LINE RIPPLE COMPENSATION FOR SHIMMERLESS LED DRIVER

摘要

A power converter controller includes an oscillator, a drive circuit, and a frequency modulator. The drive circuit receives a clock signal from the oscillator and generates a drive signal in response thereto to control switching of a switch of the power converter. The frequency modulator controls the frequency of the clock signal in response to an inductor voltage across an inductor of the energy transfer element to reduce a peak-to-peak ripple value in an output current of the power converter. The frequency modulator controls the frequency of the clock signal during each line half cycle to be a fixed frequency when the inductor voltage is less than or equal to a threshold voltage. When the inductor voltage is greater than the threshold voltage the frequency modulator varies the frequency to be less than the fixed frequency to adjust a shape of an input current of the power converter.

主权项

1. A controller for use in an ac-to-dc power converter, the controller comprising:
an oscillator coupled to generate a clock signal having a frequency; a drive circuit coupled to receive the clock signal and to generate a drive signal in response thereto, the drive signal to control switching of a switch to control a transfer of energy across an energy transfer element from an input of the power converter to an output of the power converter, wherein a switching frequency of the drive signal is based on the frequency of the clock signal and is much greater than a lower frequency of a time-varying inductor voltage across an inductor of the energy transfer element; and a frequency modulator coupled to the oscillator to control the frequency of the clock signal during each line half cycle of the time-varying inductor voltage in response to a magnitude of the time-varying inductor voltage in order to reduce a peak-to-peak ripple value in an output current of the power converter that is due to the lower frequency time variations in the inductor voltage, wherein the frequency modulator controls the frequency of the clock signal during each line half cycle to be a fixed frequency when the magnitude of the inductor voltage is less than or equal to a threshold voltage, and wherein the frequency modulator varies the frequency of the clock signal during each line half cycle to be less than the fixed frequency to adjust a shape of an input current of the power converter when the magnitude of the inductor voltage is greater than the threshold voltage.