CN104075135A - Driving system and method for light emitting diodes - Google Patents

Abstract

A light-emitting diode driving system includes a direct current/direct current converter, a current regulating unit, a control unit and a pulse width modulation controller. A DC/DC converter is used to convert the input voltage of an external power supply into a driving voltage. The control unit is used for generating and outputting control signals to the pulse width modulation controller and outputting multiple current regulation signals. The current regulation unit is used for regulating the current flowing through each LED string according to the current regulation signal of each LED string. The pulse width modulation controller is used to output a pulse width modulation signal according to the control signal. The invention also provides a light emitting diode driving method. The LED driving system and method described above quickly adjusts the driving voltage of the LED array according to the current current of the LED array in real time, which improves the thermal stress problem caused by the power loss of the electronic switch and improves the power usage efficiency at the same time.

Description

LED driving system and method

technical field

The invention relates to a backlight source driving system, in particular to a light emitting diode driving system and method of a display device.

Background technique

Light emitting diodes (light emitting diodes, LEDs) are more and more used in backlight sources of display devices due to energy saving. In order to ensure the display effect of the display device, the LED used as the backlight needs a uniform light source, so an electronic switch with balanced current needs to be added to the LED drive system and connected in series in each LED string. Usually, the traditional LED driving system must meet the requirement that the LED string with the highest voltage drop has enough forward voltage to reach the set current. However, due to the different characteristics of LEDs, the voltage drop of each string of LEDs is different under the same DC voltage drive, and for a three-dimensional LED TV, because the current in the two-dimensional mode is different from the current in the three-dimensional mode, the electronic switch A large power loss will be generated, which will cause thermal stress problems and reduce power usage efficiency.

Contents of the invention

In view of this, it is necessary to provide a light emitting diode driving system, which can improve the problem of thermal stress and improve the efficiency of power supply.

In addition, it is also necessary to provide a driving method for light emitting diodes, which can improve the problem of thermal stress and improve the efficiency of power supply.

The light-emitting diode driving method provided in this embodiment is used in a light-emitting diode driving system for driving a light-emitting diode array, the light-emitting diode array includes a plurality of parallel-connected light-emitting diode strings, and the light-emitting diode driving system includes a control unit, In the pulse width modulation controller, the control unit includes a constant current unit, a first comparison unit, a judgment unit, and a signal generation unit. The light emitting diode driving method includes: the constant current unit detects the current flowing through the plurality of light emitting diode strings and correspondingly outputs the current adjustment signal of the plurality of light emitting diode strings according to the current of the plurality of light emitting diode strings ; The first comparison unit detects the current adjustment signals of the plurality of light-emitting diode strings and finds the maximum value; the judgment unit judges whether the maximum value of the current adjustment signal is between the first set value and the second and output a judgment signal between the set values; the signal generating unit generates and outputs a control signal according to the judgment signal; the pulse width modulation controller outputs a pulse width modulation signal according to the control signal to drive the light emitting diode array.

Preferably, the step of the signal generation unit generating and outputting the control signal according to the judgment signal includes: if the judgment signal is that the maximum value of the current adjustment signal is between the first set value and the second set value , then the signal generating unit generates and outputs a control signal with a constant duty ratio; if the judgment signal is that the maximum value of the current regulation signal is greater than the second set value, the signal generating unit generates and outputs Outputting a control signal with an increased duty cycle; if the determination signal is that the maximum value of the current regulation signal is less than the first set value, the signal generating unit generates and outputs a control signal with a reduced duty cycle .

Preferably, the step of the pulse width modulation controller outputting a pulse width modulation signal according to the control signal to drive the light-emitting diode array includes: if the control signal is a control signal with an increased duty cycle, the The pulse width modulation controller judges whether the output duty cycle is greater than a threshold; if the output duty cycle of the pulse width modulation controller is greater than the threshold value, then output a pulse width modulation signal with a reduced duty cycle; if the pulse width modulation controller If the output duty ratio is not greater than the threshold value, then output a pulse width modulation signal with an increased duty ratio.

Preferably, the control unit further includes a dynamic reference level adjustment unit, a second comparison unit, and a third comparison unit, and the constant current unit detects the current flowing through the plurality of LED strings and The step of outputting current regulation signals of the plurality of LED strings corresponding to the current of the LED strings includes: the second comparison unit detects the divided voltage of the cathodes of the plurality of LED strings and finds a minimum value therefrom.

Preferably, the step of the signal generation unit generating and outputting the control signal according to the judgment signal includes: the third comparison unit judges whether the minimum value of the cathode divided voltage of the plurality of LED strings is greater than the dynamic reference standard The reference level voltage output by the bit adjustment unit; if the minimum value of the cathode divided voltage of the plurality of light-emitting diode strings is greater than the reference level voltage, the judgment unit outputs an adjustment signal that the reference level voltage remains unchanged to all In the dynamic reference level adjustment unit, the signal generation unit generates and outputs a control signal with a constant duty cycle; if the minimum value of the cathode divided voltage of the multiple LED strings is not greater than the reference level voltage and the The judging signal is that the maximum value of the current adjustment signal is between the first set value and the second set value, then the judging unit outputs an adjustment signal with a constant reference level voltage to the dynamic reference level adjustment unit, the signal generation unit generates and outputs a control signal with a constant duty ratio; if the minimum value of the cathode voltage division of the plurality of LED strings is not greater than the reference potential voltage and the judgment signal is the If the maximum value of the current adjustment signal is greater than the second set value, the judgment unit outputs an adjustment signal for increasing the reference level voltage to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a duty Ratio increased control signal;

If the minimum value of the cathode divided voltage of the plurality of LED strings is not greater than the reference level voltage and the determination signal is that the maximum value of the current adjustment signal is less than the first set value, then the determination The unit outputs an adjustment signal for reducing the reference level voltage to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a control signal for decreasing the duty cycle.

