CN103327675A - LED driving system and method - Google Patents
LED driving system and method Download PDFInfo
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- CN103327675A CN103327675A CN2012100795071A CN201210079507A CN103327675A CN 103327675 A CN103327675 A CN 103327675A CN 2012100795071 A CN2012100795071 A CN 2012100795071A CN 201210079507 A CN201210079507 A CN 201210079507A CN 103327675 A CN103327675 A CN 103327675A
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/347—Dynamic headroom control [DHC]
Abstract
An LED driving system comprises a sampling unit, a control unit, a pulse width modulator, a DC/DC converter and a current balancing unit, wherein the sampling unit is used for detecting differential voltages of the cathodes of LED strings and feeding back the differential voltages to the control unit, the control unit is used for outputting a control signal according to the minimum value of the differential voltages of the cathodes of the LED strings except the LED string corresponding to the minimum value of the differential voltages when the minimum value of the differential voltages is within an expected range and the difference value between the maximum value and the minimum value of the differential voltages is larger than a preset value, the pulse width modulator is used for outputting a pulse width modulating signal according to the control signal so as to control the DC/DC converter to generate and output a proper direct voltage to drive an LED array, and the current balancing unit comprises an electric switch. The invention further provides an LED driving method. The LED driving system and method can solve the problem of thermal stress caused by power loss of the electric switch.
Description
Technical field
The present invention relates to a kind of backlight drive system, relate in particular to a kind of LED drive system and method for display device.
Background technology
Light-emitting diode (light emitting diode, LED) is because of the power and energy saving, and more and more is applied in the backlight of display device.Be to guarantee the display effect of display device, need uniform light source as the LED of backlight, therefore need in the LED drive system, to add the electronic switch of balanced balanced current, be connected in each LED string.Usually, traditional LED drive system must satisfy the highest LED string of pressure drop enough forward voltage, to reach the electric current of setting.Yet, because the different characteristic of LED causes under identical direct voltage drive, the pressure drop of every a string LED is different, and this has caused on electronic switch corresponding to the lower LED string of pressure drop shares larger pressure drop, electronic switch can produce larger power loss like this, and causes thermal stress issues.
Summary of the invention
In view of this, a kind of LED drive system need be provided, thermal stress issues can be improved.
In addition, also a kind of LED driving method need be provided, thermal stress issues can be improved.
The LED driving method that provides in the present embodiment, be used for driving light emitting diode matrix, described light emitting diode matrix comprises the light-emitting diode string of a plurality of parallel connections, pulse width modulating signal according to Pwm controller output, the input power of external power source is converted to suitable direct voltage, driving described light emitting diode matrix, and utilize electronic switch equiulbrium flow in the current balancing unit through the electric current of described a plurality of light-emitting diode strings; Detect the dividing potential drop of described a plurality of light-emitting diode string negative electrodes, described dividing potential drop comprises maximum and minimum value.Judge that the minimum value of described dividing potential drop is whether in the expectation interval; If the minimum value of described dividing potential drop is in described expectation interval, then whether the difference of the maximum of more described dividing potential drop and minimum value is greater than threshold values; If the difference of the maximum of described dividing potential drop and minimum value is greater than described threshold values, then select except light-emitting diode string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue light-emitting diode string, and whether the minimum value that repeats to judge the dividing potential drop of negative electrode in the residue light-emitting diode string is in the expectation interval; If the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, then the minimum value according to described dividing potential drop produces and outputs control signals to described Pwm controller.
Preferably, whether the minimum value of described dividing potential drop is in the expectation interval.If the minimum value of described dividing potential drop is not in described expectation interval, then according to the minimum value of described dividing potential drop and described expectation interval apart from difference, adjust the output to the duty ratio of the control signal of described Pwm controller, thereby finely tune the duty ratio of the pulse width modulating signal of described Pwm controller output.
Preferably, if the minimum value of described dividing potential drop is not in the expectation interval, then according to the minimum value of described dividing potential drop and described expectation interval apart from difference, the step of duty ratio that adjusts the output to the control signal of described Pwm controller also comprises: if the minimum value of described dividing potential drop less than the interval minimum value of described expectation, then output duty cycle is less controls signal to described Pwm controller.If the minimum value of described dividing potential drop is greater than the interval maximum of described expectation, then output duty cycle is larger controls signal to described Pwm controller.
