JP4499865B2 - EL drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EL drive circuit capable of controlling the emission luminance of an EL (Electroluminescence) used for a backlight of a liquid crystal display, and more particularly to an EL drive circuit capable of efficiently controlling the emission luminance of a plurality of ELs.
[0002]
[Prior art]
Conventionally, this type of EL drive circuit drives a plurality of EL elements that constitute a display unit or backlight of an in-vehicle display, a personal computer, or the like. Further, this EL drive circuit changes the luminance of the EL element at the portion where the display is emphasized during a predetermined warning display or the like.
In order to change the luminance of the EL element, the driving voltage or frequency of the AC driving signal may be controlled. However, in order to change the luminance for each of a plurality of EL elements, a large number of driving circuits are required. There is a problem that the scale increases.
In order to solve this, there is a conventional circuit in which an AC drive signal from one AC drive signal generation circuit is cyclically used in a time-division manner by a plurality of EL elements to reduce the circuit scale. That is, in this conventional circuit, an AC drive signal generating circuit for generating an AC drive signal for lighting a plurality of EL elements constituting the display unit, and an AC drive signal from this circuit for each of the plurality of EL elements. It is basically composed of a switch circuit including a control unit that supplies time-division, thereby sequentially turning on a plurality of EL elements. Since the AC drive signals supplied to the plurality of EL elements are cyclically performed in a time-division manner, all the EL elements appear to be constantly lit by human eyes.
[0003]
[Problems to be solved by the invention]
In the above-described conventional circuit, pulse width modulation is used to sequentially turn on a plurality of EL elements, and an AC drive signal is supplied to each EL element for a drive allocation time for each EL element based on this modulation method. However, since the synchronization between the start point of the drive allocation time and the start point of the AC drive signal has not been considered, there are the following problems. This will be described with reference to FIG.
In the figure, the AC drive signal shown in FIG. 6C is controlled to be turned on (OFF) for a predetermined drive allocation time as shown in FIG. 6A based on pulse width modulation. The As a result, the AC drive signal is converted into a drive signal whose lighting is controlled as shown in FIG. This drive signal is supplied to a predetermined EL element, and as a result, the corresponding EL element is turned on.
However, as shown in a and b of FIG. 6B, a steep current or switching noise is generated at the rising of the lighting control signal. This current may generate radiation noise or cause deterioration of the EL element. That is, since no consideration has been given to the start of the drive allocation time or the rise timing of the lighting control signal and the period of the AC drive signal, the switching noises a and b as shown in FIG. May have occurred and caused the above problems.
Therefore, in view of the above-described situation, the present invention provides an EL drive circuit that controls the start of the drive allocation time or the rise timing of the lighting control signal and the synchronization of the AC drive signal and suppresses the generation of switching noise. It is said.
Another object of the present invention is to provide an EL drive circuit capable of efficiently adjusting the luminance of a plurality of EL elements with a simple configuration while suppressing the generation of switching noise as described above.
[0004]
[Means for Solving the Problems]
The EL drive circuit according to claim 1, which has been made to solve the above-described problems, is configured to use an AC drive signal for lighting an EL element by a lighting control signal indicating a predetermined drive allocation time allocated to the EL element. in the EL driving circuit that has a switch for switching whether to supply to the EL element, and detects the zero-cross point of the AC drive signal, to match the starting point of the lighting control signal indicative of the drive allocated time to the zero cross point And a controller for supplying the lighting control signal to the EL element.
[0005]
According to the invention of claim 1, wherein the controller supplies a lighting control signal to the switch the zero-cross point of the AC drive signal to so that to match the starting point of the drive allocated time. In addition, the zero crossing point of Claim 1 means the starting point of the fundamental period when an alternating current signal becomes a zero voltage.
[0006]
The EL drive circuit according to claim 2, which has been made to solve the above-described problem, is the EL drive circuit according to claim 1, wherein the controller controls the lighting control of the zero cross point as shown in the block diagram of FIG. 1. It is also characterized by matching the end point of the signal .
[0007]
According to the second aspect of the present invention, the start point and the end point of the drive allocation time are set to coincide with the zero cross point. Thereby, for example, as shown in FIG. 2, the AC drive signal is included in the drive allocation time in a positive / negative target form. Accordingly, the charge supplied to the EL element is not biased to the positive or negative side.
