Reduced flicker AC LED lamp with separately shortable sections of an LED string

摘要

An LED lamp with an integrated circuit, a rectifier, and a string of series-connected LEDs rectifies an incoming AC signal. The integrated circuit includes power switches that can separately and selectably short out a corresponding one of several groups of LEDs in an LED string across which the rectified AC signal is present. As the voltage across the string increases, the integrated circuit controls the power switches to increase the number of LEDs through which current flows, whereas as the voltage across the string decreases the integrated circuit controls the power switches to decrease the number of LEDs through which current flows. The flow of LED string current is broken to reduce flicker. Alternatively, a valley fill capacitor peaks LED current during the valleys of the incoming AC signal to reduce flicker. LED current is regulated to provide superior efficiency, reliability, power-factor correction, and lamp over-voltage, -current, and -temperature protection.

主权项

1. A method comprising:
increasing a number of light emitting diodes (LEDs) in a string of series-connected LEDs through which an LED current flows from a first node to a second node as a voltage amplitude of a changing voltage signal increases to a peak amplitude, wherein the number has at least two discrete nonzero values as the voltage amplitude of the changing voltage signal increases, and wherein the changing voltage signal has a cycle period; decreasing the number of LEDs in the string of series-connected LEDs through which the LED current flows from the first node to the second node as the voltage amplitude of the changing voltage signal decreases from the peak amplitude, wherein the changing voltage signal has an associated current magnitude; and reducing the LED current during the cycle period by more than half of the current magnitude of the changing voltage signal for a duration of less than 12% of the cycle period.