JP2014220200A - Illuminating device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress application of an undue voltage to a constant current circuit for driving LED without adding any element.SOLUTION: An illuminating device includes a plurality of light sources, a plurality of current supply means for supplying a current to each of the plurality of light sources, power supply control means for controlling the output voltage of a power supply to be connected with the plurality of light sources depending on the maximum value of voltage drop of the plurality of light sources, and current control means for controlling the amount of current supplied to each light source by the current supply means so that the difference of the minimum value and the maximum value of voltage drop of the plurality of light sources is smaller than a threshold.

Description

  The present invention relates to a lighting device and a control method thereof.

Conventionally, a CCFL (Cold Cathode Fluorescent Lamp) has been used as a backlight source for a liquid crystal display. However, in recent years, backlight light sources using light emitting diodes (hereinafter referred to as LEDs (Light Emitting Diodes)) are increasing. Since the LED is a point light source, there is a method of increasing the contrast of the image by changing the brightness of each LED to increase the contrast of each area of the backlight, and this technique is generally called local dimming .

  As a method for partially adjusting the brightness of the backlight in order to realize local dimming, a method of adjusting the brightness of the LED according to the amount of current flowing through the LED and the lighting time of the LED is widely used.

  The LED lighting circuit for realizing the brightness adjustment of the LED is configured as shown in FIG. 10, for example. That is, a constant current circuit for supplying a constant current to the LED, a circuit for controlling the pulse width of ON / OFF of the current, and a voltage equal to or higher than a forward drop voltage (hereinafter referred to as VF) generated when the current is supplied to the LED. Consists of a power circuit. In addition, it is a general circuit configuration that an LED string in which a plurality of LEDs are connected in series is connected to one constant current circuit and lighted with the same amount of current, and a plurality of LED strings are connected in parallel to the power supply circuit. .

  Here, a technique is widely used in which the output voltage of the power supply circuit is adjusted in accordance with the LED string having the highest VF among the plurality of LED strings connected to the power supply circuit. In other words, among the voltages applied to the constant current circuits connected in series to each LED string, the power supply voltage is set so that the voltage applied to the constant current circuit connected to the LED string having the highest VF is equal to or higher than the voltage required for constant current driving. Will be adjusted. Therefore, when the VF value of the LED array changes, for example, when the VF of the LED array increases by increasing the amount of current (hereinafter referred to as IF) that flows to the LED array corresponding to the area whose luminance is to be increased by local dimming, the change of VF The output voltage of the power supply circuit is adjusted according to the above. Since the VF value of the LED originally varies, the variation width of the VF of the LED array is further increased by increasing / decreasing the amount of current due to local dimming.

  As described above, when the output voltage of the power supply circuit is adjusted corresponding to the maximum VF value of all the LED strings, an excessive voltage of the power supply voltage minus the LED string VF value is generated in the LED string whose VF is equal to or less than the maximum VF value. The surplus voltage becomes a power loss of the constant current circuit. If the surplus voltage reaches a level exceeding the rated input voltage of the constant current circuit, the constant current circuit may be destroyed.

  In order to prevent destruction of the constant current circuit that can be generated by this surplus voltage and to distribute heat generation throughout the circuit, elements such as FETs and transistors are added between the LED array and the constant current circuit to prevent circuit destruction. There is a prior art (see, for example, Patent Document 1).

  According to this prior art, a voltage adjustment circuit is included between the LED and the current drive circuit, and even if there is a difference voltage between the N LED strings, the voltage across the current drive circuit is reduced by the voltage adjustment circuit. Is reduced to a minimum voltage that can be operated.

Moreover, in the prior art 2 shown in Patent Document 2, a voltage adjustment circuit configured by a transistor is included between the LED string and the current driving circuit, and the transistor corresponds to a voltage comparison result between the plurality of LED strings. And adjusting the applied voltage.

JP 2011-14616 A JP 2007-11070 A

  The above-mentioned prior art protects the constant current circuit between the LED and the constant current circuit in order to suppress the heat generation of the constant current circuit due to the voltage difference between the LED strings when lighting a plurality of LED strings with the same power supply circuit. In order to solve this problem, a voltage adjusting circuit such as a transistor is included.

  However, when adding a voltage adjustment circuit such as a transistor that absorbs the differential voltage in order to suppress the breakdown of the drive circuit, it is necessary to add elements corresponding to the LED string, which increases the component cost and the component mounting area. There are also issues such as.

  Therefore, an object of the present invention is to suppress an excessive voltage from being applied to the LED driving constant current circuit without adding an element.

