AC LED lamp involving an LED string having separately shortable sections
First Claim
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, and wherein the number has at least two discrete nonzero values as the voltage amplitude of the changing voltage signal increases;
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 string of series-connected LEDs draws an average LED power; and
regulating the average LED power to be substantially constant over different peak amplitudes of the changing voltage signal by controlling the LED current based on the number of LEDs in the string through which the LED current flows.
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Abstract
An LED lamp includes a rectifier, an integrated circuit and a string of series-connected LEDs. The lamp receives an incoming AC signal such that a rectified version of the signal is present across the LED string. The integrated circuit includes a plurality of power switches. Each power switch is coupled so that it can separately and selectably short out a corresponding one of several groups of LEDs in the string. As the voltage across the string increases the integrated circuit controls the power switches such that the number of LEDs through which current flows increases, whereas as the voltage across the string decreases the integrated circuit controls the power switches such that the number of LEDs through which current flows decreases. LED string current flow is controlled and regulated to provide superior efficiency, reliability, anti-flicker, regulation against line voltage variations, power factor correction, and lamp over-voltage, over-current, and over-temperature protection.
26 Citations
20 Claims
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1. A method comprising:
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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, and wherein the number has at least two discrete nonzero values as the voltage amplitude of the changing voltage signal increases; 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 string of series-connected LEDs draws an average LED power; and regulating the average LED power to be substantially constant over different peak amplitudes of the changing voltage signal by controlling the LED current based on the number of LEDs in the string through which the LED current flows. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method comprising:
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rectifying a sinusoidal alternating current (AC) voltage signal having a voltage amplitude higher than one hundred volts so as to generate a changing voltage signal, wherein the changing voltage signal has a period, a current amplitude and an instantaneous voltage, and wherein each period of the changing voltage signal has a peak voltage amplitude; supplying the changing voltage signal to a string of series-connected light emitting diodes (LEDs), wherein the string of series-connected LEDs through which an LED current flows has a total forward voltage drop that approximately equals the instantaneous voltage during a portion of the period of the changing voltage signal, and wherein the string of series-connected LEDs has a light output; and regulating the light output of the string of series-connected LEDs to be substantially constant over different peak amplitudes of the changing voltage signal by controlling the LED current based on how many LEDs of the string of LEDs the LED current flows through. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A system comprising:
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a string of series-connected LEDs through which an LED current flows from a first node to a second node, wherein the string of series-connected LEDs draws an average LED power; a first terminal of an integrated circuit, wherein the first node is coupled to the first terminal, wherein a changing voltage signal is present on the first node, and wherein the changing voltage signal has a voltage amplitude, a current amplitude and a peak voltage amplitude; and a second terminal of the integrated circuit, wherein the second node is coupled to the second terminal, wherein a number of light emitting diodes (LEDs) in the string of series-connected LEDs is increased as the voltage amplitude of the changing voltage signal increases to the peak voltage amplitude, wherein the number of LEDs in the string of series-connected LEDs is decreased as the voltage amplitude of the changing voltage signal decreases from the peak voltage amplitude, and wherein the integrated circuit regulates the average LED power to be substantially constant over different peak amplitudes of the changing voltage signal by controlling the LED current based on the number of LEDs in the string through which the LED current flows. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A system comprising:
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a string of series-connected LEDs through which an LED current flows from a first node to a second node, wherein the string of series-connected LEDs draws an average LED power; a first terminal of an integrated circuit, wherein the first node is coupled to the first terminal, wherein a changing voltage signal is present on the first node, and wherein the changing voltage signal has a voltage amplitude, a current amplitude and a peak voltage amplitude; a second terminal of the integrated circuit, wherein the second node is coupled to the second terminal, wherein a number of light emitting diodes (LEDs) in the string of series-connected LEDs is increased as the voltage amplitude of the changing voltage signal increases to the peak voltage amplitude, wherein the number of LEDs in the string of series-connected LEDs is decreased as the voltage amplitude of the changing voltage signal decreases from the peak voltage amplitude, and wherein the integrated circuit regulates the average LED power to be substantially constant over different peak amplitudes of the changing voltage signal by controlling the LED current based on the number of LEDs in the string through which the LED current flows; and a control circuit of the integrated circuit that maintains a multi-bit digital value indicative of a voltage across the string of series-connected LEDs, wherein the string of series-connected LEDs has a power factor, and wherein the control circuit performs power factor correction of the power factor of the string of series-connected LEDs by controlling the LED current based at least in part on the multi-bit digital value. - View Dependent Claims (20)
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Specification