TWI462636B - Appropriate led arrangement and power need estemation in large-scale led display and lighting apparatus and method thereof - Google Patents

Description

LED array and power demand estimation on large-size LED display and illuminator and method thereof

The invention relates to a method for managing an LED arrangement of a display and a lighting device and a method for estimating the power supply thereof, and a device thereof, in particular to a LED arrangement and power supply requirement on a light-emitting diode (LED) display and a illuminator and a method thereof.

For the purpose of saving energy and not using mercury, LED technology has become the most important light source for large-size LCD panels and illuminators. Based on thermal considerations, LEDs with a power rating of less than 1 watt and even less than 0.1 watt have become the main unit of display for today's displays or luminaires. A large number, hundreds or even thousands of LEDs need to be arranged in one device, and their connections are mainly in the form of series and/or parallel. However, in terms of design considerations, the form of LEDs connections and the power requirements are very closely related to each other. Therefore, the need to operate the power of the LEDs is highly correlated with the arrangement of the LEDs.

If a large number of LCDs are only connected in series on a series, a very high voltage is required, and if the LEDs are only connected in a parallel series, a considerable current is required. As a result, when all the LEDs are only connected in series or in parallel, it is necessary to provide a power supply having an extremely high (low) output voltage and having a very low (high) current source.

In other words, an inappropriate combination may increase the difficulty of driving the power supply design of a plurality of LEDs. In addition, when a large number of LEDs are only connected in series or in parallel, it may increase the probability of failure when operating the LED device, and may also cause heat problems. In fact, the above problem is difficult to solve by merely biasing the plurality of LEDs in a stable operation area. A preferred biasing strategy for transistors, diodes, and even power LEDs is to place the operating point around the middle of the power curve (PD curve) for superior results. However, most of the literature only focuses on the promotion of LED driver architecture, but lacks research on the above issues, even the estimation of power demand is extremely rare and scattered. Therefore, there is an urgent need for a progressive method to solve the above problems.

As a result of the job, the inventor, in view of the lack of the prior art, thought of and improved the idea of invention, and finally invented the "large-size LED display, LED arrangement and power demand estimation on the illuminator and its method".

This case uses a widely used average method that is closer to the actual problem to find an appropriate bias operating point for a plurality of LEDs, and then determines an appropriate combination and power requirements to determine the LED arrangement and power supply, respectively. design.

In addition, the case also explores a simple LED placement strategy to prevent possible electromagnetic interference and voltage overload. Finally, a design example implements an LCD backlit display for a 20-inch television to verify the feasibility of the proposed method.

Another main object of the present invention is to provide a method for estimating a power demand of a plurality of LEDs in a display, comprising the steps of: calculating an optimum voltage value and an optimum current value for the display; The optimum voltage value and the optimum current value are obtained for one of the first and second optimum operating points of the display, wherein the first and the second optimum operating point are used to arrange the plurality of LEDs.

A main object of the present invention is to provide a backlight device comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first plurality of LEDs connected in parallel are arranged in series a first string number is a ceiling value of one of the N values, and a floor value of the root number value, and the first plurality of LEDs in the series of parallel connected LED strings are one of the LEDs in the series a total of the ceiling value of the root value of the N or the floor value of the root value of the N, wherein a total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings When the value is greater than a predetermined value, each of the first plurality of parallel connected LED series includes a second plurality of LED series connected in parallel, and the second plurality of LED series connected in parallel The second total number of one of the LEDs in each of the series of the second plurality of parallel connected LED strings is one of N ^1/4 of the ceiling value or ^one of the N ^1/4 of the floor value.

Another main object of the present invention is to provide a luminaire comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first plurality of LEDs connected in parallel are arranged in series a first string number is a ceiling value of N ^1/2 or a floor value of the N ^1/2 , and the first total number of LEDs in each of the series of the first plurality of parallel connected LED strings the value of the floor ceiling or the value of N ^1/2 that of N ^1/2.

The above described objects, features, and advantages of the present invention will become more apparent and understood.