The present invention includes a plurality of light sources,
A plurality of current supply means for supplying a current to each of the plurality of light sources;
Power supply control means for controlling the output voltage of the power supply connected to the plurality of light sources according to the maximum value of the voltage drop of the plurality of light sources;
Current control means for controlling the amount of current that the current supply means supplies to each of the light sources so that the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than a threshold value;
It is an illuminating device provided with.

The present invention includes a plurality of light sources,
A plurality of current supply means for supplying a current to each of the plurality of light sources;
A power source connected to the plurality of light sources;
A method for controlling a lighting device comprising:
A power supply control step of controlling the output voltage of the power supply according to the maximum value of the voltage drop of the plurality of light sources;
A current control step of controlling the amount of current supplied to the light sources by the current supply means so that the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than a threshold value;
It is a control method of an illuminating device provided with.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that an excessive voltage is applied to the constant current circuit for LED drive, without adding an element.

The figure which shows schematic structure of the backlight apparatus which concerns on Example 1. FIG. 7 is a flowchart showing the control contents of the backlight device according to the first embodiment. Timing chart of voltage and current of each LED array when Example 1 is not applied Timing chart of voltage and current of each LED array when Example 1 is applied The figure which shows the relationship between the electric current of LED which concerns on Example 1, and a voltage. The figure which shows the relationship between the electric current of LED which concerns on Example 1, and the emitted light amount per unit time. Timing chart of voltage and current of each LED array when Example 2 is applied The figure which shows the relationship between the electric current of LED which concerns on Example 3, and luminous efficiency. The figure which shows the relationship between the electric current of LED which concerns on Example 3, and luminous efficiency. The figure which shows schematic structure of the backlight apparatus of a prior art example.

Example 1
FIG. 1 is a diagram showing a schematic configuration of a backlight device for a liquid crystal display according to an embodiment of the present invention. Hereinafter, the configuration of a backlight device for a liquid crystal display according to a first embodiment of the present invention will be described with reference to FIG. The image display device of the present invention is not limited to a liquid crystal display, and the illumination device is not limited to a backlight device for a liquid crystal display.

  The backlight for a liquid crystal display shown in FIG. 1 has LED rows 10, 20, 30, 40, LED driving constant current circuit portions 11, 21, 31, 41, and switching circuit portions 12, 22, 32, 42. This backlight is composed of a plurality of light emitting areas whose light emission can be controlled independently, and each LED row is a light source of each light emitting area. In addition, the backlight device of this embodiment includes an image signal input unit 50, an image signal analysis unit 51, a control unit 52, a current amount adjustment unit 53, a pulse width adjustment unit 54, a maximum LED column drop voltage detection circuit unit 55, a power supply The circuit unit 56, the minimum LED string drop voltage detection circuit unit 57, and the voltage comparison unit 58 are included. Regarding the connection relationship between the LED string, the LED driving constant current circuit part, and the switching circuit part, the LED driving constant current circuit part 11 and the switching circuit part 12 are connected in series to the LED string 10. Regarding the LED array 20, the LED array 30, and the LED array 40, the connection relationship between the LED array, the LED driving constant current circuit section, and the switching circuit section is the same as that of the LED array 10.

Next, details of each component will be described.
The LED rows 10, 20, 30, and 40 are light sources configured by connecting a plurality of LEDs in series. The number of LEDs connected to one LED row is determined from the luminance required for the liquid crystal display, the voltage value that can be output by the power supply circuit, the resolution of local dimming for a backlight that performs local dimming, and the like.

  The LED drive constant current circuit units 11, 21, 31, 41 supply current to the LED rows 10, 20, 30, 40. The LED driving constant current circuit units 11, 21, 31, and 41 are constants required to light the LEDs with the brightness required for the divided areas of the liquid crystal display corresponding to the LED rows 10, 20, 30, and 40. It is the circuit which flows the current of. The amount of current is adjusted by an instruction from a current amount adjustment unit 53 described later.

  The switching circuit units 12, 22, 32, and 42 are circuits that adjust the brightness by turning on / off the constant currents flowing through the LED rows 10, 20, 30, and 40 using the switching elements. Generally, the switching circuit unit is composed of switching elements such as FETs and transistors.

The image signal input unit 50 receives an image signal output from an imaging device (not shown) or an image signal reproduction device (not shown).
The image signal analysis unit 51 decodes and analyzes the image signal received by the image signal input unit 50. In the present invention, when performing local dimming or the like, the brightness of each divided area when the liquid crystal display is virtually divided into matrixes is analyzed, and the analysis result is transmitted to the control unit 52 described later. The image signal analyzing unit 51 transmits the decoded image signal to a liquid crystal display (not shown).

