Patent ID: 9241376
Filing Date: 2016-01-19
CPC Classification: G09G,H05B

Claim Text:
1. An LED backlight driver, comprising: a DC voltage input end used for inputting a DC voltage; a boost circuit used for boosting the DC voltage input from the DC voltage input end and outputting a boosted DC voltage; an LED string comprising a plurality of LEDs connected in series and a first resistor, the LED string receiving the boosted DC voltage from the boost circuit, and a sum of forward voltages of all of the LEDs in the LED string being less than or equal to the boosted DC voltage output from the boost circuit; and a constant current driver used for outputting a level signal to the boost circuit based on a voltage across the first resistor and a voltage for a triangular signal, the constant current driver comprising a triangular wave generator for generating the triangular signal, the triangular wave generator comprising a variable resistor, a first MOS transistor, a first comparator, a second comparator, a first capacitor, a second resistor, and a second MOS transistor; wherein one end of the variable resistor receives an input voltage, another end of the variable resistor is connected to a drain of the first MOS transistor, a source of the first MOS transistor is connected to one end of the second resistor and a negative terminal of a third comparator, another end of the second resistor is connected to a drain of the second MOS transistor, a source of the second MOS transistor is electrically grounded, a gate of the first MOS transistor is connected to an output terminal of the first comparator, a gate of the second MOS transistor is connected to an output terminal of the second comparator, a negative terminal of the first comparator is connected to one end of the first capacitor and the source of the first MOS transistor, another end of the first capacitor is electrically grounded, a positive terminal of the first comparator receives a first reference voltage, a negative terminal of the second comparator is connected to the output terminal of the first comparator, and a positive terminal of the second comparator receives a second reference voltage, when a charging voltage of the first capacitor is higher than the first reference voltage, the output terminal of the first comparator outputs a low voltage level to the gate of the first MOS transistor, the first MOS transistor is cut off so the input voltage stops charging the first capacitor, the low voltage level output by the output terminal of the first comparator is lower than the second reference voltage so the second MOS transistor is turned on, the first capacitor thus discharges through the second resistor, when the charging voltage of the first capacitor is decreased and lower than the first reference voltage, the output terminal of the first comparator outputs a high voltage level so the first MOS transistor is turned on, the high voltage level output by the output terminal of the first comparator is higher than the second reference voltage so the second MOS transistor is cut off, the input voltage starts charging the first capacitor again.