In the first figure, the power consumption (PD) curve of a plurality of LEDs on the current-voltage plane (iv plane) is first established to characterize its power supply behavior. A plurality of LEDs derive an average conductivity g _av between the two nominal endpoints of the PD curve and then move in a direction to shift to one of the tangent points of the PD curve, which is at the optimum operating point of the plurality of LEDs. In addition, a general deductive procedure further finds a suitable LED arrangement, and a power supply requirement is also proposed. An estimate of the appropriate combination of a large number of LEDs can be easily obtained by taking a plurality of root number values of the number of LEDs after a plurality of interpretations. The time required for the interpretation depends on whether the estimated LED arrangement is suitable for the power supply design.

In general, the consideration of moderately biasing a different LED is to place the operating point in the middle of the maximum PD curve without exceeding the safe-operating area (SOA). However, the bias concept of a plurality of LEDs is basically the same as that of individual LEDs. First define a plurality of LEDs as N LEDs, where N is a positive integer. Based on the characteristics of the device, the PD curves of the N LEDs on the iv axis can be easily depicted as shown in the first figure. Interestingly, all LEDs connected in series and all LEDs connected in parallel can be easily found at the two nominal endpoints of the PD curve presented in the first figure. Accordingly, the power consumption P _{D of the} N LEDs on the iv plane, when all connected in series, can be expressed as:

Or, when all are connected in parallel, it can be expressed as:

Where V _D and I _D are the forward voltage and forward current of the respective LEDs, respectively, and define V _max = NV _D , V _min = V _D , I _max = NI _D , and I _min = I _D . In this case, the first and second formulas are equal to each other. The PD curve for the proposed plurality of LEDs is depicted in the first figure, which is substantially true at the rated power of the SOA. The case with the maximum rated current I _max = NI _D and the minimum parallel series voltage V _min = V _D on the PD curve is exactly the case where all the LEDs are connected in parallel. On the other hand, the maximum rated voltage V _max = NV _D has a minimum rated current I _min = I _D , which is exactly the case where all the LEDs are connected in series. Accordingly, a possible combination of series and/or parallel can be easily obtained along the PD curve by changing the integer N. If an intuitive dichotomy is performed, the possible combinations of series and/or parallel can be easily established as shown in the second figures (a)-(c), which is a common case of guessing strategies.

In fact, the LED arrangement and power requirements are closely related to each other, which is significantly related to the power supply design and the operation of the plurality of LEDs for uniformly producing the illumination output as expected. Therefore, how to estimate the proper combination of multiple LEDs and the power requirements of matching power supply designs is an important issue in large-size LED displays.

Basically, the PD curve for the N LEDs as proposed in the first figure can be easily achieved by reference to the nominal power source from manufacture. The current i of the N LEDs is along the PD curve voltage v on the i-v plane and can be obtained by:

If f ( v ) in the first graph is continuous in [ V _min , V _max ] and is differentiable in ( V _min , V _max ), then there are some points v _c ( V _min , V _max ) makes

f ( V _max )- f ( V _min ): f ^' ( v _c )( V _max - V _min ) (4).

Generated from equation (3):

as well as

Available

Where v _c = V _opt is the optimum voltage. The optimum current I _opt can be given by equations (1) and (7):

The average conductivity g _{av of a} plurality of LEDs can be easily assigned by drawing a line between the two nominal endpoints of the PD curve under SOA, namely:

Where g _av is defined to be equal to a slope m .

In equation (9), a negative sign indicates that as the operating current decreases and the operating voltage increases, the conductivity decreases along the PD curve, and vice versa, which should substantially follow P _D = NV _D l _D . If attempting to move parallel to the tangential line of the PD curve having a slope m at point c, as shown in the first figure, the average conductivity line g _av , the appropriate operating point of the N LEDs by ( i _c , v _c ) = ( V _opt , l _opt ) is given, and then obtained from equations (7) and (8). Accordingly, the operating point c contributes to an appropriate estimate for the combination of multiple LEDs arranged and the power requirements. The arrangement of the LEDs defined after the estimation consists of q parallel series, and each string has p LEDs connected in series. The required power requirements, derived from equations (7) and (8), are granted through the estimated operating points and are:

as well as

And get, where V _min = V _D and I _min = I _D .

