JP2013186946A - Method and circuit of detecting short circuit failures of organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and circuit capable of detecting short circuit failures of an organic EL element independently of variation in unique characteristics of the organic EL element.SOLUTION: A short circuit failure detection circuit 20 comprises a forward voltage detector 22, an OR circuit 24, a DC voltage source 26, and a display part 28. The forward voltage detector 22 includes four resistors 22a and four PNP-type transistors 22b. One end of each resistor 22a is connected to a cathode of a corresponding organic EL element 14a, and the other end thereof is connected to a base of the corresponding PNP-type transistor 22b. An emitter of each PNP-type transistor 22b is connected to an anode of the corresponding organic EL element 14a, and a collector thereof is connected to one end of a corresponding resistor R1 of the OR circuit 24.

Description

  The present invention relates to a short failure detection method and a detection circuit of an organic EL element.

  In recent years, an organic EL panel incorporating a plurality of organic EL (electroluminescence) elements is used as a light emitting module in a lighting fixture. Such an organic EL element is a device that emits light by applying an electric field to a thin film of an organic material. Since the thickness of the thin film varies and there is a portion where the resistance is locally low, an electrical short circuit, that is, a short circuit is likely to occur at that location. Such a short circuit is not a complete short circuit state (forward voltage Vf = 0 V of the organic EL element) but has a certain impedance.

  Normally, the brightness when the organic EL element is lit is proportional to the magnitude of the drive current, and therefore a constant current source is used for the lighting fixture in order to keep the brightness constant. For this reason, when the organic EL element is short-circuited, a constant current always flows through the organic EL element, but the current is concentrated at the short-circuited portion, and the organic EL element generates heat. For this reason, it is necessary to detect a short-circuit failure in order to quickly replace a short-circuited organic EL element or to suppress heat generation by ensuring that no current flows through the organic EL panel and to ensure safety.

  For example, a method has been proposed in which an element driving transistor for controlling a driving current supplied to an organic EL element is operated in its linear region, and the light emission luminance or the cathode current at this time is observed to detect a short circuit of the organic EL element. (Patent Document 1).

JP 2008-64806 A

  However, in the above-described detection method, variations in emission luminance or cathode current occur due to variations in inherent characteristics of organic EL elements, such as VI characteristics, temperature characteristics, and impedance values at short-circuit, and the inherent characteristics are taken into consideration. Otherwise, there is a problem that a short circuit failure of the organic EL element cannot be detected.

  An object of the present invention is to provide a method and a detection circuit capable of detecting a short-circuit failure of an organic EL element regardless of variations in inherent characteristics of the organic EL element.

The organic EL element short failure detection method according to the first aspect of the present invention includes:
Energize the organic EL element, then stop energization,
Detecting the forward applied voltage of the organic EL element after energization is stopped,
Based on the detected applied voltage, it is determined whether or not a short-circuit failure has occurred in the organic EL element.

A short circuit fault detection circuit according to a second aspect of the present invention includes:
An energization control unit for energizing the organic EL element and subsequently stopping energization;
A voltage detector for detecting a forward applied voltage of the organic EL element after energization is stopped;
And a discriminator that discriminates whether or not a short failure has occurred in the organic EL element based on the detected applied voltage.

  According to the present invention, since a short-circuit failure of the organic EL element is detected according to the value of the forward voltage of the organic EL element when energization is stopped, it is not necessary to consider variation in the characteristic characteristic of the organic EL element. Has the advantage.

It is a circuit diagram of a lighting fixture provided with the short fault detection circuit based on this invention. It is a schematic block diagram of the circuit diagram of FIG. (A) shows the relationship between the forward voltage Vf generated in a normal organic EL element and time t, and (b) shows the relationship between the forward current If flowing through the organic EL element and time t. (A) shows the relationship between the forward voltage Vf generated in the short-circuited organic EL element and time t, and (b) shows the relationship between the forward current If flowing through the organic EL element and time t. It is a flowchart which shows operation | movement of the lighting fixture shown in FIG.

  Hereinafter, with reference to an accompanying drawing, a lighting fixture provided with a short circuit fault detection circuit concerning an embodiment of the invention is explained.

  As shown in FIG. 2, the luminaire 10 according to the present embodiment includes a constant current circuit 12, an organic EL panel 14, a control unit 18, and a short failure detection circuit 20.

  As shown in FIG. 1, the constant current circuit 12 is connected to, for example, an AC power supply 12 a such as a commercial power supply, and generates and outputs a constant current for driving the organic EL panel 14. For example, a constant current circuit for LED can be used as the constant current circuit 12. The constant current circuit 12 includes a switch 16 that is turned on / off to perform PWM dimming described later.

  As shown in FIG. 1, the organic EL panel 14 includes four organic EL elements 14a. The four organic EL elements 14a are connected in series with each other. Each organic EL element 14a includes an organic light emitting diode (OLED) made of an organic material that converts electrical energy into light energy. The anode of the organic EL panel 14 is connected to the current outflow end of the constant current circuit 12, and the cathode is connected to the current inflow end of the constant current circuit 12. The organic EL panel 14 emits light when a constant current supplied from the constant current circuit 12 flows.

