JP2002366101A - Driving device for light emission display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in the driving circuit of, for example, a multicolor display panel which is provided with light emitting elements having different luminous efficiency. SOLUTION: In a light emission display panel 1, a multicolor display panel is constituted by arranging organic EL(electroluminescent) elements having light emission colors, for example, such as R(red), G(green), B(blue) having different luminous efficiency in accordance with cathode scanning lines B1 to Bm. A driving voltage is supplied to respective EL elements from a boosting circuit 6 which is constituted of a DC-to-DC converter and they are driven with constant currents via constant current circuits I1 to In. The boosting circuit 6 operates so as to change the driving voltage which is to be outputted from the circuit 6 by making on and off of a switching transistor Q3 to be controlled in synchronization with the driving of lighting of light emitting elements having different luminous efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a technique for driving a light emitting element such as an (electroluminescence) element to emit light, and more particularly to a driving apparatus for a light emitting display panel configured to reduce a power loss when driving a display panel formed by arranging organic EL elements. .

[0002]

2. Description of the Related Art An organic EL display has been attracting attention as a display which can replace a liquid crystal display with low power consumption, high display quality, and be thin. This is because, by using an organic compound that can be expected to have good light-emitting characteristics in the light-emitting layer of an EL element used in an EL display, high efficiency and long service life that can withstand practical use have been advanced. is there.

An organic EL device can be electrically represented by an equivalent circuit as shown in FIG. That is, the organic EL
The element can be replaced with a configuration including a parasitic capacitance component C and a diode component E coupled in parallel with the capacitance component, and the organic EL element is considered to be a capacitive light emitting element. In the organic EL element, when a light emission driving voltage is applied, first, a charge corresponding to the electric capacity of the element flows into an electrode as a displacement current and is accumulated. Subsequently, when the voltage exceeds a certain voltage (light emission threshold = Vth) unique to the element, a current starts to flow from the electrode (the anode side of the diode component E) to the organic layer constituting the light emitting layer, and light is emitted at an intensity proportional to this current. Then you can think.

FIG. 6 shows the static light emission characteristics of such an organic EL device. According to this, as shown in FIG. 6A, when the driving voltage (V) is equal to or higher than the light emission threshold voltage (Vth), the current (I) rapidly flows to emit light. In other words, if the applied drive voltage is equal to or lower than the light emission threshold voltage, almost no drive current flows to the EL element after charging the parasitic capacitance, and the EL element does not emit light. Then, in a light emission enabling region where the driving voltage (V) is equal to or higher than the light emission threshold voltage, as shown in FIG. 6B, the light emitting device has a characteristic of emitting light at a luminance (L) substantially proportional to the driving current (I). I have. Therefore, as shown in FIG. 6 (c), the luminance characteristics of the EL element in a light emitting area where the threshold voltage is higher than the threshold voltage, the light emitting luminance (L) increases as the voltage (V) applied thereto increases. It has the property of increasing.

As a method of driving a display panel constituted by arranging a plurality of organic EL elements, a simple matrix driving method is applicable. FIG. 7 shows an example of a simple matrix display panel and its driving device. There are two methods of driving the organic EL element in this simple matrix driving method, namely, a cathode line scanning / anode line driving and an anode line scanning / a cathode line driving. The configuration shown in FIG. 4 shows a form of a drive. That is, the anode lines A1 to An as n drive lines are vertically arranged, and the cathode lines B as m scan lines are
1 to Bm are arranged in the horizontal direction, and an organic EL element OEL indicated by a diode symbol mark is arranged at each intersecting portion (a total of n × m places) to constitute the display panel 1.

Each of the EL elements constituting the pixel is arranged in a lattice pattern, and has one end corresponding to the intersection between the anode lines A1 to An extending along the vertical direction and the cathode lines B1 to Bm extending along the horizontal direction. The anode terminal of the diode component E of the equivalent circuit is connected to the anode line, and the other end (the cathode terminal of the diode component E of the equivalent circuit described above) is connected to the cathode line. The anode line is connected to the anode line drive circuit 2 and the cathode line is connected to and driven by the cathode line scanning circuit 3.

