LED backlight circuit system
View Patent ↗An improved electrical circuit design and method to drive a plurality of LEDs in an LCD backlight in order to produce a uniform color distribution across the entire viewable surface of the display. The embodiments disclosed have features that permit a predetermined reduction in the amount of current provided to the LEDs positioned along the edge of the display region. This results in color uniformity, and consequently, an improved picture quality.
1. An LED active shunt current control system for controlling current flow through an LED backlight network of an LCD display, comprising:
a plurality of backlight LEDs connected in series;
wherein edge LEDs are divided from center LEDs in the display backlight by an electrical node;
a shunt tap positioned at the electrical node between the center LEDs and the edge LEDs;
wherein the shunt tap is adapted to divert a predetermined amount of current flowing through the center LEDs away from the edge LEDs;
an analog output generator in electrical communication with an edge control circuit and a shunt control circuit;
wherein the analog output generator is adapted to generate an edge current setting and a shunt current setting;
the edge control circuit is in electrical communication with the plurality of LEDs;
wherein the edge control circuit is adapted to receive the edge setting and provides an LED voltage at an anode of a first center LED to maintain the edge current as specified by the edge setting;
a shunt control circuit in electrical communication with a shunt control transistor; and
wherein the shunt control circuit is adapted to receive the shunt setting and provide a voltage to the shunt control transistor to maintain the shunted current as specified by the shunt setting.
2. The system of claim 1 , wherein:
the amount of current reaching the edge LEDs is equal to the amount of current flowing through the center LEDs less the amount of current shunted through the shunt tap.
3. The system of claim 1 , wherein:
the output generator is a microprocessor.
4. The system of claim 1 , further comprising:
an edge current resistor connected downstream of the edge LEDs;
wherein the edge current resistor is adapted to cause an edge current feedback signal to be sent to the edge control circuit.
5. The system of claim 1 , further comprising:
a shunt current resistor downstream of the shunt control transistor;
wherein the placement of the shunt current resistor is adapted to cause a shunt current feedback signal to be sent to the shunt control circuit.
6. The system of claim 1 , including:
means for dimming the LEDs.
7. An LED active shunt current control system for controlling current flow through an LED backlight network of an LCD display, comprising:
a plurality of backlight LEDs connected in series;
wherein edge LEDs are divided from center LEDs in the display backlight by an electrical node;
a shunt tap positioned at the electrical node between the center LEDs and the edge LEDs;
wherein the shunt tap is adapted to divert a predetermined amount of current flowing through the center LEDs away from the edge LEDs;
an analog output generator;
wherein the analog output generator is adapted to generate an edge current setting and a shunt current setting;
an edge LED control circuit in electrical communication with the plurality of LEDs;
an edge current resistor in electrical communication with the edge control circuit;
wherein the edge current resistor is adapted to cause an edge current feedback signal to be sent to the edge control circuit;
wherein the edge control circuit is adapted to receive both the edge setting and the edge current feedback signal and provide an LED voltage at an anode of a first center LED to maintain an edge current as specified by the edge setting;
a shunt control circuit in electrical communication with a shunt control transistor;
wherein the shunt current resistor is downstream of the shunt control transistor and in electrical communication with the shunt control circuit;
wherein the placement of the shunt current resistor is adapted to cause a shunt current feedback signal to be sent to the shunt control circuit;
wherein the shunt control circuit is adapted to receive the shunt setting output and a shunt current feedback signal; and
wherein the shunt control circuit is adapted to produce an output voltage which controls transistor base current to maintain a shunt current specified by the output generator shunt setting.
8. The system of claim 7 , wherein:
the output generator is a microprocessor.
9. An LED active shunt current control system for controlling current flow through an LED backlight network, comprising:
a plurality of LEDs connected in series;
wherein edge LEDs are divided from center LEDs in a display backlight by an electrical node;
a shunt tap at the electrical node between the center LEDs and the edge LEDs;
a shunt control transistor in electrical communication with the shunt tap;
an analog output generator;
wherein the analog output generator is adapted to generate an edge current setting and a shunt current setting;
an edge control circuit;
an edge current resistor connected downstream of the edge LEDs;
wherein the edge current resistor is adapted to cause an edge current feedback signal to be sent to the edge control circuit;
wherein the edge control circuit is adapted to receive the edge setting and the edge current feedback signal and provide an LED voltage at an anode of a first center LED to maintain the edge current as specified by the edge setting;
a shunt control circuit in electrical communication with a shunt control transistor;
a shunt current resistor downstream of the shunt control transistor;
wherein the shunt resistor is adapted to cause a shunt current feedback signal to be sent to the shunt control circuit;
wherein the shunt control circuit is adapted to receive the shunt setting and the shunt feedback signal and provides a voltage to the shunt control transistor to maintain a shunted current as specified by the shunt setting;
wherein the shunt control transistor is adapted to operate in an analog mode to facilitate control of the shunt current; and
wherein the shunt transistor is adapted to divert a predetermined amount of current away from the edge LEDs through the shunt tap.
10. The system of claim 9 , including:
means for dimming the LEDs.
11. A method for achieving color uniformity in an LCD display with an LED backlight array, comprising:
arranging a plurality of backlight LEDs in series;
dividing edge LEDs from center LEDs with an electrical node;
placing a shunt tap at the electrical node;
diverting a predetermined amount of current away from the edge LEDs through the shunt tap in order to attenuate light emitted by the edge LEDs;
providing a shunt control transistor; and
engaging the shunt control transistor by directing a predetermined base current to the transistor.
12. The method of claim 11 , further including the steps of:
providing a shunt control circuit and a shunt current resistor downstream of the shunt control transistor;
directing a shunt current feedback signal to the shunt control circuit;
providing a voltage to the shunt control transistor to maintain the shunted current as specified by a predetermined shunt setting.
13. The method of claim 12 , further including the steps of:
providing an edge control circuit and an edge current resistor in electrical communication with the edge LEDs;
placing the edge current resistor at a location that causes an edge current feedback signal to be sent to the edge control circuit;
receiving an edge setting input and the edge current feedback signal; and
generating an LED voltage at an anode of a first center LED to maintain the edge current as specified by the edge setting.
14. The method of claim 13 , further including the steps of:
providing an analog output generator in electrical communication with the edge control circuit and the shunt control circuit;
using the output generator to output an edge current setting to set the edge current;
using the output generator to output a shunt current setting to set the shunt base current.
15. The method of claim 14 , wherein:
the analog output generator is a microprocessor.
16. The method of claim 11 , further including the steps of
providing an edge control circuit and an edge current resistor in electrical communication with the edge LEDs;
placing the edge current resistor at a location that causes an edge current feedback signal to be sent to the edge control circuit;
receiving an edge setting input and the edge current feedback signal; and
generating an LED voltage at an anode of a first center LED to maintain the edge current as specified by the edge setting.