Patent ID: 9024532
Filing Date: 2015-05-05
Classification: G02F,H05B

Abstract:
1. A direct type LED backlight, comprising: a power converting circuit, which converts an alternating voltage generated from an external liquid crystal display into a direct voltage and outputs it; multiple LED strings connected in parallel, wherein each LED string comprises a predetermined amount of LEDs connected in series, which receives the direct voltage from the power converting circuit; and a feed-back controlling circuit, which controls the power converting circuit to control an intensity of output of the direct voltage according to a voltage across the first resistor; wherein, the feed-back controlling circuit comprises: a first comparator, which compares the voltage across the first resistor of the multiple LED strings with a predetermined voltage threshold; and a square-wave generator, which generates a square-wave signal; wherein output a first level signal when the voltage across the first resistor of each LED string is larger than the predetermined voltage threshold; output a second level signal when the voltage across the first resistor in one of the multiple LED strings is smaller than the predetermined voltage threshold; wherein, the square-wave generator reduces the duty cycle of the square wave signal in response to the first level signal, the square-wave generator increases the duty cycle of the square-wave signal in response to the second level signal; wherein, the predetermined amount is limited so that a direct voltage of the LED string emitting light normally is smaller than or equal to the direct voltage output from the power converting circuit.