[0008]
The EL drive circuit according to claim 3, which has been made to solve the above-described problem, is the EL drive circuit according to claim 2, wherein the controller is included in the drive allocation time as shown in the block diagram of FIG. 1. by varying the basic number of cycles of said AC drive signal, characterized that you have to control the lighting luminance of the EL element.
[0009]
According to the third aspect of the present invention, the lighting luminance of the EL element is controlled by changing the basic cycle number of the AC drive signal included in the drive allocation time.
[0010]
The EL drive circuit according to claim 4, which has been made to solve the above-described problem, is the EL drive circuit according to claim 3, wherein the controller is configured to perform the basic operation in the drive allocation time. characterized in that said AC driving signals corresponding to the period and supplies the lighting control signal to the dispersion to thinning memorial.
[0011]
According to the fourth aspect of the invention, the AC drive signal corresponding to the basic period is thinned out in a distributed manner in the drive allocation time. That is, the lighting brightness of the EL element is controlled by changing the number of basic periods in the drive allocation time by distributed thinning.
[0012]
The EL drive circuit according to claim 5, which has been made to solve the above problem, is the EL drive circuit according to claim 3, wherein the EL element includes a plurality of EL elements, and the controller includes: The lighting control signal is supplied so that the drive allocation times corresponding to the plurality of EL elements are equal, and the basic period number included in the drive allocation time is different for each of the plurality of EL elements. It is characterized by that.
[0013]
According to the fifth aspect of the present invention, the drive allocation times allocated to the plurality of EL elements are equal. Furthermore, the number of basic periods included in this equal drive allocation time is different for each of the plurality of EL elements. Further, as described above, the start point and end point of the drive allocation time are set to coincide with the zero cross point.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of an EL drive circuit of the present invention. In the figure, an AC drive signal generation circuit 1 generates an AC drive signal for lighting a plurality of EL elements 1, 2,..., N that constitutes a display unit, and one end of the plurality of EL elements 1, 2,. And supplied to the controller 2.
[0015]
The controller 2 has storage means and control means not shown. Based on the data contained in this storage means, the control means generates a lighting control signal for controlling the lighting of each of the plurality of EL elements in a time-sharing manner from the AC drive signal from the circuit 1 and supplies it to the switch 3.
[0016]
The switch 3 is composed of SW1, 2,..., N corresponding to the plurality of EL elements 1, 2,. The other ends of the EL elements 1, 2,..., N are grounded via SW1, 2,. In response to the lighting control signal, each SW1, 2,..., N is controlled to open and close, and therefore a predetermined drive signal sequentially flows through the EL elements 1, 2,. As a result, the corresponding EL elements 1, 2,..., N are also turned on cyclically in a time division manner. Note that the drive allocation time for each EL element 1, 2,..., N by this time division is equal to each EL element 1, 2,.
[0017]
The controller 2 that has received the AC drive signal detects a zero cross point from the AC drive signal, that is, a starting point of the basic period of the AC drive signal at which zero voltage (V = 0) is obtained. In addition, the controller 2 receives a luminance control signal for a specific EL element from the outside, and generates the lighting control signal so as to control the luminance of the specific EL element in response to the luminance control signal. That is, when receiving a luminance control signal for a specific EL element, the controller 2 stores the switch open / close pattern corresponding to the luminance specified by this control signal as luminance information in the internal storage means in association with the EL element number. . The controller 2 generates a lighting control signal based on the luminance information, and supplies the lighting control signal to the corresponding switch at a predetermined timing. Specifically, the brightness of a specific EL element is controlled by increasing or decreasing the number of basic periods (described later) included in the drive allocation time based on the brightness control signal.
Since the AC drive signals supplied to the plurality of EL elements are cyclically performed in a time-division manner, all the EL elements appear to be constantly lit with a predetermined luminance to the human eye.
[0018]
Next, the luminance control method described in FIG. 1 will be described with reference to FIG.
An AC drive signal as shown in FIG. 2C is applied to one end of ELj (j = 1, 2,..., N). On the other hand, a lighting control signal as shown in FIG. 2A is supplied to SWj connected between the other end of ELj and the ground at a predetermined timing. SWj is controlled to open and close during the drive allocation time for ELj at the on (0N) off (OFF) timing specified by the lighting control signal. Since the ON period SWj of the lighting control signal is closed, the other end of the period ELj is grounded, and an AC drive signal flows to ELj. That is, the period ELj is lit. On the other hand, since the off period SWj of the lighting control signal is opened, the other end of the period ELj is not grounded and the AC drive signal does not flow to ELj. That is, the period ELj is turned off. FIG. 2B shows an AC drive signal whose lighting is controlled by the lighting control signal shown in FIG. In FIG. 2B, the basic period is thinned out twice during the drive allocation time.