The light-emitting diode drive system provided in this embodiment is used to convert the external power supply voltage into a voltage suitable for driving the light-emitting diode array. The light-emitting diode array includes a plurality of parallel-connected light-emitting diode strings. The light-emitting diode drive system includes a DC /DC converter, control unit and pulse width modulation controller. The DC/DC converter is used to electrically connect the external power supply and the LED array, and is used to convert the input voltage of the external power supply into a driving voltage to drive the LED array to emit light. The control unit is used to electrically connect the LED array, and includes a constant current unit, a first comparison unit, a judgment unit and a signal generation unit. The constant current unit is used to detect the current flowing through each LED string, so as to obtain the current regulation signal of each LED string. The judging unit is used for judging whether the maximum value of the current regulation signals of the plurality of LED strings is between a first set value and a second set value and outputs a judging signal. The signal generating unit is used for generating and outputting a control signal according to the judgment signal. The pulse width modulation controller is used to electrically connect the control unit and the DC/DC converter, and is used to output a pulse width modulation signal according to the control signal to adjust the driving of the output of the DC/DC converter Voltage.

Preferably, the LED driving system further includes a current regulation unit, which is used to electrically connect between the cathode of the LED array and the control unit, and the constant current unit is also used to detect The current flowing through each LED string is measured to obtain the current regulation signal of each LED string.

Preferably, the current adjustment unit is further configured to adjust the current flowing through each LED string according to the current adjustment signal of each LED string.

Preferably, the signal generation unit is further configured to generate and output a current regulation signal when the maximum value of the current adjustment signals of the plurality of LED strings is between the first set value and the second set value. A control signal with a constant duty ratio, when the maximum value of the current adjustment signals of the plurality of light-emitting diode strings is less than the first set value, generate and output a control signal with a reduced duty ratio, and when the plurality of LED strings When the maximum value of the current regulation signal of each light emitting diode string is greater than the second set value, a control signal with an increased duty cycle is generated and output to the pulse width modulation controller to adjust the pulse width modulation signal duty cycle.

Preferably, the pulse width modulation controller is also used to judge whether the output pulse width modulation signal is greater than a threshold, and when not greater than the threshold, output a pulse width modulation signal with an increased duty cycle, and when greater than the threshold, output A pulse width modulated signal with a reduced duty cycle.

Preferably, the control unit further includes a dynamic reference level adjustment unit, a second comparison unit, and a third comparison unit. The dynamic reference level adjustment unit is used for adjusting the reference level voltage according to the judgment signal output by the judgment unit. The second comparison unit is used for comparing the divided voltages of the cathodes of the plurality of LED strings to obtain the minimum value of the divided voltages of the cathodes of the plurality of LED strings. The third comparison unit is used for comparing the minimum value of the cathode voltage division of the plurality of LED strings with the reference level voltage, so as to control the signal generation unit to generate and output a control signal.

Preferably, the judging unit generates and outputs a judging signal that the reference level voltage does not change to the dynamic reference level when the minimum value of the cathode divided voltage of the plurality of LED strings is greater than the reference level voltage An adjustment unit, the signal generation unit generates and outputs a control signal with a constant duty ratio to the pulse width modulation controller, and the minimum value of the cathode divided voltage of the plurality of light-emitting diode strings in the judgment unit is not greater than When the reference level voltage is low and the maximum value of the current adjustment signals of the plurality of light emitting diode strings is between the first set value and the second set value, generate and output the reference level voltage A constant judgment signal is sent to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a control signal with a constant duty cycle to the pulse width modulation controller.

Preferably, the judging unit is when the minimum value of the cathode divided voltage of the multiple light emitting diode strings is not greater than the reference level voltage, and the maximum value of the current adjustment signals of the multiple light emitting diode strings is smaller than the At the first set value, generate and output a judgment signal that the reference level voltage decreases to the dynamic reference level adjustment unit to adjust the reference level voltage, and the signal generation unit generates and outputs a duty ratio decrease A small control signal to the PWM controller to adjust the duty cycle of the PWM signal.

Preferably, the judging unit is when the minimum value of the cathode divided voltage of the multiple LED strings is not greater than the reference level voltage, and the maximum value of the current adjustment signals of the multiple LED strings is greater than the At the second set value, generate and output a judgment signal that the reference level voltage increases to the dynamic reference level adjustment unit to adjust the reference level voltage, and the signal generation unit generates and outputs a duty ratio increase a large control signal to the PWM controller to adjust the duty cycle of the PWM signal.

Preferably, the current regulating unit includes an electronic switch and a sampling resistor correspondingly connected to each light-emitting diode string, the electronic switch includes a control electrode, a first electrode, and a second electrode, and the first electrode is connected to the light-emitting diode The series cathodes are electrically connected, the control electrode is electrically connected to the constant current unit, the second electrode is electrically connected to one end of the sampling resistor, and the other end of the sampling resistor is grounded.

Preferably, the current regulation signal is inversely proportional to the current of the LED string.

Preferably, the LED drive system further includes a feedback unit, configured to be electrically connected to the DC/DC converter and the pulse width modulation controller, and used to output the driving voltage according to the DC/DC converter. Generate and output a feedback signal to the PWM controller to adjust the duty ratio of the PWM signal.