The cathode line scanning circuit 3 includes scanning switches SY1 to SYm corresponding to the respective cathode scanning lines B1 to Bm. The reverse bias voltage from the reverse bias voltage generation circuit 5 for preventing crosstalk emission is provided. Either (VM) or the ground potential as a reference potential point acts to connect to the corresponding cathode scan line. The anode line drive circuit 2 has a constant current circuit I as a constant current source for supplying a drive current to each EL element through each anode line.
1 to In and drive switches SX1 to SXn are provided.

The drive switches SX1 to SXn operate to connect either the current from the constant current circuits I1 to In or the ground potential to the corresponding anode line. Therefore, the drive switches SX1 to SX
By connecting Xn to the constant current circuit side, the current from the constant current circuits I1 to In acts to be supplied to the individual EL elements arranged corresponding to the cathode scanning lines.

It is possible to use a voltage source such as a constant voltage circuit instead of the constant current circuit. However, while the current / luminance characteristics of the EL element are stable with temperature changes, In general, a constant current circuit is used as a drive source as shown in the figure because the luminance characteristics are unstable with respect to a temperature change and the element may be deteriorated due to an overcurrent. It is common.

A control bus from a light emission control circuit 4 including a CPU is connected to the anode line drive circuit 2 and the cathode line scan circuit 3, and the scan switches SY1 to SYm and the drive lines are controlled based on an image signal to be displayed. The switches SX1 to SXn are operated. Thus, the constant current circuit is connected to a desired anode line while setting the cathode scanning line to the ground potential at a predetermined cycle based on the image signal. Therefore, each of the light emitting elements selectively emits light, and an image based on the image signal is reproduced on the display panel 1.

Each of the constant current circuits I1 to In in the anode line drive circuit 2 has a DC output (drive voltage = VCOM) provided from a booster circuit 6 by a DC-DC converter.
) Is supplied. In addition, the booster circuit 6 using the DC-DC converter described below
Although the DC output is generated by the WM control (variable control of the pulse width), the PFM control (variable control of the pulse period) may be used.

This DC-DC converter is configured such that a PWM wave output from a switching regulator circuit 11 controls an npn transistor Q1 as a switching element to turn on at a predetermined duty cycle. That is, the power energy from the DC voltage source 12 is accumulated in the inductor L1 by the on operation of the transistor Q1, and the power
The power energy stored in the inductor is stored in the capacitor C1 via the diode D1. Then, by repeating the on / off operation of the transistor Q1, the boosted DC output can be obtained as the terminal voltage of the capacitor C1.

The DC output voltage is supplied to the resistors R1 and R2.
Is divided by the switching regulator circuit 11
Is supplied to the error amplifier 14 by the operational amplifier at
This error amplifier 14 compares the voltage with the reference voltage Vref. This comparison output (error output) is supplied to the PWM circuit 15, and by controlling the duty of the signal wave provided from the oscillator 16, feedback control is performed so that the output voltage is maintained at a predetermined voltage value. Therefore, the output voltage Vout1 obtained by the DC-DC converter 6 can be expressed as follows.

[0014]

(Equation 1)

On the other hand, the reverse bias voltage generating circuit 5 used for preventing the crosstalk light emission is constituted by a voltage dividing circuit for dividing the output voltage Vout1. That is, this voltage dividing circuit is composed of resistors R6 and R7 and an npn transistor Q2 functioning as an emitter follower. Therefore, if the base-emitter voltage of the transistor Q2 is expressed as Vbe, the reverse bias voltage VM obtained by this voltage dividing circuit is obtained.
Can be shown as follows:

[0016]

(Equation 2)

[0017]

By the way, R (red), G (green), B (blue) and the like have been proposed as typical emission colors of organic EL elements which can be used at present. The organic EL devices that emit these R, G, and B colors have a problem in that the luminous efficiencies with respect to forward voltages are different from each other. G
The luminous efficiency is lower than that.

Therefore, when considering a multi-color display panel in which the above-described organic EL elements for emitting the respective colors are arranged in one display panel, the forward voltage is applied so as to correspond to the EL element having the lowest luminous efficiency. DC-DC
It is necessary to set the output voltage Vout1 obtained by the converter 6. For example, when driving an EL element that emits B light, the D signal supplied to the constant current circuits I1 to In
The output voltage Vout1 from the C-DC converter 6 needs to be set to, for example, about 16 V, while E which emits G
When driving the L element, about 14 V is sufficient.