Interestingly, through equations (1), (2), (10), and (11), there is a simple, concise expression of the combination of multiple LEDs for estimation, which is:

Equation (12) intuitively shows that it is easy to estimate by taking only the square root of the total number of N LEDs to be arranged. In particular, the number of parallel strings must be the same as the number of series strings, which really simplifies the design concept developed by the present invention.

If a very large number of LEDs are to be arranged in a display panel, the estimates from equations (10) and (11) are used for point c in the first figure, most likely due to the power supply design after the first interpretation. Difficulties, and perhaps not fully meet the design considerations. This may be due to the fact that the estimated series string LEDs are still so high. Therefore, a further estimate for successively finding other combinations suitable for power supply design is necessary. This continuous estimation procedure can be seen in the third figure, for example, where only two deductive programs are explored. The second interpretation only been considered by the first estimate of the optimum point (V _opt1, I _opt1), to find a second operation point (V _opt2, I _opt2) on iv coordinates, it is easy to handle. That is, the first derived series voltage and parallel current and the point ( V _max1 , I _min1 ). In other words, in the second deduction, only the points between c1 and a on the PD curve are considered as design parameters. Notably, in the third graph, the point a at ( V _max1 , I _min1 )=( NV _D , I _D ) is exactly the point in the first graph ( V _max , I _min )=( NV _D , I _D ). Furthermore, ignoring the complex deductive procedure, the point a on the PD curve in the third graph remains unchanged forever. In the third figure, the second deductive procedure for finding the second average conductivity g _av2 with the slope m ₂ is the same as the procedure in the first deduction. By the averaging method with the triangular translation method, the g _av2 line tangential to the point c _{2 of the} PD curve gives the second optimum point on the iv plane ( V _opt2 , I _opt2 ). Referring to the third figure, the general derivation for the kth deduction can be described as follows.

V _{max, k} = p _k V _D (13),

V _{min, k} = V _D (14),

I _{max, k} = q _k I _D (15),

as well as

I _{min, k} = I _D (16).

Where k≧1 . Referring to (10)-(12), the optimum point of the kth voltage and current can be found.

as well as

Where p _k = q _k is the same as the first derivation formula (12). Obtained from equations (12), (17) and (18)

Used for k≧1 . Equation (19) gives the kth combination for arranging N = ( p _k ) ^2k LEDs. In other words, in the first deduction Parallel strings and each series string LEDs. Enter the second interpretation, each Parallel serials are further divided into Times-parallel series and each-to-serial string has LEDs. In other words, after the second deduction, there is a total Times-parallel series and each-to-serial string has LEDs. It is possible to continue with the subsequent deductive program to see if the estimated sub-serial voltage meets the appropriate power requirements for power supply design. Therefore, the total number of parallel series Q _k after the kth deduction will be

And the kth series string has the same number of LEDs as the formula (19).

Figure 4 (a) shows that the N LEDs are originally connected to a serial. After the first deduction, the combination of N LEDs estimates is shown in Figure 4(b), and the combination of N LEDs estimated after two deductions, for example, is implemented in Figure 4(c). The estimated parallel series for the first deduction is q ₁₁ +q ₁₂ +q ₁₃ +...., and then q ₁₁ will be divided into q ₂₁₁ +q ₂₁₂ +q ₂₁₃ +...., and q _{12 is} divided into q ₂₂₁ +q ₂₂₂ +q ₂₂₃ +....,....and after the second deduction. Finally, from equation (20), the second estimated parallel series in this example will be N ^{3/4 in} total, and from equation (19), each second estimated series has N ^1/4. LEDs, where N is the number of LEDs to be aligned.

If a larger number of estimated sub-parallel strings are needed after a number of deductions, adding parallel power modules to share the large current demand is feasible in design considerations. In practice, the required deduction will be no more than 2 to 4 times, because the estimate is calculated only by taking the root number of the number of LEDs.