Preferably, the difference of the maximum of described dividing potential drop and the minimum value dividing potential drop that whether also comprises more described a plurality of light-emitting diode string negative electrodes greater than the step of threshold values is with maximum and the minimum value of the dividing potential drop that obtains described a plurality of light-emitting diode string negative electrodes.Calculate the maximum of dividing potential drop of described a plurality of light-emitting diode string negative electrodes and the difference of minimum value.
The LED drive system that provides in the present embodiment, be used for driving light emitting diode matrix, described light emitting diode matrix comprises the light-emitting diode string of a plurality of parallel connections, and described LED drive system comprises DC-DC converter, sampling unit, control unit, Pwm controller and current balancing unit.Described DC-DC converter is used for the input power of external power source is converted to suitable direct voltage, to drive described light emitting diode matrix.Described sampling unit links to each other with the negative electrode of described light emitting diode matrix, is used for detecting the dividing potential drop of each light-emitting diode string negative electrode of described light emitting diode matrix.Described control unit links to each other with described sampling unit, comprises comparing unit, subtrator and signal generation unit.Described comparing unit is used for the relatively dividing potential drop of each light-emitting diode string negative electrode, with maximum and the minimum value of the dividing potential drop that obtains described a plurality of light-emitting diode string negative electrodes, and whether the minimum value of the dividing potential drop of more described a plurality of light-emitting diode string negative electrodes is in the expectation interval.Described subtrator is used for minimum value in the dividing potential drop of described a plurality of light-emitting diode string negative electrodes in described expectation interval the time, maximum and the minimum value of the dividing potential drop of described a plurality of light-emitting diode string negative electrodes are subtracted each other, with the maximum of the dividing potential drop that obtains described a plurality of light-emitting diode string negative electrodes and the difference of minimum value.Wherein said comparing unit is used for also judging that whether the difference of the maximum of dividing potential drop of described a plurality of light-emitting diode string negative electrodes and minimum value is greater than described threshold values, and in the difference of the maximum of described dividing potential drop and minimum value during greater than described threshold values, select outside light-emitting diode string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue light-emitting diode string, and whether the minimum value of dividing potential drop that continues the light-emitting diode string negative electrode more again selected is in described expectation interval.Described signal generation unit is used for when the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, according to minimum value generation and the output control signal of described dividing potential drop.Described Pwm controller links to each other with described control unit, and according to described control signal output pulse width modulation signal.The negative electrode of each light-emitting diode string all links to each other in described current balancing unit and the described light emitting diode matrix, is used for equiulbrium flow through the electric current of described a plurality of light-emitting diode strings, and described current balancing unit comprises electronic switch.
Preferably, described electronic switch comprises triode, and described triode is used for equiulbrium flow through the electric current of described a plurality of light-emitting diode strings.
Preferably, described LED drive system also comprises feedback unit, described feedback unit links to each other with the output of described DC-DC converter, be used for according to described direct voltage produce and output feedback signal to described Pwm controller, to adjust the duty ratio of described pulse width modulating signal.
Preferably, described subtrator also is used for minimum value in the dividing potential drop of described a plurality of light-emitting diode string negative electrodes not in described expectation is interval the time, calculate described a plurality of light-emitting diode string negative electrodes dividing potential drop minimum value and described expect the interval apart from difference.
Preferably, described signal generation unit also is used for minimum value in described dividing potential drop not in described expectation is interval the time, according to the minimum value of described dividing potential drop and described expectation interval apart from the difference generation and export the control signal of duty ratio corresponding.
Preferably, described LED drive system also comprises memory cell, and described memory cell is used for storing described expectation interval value and described threshold values.
Above-mentioned LED drive system and method, in the minimum value of the dividing potential drop of light-emitting diode string negative electrode in described expectation interval, and the maximum of described dividing potential drop and the difference of minimum value are during greater than described threshold values, outside light-emitting diode string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode is regulated the duty ratio of control signal in the residue light-emitting diode string, output with the control impuls width modulator, and then the control DC-DC converter exports the direct voltage of light emitting diode matrix, the thermal stress issues that causes because of power loss to improve electronic switch to.