Preferably, the feedback unit includes a first voltage dividing resistor and a second voltage dividing resistor. One end of the first voltage dividing resistor is electrically connected to the output end of the DC/DC converter, and the other end is electrically connected to the pulse width modulation controller. One end of the second voltage dividing resistor is electrically connected to the other end of the first voltage dividing resistor, and the other end is grounded.

The LED driving system and method described above quickly adjusts the driving voltage of the LED array according to the current LED array current in real time, which improves the thermal stress problem caused by the power loss of the electronic switch and improves the power usage efficiency at the same time.

Description of drawings

FIG. 1 is a block diagram of an LED driving system in an embodiment of the present invention.

FIG. 2 is a circuit diagram of an LED driving system in an embodiment of the present invention.

FIG. 3 is a circuit diagram of an LED driving system in another embodiment of the present invention.

FIG. 4 is a circuit diagram of an LED driving system in another embodiment of the present invention.

FIG. 5 is a flowchart of a method for driving a light emitting diode in an embodiment of the present invention.

FIG. 6 is a flowchart of a method for driving a light emitting diode in another embodiment of the present invention.

Description of main component symbols

External power supply 10

LED drive system 20, 20a, 20b, 20c

LED array 30

LED strings 30a, 30b, 30c

DC/DC Converter 202

Current regulation unit 204

Electronic switch Qa, Qb, Qc

Sampling resistor Ra, Rb, Rc

Control unit 206, 260a, 206b

Constant current unit 2061

The first comparison unit 2062

Judgment unit 2063

Signal generating unit 2064

Storage unit 2065

Dynamic reference level adjustment unit 2066

The second comparison unit 2067

The third comparison unit 2068

Pulse Width Modulation Controller 208

Feedback unit 210

The first to second voltage divider resistors R1, R2

The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings.

Detailed ways

FIG. 1 is a block diagram of a light emitting diode (Light Emitting Diode, LED) driving system 20 in an embodiment of the present invention. The LED driving system 20 is used to drive the LED array 30 to emit light. In this embodiment, the light-emitting diode array 30 includes a plurality of parallel-connected light-emitting diode strings 30a, 30b, 30c (in this embodiment, only three are taken as an example, but not limited to three, may include less than or more than three light emitting diode strings), each light emitting diode string 30a, 30b, 30c is composed of a plurality of light emitting diodes connected in series in forward direction. In this embodiment, the forward voltage drop of each LED string 30a, 30b, 30c is proportional to the current, and the anode of each LED string 30a, 30b, 30c refers to the first voltage drop of the LED string according to the current direction. The anode of each light-emitting diode, the cathode of the light-emitting diode string 30a, 30b, 30c refers to the cathode of the last light-emitting diode of the light-emitting diode string. Similarly, the cathode of the LED array 30 refers to the common end of the cathodes of the LED strings 30a, 30b, 30c, and the anode of the LED array 30 refers to the common end of the anodes of the LED strings 30a, 30b, 30c.

The LED driving system 20 includes a DC/DC converter 202 , a current regulation unit 204 , a control unit 206 and a PWM controller 208 . The DC/DC converter 202 is electrically connected to the external power source 10 and the LED array 30 , and converts the input voltage of the external power source 10 into a driving voltage to drive the LED array 30 to emit light. The control unit 206 is electrically connected to the LED array 30 and includes a constant current unit 2061 , a first comparison unit 2062 , a judgment unit 2063 and a signal generation unit 2064 . The constant current unit 2061 detects the current flowing through each LED string 30a, 30b, 30c to obtain a current regulation signal for each LED string 30a, 30b, 30c. The first comparing unit 2062 compares the current regulation signals of the plurality of LED strings 30a, 30b, 30c to obtain the maximum value of the current regulation signals of the plurality of LED strings 30a, 30b, 30c. The judging unit 2063 judges whether the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c is between the first set value and the second set value and outputs a judgment signal. The signal generating unit 2064 generates and outputs a control signal according to the judgment signal. The PWM controller 208 is electrically connected to the control unit 206 and the DC/DC converter 202 , and outputs a PWM signal according to the control signal to adjust the driving voltage output by the DC/DC converter 202 .

As a further improvement of an embodiment of the present invention, the LED drive system 20 further includes a current regulation unit 204, which is electrically connected between the cathode of the LED array 30 and the control unit 206, and the constant current unit 2061 is also used to pass the current regulation unit 204 detects the current flowing through each LED string 30a, 30b, 30c to obtain a current regulation signal for each LED string 30a, 30b, 30c. In other words, the constant current unit 2061 can obtain the current flowing through each LED string 30a, 30b, 30c by directly detecting each LED string 30a, 30b, 30c, or detect the current flowing through each LED string 30a, 30b, 30c through the current adjustment unit 204. The current of the LED strings 30a, 30b, 30c.

As a further improvement of an embodiment of the present invention, the LED driving system 20 further includes a feedback unit 210, electrically connected to the DC/DC converter 202 and the pulse width modulation controller 208, according to the driving voltage output by the DC/DC converter 202 Generate and output a feedback signal to the PWM controller 208 to adjust the duty cycle of the PWM signal.

