Driving apparatus of light emitting diode and liquid crystal display using the same
A driving apparatus of a light emitting diode and a liquid crystal display are disclosed. The driving apparatus of a LED includes a plurality of LED groups in which LEDs are connected in series to each other; a plurality of constant voltage supply units that supplies a constant voltage required to drive a constant current to each of the plurality of LED groups and that outputs the constant voltage in which an output voltage is equal to or lower than an input voltage; and a pulse width modulation signal supply unit that supplies a pulse width modulation signal to each of the constant voltage supply units.
1. A driving apparatus of a light emitting diode (LED) comprising:
a plurality of light emitting diode groups in which n (wherein n is greater than 2 and less than 32) light emitting diodes are connected to each other;
a plurality of constant voltage supply units that supply a constant voltage to drive a constant current to the plurality of light emitting diode groups and that output the constant voltage in which an output voltage is equal to or lower than an input voltage, wherein each of the constant voltage supply units is connected to any one of the light emitting diode groups; and
a pulse width modulation signal supply unit that supplies a pulse width modulation signal to respective ones of the plurality of constant voltage supply units,
wherein the each constant voltage supply unit comprises,
a switching control signal supply unit that supplies a switching control signal;
a switching element that is turned on depending on a switching control signal supplied from the switching control signal supply unit and that adjusts a storing amount of energy depending on a turn-on time, wherein the switching element has a base terminal connected to a fifth node, a collector terminal connected to a third node, and a emitter terminal connected to a sixth node;
an inductor that stores energy supplied through the switching element, wherein the inductor is connected between the third node and a fourth node;
a diode that transfers energy stored in the inductor to each of the plurality of light emitting diode groups, wherein the diode has a cathode connected to a first node and an anode connected to the third node;
a current sensing resistor connected between the first node and a second node to sense a current transferred to the each light emitting diode group;
a current adjusting unit connected to the first node, the second node, and a seventh node to adjust a current sensed through the current sensing resistor;
a capacitor connected between the first node and the fourth node to reduce a ripple voltage of an output voltage supplied to the light emitting diode groups;
a first resistor connected between the sixth node and a ground voltage source to adjust a magnitude of an energy amount adjustment current from the switching control signal supply unit; and
a second resistor connected between the seventh node and the ground voltage source to adjust a magnitude of a feedback voltage from the current adjusting unit,
wherein the switching control signal supply unit supplies the switching control signal to the base terminal of the switching element through the fifth node, transfers the energy amount adjustment current to the emitter terminal of the switching element through the sixth node, and receives a feedback voltage from current adjusting unit through the seventh node.
2. The driving apparatus of claim 1 , wherein the light emitting diodes are connected in series to each other.
3. The driving apparatus of claim 1 , wherein the switching element comprises a metal oxide semiconductor field effect transistor.
4. The driving apparatus of claim 1 , wherein the switching element comprises a bipolar junction transistor.
5. A liquid crystal display comprising:
a liquid crystal panel; and
a driving apparatus of a light emitting diode that illuminates the liquid crystal panel at a rear of the liquid crystal panel,
wherein the driving apparatus of the light emitting diode comprises:
a plurality of light emitting diode groups in which n (wherein n is greater than 2 and less than 32) light emitting diodes are connected to each other;
a plurality of constant voltage supply units that supply a constant voltage to drive a constant current to each of the plurality of light emitting diode groups and that output the constant voltage in which an output voltage is equal to or lower than an input voltage, wherein each of the constant voltage supply units is connected to any one of the light emitting diode groups; and
a pulse width modulation signal supply unit that supplies a pulse width modulation signal to respective ones of the plurality of the constant voltage supply units,
wherein the each constant voltage supply unit comprises,
a switching control signal supply unit that supplies a switching control signal;
a switching element that is turned on depending on a switching control signal supplied from the switching control signal supply unit and that adjusts a storing amount of energy depending on a turn-on time, wherein the switching element has a base terminal connected to a fifth node, a collector terminal connected to a third node, and a emitter terminal connected to a sixth node;
an inductor that stores energy supplied through the switching element, wherein the inductor is connected between the third node and a fourth node;
a diode that transfers energy stored in the inductor to each of the plurality of light emitting diode groups, wherein the diode has a cathode connected to a first node and an anode connected to the third node;
a current sensing resistor connected between the first node and a second node to sense a current transferred to the each light emitting diode group;
a current adjusting unit connected to the first node, the second node, and a seventh node to adjust a current sensed through the current sensing resistor;
a capacitor connected between the first node and the fourth node to reduce a ripple voltage of an output voltage supplied to the light emitting diode groups;
a first resistor connected between the sixth node and a ground voltage source to adjust a magnitude of an energy amount adjustment current from the switching control signal supply unit; and
a second resistor connected between the seventh node and the ground voltage source to adjust a magnitude of a feedback voltage from the current adjusting unit,
wherein the switching control signal supply unit supplies the switching control signal to the base terminal of the switching element through the fifth node, transfers the energy amount adjustment current to the emitter terminal of the switching element through the sixth node, and receives a feedback voltage from current adjusting unit through the seventh node.
6. The liquid crystal display of claim 5 , wherein the light emitting diodes are connected in series to each other.