LED driving device and LED driving method
The present disclosure relates to an LED driving technology. According to the present disclosure, it is possible to increase the fineness of the gray scale without increasing a frequency of a clock by combining a plurality of driving current sources to generate a driving current supplied to one driving line.
1. A light emitting diode (LED) driving device for driving a plurality of LEDs arranged on a panel, the LED driving device comprising:
a plurality of driving current sources connected in parallel to each other;
a pulse width modulation (PWM) controlling circuit configured to generate a plurality of PWM signals according to a gray scale value for an LED; and
a plurality of switch circuits configured to control an output of each driving current source for the LED according to each PWM signal,
wherein each driving current source supplies each driving current to one driving line, and wherein the driving current flowing through the one driving line is a sum of outputs of the driving current sources.
2. The LED driving device of claim 1 , wherein a PWM signal comprises an ON section and an OFF section, wherein the length of the ON section is adjusted in units of cycles of a clock.
3. The LED driving device of claim 2 , wherein a difference in the length of the ON section between the PWM signals is within the length of one cycle of the clock.
4. The LED driving device of claim 1 , wherein the gray scale value has a range corresponding to 2 to the power of N (N is a natural number) and the number of the plurality of driving current sources is N.
5. The LED driving device of claim 1 , wherein the number of the plurality of driving current sources is N and the PWM controlling circuit is configured to assign a value of a quotient, obtained by dividing the gray scale value by N, to each of the driving current sources and distribute a remainder R (R is 0 or a natural number less than N) respectively to R driving current sources to generate the plurality of PWM signals.
6. The LED driving device of claim 1 , wherein the levels of the driving currents outputted from respective driving current sources are substantially identical.
7. The LED driving device of claim 1 , wherein the plurality of driving current sources are implemented in a form of current mirrors with respect to one common current source.
8. An LED driving device for driving an LED arranged on a panel, the LED driving device comprising:
a first driving current source supplying a first driving current to one driving line;
a second driving current source connected in parallel to the first driving current source and supplying a second driving current to the one driving line;
a PWM controlling circuit configured to generate a first PWM signal and a second PWM signal by distributing a gray scale value for the LED;
a first switch circuit configured to control an output of the first driving current source for the LED according to the first PWM signal; and
a second switch circuit configured to control an output of the second driving current source for the LED according to the second PWM signal,
wherein the driving current flowing through the one driving line is a sum of the first driving current and the second driving current.
9. The LED driving device of claim 8 , wherein the PWM controlling circuit is configured to adjust the lengths of ON sections of the first PWM signal and the second PWM signal in units of cycles of a clock.
10. The LED driving device of claim 9 , wherein the PWM controlling circuit controls the first PWM signal and the second PWM signal such that the lengths of their ON sections are identical to each other or such that a difference in the length of the ON section therebetween is within the length of one cycle of the clock.
11. The LED driving device of claim 8 , further comprising a first transistor having a first terminal connected to a driving voltage and a basic current source connected to a second terminal of the first transistor,
wherein the first driving current source forms a current mirror structure with respect to the basic current source using a second transistor having a gate commonly connected with the first transistor and a first terminal connected to the driving voltage, and
wherein the second driving current source forms a current mirror structure with respect to the basic current source using a third transistor having a gate commonly connected with the first transistor and a first terminal connected to the driving voltage.
12. The LED driving device of claim 11 , wherein the first driving current source further comprises a fourth transistor connected in series with the second transistor and the second driving current source further comprises a fifth transistor connected in series with the third transistor,
wherein a gate of the fourth transistor is connected to an output terminal of a first amplifier to which a second terminal of the first transistor and a second terminal of the second transistor are connected as input terminals, and
wherein a gate of the fifth transistor is connected to an output terminal of a second amplifier to which a second terminal of the first transistor and a second terminal of the third transistor are connected as input terminals.
13. The LED driving device of claim 12 , wherein the first switch circuit comprises a first switch configured to control the connection between the second terminal of the second transistor and the first amplifier and a second switch configured to control the connection between the gate of the fourth transistor and the first amplifier and the second switch circuit comprises a third switch configured to control the connection between the second terminal of the third transistor and the second amplifier and a fourth switch configured to control the connection between the gate of the fifth transistor and the second amplifier, wherein the first amplifier and the second amplifier have the same property.
14. The LED driving device of claim 12 , wherein the first transistor, the second transistor, the third transistor, the fourth transistor, and the fifth transistor are PNP type transistors.
15. A method of driving a plurality of LEDs arranged on a panel, the method comprising:
connecting one LED to one driving line according to a scan signal;
identifying image data comprising a gray scale value for the one LED;
dividing the gray scale value into N gray scale values (N is a natural number of 2 or higher) and generating a plurality of PWM signals according to the divided gray scale values; and
controlling outputs of N driving current sources connected to the one driving line according to the plurality of PWM signals,
wherein the N driving current sources are connected in parallel to each other, and wherein the driving current flowing through the one driving line is a sum of the outputs of the driving current sources.
16. The method of claim 15 , wherein controlling the outputs of the N driving current sources comprises dividing one frame into M subframes (M is a natural number of 2 or higher), controlling the outputs of the N driving current sources such that (M−1) subframes respectively have ON sections having a same length, and controlling the outputs of the N driving current sources such that one remaining subframe has an ON section having a length different from the lengths of the ON sections in the (M−1) subframes by the length of one cycle of a clock.
17. The method of claim 15 , wherein controlling the outputs of the N driving current sources comprises dividing one frame into M subframes (M is a natural number of 2 or higher) and controlling the outputs of the N driving current sources such that a difference between two ON sections of two driving current sources is within one clock cycle in each subframe and such that a difference between any two sums of the ON sections of the N driving current sources assigned to two subframes is within one clock cycle.