  The control unit 52 is a block for instructing operations performed by the image signal analysis unit 51, a current amount adjustment unit 53, a pulse width adjustment unit 54, and a voltage comparison unit 58, which will be described later, and is configured by a microcomputer, FPGA, or the like. Specifically, the control unit 52 determines the brightness of the LED rows 10, 20, 30, 40 corresponding to the divided areas based on the result of analyzing the brightness for each divided area of the liquid crystal display received from the image signal analyzing unit 51. To decide. Then, the control unit 52 calculates an LED driving condition that realizes the determined brightness, and transmits the result to the current amount adjustment unit 53 and the pulse width adjustment unit 54. Further, the comparison result of the voltage comparison unit 58 is reflected in the control of the current amount adjustment unit 53, the VF reference value of the LED, and the like. The VF reference value will be described later.

  The current amount adjustment unit 53 is a circuit that adjusts a constant current that is flowed by the LED driving constant current circuit units 11, 21, 31, and 41 connected in series with the LED rows 10, 20, 30, and 40. When performing the local dimming control, the current amount adjusting unit 53 adjusts the current amount of each LED driving constant current circuit unit in accordance with the content (feature amount such as luminance) of the image signal in the region corresponding to each LED row. Thus, the current supplied to each LED array is controlled.

  The pulse width adjustment unit 54 is a circuit that outputs a pulse drive waveform for adjusting the ON / OFF ratio of the switching circuit units 12, 22, 32, and 42. When performing local dimming control, the pulse width adjustment unit 54 adjusts the ON / OFF ratio according to the content of the image signal of the divided area corresponding to each LED row. The pulse width adjustment unit 54 performs lighting control of each LED row by adjusting the lighting period and the light-off period of each LED row.

  The maximum LED string drop voltage detection circuit section 55 detects the largest value VFMax among the voltage drop amounts VF10, VF20, VF30, and VF40 of the LED strings 10, 20, 30, and 40. That is, the maximum LED string drop voltage detection circuit unit 55 detects the smallest value among the voltages V11, V21, V31, and V41 across the LED driving constant current circuit units 11, 21, 31, and 41. Then, the maximum LED string drop voltage detection circuit unit 55 transmits the detected VFMax to the power supply circuit unit 56 and the voltage comparison unit 58.

  The power supply circuit unit 56 is a power supply circuit that generates a voltage necessary for lighting the LED strings 10, 20, 30, and 40. The power supply circuit unit 56 operates the LED driving constant current circuit units 11, 21, 31, 41 to the voltage VFMax of the LED column having the highest VF among the LED columns 10, 20, 30, 40 with the output voltage Vout. Therefore, power supply control is performed so as to obtain a voltage obtained by adding a voltage VC necessary for this purpose.

  The minimum LED string drop voltage detection circuit unit 57 has a voltage drop amount VF10 to VF40 of the LED strings 10 to 40 during a period in which a current flows through the LED strings 10 to 40 and a period in which the switching circuit units 12 to 42 are ON. The smallest value VFMin is detected. Then, the minimum LED string drop voltage detection circuit unit 57 transmits VFMin to the voltage comparison unit 58.

  The voltage comparison unit 58 compares the VFMax detected by the maximum LED column drop voltage detection circuit unit 55 and the VFMax detected by the minimum LED column drop voltage detection circuit unit 57. The voltage value obtained by adding the difference between VFMax and VFMin and the voltage value necessary for driving the LED driving constant current circuit units 11, 21, 31, 41 is the LED driving constant corresponding to the LED row of VFMi. This is the voltage applied to the current circuit section. It is a feature of the present invention that the current value that the constant current circuit flows is adjusted so that the voltage value does not exceed the allowable value of the LED driving constant current circuit section.

Next, a series of operations performed by the control unit 52 will be described with reference to FIG.
First, the control unit 52 starts the control of the present invention in response to a power ON operation from the user.
Next, in step S100, the control unit 52 determines whether or not the power ON by the current instruction is the first power ON in the main body. When the power is turned on for the first time, the control unit 52 causes the same reference current value I to flow through all the LED strings of the backlight device, measures the VF values VF10, VF20, VF30, and VF40 of each LED string at this time. It is stored in the memory as the VF reference value of the LED array (S101). In the present embodiment, based on this VF reference value, it is estimated how much the VF value of each LED array varies from a standard value (TYP value), and the current value IF of each LED array is varied. It is used to predict the fluctuation of VF at the time. If the power is not turned on for the first time, the control unit 52 proceeds to step S102.

  Next, in step S102, the control unit 52 instructs the image signal analysis unit 51 to analyze the image signal received from the image signal input unit 50. The image signal analysis unit 51 analyzes the luminance value of each pixel of the image signal after decoding the image signal. The control unit 52 calculates the necessary brightness for each divided area when the liquid crystal display is virtually divided into matrixes based on the luminance value of the image signal analyzed by the image signal analyzing unit 51.