FIG. 2 is a detailed circuit diagram of an LED driving system 20a according to an embodiment of the present invention. In this embodiment, the current regulating unit 204 is electrically connected to the cathode of each LED string 30a, 30b, 30c in the LED array 30, and is used for adjusting the current flowing through each LED string 30a, 30b, 30c. The current regulating unit 204 includes a plurality of electronic switches Qa, Qb, and Qc, which are electrically connected to the cathodes of the LED strings 30a, 30b, and 30c in the LED array 30 one by one. The current regulating unit 204 also includes a plurality of sampling resistors Ra, Rb and Rc, which are electrically connected to a plurality of electronic switches Qa, Qb and Qc in one-to-one correspondence. In other words, the number of electronic switches Qa, Qb and Qc and sampling resistors Ra, Rb and Rc included in the current regulating unit 204 is the same as the number of LED strings 30 a , 30 b , 30 c in the LED array 30 . In this embodiment, the electronic switches Qa, Qb and Qc may be transistors, field effect transistors or other types of electronic switches. The electronic switches Qa, Qb and Qc will be described in detail below as transistors.

Please refer to Fig. 3, in another embodiment of the present invention, electronic switch Qa, Qb and Qc are transistors, the control electrode of electronic switch Qa, Qb and Qc is the base of transistor, the first electrode of electronic switch Qa, Qb and Qc One electrode is the collector of the transistor, and the second electrode of the electronic switches Qa, Qb and Qc is the emitter of the transistor. The bases of the electronic switches Qa, Qb, and Qc are electrically connected to the constant current unit 2061, and the emitters of the electronic switches Qa, Qb, and Qc are electrically connected to one end of the sampling resistors Ra, Rb, and Rc. The collectors of Qb and Qc are electrically connected to the cathodes of the LED strings 30a, 30b, and 30c corresponding to each other. The other ends of the sampling resistors Ra, Rb and Rc are grounded.

In this embodiment, the control unit 206a is electrically connected to the current regulation unit 204 and the pulse width modulation controller 208, and the control unit 206a generates and Outputting the control signal to the PWM controller 208 to control the duty ratio of the PWM signal output from the PWM controller 208 to the DC/DC converter 202, and generating and outputting a plurality of current regulation signals to the current regulation unit 204 , to control whether the electronic switches Qa, Qb, and Qc are turned on or the magnitude of the turned-on current, so as to adjust the current of the corresponding LED string. For example, by increasing the base current of the electronic switches Qa, Qb, and Qc, the current flowing from the collector to the emitter of the electronic switches Qa, Qb, and Qc is increased, thereby increasing the current of the corresponding LED string. In this embodiment, the control unit 206 a includes a constant current unit 2061 , a first comparison unit 2062 , a judgment unit 2063 , a signal generation unit 2064 and a storage unit 2065 .

The constant current unit 2061 detects the current flowing through each LED string 30a, 30b, 30c, so as to obtain a corresponding current regulation signal of each LED string 30a, 30b, 30c. At the same time, the constant current unit 2061 transmits the current adjustment signals of the plurality of LED strings 30 a , 30 b , 30 c to the current adjustment unit 204 and the first comparison unit 2062 . In this embodiment, the current regulation signal is inversely proportional to the current flowing through the LED strings 30a, 30b, 30c. In other words, the larger the current flowing through the LED strings 30a, 30b, 30c, the smaller the resulting current regulation signal.

The first comparison unit 2062 compares the current adjustment signals of the plurality of LED strings 30a, 30b, 30c to obtain the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c and obtains the maximum value of the current adjustment signals of the plurality of LED strings 30a. , 30b, 30c the maximum value of the current adjustment signal is sent to the judging unit 2063 .

The judging unit 2063 judges whether the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c is between the first set value and the second set value and outputs a judgment signal. In this embodiment, the first set value and the second set value define the stable empirical value of the LED driving system 20b, which can be set by the user according to experimental data or specific needs, and the first set value is smaller than the second set value. set value. When the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c is between the first set value and the second set value, that is, the current adjustment signal of the plurality of LED strings 30a, 30b, 30c When the maximum value is greater than or equal to the first set value and less than or equal to the second set value, a first judgment signal is generated. When the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c is smaller than the first set value, a second judgment signal is generated. When the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c is greater than the second set value, a third judgment signal is generated.

The signal generation unit 2064 generates and outputs a control signal to the PWM controller 208 according to the determination signal output by the determination unit 2063 to adjust the output of the DC/DC converter 202 . When the judgment signal received by the signal generation unit 2064 is the first judgment signal, it generates and outputs a control signal with a constant duty ratio to the PWM controller 208 . When the judgment signal received by the signal generating unit 2064 is the second judgment signal, a control signal with a reduced duty ratio is generated and output to the pulse width modulation controller 208 to adjust the duty ratio of the pulse width modulation signal, thereby controlling the DC/ The DC converter 202 outputs a reduced driving voltage to drive the LED array 30 to reduce the current of the LED array 30 . And when the judgment signal received by the signal generating unit 2064 is the third judgment signal, generate and output a control signal with an increased duty ratio to the pulse width modulation controller 208 to adjust the duty ratio of the pulse width modulation signal, thereby controlling the DC The DC/DC converter 202 outputs an increased driving voltage to drive the LED array 30 to increase the current of the LED array 30 .

As a further improvement of an embodiment of the present invention, when the judgment signal received by the signal generation unit 2064 is the third judgment signal, it generates and outputs a control signal with an increased duty ratio to the pulse width modulation controller 208 . The pulse width modulation controller 208 judges whether the output pulse width modulation signal is greater than the threshold value, if not greater than the threshold value, the pulse width modulation controller 208 outputs a pulse width modulation signal with an increased duty cycle, thereby controlling the output of the DC/DC converter 202 to increase driving voltage to drive the LED array 30 to increase the current of the LED array 30 . If it is greater than the threshold, the pulse width modulation controller 208 outputs a pulse width modulation signal with a reduced duty cycle to adjust the duty cycle of the pulse width modulation signal, thereby controlling the DC/DC converter 202 to output a reduced driving voltage to drive The light emitting diode array 30 reduces the current of the light emitting diode array 30 .