Equation (19) gives a general estimate. Through the kth deduction, the number of LEDs in the k-th estimated series string is determined by taking only the square root of k times, where the total number of parallel strings is in the formula (20). Given in ). Appropriate power requirements can be easily estimated for the power supply design based on the kth operating point of the plurality of LEDs given in equations (17) and (18). However, if multiple parallel series are required after a number of deductions, such as shown in Figure 4(c), a larger current demand may be necessary in the power supply design. In this case, adding a plurality of parallel power modules for shunting is a design consideration. In addition, in the LED arrangement, it is necessary to avoid LED failure and to prevent interference between the series and parallel series when arranging. In addition, in terms of arrangement, it is recommended to stagger to reduce electromagnetic interference and possible LED faults between adjacent strings.

An exemplary design of the present invention is shown in the fifth diagram. An LED display for a 20-inch LCD TV having an area of 41 cm x 31 cm = 1271 cm 2 is designed to achieve approximately 600 LEDs, each of which has a nominal current of 25 mA and a rated power P _D = 110 mW. After calculating the actual area of the display, the possible number of LEDs to be used is 588. The white LED has a forward voltage V _D = 3.5 V and a current I _D = 20 mA under normal conditions. In this design, the relevant parameters for the 588 LEDs are each estimated as follows. From equation (1), the maximum power consumption is:

_{P D = 3.5 V × 0.02 A} × 588 = 41.16 W (21),

Connect all LEDs in series with

V _max = 3.5 V × 588 = 2058 V (22),

as well as

l _min =20 mA (23).

Connect all LEDs in series with

_{V min = 3.5 V (24)} ,

as well as

l _max = 20 mA × 588 = 11.76 A (25).

The PD curve of the 588 LEDs can be easily drawn by referring to the first figure and according to equations (21)-(25). From equations (7) and (8), after the first deduction, it is easy to find the optimum operating point for a total of 588 LEDs, which is:

as well as

From equation (9), at the point of ( V _opt , I _opt ) of the PD curve of the i - v plane, there is an average conductivity g _av = 5.63 mS. The number q of parallel series and p LEDs in each series string can be estimated from equations (10) and (11):

as well as

Where p is equal to q to satisfy equation (12). Since the power requirements in equations (26) and (27) are suitable for power supply design, no further deduction is needed in this design. In implementation, if 24 parallel strings are used, and each string has 24 serially connected LEDs, then there will be 12 LEDs for alignment.

However, a minor revision was made in this design, using 24 series of LEDs in 12 strings, and using 25 series of LEDs in another 12 series, where the total parallel series remains It is 24. Therefore, there are a total of 24x12 + 25x12 = 588 LEDs, which is fully compliant. This approach will result in a string voltage difference of less than 3.5V between the 24 LEDs series, which will be compensated for in the power supply design. From equations (26) and (27), a boost converter with input voltage V _i =12V _dc , output voltage V _out =96V _dc , output current I _o =0.5A and switching frequency f _s =50kHz is 48W Design and implementation. With 10% tolerance, output voltages as high as 96V _dc and output power as high as 48W are considered to ensure that the power supply capability provided is in line with the estimated 88V _dc string voltage. In addition, as shown in the proposed embodiment of Figure 5, 24 current sinking circuits are listed, powered by a regulated voltage source estimated to be 96V _dc . The above experiment shows the excellent performance of producing a nearly uniform illumination output in the display in a wide range of dimming procedures with the estimated power supply for the bias voltage of the plurality of LEDs, and for each Current balancing between the strings, a linear regulator is used to sink the current into the circuit.

Because the output voltage of the designed power supply has a 10% tolerance, the current sinking circuit can regulate itself against the voltage fluctuations of the series LEDs, and the currents in the 24 series are almost very different from each other. close to. All of the LEDs in the display panel produced nearly equal illumination output in a wide range of dimming procedures from dark to 550 cd/m2 at 50 mm.