However, in the conventional driving circuit, as shown in FIG. 7, the driving voltage output from the DC-DC converter 6 is uniformly determined in correspondence with the EL element having the lowest luminous efficiency. Therefore, when applied to the above-described multi-color display device, there is a power loss, and this power loss results in being discarded as heat. That is, when driving an EL element which emits G light with good luminous efficiency, as a result, the voltage drop in each of the constant current circuits I1 to In in the anode line drive circuit 2 increases, and the power loss increases in proportion thereto. I do. Therefore, according to the conventional driving circuit shown in FIG. 7, when the display panel of B or R having low luminous efficiency is small, and most other regions have a disposition pattern of emitting G light, Resulted in greater power loss.

On the other hand, the aforementioned reverse bias voltage generation circuit 5
The resulting reverse bias voltage is applied to the cathode terminal of the EL element that is not driven to emit light, thereby acting to prevent crosstalk light emission. For this purpose, in the drive circuit shown in FIG. 7, a fixed voltage of about 8 to 9 V close to the forward voltage of the EL element is applied uniformly. When the reverse bias voltage is lower than a predetermined value, the effect of preventing the above-described crosstalk light emission is reduced, and when the reverse bias voltage is higher than a predetermined value, a leak phenomenon occurs, and A problem of deteriorating display quality occurs. Therefore,
It is important to properly manage the reverse bias voltages.

Further, the above-mentioned organic EL device has such a characteristic that the physical properties of the device change over a long period of use and the resistance value of the device itself increases. Organic E
In the L element, as shown in FIG. 6A, the VI characteristic changes in the direction indicated by the arrow (the characteristic indicated by the broken line) with the elapse of the actual use time, and thus the luminance characteristic also deteriorates. . Therefore, in order to compensate for the deterioration of the luminance characteristic assumed during an actual use time of, for example, several thousand hours, the DC-
The drive voltage output from the DC converter 6 needs to be set higher, and the drive voltage is set to about 16 V as described above in consideration of this factor. Therefore, the constant current circuit I
This causes a problem that heat loss is caused at 1 to In. Further, the above-described change in the characteristics of the EL element has a property that it also changes, for example, depending on the environmental temperature.

The present invention has been made in view of the above-mentioned problems, and in particular, when driving, for example, a multi-color display panel having display elements having different luminous efficiencies, power loss can be reduced. It is an object of the present invention to provide a driving device of a light emitting display panel.

[0023]

According to an aspect of the present invention, there is provided a driving apparatus for a light emitting display panel, wherein a plurality of light emitting elements having different luminous efficiencies are arranged. A light-emitting display panel driving device configured to selectively apply light-emitting drive power to light-emitting elements to which the light-emitting drive power is applied, and to synchronize with the light-emitting drive of each light-emitting element. The present invention is characterized in that a drive power changing means for changing the light emission drive power corresponding to each light emitting element is provided.

In this case, the drive power changing means is preferably configured to change the light emission drive power corresponding to the emission color of each light emitting element. In a preferred embodiment, the light-emitting display panel includes a plurality of drive lines and a plurality of scan lines that intersect each other, and at each of a plurality of intersections between the drive lines and the scan lines, each drive line and Each light emitting element is connected between each scanning line. Further, in this case, it is preferable that a light emitting element that emits the same luminescent color is connected to each one scanning line in the light emitting display panel.

In the driving apparatus for a light-emitting display panel according to the present invention, the light-emitting drive power is supplied to each of the light-emitting elements via each of the drive lines, and the scanning lines in the non-scanning state are supplied to the light-emitting elements. On the other hand, a reverse bias voltage is applied, and reverse bias voltage changing means for changing the reverse bias voltage corresponding to the light emitting element driven to be lit is provided.

Preferably, a constant current source is arranged in each of the drive lines, and a predetermined current is supplied to each light emitting element in a scanning state via the constant current source. The driving voltage supplied to the constant current source arranged in each of the drive lines is configured to be changed according to the light-emitting element driven to be lit.