In this embodiment, the constant current unit 2061 adjusts and outputs the current adjustment signal of each LED string 30a, 30b, 30c in real time according to the current of each LED string 30a, 30b, 30c, and the first comparison unit 2062 compares and obtains The maximum value of the current regulation signal of a plurality of light emitting diode strings 30a, 30b, 30c is then sent to the judging unit 2063, and the judging unit 2063 judges whether the maximum value of the current regulating signal of a plurality of light emitting diode strings 30a, 30b, 30c is within the first setting. Between the fixed value and the second set value and output a judgment signal. By repeating the above adjustments N (N=1, 2, 3...) times until the maximum value of the current adjustment signals of the plurality of LED strings 30a, 30b, 30c reaches a balance between the first set value and the second set value . At this moment, the signal generating unit 2064 generates and outputs a control signal with a constant duty ratio to the PWM controller 208 .

The storage unit 2065 is used for storing the first set value and the second set value.

In this embodiment, the feedback unit 210 is electrically connected to the output terminal of the DC/DC converter 202 and the pulse width modulation controller 208, so as to receive the driving voltage output by the DC/DC converter 202, and The driving voltage output by 202 generates and outputs a feedback signal to the PWM controller 208 to adjust the duty cycle of the PWM signal. In this embodiment, the feedback signal output by the feedback unit 210 and the control signal output by the control unit 206a jointly adjust the duty cycle of the pulse width modulation signal, thereby adjusting the DC voltage output from the DC/DC converter 202 to the LED array 30, Therefore, the magnitude of the current flowing through the LED array 30 is adjusted, wherein the feedback signal output by the feedback unit 210 plays a leading role, and the control signal output by the control unit 206a plays a fine-tuning role. At the same time, the current adjustment unit 204 can adjust the base currents of the electronic switches Qa, Qb, and Qc by receiving the current adjustment signal output by the control unit 206a, thereby adjusting the current flowing from the collector to the emitter of the electronic switches Qa, Qb, and Qc, Thus, the current of the LED array 30 is adjusted. In other words, the feedback signal output by the feedback unit 210 , the control signal output by the control unit 206 a and the current adjustment signal jointly adjust the current of the LED array 30 .

In this embodiment, the feedback unit 210 includes a first voltage dividing resistor R1 and a second voltage dividing resistor R2. One end of the first voltage dividing resistor R1 is electrically connected to the output end of the DC/DC converter 202 , and the other end is electrically connected to the pulse width modulation controller 208 . One end of the second voltage dividing resistor R2 is electrically connected to the other end of the first voltage dividing resistor R1, and the other end is grounded. In another embodiment of the present invention, the feedback unit 210 can also be an inductance coil to generate and output a feedback signal to the pulse width modulation controller 208 according to the driving voltage output by the DC/DC converter 202 to adjust the pulse width modulation signal duty cycle.

In this embodiment, the maximum current of the LED strings 30a, 30b, and 30c means that the corresponding LED string current adjustment signal is the smallest, while the LED string 30a, 30b, 30c has the smallest current, which means that the corresponding LED string current adjustment signal is the largest. . Therefore, the current of the LED string corresponding to the maximum value of the current adjustment signal is the smallest, and the current of the LED strings 30a, 30b, and 30c is adjusted through the current adjustment signal, reducing the pulse adjusted according to the voltage drop of the LED string with the largest voltage drop The duty cycle of the width modulation signal, thereby reducing the driving voltage output by the DC/DC converter 202, thereby reducing the excessive voltage on the corresponding electronic switches Qa, Qb, Qc of the current adjustment unit 204 in other strings , which improves the thermal stress problem caused by the large power loss of the electronic switches Qa, Qb, and Qc.

FIG. 4 is a detailed circuit diagram of a LED driving system 20c in another embodiment of the present invention. In this embodiment, the circuit of the LED driving system 20c is basically the same as that of the LED driving system 20b shown in FIG. . The dynamic reference level adjustment unit 2066 adjusts the reference level voltage according to the determination signal output by the determination unit 2063 . The second comparison unit 2067 is used for comparing the cathode voltage divisions of the plurality of LED strings 30a, 30b, 30c to obtain the minimum value of the cathode voltage division of the plurality of LED strings 30a, 30b, 30c. The third comparison unit is used to compare the minimum value of the cathode voltage division of multiple light emitting diode strings 30a, 30b, 30c with the reference level voltage output by the dynamic reference level adjustment unit 2066, so as to control the signal generation unit 2064 to generate and output the control signal , the pulse width modulation controller 208 adjusts the driving voltage output by the DC/DC converter 202 according to the control signal output by the signal generating unit 2064 .