Example:

CLAIMS 1. A method for power supply estimation of a plurality of light emitting diodes (LEDs) in a display, comprising the steps of: calculating an optimum voltage value and an optimum current value for the display; The optimum voltage value and the optimum current value are obtained for one of the first and second optimum operating points of the display, wherein the first and the second optimum operating point are used to arrange the plurality of LEDs.

2. The method according to embodiment 1 further comprising the step of: determining a first reference value by using a value of one of the total number of the plurality of LEDs, wherein the first reference value is one of the root value a floor value or a ceiling value of the root value; and arranging the plurality of LEDs according to the first optimum operating point as a first plurality of parallel connected LED strings, wherein the first plurality The number of the first string of one of the LED series connected in parallel and the number of the series LEDs in each of the first plurality of LED series connected in parallel is equal to the first reference value.

3. The method according to embodiment 1 or 2, wherein when the total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED series is greater than a predetermined value, the method further comprises the step of: Determining a second reference value, wherein the second reference value is one of the floor value of the first reference value or one of the root value of the first reference value a ceiling value; and rearranging each of the first plurality of parallel connected LED strings according to the second optimum operating point to form a second plurality of parallel connected LED strings, wherein the second plurality of parallel connected LED strings are a number of LEDs connected in series with each of the second plurality of LED series connected in parallel is equal to the second reference value, and the first optimum operating point corresponds to one of an abscissa and an ordinate An optimum voltage value and the optimum current value, and one of the horizontal coordinate and the one vertical coordinate corresponding to the second optimum operating point is a value of the one of the horizontal coordinates corresponding to the first optimal operating point and the first optimal operating point Corresponding to the value of one of the ordinates.

4. The method according to any of the preceding embodiments, when the total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings is greater than a first predetermined value, further comprising the steps of: The kth optimal operating point calculates a k+1th optimal operating point, wherein k is a positive integer, and the k+1th optimal operating point is used to rearrange the kth plurality of parallel connected LED series Each of the series, the first optimum operating point corresponds to one of the horizontal coordinates and one vertical coordinate is the appropriate voltage value and the optimum current value, and the k+1th optimal operating point corresponds to one of the horizontal coordinate and the one vertical coordinate respectively One of the ordinate values of one of the abscissas corresponding to the k-th optimal operating point and one of the ordinates of the k-th optimal operating point; when each of the k-th plurality of parallel connected LED strings When one of the series LEDs has a total voltage drop greater than a kth predetermined value, k=k+1, and returns to the previous step; and a total voltage of one of the series LEDs in each of the kth plurality of parallel connected LED strings When the drop is less than or equal to the kth predetermined value, it stops.

5. The method according to any of the above embodiments further comprising the steps of: The secondary determines a kth reference value, wherein the kth reference value is the total number a ceiling value or a floor value of the power; and rearranging, according to the k+1th optimum operating point, each of the k-th parallel connected LED series, wherein the k-th plurality of parallel-connected LEDs The number of kth strings of one of the series of the series is approximately equal to the total number a power, wherein m is a positive integer, the kth string number is equal to the kth reference value, and the total number of one of the series of LEDs included in the k-th plurality of parallel connected LED strings is the first k reference value.

6. The method of any of the preceding embodiments, wherein the plurality of LEDs are applied to a backlight of a display, and an operating voltage of any one of the plurality of LEDs is substantially 3.5 volts.

7. The method of any of the preceding embodiments, wherein the method is further applicable to any one selected from the group consisting of a notebook computer, a backlight of a mobile device, and a lighting device.

A backlight device comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first plurality of LED series of the first plurality of parallel connected LED strings is One of the N values of the ceiling value or one of the root value values, and the first total number of LEDs in each of the first plurality of parallel connected LED strings is the N The floor value of the root value or the floor value of the root value of the N, wherein when a total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings is greater than a predetermined value, Each of the first plurality of parallel connected LED strings includes a second plurality of parallel connected LED strings, and the second plurality of parallel connected LED strings is connected to the second plurality of parallel strings The second total number of LEDs in each of the series of connected LED strings is one of N ^1/4 of the ceiling value or ^one of the N ^1/4 of the floor value.

