JP5533737B2 - Organic EL drive device - Google Patents

Description

  The present invention relates to an organic EL driving device that drives an organic EL (Electroluminescence) element.

  A conventional organic EL driving device drives an organic EL element by DC (direct current) driving or PWM (pulse width modulation) driving. However, in the case of DC driving, electric charges are accumulated in the organic film of the organic EL element, and the organic EL element is deteriorated or the luminance is lowered due to light emission of the organic EL element.

  Therefore, an organic EL device that applies a reverse voltage to the organic EL element is used. The organic EL device described in Patent Document 1 extracts a charge accumulated in the organic EL element by applying a reverse voltage (negative DC voltage) to the organic EL element when the organic EL element is turned off. It is intended to extend the life by relaxing accumulation and polarization.

  In addition, the organic EL display device described in Patent Document 2 has an organic EL element in which an organic material layer having a set thickness do including a light emitting layer is sandwiched between a pair of electrodes and arranged in a dot matrix form on a substrate. An organic EL display device that selectively turns on or off an organic EL element according to a voltage applied according to an image signal, and a voltage at which dielectric breakdown occurs in an organic material layer having a thickness do is defined as Vb. At this time, the reverse voltage Vm applied at the time of non-lighting is set to Vm <(1/2) · Vb, and the continuous application time of Vm is limited within the set time. That is, the reverse voltage Vm is set to a voltage smaller than the dielectric breakdown voltage Vb at which a weak current is generated.

  Thereby, the leakage current generated after the operation time has elapsed can be prevented, and the reliability of the organic EL display device can be improved without deteriorating the yield.

Japanese Patent No. 2663648 JP 2005-156867 A

  However, in the prior arts of Patent Document 1 and Patent Document 2, a reverse voltage value (hereinafter abbreviated as a VR value) is set before energization of the organic EL element, and the energization of the organic EL element is always performed. A constant VR value is applied. For this reason, when an organic EL element deteriorates with time, the reverse current of the organic EL element increases due to the application of a constant VR value.

That is, a constant VR value causes a great stress on the organic EL element, and the life of the organic EL element cannot be extended.

  The subject of this invention is providing the organic electroluminescent drive device which can aim at the lifetime improvement of an organic electroluminescent element with respect to a reverse voltage drive.

In order to solve the above problems, an organic EL driving device of the present invention is an organic EL driving device that supplies direct current power to an organic EL element, and applies a predetermined forward voltage when the organic EL element is turned on, A driving unit that applies a predetermined reverse voltage when the organic EL element is turned off, a reverse current detection unit that detects a reverse current flowing through the organic EL element when the organic EL element is turned off, and the reverse current And a control unit that changes the peak value of the reverse voltage with time.

According to the present invention, when the reverse current detection unit detects the reverse current flowing through the organic EL element when the organic EL element is turned off, the control unit changes the peak value of the reverse voltage with time based on the reverse current. Therefore, the reverse current is not increased and no stress is applied to the organic EL element. Accordingly, it is possible to provide an organic EL driving device capable of extending the lifetime of the organic EL element with respect to reverse voltage driving.

1 is a block diagram of a conceptual configuration of an organic EL drive device according to Embodiment 1 of the present invention. It is a specific circuit block diagram of the organic EL drive device of Example 1 of the present invention. It is a wave form diagram of the drive signal for lighting and extinguishing the organic EL element of Example 1 of this invention. It is a figure which shows the setting of the reverse voltage with respect to the reverse current of the organic EL element of Example 1 of this invention. (A) shows a time-dependent change of the reverse current of the organic EL element of Example 1 of this invention, (b) is a figure which shows a time-dependent change of the reverse voltage of an organic EL element. It is a figure which shows the relationship between time and a brightness | luminance about each of the reverse bias application drive by this invention, the conventional reverse bias application drive, and DC continuous drive. It is a conceptual structure block diagram of the organic electroluminescent drive device of Example 2 of this invention. It is a concrete circuit block diagram of the organic electroluminescent drive device of Example 2 of this invention. (A) shows the reverse current of the organic EL element of Example 2 of this invention, (b) shows the time-dependent change of the reverse voltage of an organic EL element, (c) shows the pulse signal of a duty control part. FIG.

  Hereinafter, an organic EL driving device according to an embodiment of the present invention will be described in detail with reference to the drawings. The organic EL driving device according to the embodiment of the present invention constantly monitors deterioration of the organic EL element over time while the organic EL element is energized, and adjusts the VR value according to the deterioration of the organic EL element and applies it to the organic EL element. It is characterized by doing.

FIG. 1 is a block diagram of a conceptual configuration of an organic EL driving device according to Embodiment 1 of the present invention. The organic EL driving device shown in FIG. 1 supplies pulsed power to an organic EL element, and has an organic EL element 1 and a drive circuit 2 that drives the organic EL element 1. The drive circuit 2 includes a control unit 20 and a drive unit 23, and the control unit 20 includes a reverse current detection unit 21 and a reverse voltage control unit 22.