  Next, in step S103, the control unit 52, based on the brightness required for each divided area calculated in S103, based on the correspondence between the divided area and each LED row, the LED rows 10, 20, 30, 40. Calculate the amount of light that must emit.

  Next, in step S104, the control unit 52 determines adjustment values of the current amount adjustment unit 53 and the pulse width adjustment unit 54 based on the light emission amount necessary for each LED row calculated in S103. Here, how to determine the current amount and the pulse width when realizing a certain light emission amount will be described. In general, blue and green LEDs have a dominant wavelength that changes due to fluctuations in the amount of current, and therefore, it is often desirable to minimize adjustment with the amount of current. Therefore, when adjusting the brightness, the pulse width adjustment unit 54 first adjusts the current value to the specified current value. Then, the current amount adjustment unit 53 increases the amount of current when the LED array cannot achieve the required luminance even after adjusting to the upper limit value of the adjustment value of the pulse width adjustment unit 54 (that is, in the DC drive state).

  Next, in step S105, the control unit 52 acquires the theoretical values of the VF values VF10, VF20, VF30, and VF40 of the LED rows 10, 20, 30, and 40. The theoretical value is obtained as follows. That is, information on a curve indicating the relationship between the VF and IF of the LED being used is stored in a storage device (not shown) in advance, and this curve, the VF reference value stored in step S101 and the current amount of each LED array are stored. Calculated from IF. Of the theoretical VF values of the LED arrays calculated here, the maximum value is VFMax and the minimum value is VFMi.

  Next, in step S106, the control unit 52 calculates the difference between the maximum value VFMax and the minimum value VFmin of the theoretical VF value of each LED array calculated in S105, and this difference is smaller than a predetermined specified value VLimit. It is determined whether or not. In this embodiment, the predetermined value VLimit is a threshold value determined based on a voltage value that can be allowed by the LED driving constant current circuit unit.

  In step S106, when the difference between the maximum value VFMax and the minimum value VFmin of the theoretical VF value is equal to or greater than the specified value VLimit, the control unit 52 sets the LED string that has the minimum VF value to protect the LED driving constant current circuit unit. Adjust the amount of current. (S107)

Here, examples of current amount adjustment performed in steps S107 and S108 will be described with reference to FIGS. 3, 4, 5, and 6. FIG.
In FIGS. 3 and 4, the current amount and pulse width of each LED array constituting the backlight are adjusted according to the contents of the image signal input in the nth frame, the n + 1th frame, and the n + 2th frame. Is shown. FIG. 3 is an LED lighting chart before application of the first embodiment, and FIG. 4 is an LED lighting chart after application of the first embodiment. FIG. 5 is a diagram illustrating a change in the voltage drop amount VF with respect to a change in the current amount IF of the LED used in the first embodiment. FIG. 6 is a diagram showing a change in the light emission amount with respect to a change in the current amount IF of the LED used in the first embodiment.

  According to FIG. 3, before the application of Example 1, all the LED strings are lit with the reference current I in the nth frame, and at this time, the VF values of all the LED strings indicate the value of V1. The output voltage Vout of the power supply circuit unit 56 is Vout = V1 + VC by adding the voltage VC necessary for driving the LED driving constant current circuit unit to V1. Here, as a result of analyzing the image signal of the (n + 1) th frame, since it is necessary to increase the luminance of the area corresponding to the LED row 10, the current amount IF10 is increased to 2I. As a result, VF10, which is the VF value of the LED array 10, is expected to increase to V2 from the relationship of FIG. At this time, since the power supply circuit unit 56 outputs a voltage of Vout = V2 + VC as the VF value of the LED array 10 changes to V2, the difference between the VF values of the LED array 10 and the LED array 20 is V2−V1. It becomes more than VLimit.

  Here, the present embodiment is applied to the LED array 20. FIG. 4 shows a timing chart when the first embodiment is applied to the timing chart of FIG. In FIG. 3, in order to make the difference between the VF values of the LED array 10 and the LED array 20 smaller than VLimit, VF20, which is the VF value of the LED array 20, may be set to V3. When the current amount for setting the VF value VF20 of the LED array 20 to V3 is obtained from FIG. 5, the voltage drop amount is calculated with respect to the voltage drop amount V1 corresponding to the current amount I and the voltage drop amount V2 corresponding to the current amount 2I. It can be seen that the current amount should be 1.5 I in order to set V3. Therefore, the control unit 52 instructs the current amount adjusting unit 53 to set the amount of current flowing through the LED driving constant current circuit unit 21 to 1.5I. (S107)

  Next, the control unit 52 determines the ON / OFF ratio of the pulse width adjustment unit 54 from the light emission amount per unit time when the amount of current flowing to the LED array 20 is 1.5I in step S108. FIG. 6 shows the relationship between the amount of emitted light per unit time and the amount of current flowing through the LED. FIG. 6 shows that the light emission amount per unit time when the current amount is 1.5 I is 1.45 Iv with respect to the light emission amount Iv per unit time when the current amount is I.