Further, the drive voltage supplied to the constant current source is preferably supplied from a DC-DC booster circuit, and the output voltage of the DC-DC booster circuit is equal to the output voltage. It is configured to be controlled based on a difference between the voltage and the reference voltage, and is configured to change a voltage dividing ratio for generating the divided voltage corresponding to the light emitting element driven to be lit. Further, the reverse bias voltage changing means is preferably configured such that a voltage dividing ratio of a driving voltage is changed corresponding to the light emitting element driven to be lit.

On the other hand, in the above-described driving device, it is desirable that the light-emitting driving power is further changed in accordance with the aging of each light-emitting element and the change of the environmental temperature. In addition, the above-described configuration can be suitably used for a driving device of a light-emitting display panel using organic electroluminescence as a light-emitting element.

According to the driving device for a light emitting display panel having the above-described configuration, when driving, for example, a multi-color display panel in which light emitting elements having different luminous efficiencies are arranged, each light emitting element is driven in synchronization with the lighting drive of each light emitting element. The light emitting drive power corresponding to the element is supplied. That is, in a configuration in which each light emitting element is driven to be lit through a constant current circuit, the drive voltage applied to the constant current circuit is changed in synchronization with the driving of each light emitting element to be lit. This allows
Power loss in the constant current circuit can be minimized.

Also, the reverse bias voltage applied to the light emitting element in the non-lighting state changes its voltage value in accordance with the light emitting element driven to be lit, so that a necessary and sufficient reverse bias voltage is obtained. And the occurrence of a leak phenomenon can be suppressed. In addition, in the case where the light emission drive power is configured to be further changed in accordance with the aging of each light emitting element, the drive applied to the constant current circuit from the beginning to compensate for the change in the luminance characteristic of the light emitting element. It is not necessary to set the voltage higher, and the power loss caused by this can be reduced.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a driving apparatus for a light emitting display panel according to the present invention will be described below with reference to the drawings. FIG. 1 shows the first embodiment. In FIG. 1, portions corresponding to the respective components of FIG. 7 described above are denoted by the same reference numerals, and therefore, detailed description thereof will be appropriately omitted. In the configuration shown in FIG. 1, in the voltage dividing circuit composed of the resistors R1 and R2 for dividing the output voltage of the DC-DC converter 6, a pnp transistor Q is further added to the resistor R2.
3 and a series circuit composed of a resistor R3 are connected in parallel. The switching signal is supplied from the light emission control circuit to the base of the transistor Q3.

The switching signal applied to the base of the transistor Q3 is switched on or off in synchronization with the cathode scanning signal transmitted from the light emission control circuit 4 to the cathode line scanning circuit 3. In this case, for example, the first to third cathode scanning lines B1 to B1 on the display panel 1
3 is connected to an EL element that emits G (green), and the m-th cathode scanning line Bm is an E element that emits B (blue).
Assuming that the L element is connected, in the configuration shown in FIG. 1, when scanning the first to third cathode scanning lines B1 to B3, a switching signal for turning on the transistor Q3 is applied to the base. Is controlled as follows.
When scanning the m-th cathode scanning line Bm, control is performed so that a switching signal for turning off the transistor Q3 is applied to the base.

That is, the EL element that emits G light has high luminous efficiency as described above, and the EL element that emits B light has low luminous efficiency. Therefore, E which emits G
In the case where the L element is driven for lighting (when the first to third cathode scanning lines B1 to B3 are scanned), DC-DC
When the driving voltage generated by the converter 6 is set to be low, and when the EL element that emits B light is driven to light (when the m-th cathode scanning line Bm is scanned), the DC-DC converter is used. 6 is set so as to increase the driving voltage output therefrom.

As described above, by changing the drive voltage in synchronization with the cathode scanning, for example, when driving an EL element having a high luminous efficiency (an EL element that emits G light) to be turned on, the cathode scanning circuit 2 Constant current circuits I1 to In
Is set relatively low. Thus, the voltage drop in the constant current circuits I1 to In can be reduced, and the power loss generated in the constant current circuits can be suppressed.