The working principle of the circuit in this embodiment is basically the same as that in the first embodiment, except that the judging unit 2063 determines that the minimum value of the cathode voltage division of the plurality of LED strings 30a, 30b, 30c is greater than the dynamic reference level adjustment When the reference level voltage output by the unit 2066, a judgment signal that the reference level voltage remains constant is generated and output to the dynamic reference level adjustment unit 2066, and the signal generation unit 2064 generates and outputs a control signal with a constant duty cycle to the pulse width modulation controller 208 . The judging unit 2063 is when the minimum value of the cathode divided voltage of the plurality of LED strings 30a, 30b, 30c is not greater than the reference level voltage output by the dynamic reference level adjustment unit 2066, and the multiple LED strings 30a, 30b, 30c When the maximum value of the current adjustment signal is between the first set value and the second set value, a judgment signal that the reference level voltage remains unchanged is generated and output to the dynamic reference level adjustment unit 2066, and the signal generation unit 2064 generates and outputs A control signal with a constant duty cycle is sent to the PWM controller 208 . The judging unit 2063 is when the minimum value of the cathode divided voltage of the plurality of LED strings 30a, 30b, 30c is not greater than the reference level voltage output by the dynamic reference level adjustment unit 2066, and the multiple LED strings 30a, 30b, 30c When the maximum value of the current adjustment signal is less than the first set value, a judgment signal for reducing the reference level voltage is generated and output to the dynamic reference level adjustment unit 2066, thereby reducing the reference level output by the dynamic reference level adjustment unit 2066 Voltage, the signal generation unit 2064 generates and outputs a control signal with a reduced duty ratio to the PWM controller 208 to adjust the duty ratio of the PWM signal. The judging unit 2063 is when the minimum value of the cathode divided voltage of the plurality of LED strings 30a, 30b, 30c is not greater than the reference level voltage output by the dynamic reference level adjustment unit 2066, and the multiple LED strings 30a, 30b, 30c When the maximum value of the current adjustment signal is greater than the second set value, a judgment signal for increasing the reference level voltage is generated and output to the dynamic reference level adjustment unit 2066, thereby increasing the reference level output by the dynamic reference level adjustment unit 2066 Voltage, the signal generating unit 2064 generates and outputs a control signal with an increased duty ratio to the PWM controller 208 to adjust the duty ratio of the PWM signal. Therefore, it will not be described in detail here.

FIG. 5 is a flowchart of a method for driving a light emitting diode in an embodiment of the present invention. First, in step S5000, the constant current unit 2061 detects the current flowing through the multiple LED strings 30a, 30b, 30c, and outputs multiple LED strings 30a according to the currents of the multiple LED strings 30a, 30b, 30c , 30b, 30c current regulation signals. In step S5001, the first comparison unit 2062 detects the current regulation signals of the plurality of LED strings 30a, 30b, 30c and finds the maximum value therefrom. In step S5002, the judging unit 2063 judges whether the maximum value of the current regulation signal is between the first set value and the second set value. If the maximum value of the current regulation signal is between the first set value and the second set value, then in step S5003, the signal generating unit 2064 generates and outputs a control signal with a constant duty ratio to the pulse width modulation controller 208 , the pulse width modulation controller 208 outputs a pulse width modulation signal with a constant duty ratio to the DC/DC converter 202 , and at this time, the driving voltage output by the DC/DC converter 202 remains unchanged. If the maximum value of the current adjustment signal is not between the first set value and the second set value, then in step S5004 , the determining unit 2063 determines whether the maximum value of the current adjustment signal is greater than the second set value. If the maximum value of the current regulation signal is greater than the second set value, then in step S5006, the PWM controller 208 determines whether the output duty cycle is greater than the threshold. If the output duty ratio of the PWM controller 208 is greater than the threshold, then in step S5007, the PWM controller 208 outputs a pulse width modulation signal with a reduced duty ratio to the DC/DC converter 202, and the DC/DC The driving voltage output by the converter 202 decreases. If the output duty ratio of the PWM controller 208 is not greater than the threshold, then in step S5008, the PWM controller 208 outputs a pulse width modulation signal with an increased duty ratio to the DC/DC converter 202, at this time the DC/DC The drive voltage output by the DC converter 202 increases. If the maximum value of the current regulation signal is less than the second set value, then in step S5005, the signal generation unit 2064 generates and outputs a control signal with a reduced duty cycle to the pulse width modulation controller 208, and the pulse width modulation controller 208 outputs The pulse width modulation signal with reduced duty ratio is sent to the DC/DC converter 202 , and the driving voltage output by the DC/DC converter 202 decreases at this time.

FIG. 6 is a flowchart of a method for driving a light emitting diode in another embodiment of the present invention. Steps S6000 , S6001 , S6005 , and S6007 in the flow chart in this embodiment are similar to steps S5000 , S5001 , S5002 , and S5004 in the flow chart in FIG. 5 , and thus will not be described in detail. Wherein, in step S6002, the second comparison unit 2067 detects the divided voltages of the cathodes of the plurality of LED strings 30a, 30b, 30c and finds the minimum value therefrom. In step S6003, the third comparing unit 2068 determines whether the minimum value of the cathode voltage division of the plurality of LED strings 30a, 30b, 30c is greater than the reference level voltage output by the dynamic reference level adjustment unit. If the minimum value of the cathode divided voltage of the plurality of light emitting diode strings 30a, 30b, 30c is greater than the reference level voltage output by the dynamic reference level adjustment unit, then in step S6004, the judging unit 2063 outputs an adjustment that the reference level voltage remains unchanged The signal is sent to the dynamic reference level adjustment unit 2066, the signal generating unit 2064 generates and outputs a control signal with a constant duty ratio to the pulse width modulation controller 208, and the pulse width modulation controller 208 outputs a pulse width modulation signal with a constant duty ratio to the DC/DC converter 202 . If the minimum value of the cathode divided voltage of the plurality of LED strings 30a, 30b, 30c is not greater than the reference level voltage output by the dynamic reference level adjustment unit, go to step S6005. If the maximum value of the current adjustment signal is between the first set value and the second set value, then in step S6006, the judging unit 2063 outputs an adjustment signal to the dynamic reference level adjustment unit 2066 with a constant reference level voltage, The signal generation unit 2064 generates and outputs a control signal with a constant duty ratio to the PWM controller 208 , and the PWM controller 208 outputs a PWM signal with a constant duty ratio to the DC/DC converter 202 . If the maximum value of the current adjustment signal is not between the first set value and the second set value, go to step S6007. If the maximum value of the current adjustment signal is greater than the second set value, then in step S6008, the judgment unit 2063 outputs an adjustment signal for increasing the reference level voltage to the dynamic reference level adjustment unit 2066, and the signal generation unit 2064 generates and outputs The control signal with increased duty ratio is sent to the PWM controller 208 , and the PWM controller 208 outputs the pulse width modulated signal with increased duty ratio to the DC/DC converter 202 . If the maximum value of the current adjustment signal is less than the second set value, then in step S6009, the judging unit 2063 outputs an adjustment signal for reducing the reference level voltage to the dynamic reference level adjustment unit 2066, and the signal generating unit 2064 generates and outputs The control signal with reduced duty cycle is sent to the PWM controller 208 , and the PWM controller 208 outputs the pulse width modulated signal with reduced duty cycle to the DC/DC converter 202 .

