical Electronics, Inc.

William F Slack

James C Wadlington

Simon Fraidlin

Gerald Michael Hogan

Wing K Eng

AC power is converted to a low-voltage, high-current DC output by a power supply which contains two stages. The first stage is an AC to DC converter using a full wave bridge rectifier to convert the voltage from the AC source to an intermediate raw DC voltage. The second stage is a DC to DC forward converter using a transformer with its primary winding connected to the intermediate raw DC voltage through a switch which is cycled 'on' and 'off' at a predetermined frequency. During the switch 'on' portions of the cycle a current flows in the primary winding powering the output and charging an inductor which is connected to the secondary winding. When the switch is turned 'off', no current flows through the transformer and the load is powered by the energy stored in the inductor. A secondary coil is magnetically coupled to the inductor and has a induced voltage proportional to the output voltage. A controller is used to control the duty cycle of the switch based on the voltage in the secondary coil which determines the power supply output. The duty cycle of the switch is varied in response to variations in the load.

Dual stage AC to DC switching power supply with high voltage, low

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

A SEPIC converter powered off line is controlled to improve the input power factor by forcing the current in the input inductor to assume the same wave shape as the voltage across the inductor in series with the power switch to insure a sinewave input current. A switched capacitor is provided to provide brief holdover power to the converter should the input AC voltage fail.

Single conversion power factor correction using septic converter

An arrangement for improving the power factor at the input of an off-line switching type power supply is operative to extend the duration of the pulse current conducted by the diode rectifiers. A parallel LC ringing circuit is introduced between the AC line and the rectifier of the switching type power supply to enhance the voltage enabling conduction of the rectifying diodes and hence initiate current flow through the rectifying diodes earlier in each half cycle. This extends the conduction interval of the rectifying diodes significantly and enhances the power factor at the input to the switching type power supply.

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Garland, TX, United States of America

William F Slack