Incidentally, when the transistor Q3 is off, the switching regulator circuit 11
Is applied with a divided voltage determined by the resistors R1 and R2. Therefore, the output voltage at this time is set to Vout1 shown in the above-mentioned equation (1). On the other hand, when the transistor Q3 is turned on, the impedance between the emitter and the collector of the transistor Q3 is negligibly small in the configuration shown in FIG. R
3 is connected in parallel. In this case,
The output voltage Vout2 obtained by the DC-DC converter 6 can be expressed as follows. In the following equation, (R2 // R3) indicates a parallel combined resistance value of the resistors R2 and R3.

[0036]

(Equation 3)

Therefore, when Equations 1 and 3 are compared, the relationship of Vout1> Vout2 is established. As described above, when the EL element having high luminous efficiency is driven for lighting, it is possible to suppress the power loss. it can.

Next, FIG. 2 shows a second embodiment of the driving device according to the present invention. In FIG. 2, parts corresponding to the respective components in FIGS. 1 and 7 already described are denoted by the same reference numerals, and therefore, detailed description thereof will be omitted as appropriate. In the configuration shown in FIG. 2, in addition to the configuration shown in FIG. 1, in a voltage dividing circuit for dividing the output voltage of the DC-DC converter 6, a series circuit including a pnp transistor Q4 and a resistor R4 is further paralleled to the resistor R2. It is connected. The switching signal is supplied from the light emission control circuit to the base of the transistor Q4.

The switching signal applied to the base of the transistor Q4 is switched on or off in synchronization with the cathode scanning signal transmitted from the light emission control circuit 4 to the cathode line scanning circuit 3. That is, according to the circuit configuration shown in FIG. 2, the transistor Q3 is turned on / off and the transistor Q4 is turned on / off in synchronization with the cathode scanning signal. In this embodiment, the transistors Q3 and Q
4 are programmed so that they are not turned on at the same time.

In this case, in the display panel 1, for example, an EL element emitting R (red) is connected to the first cathode scanning line B1, and the second and third cathode scanning lines B2, B3 are connected. 2 is connected to the EL element that emits G (green), and the EL element that emits B (blue) is connected to the m-th cathode scanning line Bm. In the configuration, when scanning the first cathode scanning line B1, the switching signal for turning on only the transistor Q4 is controlled so as to be applied to the base. Further, the second and third cathode scanning lines B2
, B3 is controlled so that a switching signal for turning on only the transistor Q3 is applied to the base. Further, when scanning the mth cathode scanning line, both transistors Q3 and Q4 are turned off.

That is, here, the EL element that emits G light has high luminous efficiency as described above, and the EL element that emits B light has low luminous efficiency. Further, it is assumed that the EL element that emits R light has a slightly higher luminous efficiency than the EL element that emits B light. Therefore, when the EL element that emits G light is driven for lighting (when the second and third cathode scanning lines B2 to B3 are scanned), the DC-
When the driving voltage generated by the DC converter 6 is set to be low, and the EL element that emits R light is driven to light (when the first cathode scanning line B1 is scanned).
Is set so that the drive voltage output from the DC-DC converter 6 becomes higher. Further, when the EL element that emits B light is driven to be driven (when the m-th cathode scanning line Bm is scanned), the driving voltage output from the DC-DC converter 6 is set to be the highest. .

As described above, by changing the drive voltage in synchronization with the cathode scanning, for example, when driving an EL element having high luminous efficiency (an EL element which emits G light) to be lit, the cathode scanning circuit 2 Constant current circuits I1 to In
Is set relatively low. Thus, the voltage drop in the constant current circuits I1 to In can be reduced, and the power loss in the constant current circuits can be suppressed.

By the way, in the state shown in FIG. 2, when both the transistors Q3 and Q4 are off, the error amplifier 1 in the switching regulator circuit 11
4, a divided voltage determined by the resistors R1 and R2 is applied. Therefore, the output voltage at this time is set to Vout1 shown in the above-mentioned equation (1). When only the transistor Q3 is turned on and a sufficient base current flows through the transistor Q3, the impedance between the emitter and the collector of the transistor Q3 is substantially negligible in the configuration shown in FIG. The resistor R3 is connected in parallel with the resistor R2. In this case, the output voltage obtained by the DC-DC converter 6 is set to Vout2 represented by the above-described Expression 3.