Description of drawings
Fig. 1 is the module map of LED drive system in an embodiment of the present invention.
Fig. 2 is the module map of LED drive system in another execution mode of the present invention.
Fig. 3 is the flow chart of LED driving method in an embodiment of the present invention.
The main element symbol description
External power source Vin
Led array 20
LED string 20a, 20b, 20c
Comparing unit 1013
Signal generation unit 1014
DC-DC converter 103
Feedback unit 104
Divider resistance 104a, 104b
Following embodiment further specifies the present invention in connection with above-mentioned accompanying drawing.
Embodiment
Fig. 1 is the module map of light-emitting diode in an embodiment of the present invention (Light Emitting Diode, LED) drive system 10.LED drive system 10 is used for driving LED array 20, comprises sampling unit 100, control unit 101, Pwm controller 102, DC-DC converter 103 and current balancing unit 105.In the present embodiment, led array 20 comprises LED string 20a, 20b, the 20c of a plurality of parallel connections, each LED string 20a, 20b, 20c forward are composed in series by a plurality of LED, the anode of each LED string 20a, 20b, 20c refers to the anode of first LED of this LED string, and the negative electrode of LED string 20a, 20b, 20c refers to the negative electrode of last LED of this LED string.In like manner, the negative electrode of led array 20 refers to the common end of LED string 20a, 20b, 20c negative electrode, and the anode of led array 20 refers to the common end of LED string 20a, 20b, 20c anode.DC-DC converter 103 links to each other with external power source Vin, Pwm controller 102 and led array 20, be used for the pulse width modulating signal according to Pwm controller 102 outputs, the input power of external power source Vin is converted to suitable direct voltage, with driving LED array 20.
In the present embodiment, current balancing unit 105 is connected to the negative electrode of each LED string 20a, 20b, 20c in the led array 20, is used for equiulbrium flow through the electric current of each LED string 20a, 20b, 20c.In the present embodiment, current balancing unit 105 comprises a plurality of electronic switch 105a, 105b and 105c, the negative electrode of LED string 20a, 20b and 20c in the led array 20 that connects one to one.In other words, the quantity of a plurality of LED string 20a, 20b, 20c is identical in the quantity of the included a plurality of electronic switch 105a of current balancing unit 105,105b, 105c and the led array 20.In the present embodiment, electronic switch 105a, 105b and 105c can be the electronic switch of triode, field effect transistor or other type.
Comparing unit 1013 is used for the relatively dividing potential drop of each LED string 20a, 20b, 20c negative electrode, with maximum and the minimum value of the dividing potential drop that obtains described LED string 20a, 20b, 20c negative electrode, and whether the minimum value of the dividing potential drop of more described LED string 20a, 20b, 20c negative electrode is in described expectation interval.Subtrator 1012 is used for minimum value in the dividing potential drop of described LED string 20a, 20b, 20c negative electrode in described expectation interval the time, maximum and the minimum value of the dividing potential drop of described LED string 20a, 20b, 20c negative electrode are subtracted each other, with the maximum of the dividing potential drop that obtains described LED string 20a, 20b, 20c negative electrode and the difference of minimum value, and when the minimum value of the dividing potential drop of described LED string 20a, 20b, 20c negative electrode is not in described expectation is interval, calculate described LED string 20a, 20b, 20c negative electrode dividing potential drop minimum value and described expect the interval apart from difference.Comparing unit 1013 is used for also judging that whether the difference of the maximum of dividing potential drop of described LED string 20a, 20b, 20c negative electrode and minimum value is greater than described threshold values, and in the difference of the maximum of described dividing potential drop and minimum value during greater than described threshold values, select except LED string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue LED string continues the minimum value of dividing potential drop of the LED string negative electrode more again selected whether in described expectation interval.Signal generation unit 1014 is used for when the minimum value of described dividing potential drop is not being expected in the interval, according to the minimum value of described dividing potential drop and the control signal apart from difference generation and output duty ratio corresponding in described expectation interval, and when the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, control signal to Pwm controller 102 according to what the minimum value of dividing potential drop produced and exported duty ratio corresponding.
