AC LED lamp involving an LED string having separately shortable sections
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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.
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Citations
54 Claims
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1-30. -30. (canceled)
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31. An apparatus comprising:
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a first terminal that receives an alternating current (AC) input voltage; a second terminal that receives the AC input voltage, wherein an input voltage magnitude is present between the first terminal and the second terminal; a rectifier coupled to the first terminal and to the second terminal; a first string of one or more light emitting diodes (LEDs); and a second string of one or more LEDs, wherein during a first time period a first current flows through the first string of LEDs but no current flows through the second string of LEDs, wherein during a second time period a second current flows through both the first string of LEDs and through the second string of LEDs, and wherein the input voltage magnitude during the second time period is greater than the input voltage magnitude during the first time period. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45)
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46. An apparatus comprising:
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a rectifier that receives an alternating current input voltage and outputs an instantaneous rectified line voltage; a first string of one or more light emitting diodes (LEDs), wherein the instantaneous rectified line voltage is present on an input node of the first string of LEDs; a second string of one or more LEDs; and a control circuit that during a first time period causes a first current to flow through the first string of LEDs but does not allow any current to flow through the second string of LEDs, wherein during a second time period the control circuit causes a second, current to flow through both the first string of LEDs and through the second string of LEDs, and wherein the instantaneous rectified line voltage is greater during the second time period than during the first time period. - View Dependent Claims (47, 48, 49, 50, 51, 52, 53)
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54. An apparatus comprising:
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a first string of one or more light emitting diodes (LEDs), wherein a rectified line voltage is present on an input node of the first string of LEDs; a second string of one or more LEDs connected in series with the first string of LEDs; a third string of one or more LEDs connected in series with the second string of LEDs; a first terminal coupled to an input node of the second string of LEDs, wherein the first terminal is operable to prevent a current from flowing through the second string of LEDs during a first time period but to allow the current to flow through the second string of LEDs during a second time period and during a third time period; and a second terminal coupled to an input node of the third string of LEDs, wherein the second terminal is operable to prevent the current from flowing through the third string of LEDs during the first time period and during the second time period but to allow the current to flow through the third string of LEDs during a third time period, wherein each of the first string of LEDs, the second string of LEDs and the third string of LEDs has a different number of LEDs, and wherein each of the LEDs in the first string of LEDs is a white LED.
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Specification