LED Backlight Driving Circuit and Method for Driving the LED Backlight Driving Circuit

1. A light emitting diode (LED) backlight driving circuit, comprising: a power supply; at least two connected-in-parallel LED lightbars connected to an output end of the power supply; a power feedback assembly coupled to each of the LED lightbars; and an adjusting-power block coupled to the power feedback assembly; wherein a reference end of the power feedback assembly receives a reference power, and the power feedback assembly receives an output power of each of the LED lightbars; wherein the power feedback assembly obtains a difference value of the reference power compared with the output power of the LED lightbar, and the adjusting-power block adjusts the output power of a corresponding LED lightbar according to the difference value until the difference value is less than a preset threshold value; wherein the power feedback assembly comprises a detecting voltage block that detects a voltage of the LED lightbar, a detecting current block that detects current of the LED light bar, and a comparing power block coupled to the detecting voltage block and the detecting current block, the comparing power block is coupled to the adjusting-power block; wherein the detecting voltage block comprises a first amplifier, a first resistor, a second resistor, a third resistor, and a fourth resistor; a first input end of the first amplifier receives an output voltage of the power supply through the first resistor and is coupled to an output end of the first amplifier through the second resistor, and a second input end of the first amplifier receives the voltage of the cathode end of the LED lightbar through the third resistor and is coupled to a ground terminal of the LED backlight driving circuit through the fourth resistor; the output end of the first amplifier is coupled to the power feedback assembly.

2. The LED backlight driving circuit of claim 1 , wherein the adjusting-power block comprises a third amplifier, a fourth amplifier, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor; a second input end of the third amplifier is coupled to an output end of the power feedback assembly through the fifth resistor, receives a reference voltage through the sixth resistor, and is coupled to an output end of the third amplifier through the seventh resistor;- the output end of the third amplifier is coupled to a first input end of the fourth amplifier through the eighth resistor, and the first input end of the fourth amplifier is coupled to an output end of the fourth amplifier through the ninth resistor; a second input end of the fourth amplifier is coupled to a ground terminal of the LED backlight driving circuit; wherein the adjusting-power block further comprises a converting unit; the converting unit comprises a first controllable switch, a second controllable switch, and a storage capacitor; a first end of the storage capacitor is coupled to the ground terminal of the LED backlight driving circuit, and a second end of the storage capacitor is coupled to the sixth resistor through the second controllable switch and is coupled to the output end of the fourth amplifier through the first controllable switch; the first controllable switch and the second controllable switch alternately turn on; when the first controllable switch turns on, the reference voltage is provided by the storage capacitor.

3. The LED backlight driving circuit of claim 2 , wherein resistance value of the sixth resistor is equal to resistance value of the seventh resistor, resistance value of the fifth resistor is less than resistance value of the seventh resistor.

4. The LED backlight driving circuit of claim 1 , further comprising a reference power selecting block; the reference power selecting block comprises a multichannel selecting comparator coupled to a cathode end of each of the LED lightbars; the multichannel selecting comparator is used to select a minimum voltage of the cathode end of the LED lightbar in all voltages of the cathode ends of the LED lightbars; each of the LED lightbars corresponds to one comparing unit; a first input end of the comparing unit is coupled to an output end of the multichannel selecting comparator, and a second input end of the comparing unit is coupled to the cathode end of the corresponding LED lightbar; wherein the reference power selecting block further comprises an encoder, a decoder, a switching unit; the encoder reads an output value of each of the comparing unit; the decoder finds the LED lightbar having the minimum voltage in the cathode end of the LED lightbar and controls the switching unit to switch the output power of the LED lightbar having the minimum voltage in the cathode end of the LED lightbar to a reference end of a corresponding power feedback assembly; the output power of the corresponding LED lightbar is regarded as the reference power.

5. The LED backlight driving circuit of claim 1 , wherein the comparing power block comprises a first multiplier and a second amplifier; output ends of the detecting voltage block and the detecting current block are coupled to the first multiplier; an output end of the first multiplier is coupled to a second input end of the second amplifier; a first input end of the second amplifier receives the reference power, an output end of the second amplifier is coupled to the adjusting-power block.

6. The LED backlight driving circuit of claim 1 , wherein the power feedback assembly comprises a detecting voltage block that detects a voltage of the LED lightbar, a detecting current block that detects current of the LED lightbar, and a comparing power block coupled to the detecting voltage block and the detecting current block; the comparing power block is coupled to the adjusting-power block, and a reference end of the comparing power block receives the reference power; the detecting current block comprises a sampling resistor connected in series between a cathode end of the LED lightbar and a ground terminal of the LED backlight driving circuit; the adjusting-power block provides an adjusting voltage to the cathode end of the LED lightbar; the power feedback assembly receives the adjusting voltage.

7. The LED backlight driving circuit of claim 6 , wherein the comparing power block comprises a first multiplier and a second amplifier; output ends of the detecting voltage block and the detecting current block are coupled to the first multiplier; an output end of the first multiplier is coupled to a second input end of the second amplifier; a first input end of the second amplifier receives the reference power, an output end of the second amplifier is coupled to the adjusting-power block.