In the present embodiment, the dividing potential drop of comparing unit 1013 more described LED string 20a, 20b, 20c negative electrode, with maximum and the minimum value that obtains described dividing potential drop, and whether whether the minimum value of more described dividing potential drop stable to judge LED drive system 10 in described expectation interval.If it is stable that the minimum value of described dividing potential drop in described expectation interval, then represents LED drive system 10, if the minimum value of described dividing potential drop not in described expectation interval, then represents the output that needs to regulate DC-DC converter 103, LED drive system 10 is unstable.When the minimum value of described dividing potential drop is not in described expectation is interval, the minimum value that subtrator 1012 calculates described dividing potential drop and described expectation interval apart from difference, namely in the minimum value of described dividing potential drop during less than the interval minimum value of described expectation, the minimum value that described expectation is interval and the minimum value of described dividing potential drop are subtracted each other, in the minimum value of described dividing potential drop during greater than the interval maximum of described expectation, the maximum that the minimum value of described dividing potential drop and described expectation is interval is subtracted each other, with the minimum value that obtains described dividing potential drop and described expectation interval apart from difference.
Described signal generation unit 1014 according to the minimum value of described dividing potential drop and described expectation interval control signal to Pwm controller 102 apart from what difference produced duty ratio corresponding.When the minimum value of described dividing potential drop is not in described expectation is interval, and during the minimum value in the minimum value of described dividing potential drop is interval less than described expectation, the control signal that signal generation unit 1014 output duty cycles are less, with the less pulse width modulating signal of control impuls width modulation controller 102 output duty cycles, thereby the less direct voltage of control DC-DC converter 103 outputs, with driving LED array 20, the electric current of led array 20 and brightness are reduced.During maximum in minimum value interval in described expectation when the minimum value of described dividing potential drop and described dividing potential drop is interval greater than described expectation, the control signal that signal generation unit 1014 output duty cycles are larger, with the larger pulse width modulating signal of control impuls width modulation controller 102 output duty cycles, thereby the larger direct voltage of control DC-DC converter 103 outputs, with driving LED array 20, the electric current of led array 20 and brightness are increased.
When the minimum value of described dividing potential drop was in described expectation is interval, subtrator 1012 subtracted each other maximum and the minimum value of described dividing potential drop, with the difference of the maximum that obtains described dividing potential drop and minimum value and by comparing unit 1013 and the comparison of described threshold values.The maximum of described dividing potential drop and the difference of minimum value are during greater than described threshold values, comparing unit 1013 is selected the sub-minimum of described dividing potential drop, namely select except LED string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue LED string, the compound ratio of laying equal stress on than the minimum value of the dividing potential drop of LED string whether in described expectation interval.When the maximum of described dividing potential drop and the difference of minimum value were not more than described threshold values, signal generation unit 1014 produced and outputs control signals to Pwm controller 102 according to the minimum value of described dividing potential drop.
In the present embodiment, when if the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, signal generation unit 1014 produces according to the minimum value of described dividing potential drop and output duty cycle is constant controls signal to Pwm controller 102, with the constant pulse width modulating signal of output duty cycle, thereby the constant direct voltage of control DC-DC converter 103 outputs, with driving LED array 20, make the electric current of led array 20 and brightness constant.If except LED string corresponding to the minimum value of dividing potential drop, when the difference of the maximum of the dividing potential drop of negative electrode and minimum value is not more than described threshold values in the residue LED string, signal generation unit 1014 produces according to the minimum value of negative electrode dividing potential drop in the described residue LED string and output duty cycle is less controls signal to Pwm controller 102, with the less pulse width modulating signal of output duty cycle, thereby the less direct voltage of control DC-DC converter 103 outputs, with driving LED array 20, the electric current of led array 20 and brightness are diminished.
In the present embodiment, described control signal and described pulse width modulating signal are square wave.