また、ｎ＋１フレーム目の発光量は

となる。 Returning to FIG. 3, when the lighting state of the LED array 20 is confirmed, the time during which the LED array 20 is lit in the section A in which the current amount of the LED array 10 is 2I is t2, t3, immediately before the section A. The lighting time is t1, and the lighting time immediately after section A is t4. When calculating the light emission amount of the LED array 20 in the nth frame of FIG.

Also, the amount of light emitted in the (n + 1) th frame is

It becomes.

の式で表される。よって、

の関係から、

となる。
同様にｎ＋１フレーム目についても計算すると、電流量１．５Ｉで点灯する時間をＴ_ｎ＋１とすれば、

となる。
同様にＬＥＤ列３０、４０についても電流量を１．５ＩとしてＬＥＤ列３０，４０のＶＦをＶ３とし、ＬＥＤ列の発光時間を調整することで、ＶＦＭａｘ−ＶＦＭｉｎをＶＬｉｍｉｔより小さくすることができる。 Here, let us consider that the light emission amount of the LED array 20 in FIG. 4 after application of the first embodiment is the same as the value based on FIG. 3 calculated as described above. Since the LED row 20 is lighted in the last position, the times t2 and t4 cannot be changed (lighting end timing cannot be adjusted in a one-cycle lighting pattern). Therefore, the light-emitting amount of the n th frame, if the time which is turned by the amount of current I and T _n,

It is expressed by the following formula. Therefore,

From the relationship

It becomes.
Similarly, when calculating for the (n + 1) th frame, if the lighting time at a current amount of 1.5I is Tn _{+ 1} ,

It becomes.
Similarly, for the LED strings 30 and 40, VFMax-VFMi can be made smaller than VLimit by adjusting the light emission time of the LED strings 30 and 40 by setting the current amount to 1.5I and V3 of the LED strings 30 and 40 to V3.

  Next, in step S109, the control unit 52 controls the current amount adjusting unit 53 and the pulse width adjusting unit 54 in order to cause all the LED arrays 10, 20, 30, 40 to emit light. The current amount adjustment unit 53 and the pulse width adjustment unit 54 control the LED driving constant current circuit units 11, 21, 31, 41 and the switching circuit units 12, 22, 32, 42 according to instructions from the control unit 52. The LED array operates so as to light up in the state calculated by the unit 52.

Next, in step S110, the control unit 52 instructs the voltage comparison unit 58 to compare VFMax and VFMin. Here, the VF value when actually lit is observed, and it is confirmed whether or not the difference in VF value is smaller than VLimit. Here, when the difference of VF value is more than VLimit, the control part 52 progresses to step S111 and updates VF reference value.

After all the LED strings are turned on, the maximum LED string drop voltage detection circuit unit 55 feeds back the detection result of the maximum LED string drop voltage to the power supply circuit unit 56 in step S112.
In step S113, the power supply circuit unit 56 adjusts the output voltage Vout based on the detection result of the maximum LED string drop voltage (adjusts to V2 + VC in the example of FIG. 4).
The control unit 52 repeats the series of operations until a power-off instruction is received from the user. (S114)

The above is the current amount control of the first embodiment. According to the present embodiment, the constant current circuit unit for driving the LED can be protected without adding a voltage adjusting element in the backlight that performs local dimming.
In the above example, adjustment of the current amount of the LED string that becomes VFMin has been described. However, in the present invention, control is performed to increase the current supplied to the LED string whose VF value is smaller than the threshold by VFMax. Accordingly, when there is an LED array other than the LED array that becomes the VF citizen, the difference between the VF value and VFMax is equal to or greater than VLimit, the current amount is also adjusted for the LED array.

(Example 2)
The second embodiment is an embodiment in which the light emission amount adjustment of the LED rows 10, 20, 30, and 40 is executed for each frame period.

  In the first embodiment, since the time unit for adjusting the current amount and the lighting period is not limited to the frame period, the timing at which the current amount of the LED array 10 increases and the timing at which the current amount of the other LED arrays is increased are synchronized. I was able to. However, depending on the specifications of the control unit 52, the control to the current amount adjustment unit 53 and the pulse width adjustment unit 54 may be in units of frames. Example 2 explains that even in such a case, the constant current circuit unit for LED driving can be protected without adding a voltage adjusting element by current amount control.