8. The LED backlight driving circuit of claim 1 , further comprising a reference power selecting block; the reference power selecting block comprises a multichannel selecting comparator coupled to the cathode end of each of the LED lightbars; the multichannel selecting comparator is used to select a minimum voltage of the cathode end of the LED lightbar in all voltages of the cathode ends of the LED lightbars; each of the LED light bars corresponds to one comparing unit; a first input end of the comparing unit is coupled to an output end of the multichannel selecting comparator, and a second input end of the comparing unit is coupled to the cathode end of the corresponding LED lightbar; wherein the power feedback assembly comprises a detecting voltage block that detects a voltage of the LED lightbar, a detecting current block that detects current of the LED lightbar, and a comparing power block coupled to the detecting voltage block and the detecting current block: the comparing power block is coupled to the adjusting-power block; wherein the reference power selecting block further comprises an encoder, a decoder, a switching unit; the encoder reads an output value of each of the comparing unit; the decoder finds the LED lightbar having the minimum voltage in the cathode end of the LED lightbar and controls the switching unit to switch the output power of the LED lightbar having the minimum voltage in the cathode end of the LED lightbar to a reference end of a corresponding comparing power block; the output power of the corresponding LED lightbar is regarded as the reference power; wherein the detecting voltage block comprises a first amplifier, a first resistor, a second resistor, a third resistor, and a fourth resistor; a first input end of the first amplifier receives an output voltage of the power supply through the first resistor and is coupled to an output end of the first amplifier through the second resistor, and a second input end of the first amplifier receives the voltage of the cathode end of the LED lightbar through the third resistor and is coupled to a ground terminal of the LED backlight driving circuit through the fourth resistor; wherein the cathode end of the LED light bar is connected with a dimming controllable switch in series; the detecting current block comprises a sampling resistor connected in series between the dimming controllable switch and the ground terminal of the LED backlight driving circuit; the adjusting-power block provides an adjusting voltage to an output end of the dimming controllable switch; wherein the comparing power block comprises a first multiplier, a second multiplier, and a second amplifier; the first multiplier receives the adjusting voltage of the adjusting-power block and is coupled to the output end of the first amplifier, and an output end of the first multiplier is coupled to a second input end of the second amplifier; the switching unit of the reference power selecting block switches the output end of the first amplifier corresponding to the LED lightbar having the minimum voltage in the cathode end of the LED lightbar and the adjusting voltage to the second multiplier; the second multiplier outputs the reference power to a first input end of the second amplifier; an output end of the second amplifier is coupled to the adjusting-power block; wherein the adjusting-power block comprises a third amplifier, a fourth amplifier, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor; a second input end of the third amplifier is coupled to an output end of the comparing power block through the fifth resistor, receives a reference voltage through the sixth resistor, and is coupled to an output end of the third amplifier through the seventh resistor; the output end of the third amplifier is coupled to a first input end of the fourth amplifier through the eighth resistor, and the first input end of the fourth amplifier is coupled to an output end of the fourth amplifier through the ninth resistor; a second input end of the fourth amplifier is coupled to the ground terminal of the LED backlight driving circuit; wherein the adjusting-power block further comprises a converting unit; the converting unit comprises a first controllable switch, a second controllable switch, and a storage capacitor; a first end of the storage capacitor is coupled to the ground terminal of the LED backlight driving circuit, and a second end of the storage capacitor is coupled to the sixth resistor through the second controllable switch and is coupled to the output end of the fourth amplifier through the first controllable switch; the first controllable switch and the second controllable switch alternately turn on; the fourth amplifier outputs the adjusting voltage to an output end of a. corresponding dimming controllable switch; when the first controllable switch turns on, the reference voltage is provided by the storage capacitor; resistance value of the sixth resistor is equal to resistance value of the seventh resistor, and resistance value of the eighth resistor is equal to resistance value of the ninth resistor; resistance value of the sampling resistor is 1Ω.

9. A method for driving a light emitting diode (LED) backlight driving circuit, the LED backlight driving circuit comprising a power supply and at least two connected-in-parallel LED lightbars coupled to an output end of the power supply; the method comprising: A: detecting an output power of each of the LED lightbars, presetting a reference power, and obtaining a difference value of the reference power compared with the output power of each of the LED lightbars; and B: adjusting the output power of each of the LED lightbars until the difference value is less than a preset threshold value, wherein the step B comprises: presetting a number increased or decreased: if the difference value is a positive value and greater than the preset threshold value, adding the number increased to the output power of the LED lightbar, and determining whether the difference value between the added output power of the LED lightbar and the reference power is less than the preset threshold value: if the difference value between the added output power of the LED lightbar and the reference power is greater than or equal to the preset threshold value, continually adding the number increased to the output power of the LED lightbar until the different value is less than the preset threshold value; if the difference value is a negative value, and an absolute value of the difference value is greater than the preset threshold value, subtracting the number decreased fro m the output power of the LED lightbar, and determining whether the difference value between the subtracted output power of the LED lightbar and the reference power is less than the preset threshold value; if the difference value between the subtracted output power of the LED lightbar and the reference power is greater than or equal to the preset threshold value, continually subtracting the number decreased from the output power of the LED lightbar until the different value is less than the preset threshold value.