  The drive unit 23 is connected to the organic EL element 1, the reverse current detection unit 21, and the reverse voltage control unit 22, and the pulse signal having a certain duty from the reverse voltage control unit 22 is used for the organic EL element 1. A predetermined forward voltage is applied during lighting, and a predetermined reverse voltage is applied when the organic EL element 1 is turned off.

  The reverse current detection unit 21 includes a current detection resistor and a current transformer, detects a reverse current that flows when a reverse voltage is applied to the organic EL element 1, and detects the detected reverse current as a reverse voltage control unit. 22 to output.

  The reverse voltage control unit 22 controls the drive unit 23 so as to repeat the application of the forward voltage and the application of the reverse voltage with a pulse signal having a constant duty, so that the forward voltage applied to the organic EL element 1 is repeated. Switch between directional voltage and reverse voltage. Moreover, the reverse voltage control part 22 changes the peak value of the reverse voltage applied to the organic EL element 1 with time according to the magnitude of the reverse current.

FIG. 2 is a specific circuit configuration diagram of the organic EL driving device according to the first embodiment of the present invention. The organic EL element 1 is equivalently composed of a diode D1 and a capacitor C1. The drive unit 23 includes a switching unit 24, a forward power supply V1, and a reverse power supply V2.

  The forward power supply V1 has a positive electrode disposed on the anode side of the diode D1 and a negative electrode disposed on the cathode of the diode D1. The switching unit 24 has three terminals a, b, and c, the terminal a is connected to the organic EL element 1, the terminal b is connected to the positive electrode of the forward power supply V1, and the terminal c is the reverse current detection unit 21. Connected to one end.

  The other end of the reverse current detector 21 is connected to the negative electrode of the reverse power supply V2, and the positive electrode of the reverse power supply V2 is connected to the cathode of the diode D1 and the negative electrode of the forward power supply V1.

  The switching unit 24 switches and selects the terminal b and the terminal c by a pulse signal from the reverse voltage control unit 22, thereby applying the forward power source V <b> 1 for a predetermined time when the organic EL element 1 is turned on. The reverse power supply V2 is applied for a predetermined time when the light is turned off. The pulse signal is an on / off signal having a period T shown in FIG.

FIG. 3 is a waveform diagram of drive signals for turning on and off the organic EL element 1 according to the first embodiment of the present invention. The drive signal shown in FIG. 3 is a VR composed of a forward voltage VF (positive voltage) when the organic EL element 1 is turned on and a reverse voltage VR value (negative voltage is VR time T1) when the organic EL element 1 is turned off. It consists of a pulse signal with period T. That is, the drive unit 23 drives the organic EL element 1 with a cycle T.

  The reverse current detector 21 detects and monitors the reverse current IR when the reverse voltage VR value is applied (VR time T1 shown in FIG. 3).

FIG. 4 is a diagram showing the setting of the reverse voltage with respect to the reverse current of the organic EL element 1 of Example 1 of the present invention. As shown in FIG. 4, the reverse current of the organic EL element 1 increases rapidly as the reverse voltage increases. Due to the deterioration of the organic EL element 1 with the passage of time, the reverse current exceeds a predetermined value of, for example, 1 μA.

Therefore, the reverse voltage control unit 22 controls the drive unit 23 to decrease the reverse voltage VR value when the reverse current detected by the reverse current detection unit 21 is, for example, 1 μA (predetermined value) or more. To do.

FIG. 5A shows the change with time of the reverse current IR of the organic EL element 1 of Example 1 of the present invention, and FIG. 5B shows the change with time of the reverse voltage VR of the organic EL element 1. FIG. As shown in FIGS. 5 (a) and 5 (b), when the reverse current IR exceeds 1 μA at time t1, the reverse voltage VR is decreased from VR1 by ΔVR to VR2, thereby reducing the reverse current IR to 1 μA. It can suppress to less than.

Further, when the reverse current exceeds 1 μA at time t2, the reverse current IR can be suppressed to less than 1 μA by reducing the reverse voltage VR from VR2 by ΔVR to VR3. Further, when the reverse current exceeds 1 μA at time t3, the reverse current IR can be suppressed to less than 1 μA by reducing the reverse voltage VR from VR3 by ΔVR to VR4.

As described above, according to the organic EL driving device of Example 1, when the reverse current detection unit 21 detects the reverse current flowing through the organic EL element 1 when the organic EL element 1 is turned off, the reverse voltage control unit 22 Since the reverse voltage is controlled in accordance with the detected reverse current, the reverse current is not increased and no stress is applied to the organic EL element 1. Therefore, it is possible to provide an organic EL driving device capable of extending the life of the organic EL element 1 against a reverse voltage.

FIG. 6 is a diagram showing the relationship between time and luminance for each of the reverse bias application drive according to the present invention, the conventional reverse bias application drive, and the DC continuous drive. As can be seen from FIG. 6, the reverse bias application driving according to the present invention can extend the life of the organic EL element 1 compared to the conventional reverse bias application driving and DC continuous driving.