The LED driving system and method described above quickly adjusts the driving voltage of the LED array according to the current LED array current in real time, which improves the thermal stress problem caused by the power loss of the electronic switch and improves the power usage efficiency at the same time.

Claims (18)

1. A light-emitting diode driving method, used in a light-emitting diode driving system, for driving a light-emitting diode array, the light-emitting diode array includes a plurality of parallel-connected light-emitting diode strings, and the light-emitting diode driving system includes a control unit, a pulse width A modulation controller, the control unit includes a constant current unit, a first comparison unit, a judgment unit, and a signal generation unit, wherein the light emitting diode driving method includes: The constant current unit detects the current flowing through the plurality of LED strings and correspondingly outputs the current adjustment signal of the plurality of LED strings according to the current of the plurality of LED strings; The first comparison unit detects the current regulation signals of the plurality of LED strings and finds the maximum value therefrom; The judgment unit judges whether the maximum value of the current adjustment signal is between the first set value and the second set value and outputs a judgment signal; The signal generation unit generates and outputs a control signal according to the judgment signal; The pulse width modulation controller outputs a pulse width modulation signal according to the control signal to drive the LED array. 2. The LED driving method according to claim 1, wherein the step of generating and outputting a control signal according to the judgment signal by the signal generating unit comprises: If the judgment signal is that the maximum value of the current adjustment signal is between the first set value and the second set value, the signal generation unit generates and outputs a control signal with a constant duty ratio; If the determination signal is that the maximum value of the current adjustment signal is greater than the second set value, the signal generation unit generates and outputs a control signal with an increased duty cycle; and If the determination signal is that the maximum value of the current adjustment signal is smaller than the first set value, the signal generation unit generates and outputs a control signal with a reduced duty cycle. 3. The light emitting diode driving method according to claim 2, wherein the step of outputting a pulse width modulation signal by the pulse width modulation controller according to the control signal to drive the light emitting diode array comprises: If the control signal is a control signal with an increased duty cycle, the pulse width modulation controller judges whether the output duty cycle is greater than a threshold; outputting a pulse width modulated signal with a reduced duty cycle if the pulse width modulation controller output duty cycle is greater than a threshold; and If the output duty ratio of the pulse width modulation controller is not greater than the threshold value, output a pulse width modulation signal with an increased duty ratio. 4. The LED driving method according to claim 1, wherein the control unit further comprises a dynamic reference level adjustment unit, a second comparison unit, and a third comparison unit, and the constant current unit detects the The step of correspondingly outputting current adjustment signals of the plurality of LED strings according to the currents of the plurality of LED strings includes: the second comparison unit detects that the plurality of light emitting diodes Divide the voltage at the cathodes of the diode string and find the minimum value from it. 5. The LED driving method according to claim 4, wherein the step of generating and outputting a control signal according to the judgment signal by the signal generating unit comprises: The third comparison unit judges whether the minimum value of the cathode voltage division of the plurality of LED strings is greater than the reference level voltage output by the dynamic reference level adjustment unit; If the minimum value of the cathode divided voltage of the plurality of light emitting diode strings is greater than the reference level voltage, the judgment unit outputs an adjustment signal that the reference level voltage remains unchanged to the dynamic reference level adjustment unit, the said dynamic reference level adjustment unit. The signal generating unit generates and outputs a control signal with a constant duty ratio; If the minimum value of the cathode divided voltage of the plurality of light emitting diode strings is not greater than the reference level voltage and the determination signal is that the maximum value of the current adjustment signal is between the first set value and the second set value , the judgment unit outputs an adjustment signal with a constant reference level voltage to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a control signal with a constant duty cycle; If the minimum value of the cathode divided voltage of the plurality of light-emitting diode strings is not greater than the reference level voltage and the determination signal is that the maximum value of the current adjustment signal is greater than the second set value, then the determination The unit outputs an adjustment signal for increasing the reference level voltage to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a control signal for increasing the duty cycle; and If the minimum value of the cathode divided voltage of the plurality of LED strings is not greater than the reference level voltage and the determination signal is that the maximum value of the current adjustment signal is less than the first set value, then the determination The unit outputs an adjustment signal for reducing the reference level voltage to the dynamic reference level adjustment unit, and the signal generation unit generates and outputs a control signal for decreasing the duty cycle. 6. A light-emitting diode driving system, which is used to convert an external power supply voltage into a voltage suitable for driving a light-emitting diode array, and the light-emitting diode array includes a plurality of parallel-connected light-emitting diode strings, wherein the light-emitting diode driving system include: A DC/DC converter, configured to be electrically connected to the external power supply and the LED array, for converting the input voltage of the external power supply into a driving voltage to drive the LED array to emit light; A control unit, for being electrically connected to the LED array, comprising: A constant current unit, configured to detect the current flowing through each LED string, so as to obtain a current regulation signal of each LED string; A first comparison unit, configured to compare the current regulation signals of the plurality of LED strings to obtain a maximum value of the current regulation signals of the plurality of LED strings; a judging unit, configured to judge whether the maximum value of the current adjustment signals of the plurality of LED strings is between the first set value and the second set value and output a judgment signal; and a signal generating unit, configured to generate and output a control signal according to the judgment signal; and a pulse width modulation controller, used to be electrically connected to the control unit and the DC/DC converter, and used to output a pulse width modulation signal according to the control signal to adjust the driving output of the DC/DC converter Voltage. 