In the present embodiment, the minimum value of control unit 101 dividing potential drop of LED string in led array 20 is in described expectation interval, and the maximum of described dividing potential drop and the difference of minimum value are during greater than described threshold values, select except LED string corresponding to the minimum value of described dividing potential drop, the minimum value of negative electrode dividing potential drop in the residue LED string, and whether the minimum value that repeats to judge negative electrode dividing potential drop in the residue LED string is in described expectation interval.The minimum value of negative electrode dividing potential drop is in described expectation interval in residue LED string, and when the difference of the maximum of negative electrode dividing potential drop and minimum value is greater than described threshold values in the residue LED string, then select LED string corresponding to the minimum value of negative electrode dividing potential drop in residue LED string the minimum value of negative electrode dividing potential drop in the residue LED string.By that analogy, constantly select the minimum value of negative electrode dividing potential drop in the residue LED string, until in the residue LED string minimum value of negative electrode dividing potential drop not in the expectation interval, then according to the minimum value of negative electrode dividing potential drop in the residue LED string and described expectation interval apart from difference, adjust the output to the duty ratio of the control signal of Pwm controller 102, thereby the duty ratio of the pulse width modulating signal of control impuls width modulation controller 102 output exports the direct voltage of led array 20 to adjustment.Or until in the residue LED string maximum of negative electrode dividing potential drop and the difference of minimum value be not more than described threshold values, the minimum value of negative electrode dividing potential drop in then going here and there according to residue LED, produce and output control signals to Pwm controller 102, namely produce the smaller control signal of duty, with the less pulse width modulating signal of control impuls width modulation controller 102 output duty cycles, thereby the less direct voltage of control DC-DC converter 103 outputs, with driving LED array 20, the electric current of led array 20 and brightness are diminished.
Because LED string 20a, 20b, 20c negative electrode dividing potential drop is minimum, represent that then the pressure drop of corresponding LED string is maximum, therefore, select except LED string corresponding to the minimum value of LED string negative electrode dividing potential drop, the minimum value of residue LED string negative electrode, avoided going here and there according to the LED of pressure drop maximum the duty ratio of regulating impulse bandwidth modulation signals, thereby reduced the direct voltage of DC-DC converter 103 outputs, and then reduced in other string minute electronic switch 105a to current balancing unit 105, excessively multivoltage on 105b and the 105c has improved electronic switch 105a, the thermal stress issues that 105b and 105c cause because producing larger power loss.
Fig. 2 is the module map of LED drive system 10a in another execution mode of the present invention.LED drive system 10a is similar to framework and the principle of LED drive system 10 among Fig. 1 in the present embodiment, and difference only is: LED drive system 10a also comprises feedback unit 104.
In the present embodiment, feedback unit 104 links to each other with the output of DC-DC converter 103, to receive the direct voltage of DC-DC converter 103 outputs, and according to described direct voltage produce and output feedback signal to Pwm controller 102, to adjust the duty ratio of described pulse width modulating signal.In the present embodiment, the common duty ratio of adjusting described pulse width modulating signal of described feedback signal and described control signal, thereby adjust the direct voltage that DC-DC converter 103 exports led array 20 to, wherein, described feedback signal plays a leading role, and described control signal plays the fine setting effect.
In the present embodiment, feedback unit 104 comprises two divider resistance 104a and 104b, is series between the output and ground of DC-DC converter 103, and Pwm controller 102 links to each other with the common port of divider resistance 104a and 104b.In another embodiment of the present invention, feedback unit 104 also can comprise coil, with produce according to described direct voltage and output feedback signal to Pwm controller 102, to adjust the duty ratio of described pulse width modulating signal.
Fig. 3 is the flow chart of LED driving method in an embodiment of the present invention.At first, enter step S1000, DC-DC converter 103 is according to the pulse width modulating signal of Pwm controller 102 output, the input power of external power source Vin is converted to suitable direct voltage, with driving LED array 20.At step S1001, sampling unit 100 continues the dividing potential drop of each LED string 20a, 20b, 20c negative electrode in the detecting led array 20, and described dividing potential drop is fed back to control unit 101.Enter step S1003, control unit 101 is maximum and the minimum value of LED string 20a, 20b, 20c negative electrode dividing potential drop relatively, and whether whether the minimum value of judging LED string 20a, 20b, 20c negative electrode dividing potential drop in the expectation interval, stablized to judge LED drive system 10.If it is stable that the minimum value of described dividing potential drop in described expectation interval, then represents LED drive system 10.If the minimum value of described dividing potential drop is not in described expectation interval, then representative needs to regulate the output of DC-DC converter 103, and LED drive system 10 is unstable.If the minimum value of LED string negative electrode dividing potential drop is not in described expectation interval, then enter step S1005, control unit 101 according to the minimum value of described dividing potential drop and described expectation interval adjust the output to the duty ratio of the control signal of Pwm controller 102 apart from difference, thereby the duty ratio of the pulse width modulating signal of control impuls width modulation controller 102 output exports the direct voltage of led array 20 to adjustment.