[0019]
Note that the pulse width of the signal shown in FIG. 2A is determined in units of a basic period to be described later. In the example of FIG. 2A, the ON signal has a pulse width corresponding to the basic period number 1, but for example, the pulse width corresponding to the basic period number 2 is a pulse width corresponding to two basic periods. This width applies not only to the on state but also to the off state.
[0020]
When a lighting control signal as shown in FIG. 2 (a) is supplied to SWj, as a result, a lighting-controlled EL driving signal as shown in FIG. 2 (b) flows through ELj. That is, the brightness of ELj is controlled based on such an EL drive signal. As shown in FIGS. 2A and 2B, the controller 2 detects the zero-cross point c from the AC drive signal, that is, the start point of the basic period of the AC drive signal where V = 0, and uses this point as a reference. The lighting control signal is generated as
[0021]
As described above, in response to the ON / OFF of the lighting control signal shown in FIG. 2A, an EL drive signal composed of a combination of lighting and thinning-out lighting with a basic period as shown in FIG. can get.
Note that the number of basic periods included in the EL lighting time assigned to ELj is controlled in accordance with the required luminance, but at this time, the basic period corresponding to turning off is thinned out.
[0022]
Since the zero cross point c of the AC drive signal, that is, the zero voltage point is made coincident with the start point of the drive allocation time in this way, the switching noise a or the start time of the drive allocation time shown in FIG. Prevents steep current generation due to b. As a result, generation of radiation noise and deterioration of the EL element can be prevented. Furthermore, the end point of the drive allocation time is also set to coincide with the zero cross point. Thereby, for example, as shown in FIG. 2B, the AC drive signal is included in the drive allocation time in a positive / negative target form. Therefore, the charge supplied to the EL element is not biased to the positive or negative side, and as a result, the life of the EL element is extended.
[0023]
FIG. 3 shows a memory map in the storage means for storing the luminance information explained in FIG.
In the figure, in response to a luminance control signal for each ELj (j = 1 to n) from the outside, each luminance information Bj corresponding to each ELj is stored in each area j. Each luminance information Bj is composed of ELj indicating the number of the EL element and a switch opening / closing pattern indicated by 1 or 0 of 10 digits corresponding thereto. This 1 is control information for controlling the corresponding switch to be open during the basic period, and 0 is for controlling the corresponding switch to be closed during the basic period. In this example, the corresponding switch opening / closing information from the first period to the tenth period is sequentially represented by 1 or 0.
[0024]
In addition, the said brightness | luminance control signal is a display part of a vehicle-mounted display, a personal computer, or the external part which controls the brightness | luminance of the EL element corresponding to the part which carries out a warning display or an emphasis display among several EL elements which comprise a backlight. It is a control signal.
[0025]
Next, a processing flow when performing luminance control will be described with reference to FIG.
FIG. 4 is a flowchart showing a process related to the present invention performed by the controller of FIG. Here, it is assumed that there are three EL elements EL1 to EL3, and that different luminance control is performed on EL1 to EL3. In this example, drive times are equally allocated to the ELs 1 to 3. This drive allocation time is set to a time corresponding to the aforementioned basic period number of 10. In this example, as shown in FIG. 5E, it is assumed that the drive allocation time is composed of first to tenth periods. Here, for convenience, i is referred to as a cycle number. Each of the first to tenth periods is on / off controlled for each basic period, and the luminance is adjusted by changing the number of basic periods included in the allocated time.
[0026]
In step S1, the cycle number i (i = 1 to 10) and the EL number j (j = 1 to 3) are initialized, and the process proceeds to step S2.
[0027]
In step S2, it is determined whether EL number j is 3 or more. That is, since the number of EL elements is 3 in this example, when the EL number j is 3 or more, the determination for returning the EL number j to 1 is performed here. Based on this determination, EL1 to EL3 are turned on cyclically. If the EL number j is 3 or more, the process proceeds to step S3 (Y in step S2). If the EL number j is not 3 or more, that is, if the EL number j = 1 or 2 (N in step S2), the process proceeds to step S4. To do.
