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High Power Factor AC-DC Converter

IP.com Disclosure Number: IPCOM000119249D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 3 page(s) / 77K

Publishing Venue

IBM

Related People

Ohnstad, GA: AUTHOR

Abstract

A high power factor AC-DC power supply is capable of producing a regulated low voltage DC output that is safety isolated from the AC power line using only a single power conversion stage. The power factor is about 0.9, where power factor is defined as the ratio of real power (watts) to apparent power (volt-amps).

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High Power Factor AC-DC Converter

      A high power factor AC-DC power supply is capable of
producing a regulated low voltage DC output that is safety isolated
from the AC power line using only a single power conversion stage.
The power factor is about 0.9, where power factor is defined as the
ratio of real power (watts) to apparent power (volt-amps).

      A power converter (refer to Fig. 1) utilizes a step-down
buck-derived topology operating with current mode feedback.  The AC
input is rectified, but not capacitively filtered.  Thus, rectified
AC is applied to the high frequency switching section of the power
converter.  The absence of a large input filter capacitance means
that the AC line current is determined by the average power converter
current flowing through the HF switches rather than capacitive
charging current.  This power converter current is controlled by a
feedback control system to the HF switch section.

      Two feedback loops are used.  The voltage feedback loop
compares the output DC voltage to a reference, and controls the
average current flowing into the output filter as needed to maintain
a constant DC output voltage.  The bandwidth of this control loop
must be less than the power line frequency to assure that it controls
only average line current, while not appreciably influencing the
waveshape of AC line current.  A larger output capacitance is
utilized in the DC output filter section to compensate for the power
line frequency ripple that cannot be removed by the voltage control
loop du...