The current amount control according to the second embodiment will be described with reference to FIG. FIG. 7 is a timing chart of all LED rows when Example 2 is applied to the timing chart of FIG.
In the second embodiment, the control unit 52 instructs the image signal analysis unit 51 to analyze both the nth frame and the (n + 1) th frame image signals.
The image signal analysis unit 51 analyzes the image signals of the nth frame and the (n + 1) th frame, and transmits the light / dark analysis result for each divided area for two frames to the control unit 52.

  The control unit 52 calculates the light emission amount that each of the LED arrays 10, 20, 30, and 40 should emit light based on the analysis result for two frames received from the image signal analysis unit 51. And the control part 52 determines the adjustment value of the electric current amount adjustment part 53 and the pulse width adjustment part 54 based on the light emission amount required for each LED row calculated.

  The result of the calculation is shown in FIG. According to FIG. 7, it is assumed that the current amount of the LED array 10 is increased to 2I in the (n + 1) th frame. Therefore, since the difference between VFMax and VFMi may exceed VLimit during the period when the amount of current in the LED array 10 is increasing, the amount of current in the LED arrays 20, 30, and 40 is adjusted.

Here, in Example 2, it is determined whether or not the LED rows 20, 30, and 40 are lit in the section A in which the current amount of the LED row 10 is 2I. That is, it is determined whether or not the section A of the LED array 10 where the light emission amount increases and the lighting period of the LED arrays 20, 30, and 40 overlap at least partially. And control which increases the electric current amount of LED row 20,30,40 in the frame period of LED row 20,30,40 including such a lighting period is performed. According to FIG. 7, it is understood that the lights that are turned on simultaneously with the section A are the nth frame and the (n + 1) th frame of the LED array 20, the nth frame of the LED array 30, and the nth frame of the LED array 40. In the second embodiment, the start timing of one frame period is different for each light source. The start timing of one frame period may not be different for each light source.

としてもよい。ＶＦ値がＶ３となる電流量は、図５から１．５Ｉとなる。電流量が１．５Ｉのときの単位時間あたり発光量は図６から１．４５Ｉｖである。上記の関係から、ＬＥＤ列２０のｎフレーム目における発光時間Ｔ_ｎを計算すると、

同様にｎ＋１フレーム目の発光時間Ｔ_ｎ＋１は、

となる。 Therefore, the control unit 52 adjusts the current amount for the nth frame and the (n + 1) th frame of the LED array 20, the nth frame of the LED array 30, and the nth frame of the LED array 40. Here, the VF value V3 of the LED arrays 20, 30, and 40 is determined to be a value between the VF value V1 at the time of the current amount I and the VF value V2 at the time of the current amount 2I, and the difference from the V1. And the difference from V2 are both determined to be equal to or lower than VLimit. If you want to simplify your calculations,

It is good. The amount of current at which the VF value is V3 is 1.5I from FIG. The light emission amount per unit time when the current amount is 1.5 I is 1.45 Iv from FIG. From the above relationship, when the light emission time T _n in the nth frame of the LED array 20 is calculated,

Similarly, the emission time T _{n + 1} of the ( _{n + 1) th} frame is

It becomes.

  The above is the current amount control processing of the second embodiment. According to the present embodiment, even when the current amount of each LED array is adjusted in units of frames, the LED drive constant current circuit unit can be protected without adding a voltage adjusting element by the current amount control process.

Example 3
The third embodiment is different from the first and second embodiments described above in that the current adjustment amount of each LED array is limited.
8 and 9 show the relationship between the amount of current of the LEDs used in Example 3 and the light emission efficiency. As can be seen from FIG. 8, the luminous efficiency of the LED used in Example 3 is the highest when the amount of current is I3. Further, according to FIG. 8, the range in which the difference between the VF value (V2) of the LED array whose luminance is increased and the VF values of the other LED arrays is equal to or less than VLimit is within the black frame of FIG. In the case of such LED characteristics, it is a feature of the third embodiment that the current value other than the LED array with increased luminance is set to I3 having the highest luminous efficiency.

  In addition, in the case of an LED having an inversely proportional characteristic between current and light emission efficiency as shown in FIG. 9, the current value other than the LED array with increased luminance is used to minimize the increase in the amount of current and suppress the decrease in light emission efficiency. Is I4 which is the minimum current value within a range where the difference from V2 is smaller than VLimit.