If the minimum value of LED string 20a, 20b, 20c negative electrode dividing potential drop then enters step S1007 in described expectation interval, control unit 101 calculates the maximum of described dividing potential drop and the difference of minimum value.Enter step S1009, whether control unit 101 judges the difference of the maximum of described dividing potential drop and minimum value greater than described threshold values, to judge minute to electronic switch 105a, the 105b of described current balancing unit 105 and the maximum voltage difference of 105c whether can cause thermal stress issues.If described difference is greater than described threshold values, represent to divide the maximum voltage difference to electronic switch 105a, 105b and 105c can cause thermal stress issues, enter step S1011, control unit 101 is selected outside LED string corresponding to the minimum value of dividing potential drop, the minimum value of negative electrode dividing potential drop in the residue LED string, and repeating step S1003.If described difference is not more than described threshold values, represent to divide the maximum voltage difference to electronic switch 105a, 105b and 105c can not cause thermal stress issues, then enter step S1013, control unit 101 produces according to the minimum value of dividing potential drop and output is corresponding controls signal to Pwm controller 102.Feedback unit 104 produce according to the direct voltage of DC-DC converter 103 output and output feedback signal to Pwm controller 102, to adjust the duty ratio of described pulse width modulating signal.
Above-mentioned LED drive system 10 and method, at LED string 20a, 20b, the minimum value of 20c negative electrode dividing potential drop is in described expectation interval, and the maximum of described dividing potential drop and the difference of minimum value are during greater than described threshold values, select except LED string corresponding to the minimum value of described dividing potential drop, the minimum value of negative electrode dividing potential drop in the residue LED string, thereby regulate the duty ratio of control signal according to the minimum value of negative electrode dividing potential drop in the residue LED string, output with control impuls width modulation controller 102, and then control the direct voltage that DC-DC converter 103 exports led array 20 to, to improve electronic switch 105a, the thermal stress issues that 105b and 105c cause because of power loss.
Claims (10)
1. a LED driving method is used for driving light emitting diode matrix, and described light emitting diode matrix comprises the light-emitting diode string of a plurality of parallel connections, it is characterized in that, described LED driving method comprises:
Pulse width modulating signal according to Pwm controller output, the input power of external power source is converted to suitable direct voltage, driving described light emitting diode matrix, and utilize electronic switch equiulbrium flow in the current balancing unit through the electric current of described a plurality of light-emitting diode strings;
Detect the dividing potential drop of described a plurality of light-emitting diode string negative electrodes, described dividing potential drop comprises maximum and minimum value;
Judge that the minimum value of described dividing potential drop is whether in the expectation interval;
If the minimum value of described dividing potential drop is in described expectation interval, then whether the difference of the maximum of more described dividing potential drop and minimum value is greater than threshold values;
If the difference of the maximum of described dividing potential drop and minimum value is greater than described threshold values, then select except light-emitting diode string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue light-emitting diode string, and whether the minimum value of dividing potential drop that repeats to judge described residue light-emitting diode string negative electrode is in the expectation interval;
If the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, then the minimum value according to described dividing potential drop produces and outputs control signals to described Pwm controller; And
If the minimum value of described dividing potential drop not in described expectation interval, the difference of the maximum of more described dividing potential drop and minimum value not then.
2. LED driving method as claimed in claim 1 is characterized in that, also comprises:
If the minimum value of described dividing potential drop is not in described expectation interval, then according to the minimum value of described dividing potential drop and described expectation interval apart from difference, adjust the output to the duty ratio of the control signal of described Pwm controller, thereby finely tune the duty ratio of the pulse width modulating signal of described Pwm controller output.