FIG. 7 is a conceptual configuration block diagram of an organic EL drive device according to Embodiment 2 of the present invention. The organic EL drive device shown in FIG. 7 includes an organic EL element 1 and a drive circuit 2a. The drive circuit 2a includes a control unit 20a and a drive unit 23a, and the control unit 20a includes a reverse current detection unit 21 and a duty control unit 22a.

  The drive unit 23a is connected to the organic EL element 1, the reverse current detection unit 21, and the duty control unit 22a, and a predetermined forward direction when the organic EL element 1 is turned on by a duty variable pulse signal from the duty control unit 22a. A voltage is applied, and a predetermined reverse voltage is applied when the organic EL element 1 is turned off.

  The duty control unit 22a switches the forward voltage / reverse voltage applied to the organic EL element 1 based on the reverse current from the reverse current detection unit 21, and determines a predetermined value according to the magnitude of the reverse current. A pulse signal having a variable duty is output as a synchronizing signal to a reverse power source 25 that outputs a reverse voltage of a sawtooth wave (which may be a triangular wave) that rises with a time constant of.

FIG. 8 is a specific circuit configuration diagram of the organic EL drive device according to the second embodiment of the present invention. The drive unit 23a includes a switching unit 24, a forward power source V1, and a reverse power source 25. The reverse power supply 25 is connected to the reverse current detection unit 21, the negative electrode of the forward power supply V1, and the cathode of the diode D1, and is a sawtooth wave (triangular wave) that rises with a predetermined time constant as shown in FIG. 9B. It is a power source that outputs a reverse voltage.

FIG. 9A shows the reverse current of the organic EL element of Example 2 of the present invention, FIG. 9B shows the change over time of the reverse voltage of the organic EL element, and FIG. 9C shows the duty control unit. It is a figure which shows a pulse signal.

  The operation of the organic EL drive device according to the second embodiment will be described with reference to FIG. First, when the pulse signal generated by the duty control unit 22a is at the H level, the terminal c of the switching unit 24 is selected by the H level, and a reverse voltage from the reverse power source 25 is applied to the organic EL element 1. Is done. Then, the reverse voltage VR gradually rises and the reverse current IR gradually increases.

  Thereafter, as illustrated in FIG. 9A, when the reverse current exceeds a predetermined threshold (for example, 1 μA), the duty control unit 22 a outputs an L level pulse signal to the switching unit 24. For this reason, the terminal b of the switching unit 24 is selected, and the forward voltage from the forward power source V <b> 1 is applied to the organic EL element 1.

  Due to the change with time of the organic EL element 1, the time for the reverse current to reach the predetermined threshold gradually decreases. Therefore, the duty control unit 22a gradually shortens the on-duty of the pulse signal in accordance with the arrival time when the reverse current detected by the reverse current detection unit 21 reaches a predetermined threshold (FIG. 9C). ). That is, the duty control unit 22a controls the drive unit 23a so as to shorten the application time of the reverse voltage when the value of the reverse current exceeds a predetermined threshold value.

  Therefore, the peak value of the reverse voltage decreases as the organic EL element 1 changes over time, so that the reverse current does not increase and no stress is applied to the organic EL element 1 as shown in FIG. . Therefore, it is possible to provide an organic EL driving device capable of extending the life of the organic EL element 1 against a reverse voltage.

  The present invention is applicable to an organic EL display device.

DESCRIPTION OF SYMBOLS 1 Organic EL element 2, 2a Drive circuit 20, 20a Control part 21, 21a Reverse current detection part 22 Reverse voltage control part 22a Duty control part 23, 23a Drive part 24 Switching part 25 Reverse power supply V1 Forward power supply D1 Diode C1 capacitor T VR period T1 VR time

Claims (5)

An organic EL driving device for supplying direct current power to an organic EL element,
A driving unit that applies a predetermined forward voltage when the organic EL element is turned on and applies a predetermined reverse voltage when the organic EL element is turned off;
A reverse current detection unit for detecting a reverse current flowing in the organic EL element when the organic EL element is turned off;
A controller that changes the peak value of the reverse voltage over time based on the reverse current;
An organic EL driving device comprising:   2. The organic EL drive device according to claim 1, wherein the control unit controls the drive unit so that the reverse voltage decreases when the value of the reverse current becomes a predetermined value or more.   3. The organic EL drive device according to claim 1, wherein the control unit controls the drive unit to repeat the application of the forward voltage and the application of the reverse voltage with a constant duty. 4.   2. The organic EL drive device according to claim 1, wherein the control unit controls the drive unit to shorten the application time of the reverse voltage when the value of the reverse current becomes a predetermined value or more. 3. . 5. The organic EL drive device according to claim 4, wherein the drive unit has a reverse power supply that outputs the reverse voltage that rises with a predetermined time constant.

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