Circuit and method of driving light emitting diodes
An LED drive method is disclosed. In this way, the LED drive method allows not only the reference voltage to be periodically updated on the basis of the feedback drive voltages but also the drive voltage control signal to be generated using the updated reference voltage, in order to adjust the LED drive voltage applied to the LED array. Therefore, the LED drive circuit is hardly affected by the external environmental noise.
1. A light-emitting diode drive circuit comprising:
a light-emitting diode array configured to include light-emitting diode strings which each include a plurality of serially connected light-emitting diodes;
a power supplier configured to apply a drive voltage to the light-emitting diode array;
current drivers connected to the respective light-emitting diode strings and configured to control current signals flowing along the respective light-emitting diode strings in response to a first control signal including light-emitting diode current information; and
a main controller configured to irregularly input each feedback drive voltage from the light-emitting diode strings and generate a second control signal which is used to adjust to the drive voltage applied from the power supplier to the light-emitting diode array.
2. The light-emitting diode drive circuit of claim 1 , wherein the main controller includes:
an analog-to-digital converter configured to convert the feedback drive voltages from the light-emitting diode strings into digital signals;
a head room controller configured to irregularly input each of the digital feedback drive voltages from the analog-to-digital converter and generate a digital control signal;
a digital-to-analog converter configured to convert the digital control signal from the head room controller into the second control signal corresponding to an analog signal;
a memory into which information necessary to generate the second control signal is stored; and
a controller configured to control the analog-to-digital converter, the head room controller, the digital-to-analog converter and the memory.
3. The light-emitting diode drive circuit of claim 2 , wherein the head room controller includes:
a drive voltage sampler configured to sample multiple times each of the digital feedback drive voltages from the analog-to-digital converter in irregular intervals;
a median filter configured to calculate an average value of the multiple samples for each of the feedback drive voltages; and
a reference voltage estimator configured to periodically update a reference voltage using the average values of the feedback drive voltages applied from the median filter.
4. The light-emitting diode drive circuit of claim 3 , wherein the head room controller further includes a control signal generator configured to generate the digital control signal, which is used to adjust the drive voltage being generated in the power supplier, using the reference voltage from the reference voltage estimator and the average values of the digital feedback drive voltages from the median filter.
5. The light-emitting diode drive circuit of claim 1 , wherein the main controller generates the second control signal being used in the adjustment of the drive voltage when gate signals applied to the current drivers have a high level.
6. A method of driving a light-emitting diode drive circuit which includes a light-emitting diode array configured to include light-emitting diode strings each having a plurality of serially connected light-emitting diodes, a power supplier configured to apply a drive voltage to the light-emitting diode array, and current drivers connected to the respective light-emitting diode strings and configured to control current signals flowing along the respective light-emitting diode strings in response to a first control signal including light-emitting diode current information, the method comprising:
measuring multiple times a feedback drive voltage from each of the light-emitting diode strings in irregular intervals;
calculating an average value of the measured multiple signals for each of the feedback drive voltages to generate average values of the feedback drive voltages;
periodically updating a reference voltage using the average values of the feedback drive voltages applied from the median filter; and
generating a second control signal, which is used to adjust the drive voltage being applied from the power supplier to the light-emitting diode array, using the updated reference voltage and the average values of the digital feedback drive voltages.
7. The method of claim 6 , further comprises detecting whether gate signals being applied to the current drivers have any one of high and low levels.
8. The method of claim 7 , wherein the second control signal used to adjust the drive voltage applied to the light-emitting diode array is generated when the gate signals being applied to the current drivers have the high level.
9. The method of claim 6 , wherein the measurement of the feedback drive voltages includes:
converting the feedback drive voltages from the light-emitting diode strings into digital signals; and
sampling multiple times each of the digital feedback drive voltages in the irregular intervals.
10. The method of claim 9 , wherein the calculation of the average values calculates an average value of the multiple samples for each the feedback drive voltages using a median filter.
11. The method of claim 9 , wherein the measurement of the feedback drive voltages enables measuring time points of the feedback drive voltages to be differently set every period.