3. LED driving method as claimed in claim 2, it is characterized in that, if the minimum value of described dividing potential drop is not in the expectation interval, then according to the minimum value of described dividing potential drop and described expectation interval apart from difference, the step of duty ratio that adjusts the output to the control signal of described Pwm controller also comprises:
If the minimum value of described dividing potential drop is less than the interval minimum value of described expectation, then output duty cycle is less controls signal to described Pwm controller; And
If the minimum value of described dividing potential drop is greater than the interval maximum of described expectation, then output duty cycle is larger controls signal to described Pwm controller.
4. LED driving method as claimed in claim 1 is characterized in that, whether the maximum of more described dividing potential drop and the difference of minimum value also comprise greater than the step of threshold values:
Maximum and the minimum value of the dividing potential drop of more described a plurality of light-emitting diode string negative electrodes; And
Calculate the maximum of dividing potential drop of described a plurality of light-emitting diode string negative electrodes and the difference of minimum value.
5. a LED drive system is used for driving light emitting diode matrix, and described light emitting diode matrix comprises the light-emitting diode string of a plurality of parallel connections, it is characterized in that, described LED drive system comprises:
DC-DC converter is used for the input power of external power source is converted to suitable direct voltage and suitable direct current, to drive described light emitting diode matrix;
Sampling unit links to each other with the negative electrode of described light emitting diode matrix, is used for detecting the dividing potential drop of each light-emitting diode string negative electrode of described light emitting diode matrix;
Control unit links to each other with described sampling unit, comprising:
Comparing unit, the dividing potential drop that is used for more described a plurality of light-emitting diode string negative electrodes, with maximum and the minimum value of the dividing potential drop that obtains described a plurality of light-emitting diode string negative electrodes, and whether the minimum value of the dividing potential drop of more described a plurality of light-emitting diode string negative electrodes is in the expectation interval;
Subtrator, be used for minimum value in the dividing potential drop of described a plurality of light-emitting diode string negative electrodes in described expectation interval the time, maximum and the minimum value of the dividing potential drop of described a plurality of light-emitting diode string negative electrodes are subtracted each other, with the maximum of the dividing potential drop that obtains described a plurality of light-emitting diode string negative electrodes and the difference of minimum value, wherein said comparing unit is used for also judging that whether the difference of the maximum of dividing potential drop of described a plurality of light-emitting diode string negative electrodes and minimum value is greater than threshold values, and in the difference of the maximum of described dividing potential drop and minimum value during greater than described threshold values, select except light-emitting diode string corresponding to the minimum value of described dividing potential drop, the minimum value of the dividing potential drop of negative electrode in the residue light-emitting diode string, and whether the minimum value of dividing potential drop that continues the light-emitting diode string negative electrode more again selected is in described expectation interval; And
The signal generation unit is used for when the difference of the maximum of described dividing potential drop and minimum value is not more than described threshold values, produces and export control signal according to the minimum value of described dividing potential drop;
Pwm controller links to each other with described control unit, and according to described control signal output pulse width modulation signal; And
Current balancing unit all links to each other with the negative electrode of each light-emitting diode string in the described light emitting diode matrix, is used for equiulbrium flow through the electric current of described a plurality of light-emitting diode strings, and described current balancing unit comprises electronic switch.
6. LED drive system as claimed in claim 5 is characterized in that, described electronic switch comprises triode, and described triode is used for equiulbrium flow through the electric current of described a plurality of light-emitting diode strings.
7. LED drive system as claimed in claim 5 is characterized in that, also comprises:
Feedback unit links to each other with the output of described DC-DC converter, be used for according to described direct voltage produce and output feedback signal to described Pwm controller, to adjust the duty ratio of described pulse width modulating signal.
8. LED drive system as claimed in claim 5, it is characterized in that, described subtrator also is used for minimum value in the dividing potential drop of described a plurality of light-emitting diode string negative electrodes not in described expectation is interval the time, calculate described a plurality of light-emitting diode string negative electrodes dividing potential drop minimum value and described expect the interval apart from difference.
9. LED drive system as claimed in claim 8, it is characterized in that, described signal generation unit also is used for minimum value in described dividing potential drop not in described expectation is interval the time, according to the minimum value of described dividing potential drop and described expectation interval apart from the difference generation and export the control signal of duty ratio corresponding.
10. LED drive system as claimed in claim 5 is characterized in that, described control unit also comprises:
Memory cell is used for storing described expectation interval value and described threshold values.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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Application publication date: 20130925 |