9. A luminaire comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first plurality of LED series of the first plurality of parallel connected LED strings is one of each of the series one ceiling value N ^1/2 or ^{1/2 of} one of the N values of the floor, and the first plurality of LED strings are connected in parallel in the total number of LEDs for a first ^1/2 N The ceiling value or the floor value of the N ^1/2 .

10. The luminaire of embodiment 9, wherein each of the first plurality of parallel connections is connected when a total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings is greater than a predetermined value The LED series includes a second plurality of LED series connected in parallel, and the second plurality of LED series connected in parallel and the second plurality of LED series connected in parallel with the second plurality The second total of one of the LEDs in the column is one of N ^1/4 of the ceiling value or ^one of the N ^1/4 of the floor value.

In summary, in the present invention, an appropriate combination of a very large number of LEDs arranged in a display and power requirements are estimated by taking only the square root value of the number of LEDs. In addition, a general estimate for a very large number of LEDs is also achieved by taking only the square root of the number of LEDs. Considerations for the implementation of estimated parameter values such as LED alignment, power supply design, and current balancing have been thoroughly explored in the examples. A design example for a 20-inch LCD television display with 588 LEDs was examined to verify the feasibility of the proposed strategy. The results of the tests demonstrate that the proposed strategy allows a large number of LEDs to be biased in a well-functioning state, as well as in a wide range of dimming procedures ranging from dark to 550 cd/m2 at 50 mm. Almost equal illumination output is produced in the display.

In summary, the present invention provides a widely used method that is closer to the actual problem to find an appropriate bias operating point of a plurality of LEDs, and then determines an appropriate combination and power requirements to determine the LEDs, respectively. Arrangement and power supply design; in addition, the present invention also explores a simple LED placement strategy to prevent possible electromagnetic interference and voltage overload; therefore, the present invention does have novelty and advancement.

Therefore, even though the present invention has been described in detail by the above-described embodiments, it can be modified by those skilled in the art, and is not intended to be protected as claimed.

First: it shows a waveform diagram of the PD curve of the LEDs proposed in accordance with the teachings of the present invention to find its optimum operating point for the combination of the power supply requirements and the power supply requirements;

Figure 2 (a) is a schematic diagram showing a circuit in which LEDs according to the present invention are connected in a series;

Second diagram (b): showing a schematic diagram of a circuit in which LEDs according to the present invention are connected in two parallel strings;

Figure 2 (c) is a schematic diagram showing a circuit in which LEDs according to the present invention are connected to N parallel strings;

Third diagram: showing a waveform diagram comprising first and second deductive procedures for finding an optimum operating point of a plurality of LEDs for combining an estimate of power requirements in accordance with the teachings of the present invention;

FIG. 4(a) is a schematic diagram showing a circuit in which N LEDs according to the present invention are connected in a series;

Fourth (b): a circuit diagram showing an estimated combination of N LEDs after the first deduction according to the present invention;

Figure 4 (c): is a circuit diagram showing an estimated combination of N LEDs after the second deduction according to the present invention;

Fifth Figure: A circuit diagram showing an exemplary circuit mechanism in accordance with the teachings of the present invention for driving a plurality of LEDs in a 20" LCD television panel.

Claims (10)