[0028]
In step S3, the EL number j is returned to 1, and the process proceeds to step S5. On the other hand, in step S4, the EL number j is counted up, and the process proceeds to step S5.
[0029]
In step S5, the aforementioned zero cross point is detected from the AC drive signal supplied from the AC drive signal generation circuit 1, and the process proceeds to step S6.
[0030]
In step S6, the cycle number i is counted up, and the process proceeds to step S7.
[0031]
In step S7, the lighting control of the i-th period of ELj is performed. At this time, based on the luminance information Bj stored in the storage means, the switch SWj is controlled to open and close at a timing corresponding to the i-th cycle. Then, the process proceeds to the next step S8.
[0032]
In step S8, it is determined whether or not the cycle number i is 10 or more. That is, in this example, since the cycle number i assigned to each ELj is 10 at the maximum, the EL to be lit is changed when the cycle number i is 10 or more, and the judgment for returning the cycle number i to 1 is performed here. Do. In step S8, when the cycle number i is 10 or more (Y in step S8), the cycle number i is initialized in step S9, and the process returns to step S2 to turn on the next EL. On the other hand, if the cycle number i is not yet 10 or more, that is, if the cycle number i = 1 to 9 (N in step S8), the process returns to step S5 to count up the cycle number i.
[0033]
FIG. 5 is an example of a waveform diagram generated by luminance control according to the control flow of FIG.
5A, 5B, and 5C show the lighting control signals of EL1, 2, and 3, respectively. A drive allocation time for every 10 basic periods is allocated to each EL element in a time-sharing and cyclic manner. In the EL1 lighting control signal, AC driving signals for one basic period out of 10 basic periods are thinned out. In the EL2 and 3 lighting control signals, AC driving signals for 2 and 3 basic periods are thinned out, respectively. Therefore, among these EL1 to EL3, EL1 is the highest and EL3 is the lowest.
[0034]
For example, FIGS. 5D and 5E show examples of EL3 AC drive signals during one drive allocation time controlled by the EL3 lighting control signal shown in FIG. 5C. As shown here, the luminance is adjusted by thinning out the AC drive signals in the second, fourth and sixth cycles in 10 basic cycles.
[0035]
In this way, the controller 2 detects the zero-cross signal that is the starting point of the basic cycle of the AC drive signal, and performs opening / closing control of the switch corresponding to each EL in units of the basic cycle in synchronization with the detection. The luminance control is performed by changing the thinning number of the basic cycle unit. For example, when the example of FIG. 5 is developed and 10 levels of luminance are provided to 10 EL elements, the maximum luminance EL element is not thinned, and the second luminance EL element is thinned from 10 basic periods to one basic period. 9/10 lighting and 3rd luminance EL elements can be set up to 10th luminance by setting 10/10 periodic brightness to 8/10 lighting by thinning out 2 fundamental periods. Keys can be displayed.
[0036]
A method of generating a sine wave, which is an AC drive signal, by the controller 2 itself and generating an AC drive signal for each EL in synchronization therewith is also conceivable. In this case, since the zero cross point is under the control of the controller 2, the opening / closing timing of the switch 3 can be easily controlled. Further, in the above embodiment, the frequency decreases as the number of thinnings is increased, but thinning control can be performed up to several tens of Hz where a person feels flickering. it can.
[0037]
As described above, since the lighting luminance is designated by the basic cycle number, the luminance can be designated quantitatively. That is, the luminance can be specified in gradation in proportion to the number of basic cycles. Therefore, since the brightness can be controlled with a simple configuration, the manufacturing cost can be reduced.
In particular, as shown in FIG. 5, thinning is performed in a distributed manner, that is, the lighting brightness of the EL element is controlled by thinning out the basic period so as not to continue during one drive allocation time. Accordingly, the basic period included in the drive allocation time is dispersed and averaged, and brightness adjustment with high display quality can be performed.
In addition, since the start point and end point of the drive allocation time coincide with the zero cross point, it is efficient when lighting control is performed by switching a plurality of EL elements in a time-sharing and cyclic manner. That is, since the lighting end of the EL element coincides with the lighting timing of the next EL element, it is possible to perform lighting control with no waste for a plurality of EL elements.
