Method and apparatus achieving a high power factor with a flyback transformer
First Claim
1. An AC-to-DC converter, comprising:
- a full-wave rectifier;
a transformer, with a primary side and a secondary side, coupled to an output of the full-wave rectifier;
a power switch coupled in series with the primary side of the transformer in a flyback arrangement and operable to enable and disable current flow through the primary side of the transformer;
a current sense element coupled to the primary side of the transformer to sense current flow through the primary side of the transformer; and
a switching controller coupled to the current sense element and power switch and configured to measure current through the primary side of the transformer via the current sense element and generate a power switch control signal to control the power switch at a frequency with a duty factor that changes non-linearly as a function of an instantaneous current through the primary side of the transformer.
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Abstract
Common household power transformers (e.g., “wall warts”) typically exhibit poor power factors, which, in turn, cause energy losses to power grids and adversely affect current waveforms in the power grids. AC-to-DC power conversion with good power factor is achieved using a transformer, power switch coupled in series with the primary side of the transformer, and switching controller. The switching controller measures current through the primary side of the transformer, via a current sense element, and controls the power switch to enable and disable current through the primary side of the transformer. The switching controller generates a power switch control signal at a frequency with a duty factor that changes non-linearly as a function of an instantaneous current through the primary side of the transformer. As a result, a power factor of greater than 90% or even 95% can be achieved.
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Citations
23 Claims
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1. An AC-to-DC converter, comprising:
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a full-wave rectifier; a transformer, with a primary side and a secondary side, coupled to an output of the full-wave rectifier; a power switch coupled in series with the primary side of the transformer in a flyback arrangement and operable to enable and disable current flow through the primary side of the transformer; a current sense element coupled to the primary side of the transformer to sense current flow through the primary side of the transformer; and a switching controller coupled to the current sense element and power switch and configured to measure current through the primary side of the transformer via the current sense element and generate a power switch control signal to control the power switch at a frequency with a duty factor that changes non-linearly as a function of an instantaneous current through the primary side of the transformer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of providing AC-to-DC conversion, comprising:
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rectifying an AC input signal to produce a rectified signal; transferring the rectified signal through a primary side of a transformer; measuring instantaneous current through the primary side of the transformer; and switching current through the primary side of the transformer at a frequency with a duty factor that changes non-linearly as a function of the instantaneous current through the primary side of the transformer. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A switching controller for controlling current through a flyback transformer in an AC-to-DC converter, comprising:
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calculation circuitry to produce a first signal derived as a function of an output voltage of a flyback transformer and a current through a primary side of the flyback transformer; non-linear circuitry configured to generate a second signal to have a non-linear, time-varying function defined in part by operation of the flyback transformer; and a comparator configured to generate a power switch control signal having an active state set by a clock signal and reset by a result of comparing the first signal with the second signal to enable and disable current through the flyback transformer.
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Specification