A method for estimating a power demand of a plurality of light emitting diodes (LEDs) in a display, comprising the steps of: calculating an optimum voltage value and an optimum current value for the display; and determining according to the optimum The voltage value and the optimum current value are obtained for one of the first and second optimum operating points of the display, wherein the first and the second optimum operating point are used to arrange the plurality of LEDs. The method of claim 1, further comprising the step of: determining a first reference value by using a value of one of the total number of the plurality of LEDs, wherein the first reference value is the root value a floor value or a ceiling value of the root value; and arranging the plurality of LEDs according to the first optimum operating point as a first plurality of parallel connected LED strings, wherein the The number of the first string of one of the plurality of parallel connected LED strings and the number of the series of LEDs in each of the first plurality of parallel connected LED strings are equal to the first reference value. The method of claim 2, wherein when the total voltage drop of one of the series LEDs in the first plurality of parallel connected LED series is greater than a predetermined value, the method further comprises the step of: Determining a second reference value, wherein the second reference value is one of the root value of the first reference value or one of the root value of the first reference value And rearranging each of the first plurality of parallel connections according to the second optimal operating point The LED string is a second plurality of LED series connected in parallel, wherein the number of strings of the second plurality of parallel connected LED strings and the LEDs connected in series in each of the second plurality of LED series connected in parallel One quantity is equal to the second reference value, and one of the horizontal coordinate and the one vertical coordinate corresponding to the first optimum operating point is the optimum voltage value and the optimum current value, respectively, and the second optimum operating point corresponds to one of the horizontal coordinates An ordinate is a value of one of the ordinates corresponding to the first optimum operating point and one of the ordinate values corresponding to the first optimal operating point. The method of claim 2, when the total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED series is greater than a first predetermined value, further comprising the step of: The kth optimal operating point calculates a k+1th optimal operating point, where k is a positive integer, and the k+1th optimal operating point is used to rearrange the kth plurality of parallel connected LED series In the series, the first optimal operating point corresponds to one of the horizontal coordinate and the one vertical coordinate is the appropriate voltage value and the optimum current value, and one of the horizontal coordinate and the one vertical coordinate corresponding to the k+1 optimal operating point is The kth optimal operating point corresponds to one of the abscissas and one of the ordinates of the k-th optimal operating point; and the tandem of the k-th parallel connected LED series When one of the LEDs has a total voltage drop greater than a kth predetermined value, k=k+1, and returns to the previous step; and a total voltage drop of one of the series LEDs in each of the kth plurality of parallel connected LED strings When it is less than or equal to the kth predetermined value, it stops. The method of claim 4, further comprising the steps of: The secondary determines a kth reference value, wherein the kth reference value is the total number a ceiling value or a floor value of the power; and rearranging, according to the k+1th optimum operating point, each of the k-th parallel connected LED series, wherein the k-th plurality of parallel-connected LEDs The number of kth strings of one of the series of the series is approximately equal to the total number a power, wherein m is a positive integer, the kth string number is equal to the kth reference value, and the total number of one of the series of LEDs included in the k-th plurality of parallel connected LED strings is the first k reference value. The method of claim 1, wherein the plurality of LEDs are applied to a backlight of a display, and an operating voltage of any one of the plurality of LEDs is substantially 3.5 volts. The method of claim 1, wherein the method is further applicable to any one selected from the group consisting of a notebook computer, a backlight of a mobile device, and a lighting device. A backlight device comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first string number of the first plurality of parallel connected LED strings is the N a ceiling value of one of the root value values or a floor value of the root number value, and the first total number of LEDs in each of the series of the first plurality of parallel connected LED strings is the root of the N The floor value of the value or the floor value of the root value of the N, wherein when a total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings is greater than a predetermined value, each of the values The first plurality of parallel connected LED strings includes a second plurality of parallel connected LED strings, and the second plurality of parallel connected LED strings is connected in parallel with the second plurality of parallel strings The second total number of LEDs in each of the series of LED strings is one of N ^1/4 of the ceiling value or ^one of the N ^1/4 of the floor value. An illuminator comprising: a first plurality of LED series connected in parallel with N LEDs, wherein the N is a positive integer, and the first plurality of LED series of the first plurality of parallel connected LED strings is N ^{1 a} ceiling value of ^/2 or a floor value of the N ^1/2 , and the first total number of LEDs in each of the series of the first plurality of parallel connected LED strings is the N ^1/2 The ceiling value or the floor value of the N ^1/2 . The illuminator of claim 9, wherein when the total voltage drop of one of the series LEDs in each of the first plurality of parallel connected LED strings is greater than a predetermined value, each of the first plurality of parallel connections The LED series includes a second plurality of LED series connected in parallel, and the second plurality of LED series connected in parallel and the second plurality of LED series connected in parallel The second total of one of the LEDs in the series is one of N ^1/4 of the ceiling value or ^one of the N ^1/4 of the floor value.