  The above is the current amount control of the third embodiment. According to the present embodiment, when determining the current amount of the LED strings other than the LED string whose luminance is increased, the difference between the VF value of the LED string whose luminance is increased and the VF value of the other LED strings is within VLimit. The amount of current with the highest luminous efficiency within the range is employed. Therefore, it is possible to protect the LED driving constant current circuit section with minimal reduction in luminous efficiency.

DESCRIPTION OF SYMBOLS 10 LED row | line | column, 11 Constant current circuit for LED row | line | column 10, 20 LED row | line | column, 21 Constant current circuit for LED row | line | column 20, 30 LED row | line | column, 31 Constant current circuit for LED row | line | column 30, 40 LED row | line | column, 41 Constant current for LED row | line | column 40 Circuit, 52 control unit, 53 current amount adjustment unit, 56 power supply circuit unit

Claims (33)

Multiple light sources;
A plurality of current supply means for supplying a current to each of the plurality of light sources;
Power supply control means for controlling the output voltage of the power supply connected to the plurality of light sources according to the maximum value of the voltage drop of the plurality of light sources;
Current control means for controlling the amount of current that the current supply means supplies to each of the light sources so that the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than a threshold value;
A lighting device comprising:   The lighting device according to claim 1, wherein the current control unit increases an amount of current supplied to a light source whose voltage drop is smaller than a maximum value by a threshold value.   The current control means supplies the amount of current supplied to a light source having a voltage drop smaller than the maximum value by a threshold value within a range where the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than the threshold value. The lighting device according to claim 2, wherein the current amount is such that the luminous efficiency of the light becomes the highest. A lighting control means for controlling a lighting period and a lighting period of each light source;
The lighting device according to claim 2, wherein the lighting control unit shortens a lighting period of a light source in which a current amount increases by the control of the current control unit.   The illumination according to any one of claims 1 to 4, wherein the power supply control means uses a sum of a voltage necessary for operating the current supply means and a maximum value of the voltage drop as an output voltage of the power supply. apparatus. Determining means for determining a light emission amount of each light source, and determining a current amount to be supplied to each light source and a lighting period of each light source according to the light emission amount;
Based on the relationship between the amount of current supplied to the light source and the voltage drop, acquisition means for acquiring the voltage drop of each light source according to the amount of current determined by the determination means;
Further comprising
When the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources acquired by the acquisition unit is equal to or greater than a threshold value, the current control unit determines the light source whose voltage drop is smaller than the threshold value by a threshold value or more. The lighting device according to claim 1, wherein the amount of current determined by the means is increased. Further comprising detection means for detecting a voltage drop of each light source,
The illumination device according to claim 6, wherein the acquisition unit acquires a voltage drop of each light source by the detection unit.   The acquisition means includes a voltage drop detected by the detection means when a reference current is supplied to each light source, a relationship between a current amount and a voltage drop supplied to the light source, and a current determined by the determination means. The lighting device according to claim 7, wherein a voltage drop of each light source is calculated based on the amount.   The power supply control means uses the sum of the voltage required to operate the current supply means and the maximum value of the voltage drop of the plurality of light sources detected by the detection means as the output voltage of the power supply. Or the illuminating device of 8. It further comprises input means for inputting an image signal,
The lighting device according to any one of claims 6 to 9, wherein the determining unit determines a light emission amount of each light source according to an image signal. The lighting device is composed of a plurality of light emitting areas,
Each of the plurality of light sources corresponds to each of the plurality of light emitting regions,
The lighting device according to claim 10, wherein the determination unit determines a light emission amount of a light source corresponding to each light emission region based on a feature amount of an image of a region corresponding to each light emission region.   The current control means is a light source whose voltage drop is smaller than the maximum value by a threshold value in a period in which the difference between the minimum value and the maximum value of the voltage drops of the plurality of light sources acquired by the acquisition means is a threshold value or more. The lighting device according to claim 6, wherein the amount of current determined by the determination unit is increased. The determining means determines the light emission amount of each light source for each frame period of the input image signal,
The current control means is a light source whose voltage drop is smaller than the maximum value by a threshold with respect to the maximum value in a frame period in which the difference between the minimum value and the maximum value of the voltage drops of the plurality of light sources acquired by the acquisition means is not less than the threshold value. The lighting device according to claim 6, wherein the current amount determined by the determining unit is increased. The start timing of the frame period is different between two or more of the plurality of light sources,
The current control means includes a lighting period of light sources whose voltage drop is smaller than the maximum value by a threshold value or more, and a difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources acquired by the acquisition means. The lighting device according to claim 13, wherein a control for increasing the amount of current is performed in a frame period including the lighting period for a light source that overlaps at least part of a period that is equal to or greater than a threshold value.   The lighting device according to claim 1, wherein the light source is an LED.   The lighting device according to claim 1, wherein each of the current supply units is a constant current circuit that supplies a constant current to each of the light sources.   An image display apparatus provided with the illuminating device of any one of Claims 1-16 as a backlight. Multiple light sources;