[0038]
【The invention's effect】
As described above, according to the first aspect of the present invention, the AC drive signal is supplied to the EL element for a predetermined drive allocation time by making the zero cross point of the AC drive signal coincide with the start point of the drive allocation time.
As described above, since the zero cross point of the AC drive signal, that is, the zero voltage point is made coincident with the start point of the drive allocation time, a steep current generation due to switching noise at the start of the drive allocation time is prevented. As a result, it is possible to prevent the generation of radiation noise and the deterioration of the EL element.
[0039]
According to the second aspect of the present invention, the start point and the end point of the drive allocation time are set to coincide with the zero cross point. Thereby, for example, as shown in FIG. 2, the AC drive signal is included in the drive allocation time in a positive / negative target form. Therefore, the charge supplied to the EL element is not biased to the positive or negative side, and as a result, the effect added to the invention according to claim 1 of extending the life of the EL element can be obtained.
[0040]
According to the third aspect of the present invention, the lighting luminance of the EL element is controlled by changing the basic cycle number of the AC drive signal included in the drive allocation time.
In this way, since the lighting luminance is designated by the number of basic cycles, the luminance can be designated quantitatively. That is, the luminance can be specified in gradation in proportion to the number of basic cycles. Therefore, since the brightness can be controlled with a simple configuration, the effect added to the inventions according to claims 1 and 2 can be obtained.
[0041]
According to the fourth aspect of the invention, the AC drive signal corresponding to the basic period is thinned out in a distributed manner in the drive allocation time. That is, the lighting brightness of the EL element is controlled by changing the number of basic periods in the drive allocation time by distributed thinning. Therefore, in addition to the effects of the first to third aspects of the invention, the basic period included in the drive allocation time is averagely dispersed, and as a result, the EL display quality can be improved when adjusting the luminance. It is done.
[0042]
According to the fifth aspect of the present invention, the drive allocation times allocated to the plurality of EL elements are equal. Furthermore, the number of basic periods included in this equal drive allocation time is different for each of the plurality of EL elements. Further, as described above, the start point and end point of the drive allocation time are set to coincide with the zero cross point. Accordingly, it is possible to easily change the luminance of a plurality of EL elements simply by changing the number of basic periods within the drive allocation time. In addition, since the start point and end point of the drive allocation time coincide with the zero cross point, it is efficient when lighting control is performed by cyclically switching a plurality of EL elements in a time division manner. That is, since the lighting control end of the EL element coincides with the lighting start time of the next EL element, lighting control without waste is possible for a plurality of EL elements. The added effect is obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an EL drive circuit of the present invention.
FIG. 2 is a waveform diagram of an EL drive circuit according to the present invention.
FIG. 3 is a memory map in a storage means for storing luminance information.
4 is a flowchart showing processing related to the present invention performed by the controller of FIG. 1; FIG.
5 is a waveform diagram generated by luminance control according to the control flow of FIG.
FIG. 6 is a waveform diagram of a conventional EL drive circuit.
[Explanation of symbols]
1 AC drive signal generation circuit 2 Controller 3 Switch

Claims (5)

The AC drive signal for turning on the EL element, the EL driving circuit that has a switch for switching whether to supply to the EL element by the lighting control signal indicating a predetermined drive allocated time allocated to the EL element ,
Detecting a zero-cross point of the AC drive signal, the lights of the start point of the control signal to match the zero-cross point, EL driving circuit, characterized in that the lighting control signal and a controller for outputting to the switch . The EL driving circuit according to claim 1,
The EL driving circuit , wherein the controller matches an end point of the lighting control signal with the zero cross point . The EL drive circuit according to claim 2, wherein
Said controller, by changing the basic number of cycles of said AC drive signal included in the drive allocated time, EL driving circuit, characterized in that you are controlling the lighting luminance of the EL element. The EL drive circuit according to claim 3.
EL driving circuit wherein the controller is characterized in that it supplies the lighting control signal to the AC driving signal corresponding to the fundamental period in a distributed manner thinning memorial in the drive allocated time. The EL drive circuit according to claim 3.
The EL element is plural,
The lighting control is performed so that the controller has the same drive allocation time corresponding to the plurality of EL elements, and the basic period number included in the drive allocation time is different for each of the plurality of EL elements. An EL driving circuit which supplies a signal .

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