Method and apparatus to reduce line current harmonics from a power supply

#1. Field of the Disclosure

#The present invention relates generally to power supplies, and more specifically, the invention relates to reducing the input current harmonics of a power supply.

#2. Background

#Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

#FIG. 1 illustrates an example schematic of a boost converter including an example controller in accordance with the teachings of the present invention;

#FIG. 2A is a functional block diagram illustrating an example controller of FIG. 1 in accordance with the teachings of the present invention;

#In one aspect of the present invention, methods and apparatuses disclosed here for explanation purposes use a power converter to limit line current harmonics. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. Well-known methods related to the implementation have not been described in detail in order to avoid obscuring the present invention.

#Reference throughout this specification to “one embodiment,” “an embodiment,” “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment or example of the present invention. Thus, the appearances of the phrases “in one embodiment,” “in an embodiment,” “in one example” or “in an example” in various places throughout this specification are not necessarily all referring to the same embodiment. The particular features, structures or characteristics may be combined for example into any suitable combinations and/or sub-combinations in one or more embodiments or examples.

#As will be discussed below, various examples in accordance with the teachings of the present invention allow a power converter to employ a control technique to shape an input current waveform of the power converter. In the examples discussed, the input current waveform is controlled to be proportional to an input voltage waveform by varying an on time and an off time of a power switch in the power converter. More specifically, the control technique forces the on time of the power switch to be inversely proportional to a rectified time-varying input voltage VIN(t) by setting a constant volt-seconds for the off time. The off-time is controlled to be a constant product of (VOUT−VIN)×TOFF. In particular, integrating the quantity VOUT−VIN during the off time allows for a constant volt-seconds to be set during the off time. By setting the off time to have a constant volt-seconds, the on-time volt-seconds is forced to be substantially constant over a few switching cycles in order to maintain a volt-second balance that satisfies the properties of a boost inductor. A balance of volt-seconds on the boost inductor allows the on-time to be substantially inversely proportional to the input voltage. This relationship of on-time to input voltage sets up a convenient and simple means for controlling the input current as a function of the rectified time varying input voltage VIN(t) which is representative of the input line voltage. If the input current is sensed by integrating the input current during the on time, the on time can be terminated by reaching a constant integral value of