Patent number 8564270 is assigned to iWatt Inc. (
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present disclosure relates to switching power converters, and more specifically to improved on-time compensation for switching power converters.
"Switching power converters are used in many different electronic devices to generate a regulated output voltage from an input voltage by cyclically turning a switch on and off to adjust a level of the regulated output voltage. Some power converters operate in discontinuous current mode (DCM). In DCM, the switch is turned on to allow current to flow into an inductor of the switching power converter. The switch is then turned off to allow current to flow out of the inductor and out towards the load, thereby resetting the inductor. A dead time is inserted after the reset time that limits the switching frequency of the switch. If there is voltage ringing at the top side of the switch, the length of the dead time can be modified to allow the switching to occur at the valley of the ringing.
"Inserting the dead time is useful for reducing an amount of power lost in the switch itself, but has the negative side effect of reducing the power factor of the switching power converter. The power factor of a power converter impacts the power delivery system, such as the utility transmission lines that supply AC power to the power converter. If the power factor of a converter is low, the utility company must waste more power to deliver the required power to a load. To maximize the power factor, the average input current to the switching power converter should be proportional to the input voltage. In power converters that have a fixed on-time and no dead time, the average input current is naturally proportional to the input voltage and good power factor can be achieved. However, in power converters that have a dead time, the length of the dead time affects the level of the average input current and causes the average input current to deviate from being proportional to the input voltage. As a result, the power factor of the power converter is reduced by the dead time."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Embodiments of an improved DCM switching power converter that compensates for the effect of dead time duration when computing on-time duration. The dead time duration of the switching power converter is measured during a switching cycle and a baseline on-time duration for a switch of the switching power converter is determined. The dead time duration and baseline on-time duration are used in calculating the desired on-time duration of the switch for a subsequent switching cycle. The desired switch on-time duration regulates the output voltage to a desired voltage level. The desired switch on-time duration also maintains the average input current to the power converter substantially in proportion to the input voltage, thereby making the power converter appear as a resistive load and improving the power factor of the switching power.
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