A plurality of current supply means for supplying a current to each of the plurality of light sources;
A power source connected to the plurality of light sources;
A method for controlling a lighting device comprising:
A power supply control step of controlling the output voltage of the power supply according to the maximum value of the voltage drop of the plurality of light sources;
A current control step of controlling the amount of current supplied to the light sources by the current supply means so that the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than a threshold value;
The control method of an illuminating device provided with.   The lighting device control method according to claim 18, wherein in the current control step, the amount of current supplied to a light source whose voltage drop is smaller than a maximum value by a threshold is increased. In the current control step, the amount of current supplied to the light source whose voltage drop is smaller than the maximum value by a threshold value or less is set within a range where the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources is smaller than the threshold value. The control method of the illuminating device according to claim 19, wherein the current amount is the highest in luminous efficiency. A lighting control step of controlling a lighting period and a lighting period of each light source;
The lighting device control method according to claim 19 or 20, wherein in the lighting control step, a lighting period of a light source in which a current amount is increased by the control in the current control step is shortened.   The illumination according to any one of claims 18 to 21, wherein in the power supply control step, a sum of a voltage necessary for operating the current supply means and a maximum value of the voltage drop is used as an output voltage of the power supply. Control method of the device. Determining a light emission amount of each light source, and determining a current amount to be supplied to each light source and a lighting period of each light source according to the light emission amount;
Based on the relationship between the amount of current supplied to the light source and the voltage drop, an acquisition step of acquiring the voltage drop of each light source according to the amount of current determined in the determination step;
Further comprising
In the current control step, when the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources acquired in the acquisition step is greater than or equal to a threshold value, the determination is made on a light source whose voltage drop is smaller than the threshold value by the threshold value or more. The control method of the illuminating device of any one of Claims 18-22 which increase the amount of electric current determined at the process. The illumination device further includes detection means for detecting a voltage drop of each light source,
24. The method of controlling an illumination device according to claim 23, wherein in the obtaining step, the voltage drop of each light source is obtained by the detection means.   In the acquisition step, the voltage drop detected by the detection means when a reference current is supplied to each light source, the relationship between the amount of current supplied to the light source and the voltage drop, and the current determined in the determination step The lighting device control method according to claim 24, wherein a voltage drop of each light source is calculated based on the amount.   25. In the power supply control step, a sum of a voltage necessary for operating the current supply means and a maximum value of voltage drops of the plurality of light sources detected by the detection means is used as an output voltage of the power supply. Or the control method of the illuminating device of 25. It further has an input process for inputting an image signal,
27. The method for controlling an illuminating device according to any one of claims 23 to 26, wherein in the determining step, a light emission amount of each light source is determined according to an image signal. The lighting device is composed of a plurality of light emitting areas,
Each of the plurality of light sources corresponds to each of the plurality of light emitting regions,
28. The method of controlling an illumination device according to claim 27, wherein, in the determining step, a light emission amount of a light source corresponding to each light emitting region is determined based on a feature amount of an image of a region corresponding to each light emitting region.   In the current control step, for a light source in which the voltage drop is smaller than the threshold value by the threshold value or less during the period in which the difference between the minimum value and the maximum value of the voltage drops of the plurality of light sources acquired in the acquisition step is equal to or more than the threshold value 29. The method for controlling an illumination device according to any one of claims 23 to 28, wherein the amount of current determined in the determination step is increased. In the determining step, the light emission amount of each light source is determined for each frame period of the input image signal,
In the current control step, in the frame period in which the difference between the minimum value and the maximum value of the voltage drop of the plurality of light sources acquired in the acquisition step is greater than or equal to a threshold value, the light source has a voltage drop that is smaller than the threshold value by the threshold value or less. The method for controlling an illumination device according to any one of claims 23 to 28, wherein the current amount determined in the determination step is increased. The start timing of the frame period is different between two or more of the plurality of light sources,
In the current control step, among the light sources whose voltage drop is smaller than the threshold value by the threshold value or more, the difference between the lighting period and the minimum value and the maximum value of the voltage drop of the plurality of light sources acquired in the acquisition step is The lighting device control method according to claim 30, wherein control is performed to increase the amount of current in a frame period including the lighting period for a light source that overlaps at least in part with a period equal to or greater than a threshold value.   The method of controlling an illumination device according to any one of claims 18 to 31, wherein the light source is an LED.   The lighting device control method according to any one of claims 18 to 32, wherein each of the current supply means is a constant current circuit that supplies a constant current to each of the light sources.

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