Further, when only the transistor Q4 is turned on and a sufficient base current flows through the transistor Q4, the impedance between the emitter and the collector of the transistor Q4 is negligibly small in the configuration shown in FIG. Therefore, the resistor R4 is substantially connected in parallel with the resistor R2. In this case, the output voltage Vout3 obtained by the DC-DC converter 6 can be expressed as follows.
In the following equation, (R2 // R4) is the resistance of R2 and R
4 shows the parallel combined resistance value.

[0045]

(Equation 4)

Therefore, when Equations 1 and 3 are compared, the relationship Vout1> Vout2 is established. When Equations 1 and 4 are compared, Vout1> Vout3
When the EL element having high luminous efficiency is driven to light as described above, power loss can be suppressed.

According to the configuration shown in FIG.
The output voltage from the DC converter 6 can be output in three stages. If necessary, a series circuit of a switching transistor and a resistor may be connected in parallel to the resistor R2 to provide a DC-DC converter 6
Can be further divided into multiple stages and output. In the configuration shown in FIG. 2, the mode in which the transistors Q3 and Q4 are simultaneously turned on is selected, and the values of the resistors R3 and R4 connected in series to the respective transistors are appropriately selected. 6 can be output in more stages.

Next, FIG. 3 shows a third embodiment of the driving device according to the present invention. Note that, in FIG. 3, portions corresponding to the respective components in FIGS. 1 and 7 already described are denoted by the same reference numerals, and therefore, detailed description thereof will be omitted as appropriate. In the configuration shown in FIG. 3, the reverse bias voltage supplied from the reverse bias voltage generation circuit 5 is changed in synchronization with the on / off control of the transistor Q3.

That is, the reverse bias voltage generating circuit 5 has a connection point between the resistor R6 and the Zener diode ZD1.
The base of an npn-type transistor Q2 functioning as an emitter follower is connected to this transistor Q2.
Is supplied to the cathode line scanning circuit 3 as a reverse bias voltage. Further, a Zener diode Z is further added to the base of the transistor Q2.
D2 and npn transistor Q5 are connected in series. A switching signal for turning on or off the transistor Q5 is supplied from the light emission control circuit 4 to the base of the transistor Q5 in synchronization with the cathode scanning.

In the configuration shown in FIG.
Of the two Zener diodes, the one with a lower Zener voltage is used as the Zener diode ZD2 connected in series to the transistor Q5. Therefore, when the transistor Q5 is off, the voltage VM1 obtained by subtracting the base-emitter voltage Vbe of the transistor Q2 from the Zener voltage VZD1 of the Zener diode ZD1 is supplied as a reverse bias voltage. Also,
When the transistor Q5 is turned on, a voltage VM2 obtained by subtracting the base-emitter voltage Vbe of the transistor Q2 from the Zener voltage VZD2 of the Zener diode ZD2 is supplied as a reverse bias voltage. Therefore, these reverse bias voltages can be expressed by the following equations, and the relationship of VM1> VM2 is established.

[0051]

(Equation 5)

Here, in the light emitting display panel 1 shown in FIG. 3, G (green) is applied to the first to third cathode scanning lines B1 to B3 as described with reference to FIG. An EL element that emits light is connected, and an EL element that emits B (blue) light is connected to the mth cathode scanning line Bm. When scanning the first to third cathode scanning lines B1 to B3 as in the case shown in FIG. 1, the transistor Q3 is turned on, and when scanning the mth cathode scanning line Bm. Means that when the transistor Q3 is turned off, the first to third cathode scanning lines B1 to B3 are scanned, and when the EL element for emitting G (green) is driven to light, DC- The drive voltage generated by the DC converter 6 is set to be low. When the m-th cathode scanning line Bm is scanned and the EL element emitting B (blue) is driven to light, the driving voltage generated by the DC-DC converter 6 is set to be high. You.