7. The light-emitting diode drive system according to claim 6, further comprising a current regulation unit for being electrically connected between the cathode of the light-emitting diode array and the control unit, the constant current unit It is also used for detecting the current flowing through each LED string through the current regulation unit, so as to obtain the current regulation signal of each LED string. 8. The light-emitting diode drive system according to claim 7, wherein the current regulation unit is further configured to adjust the current flowing through each light-emitting diode string according to the current regulation signal of each light-emitting diode string current. 9. The light-emitting diode driving system according to claim 6, wherein the signal generation unit is further configured to adjust the maximum value of the current adjustment signal of the plurality of light-emitting diode strings between the first set value and When the second set value is between, generate and output a control signal with a constant duty ratio; outputting a control signal for decreasing the duty cycle, and generating and outputting a control signal for increasing the duty cycle to the a pulse width modulation controller to adjust the duty cycle of the pulse width modulation signal. 10. The light-emitting diode drive system according to claim 9, wherein the pulse width modulation controller is also used to judge whether the output pulse width modulation signal is greater than a threshold value, and when the output duty cycle is not greater than the threshold value, the output duty cycle increase the pulse width modulation signal, and output a pulse width modulation signal with a reduced duty cycle when it is greater than the threshold. 11. The LED driving system according to claim 6, wherein the control unit further comprises: A dynamic reference level adjustment unit, configured to adjust the reference level voltage according to the judgment signal output by the judgment unit; The second comparison unit is used to compare the cathode voltage division of the plurality of light emitting diode strings to obtain the minimum value of the cathode voltage division of the plurality of light emitting diode strings; and The third comparison unit is used for comparing the minimum value of the cathode voltage division of the plurality of LED strings with the reference potential voltage, so as to control the signal generation unit to generate and output a control signal. 12. The light-emitting diode driving system according to claim 11, wherein the judging unit generates and outputs a reference voltage when the minimum value of the cathode divided voltage of the plurality of light-emitting diode strings is greater than the reference level voltage. The judgment signal that the level voltage is constant is sent to the dynamic reference level adjustment unit, the signal generation unit generates and outputs a control signal with a constant duty cycle to the pulse width modulation controller, and the judgment unit is in the When the minimum value of the cathode divided voltage of the plurality of light emitting diode strings is not greater than the reference level voltage, and the maximum value of the current adjustment signal of the plurality of light emitting diode strings is between the first set value and the second When between two set values, generate and output a judgment signal that the reference level voltage is constant to the dynamic reference level adjustment unit, and the signal generating unit generates and output a control signal with a constant duty cycle to the pulse width modulation controller. 13. The light-emitting diode drive system according to claim 11, wherein the judging unit is when the minimum value of the divided voltage of the cathodes of the plurality of light-emitting diode strings is not greater than the reference level voltage, and the When the maximum value of the current adjustment signals of multiple light emitting diode strings is less than the first set value, a judgment signal that the reference level voltage decreases is generated and output to the dynamic reference level adjustment unit to adjust the reference level bit voltage, the signal generating unit generates and outputs a control signal with a reduced duty ratio to the PWM controller, so as to adjust the duty ratio of the PWM signal. 14. The light emitting diode drive system according to claim 11, characterized in that, when the minimum value of the cathode divided voltage of the plurality of light emitting diode strings is not greater than the reference level voltage, and the judgment unit When the maximum value of the current adjustment signals of multiple light emitting diode strings is greater than the second set value, a judgment signal that the reference level voltage increases is generated and output to the dynamic reference level adjustment unit to adjust the reference level The signal generation unit generates and outputs a control signal with an increased duty ratio to the pulse width modulation controller, so as to adjust the duty ratio of the pulse width modulation signal. 15. The LED driving system according to claim 7, wherein the current regulating unit comprises: An electronic switch and a sampling resistor electrically connected to each light-emitting diode string, the electronic switch includes a control electrode, a first electrode, and a second electrode, and the first electrode is electrically connected to the cathode of the light-emitting diode string. The control electrode is electrically connected to the constant current unit, the second electrode is electrically connected to one end of the sampling resistor, and the other end of the sampling resistor is grounded. 16. The LED driving system according to claim 6, wherein the current regulation signal is inversely proportional to the current of the LED string. 17. The LED driving system according to claim 6, further comprising: a feedback unit, for being electrically connected to the DC/DC converter and the pulse width modulation controller, for generating and outputting a feedback signal to the pulse width modulation according to the driving voltage output by the DC/DC converter a controller to adjust the duty cycle of the pulse width modulation signal. 18. The LED drive system according to claim 17, wherein the feedback unit comprises: a first voltage dividing resistor, one end is electrically connected to the output end of the DC/DC converter, and the other end is electrically connected to the pulse width modulation controller; and One end of the second voltage dividing resistor is electrically connected to the other end of the first voltage dividing resistor, and the other end is grounded.