In synchronization with this, the first to third cathode scanning lines B1 to B3 are scanned, and when the EL element for emitting G (green) is driven to light, the reverse bias voltage generating circuit 5 Is turned on. As a result, a low-level voltage VM2 is applied to each EL element in the non-scanning state as a reverse bias voltage. When the m-th cathode scanning line Bm is scanned and the EL element that emits B (blue) light is driven for lighting, the transistor Q5 constituting the reverse bias voltage generation circuit 5 is turned off. As a result, the high-level voltage VM1 is applied to each EL element in the non-scanning state as the reverse bias voltage.

That is, the reverse bias voltage generation circuit 5
It acts to change the reverse bias voltage in synchronization with the magnitude of the drive voltage supplied from the DC-DC converter 6 to the anode line drive circuit 2. In this case, when the drive voltage supplied to the anode line drive circuit 2 is large, a higher level of the reverse bias voltage VM1 is supplied, and when the drive voltage supplied to the anode line drive circuit 2 is small,
A small level of reverse bias voltage VM2 is provided. As a result, a substantially constant reverse bias voltage can always be applied between the cathode and anode terminals of each EL element in the non-scanning state. Therefore, it is possible to suppress the occurrence of the above-described leak phenomenon due to the application of the reverse bias voltage exceeding the predetermined value.

The reverse bias voltage generating circuit 5 shown in FIG. 3 generates two levels of reverse bias voltage. For example, the reverse bias voltage is output from the DC-DC converter 6 as shown in FIG. If the driving voltage is to be used in a configuration controlled in three stages, a combination of a diode having a different Zener voltage and a switching transistor may be added. If necessary, the reverse bias voltage can be switched independently of the drive voltage.

By the way, as described above, this type of EL element has a problem that the luminance characteristic changes due to a change over time and a change in environmental temperature. FIG. 4 shows a preferred example of a case where the circuit configuration shown in FIGS. 1 to 3 is used in addition to the circuit configuration shown in FIGS. That is, FIG.
Numeral 11 indicates the switching regulator circuit indicated by the same numeral in FIGS. In the configuration shown in FIG. 4, the reference voltage Vref used in the switching regulator circuit 11 is configured to change in accordance with the aging of the EL element.

That is, in the circuit configurations shown in FIGS. 1 to 3, the driving voltage output from the DC-DC converter 6 is output in a state proportional to the reference voltage Vref, as is clear from the equations described above. Is done. Therefore, if the reference voltage Vref is configured to follow the luminance characteristic of the EL element due to the change over time and the environmental temperature, the luminance characteristic of the EL element can be compensated.

For this reason, in the configuration shown in FIG.
A dummy organic EL element Ex that does not contribute to light emission is formed in the light emitting display panel 1 in advance, and a current is supplied to the EL element Ex via the constant current circuit 20. The forward voltage of the EL element Ex has the property of changing with time and environmental temperature. Therefore, the forward voltage is divided by the resistors R10 and R11, and the divided voltage functions as an emitter follower. It is configured to be used as the reference voltage Vref via the transistor Q10.

According to the above-described configuration, when the luminance characteristics of each of the organic EL elements OEL contributing to light emission change with time and changes in environmental temperature, the DC-DC converter 6
Since the output drive voltage acts so as to follow it, it is possible to compensate for the luminance characteristics of each organic EL element. Therefore, it is not necessary to previously set the driving voltage output from the DC-DC converter 6 to be high in order to compensate for the luminance characteristics of each organic EL element, and the power loss caused by setting the converter output in advance in this way is unnecessary. Can also be reduced.

In the structure shown in FIG. 4, the luminance characteristics are compensated for by using a dummy organic EL element. At the initial stage of turning on the power, a constant current may be supplied to the EL element to measure the forward voltage at that time. In this case, the data of the measured forward voltage is temporarily stored in a memory, and the reference voltage Vre shown in FIG.
It is made to set f.

[0061]

As apparent from the above description, according to the light emitting display panel driving apparatus of the present invention, the light emission driving power corresponding to each light emitting element is changed in synchronization with the lighting drive of each light emitting element. Therefore, power loss can be reduced in driving, for example, a multi-color display panel in which light-emitting elements having different luminous efficiencies are arranged.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a first embodiment of a driving device according to the present invention.

FIG. 2 is a connection diagram showing a second embodiment.

FIG. 3 is a connection diagram showing a third embodiment.

FIG. 4 is a connection diagram showing a configuration of a luminance compensation circuit that can be suitably used for the driving device shown in FIGS. 1 to 3;

FIG. 5 is a diagram showing an equivalent circuit of the organic EL element.

FIG. 6 is a characteristic diagram showing various characteristics of the organic EL element.

FIG. 7 is a connection diagram illustrating an example of a conventional light emission driving device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emitting display panel 2 anode line drive circuit 3 cathode line scanning circuit 4 light emission control circuit 5 reverse bias voltage generation circuit 6 DC-DC converter (boost circuit) 11 switching regulator circuit 12 DC voltage source 14 error amplifier 15 PWM circuit 16 oscillator A1- An Anode (drive) line B1 to Bm Cathode (scan) line D1 Diode Ex dummy EL element I1 to In Drive source (constant current circuit) L1 Inductor OEL Organic EL element Q1 to Q10 Transistor R1 to R11 Resistance SX1 to SXn Drive switch SY1 ~ SYn Scan switch Vref Reference voltage

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 33/14 H05B 33/14 A (72) Inventor Ken Okuyama 4- 3146-7, Yawatahara, Yonezawa-shi, Yamagata 7 Yonezawa Plant, Tohoku Pioneer Co., Ltd. No. 7 Tohoku Pioneer Co., Ltd. Yonezawa Plant F term (reference) 3K007 AB02 AB03 AB04 AB05 AB11 BA06 DA01 DB03 EB00 GA01 GA04 5C080 AA06 BB05 CC03 DD26 FF12 JJ02 JJ03 JJ05

Claims (10)

[Claims] 1. A plurality of light-emitting elements having different light-emitting efficiencies are arranged, and light-emitting drive power is selectively applied to each of the light-emitting elements, so that the light-emitting elements to which the light-emitting drive power is applied are driven to light. The driving apparatus for a light emitting display panel configured as described above, comprising: a driving power changing unit that changes a light emitting driving power corresponding to each light emitting element in synchronization with lighting driving of each light emitting element. Characteristic display device driving device. 2. The driving apparatus for a light emitting display panel according to claim 1, wherein said driving power changing means is configured to change a light emitting driving power corresponding to a light emission color of each light emitting element. 3. The light emitting display panel includes a plurality of drive lines and a plurality of scanning lines that intersect each other, and a plurality of drive lines and a plurality of scanning lines intersect each other at a plurality of intersections between the drive lines and the scanning lines. 3. The driving device for a light-emitting display panel according to claim 1, wherein each of the light-emitting elements is connected to the light-emitting element. 4. The driving apparatus for a light emitting display panel according to claim 3, wherein each scanning line in the light emitting display panel is connected to a light emitting element that emits the same light emission color. 5. A light-emitting drive power is supplied to each of the light-emitting elements via each of the drive lines, and
A reverse bias voltage is applied to the scanning line in the non-scanning state, and reverse bias voltage changing means for changing the reverse bias voltage corresponding to the light emitting element driven to be lit is further provided. The driving device for a light emitting display panel according to claim 3 or 4, wherein 6. A constant current source is arranged on each drive line, and a predetermined current is supplied to each light emitting element in a scanning state via the constant current source. The light emission according to any one of claims 3 to 5, wherein a drive voltage supplied to a constant current source arranged on the drive line is changed according to a light emitting element to be driven to light. Display panel driving device. 7. A driving voltage supplied to the constant current source,
The DC-DC boost circuit is configured to be supplied from a DC-DC boost circuit, and an output voltage of the DC-DC boost circuit is controlled based on a difference between a divided voltage of the output voltage and a reference voltage, The driving device of a light emitting display panel according to claim 6, wherein a voltage division ratio for generating the divided voltage is changed corresponding to the light emitting element driven to be lit. 8. The driving apparatus for a light emitting display panel according to claim 5, wherein said reverse bias voltage changing means is configured to change a voltage dividing ratio of a driving voltage corresponding to said light emitting element driven to be lit. 9. The light-emitting display panel according to claim 1, wherein said light-emitting drive power is further changed in accordance with a change over time and a change in environmental temperature of each light-emitting element. Drive. 10. The driving device for a light emitting display panel according to claim 1, wherein the light emitting element is organic electroluminescence.