  The switch 16 is composed of a semiconductor switch such as a MOS transistor or IGBT, and is disposed inside the constant current circuit 12. The switch 16 is connected to the organic EL panel 14 and connects / disconnects the current path according to the control of the control unit 18.

  The control unit 18 includes a CPU (Central Processing Unit), a memory, and the like, and executes a lighting process and a short failure detection process described later by executing a program stored in the memory. Details of the lighting process and the short failure detection process will be described later.

  As illustrated in FIG. 2, the short failure detection circuit 20 includes a forward voltage detection unit 22, a logical sum circuit 24, a DC voltage source 26, and a display unit 28.

  As shown in FIG. 1, the forward voltage detector 22 includes four resistors 22a and four PNP transistors 22b. One end of each resistor 22a is connected to the cathode of the corresponding organic EL element 14a, and the other end is connected to the base of the corresponding transistor 22b. The emitter of each transistor 22b is connected to the anode of the corresponding organic EL element 14a, and its collector is connected to one end of a later-described resistor R1 of the OR circuit 24.

  The OR circuit 24 includes resistors R1 to R4, a resistor R5, an NPN-type first transistor 24a, and an NPN-type second transistor 24b for each organic EL element 14a.

  The other end of each resistor R1 is connected to the base of the corresponding first transistor 24a and one end of the corresponding resistor R3. The collector of each transistor 24a is connected to one end of the corresponding resistor R4 and one end of the corresponding resistor R2, and its emitter is connected to the other end of the corresponding resistor R3 and grounded. The power supply voltage VDD is applied from the DC voltage source 26 to the other end of each resistor R4.

  The base of each second transistor 24b is connected to the other end of the corresponding resistor R2, and the power supply voltage VDD from the DC voltage source 26 is applied to its collector, for example. The emitter is grounded via a resistor R5.

  The output terminals TA of the short failure detection circuit 20 are commonly connected to the emitters of the four second transistors 24b.

  The output terminal TA is connected to the control unit 18, and the control unit 18 detects the presence / absence of a short-circuit failure based on the voltage of the output terminal TA and causes the display unit 23 to display the presence / absence of the voltage. If the display part 23 can show the presence or absence of a voltage, the warning by an alarm sound may be sufficient instead of a display, for example.

  The DC voltage source 26 is connected to the AC power supply 12 a, rectifies the AC voltage, generates a constant voltage, for example, a power supply voltage VDD of 5 V, and applies it to the OR circuit 24.

  The display unit 28 is configured by an LED or the like, and lights up when the organic EL panel 14 has a short circuit failure under the control of the control unit 18.

  Here, the characteristics of the organic EL element 14a will be described with reference to FIGS.

  3A and 3B show the relationship between the forward voltage Vf generated in the normal organic EL element 14a and time t, and the relationship between the forward current If flowing through the organic EL element 14a and time t.

  As shown in FIGS. 3 (a) and 3 (b), even when the energization to the organic EL element 14a is stopped at the timing T and the current If flowing through the organic EL element 14a is set to 0, the forward voltage drop is as follows. The value Vf ′ is slightly smaller than the forward voltage Vf, and does not become zero. This characteristic is due to the fact that the organic EL element 46 has a capacitive impedance component.

  On the other hand, as shown in FIGS. 4 (a) and 4 (b), when the energization to the organic EL element 14a that has caused the short failure is stopped at timing T and the flowing current is set to 0, the forward voltage drop is as follows. , Vf ′, but almost zero. This characteristic is due to the fact that the organic EL element 14a in which a short circuit failure has occurred has a resistive impedance component rather than a capacitive component.

  As described above, when the current flowing through the organic EL element 14a is instantaneously set to 0, the forward voltage drop is almost 0 when the organic EL element 16a is short-circuited, and the forward voltage is almost normal when normal. Vf is maintained.

  Therefore, if the current flowing through the organic EL element 10 is instantaneously interrupted and the forward voltage drop at that time is measured, it is possible to determine whether the organic EL element 10 is normal or has a short circuit failure. is there.

  Next, a short failure detection operation by the short failure detection circuit 20 will be described.

Here, the applied voltage of each organic EL element 14a is applied between the base emitters of the corresponding PNP transistor 22b.

  Here, assuming that the organic EL element 14a is normal, the forward voltage is substantially Vf regardless of whether or not a current flows through the organic EL element. Therefore, a reverse bias voltage is applied between the base and emitter of the corresponding PNP transistor 22b, and the corresponding transistor 22b continues to be turned on.

  By this turning on, the corresponding first transistor 24a is also turned on. As a result, the base voltage of the transistor 24b in the output stage becomes the ground level, and the transistor 24b is turned off.

  On the other hand, the forward voltage during energization of the organic EL element 14a that has caused the short failure is substantially equal to the forward voltage Vf. For this reason, like the normal organic EL element 14a, the corresponding output stage transistor 24b is turned off.

  However, when the energization to the organic EL element 14a in which the short circuit failure has occurred is stopped, the forward voltage drop becomes almost zero. For this reason, a reverse bias voltage cannot be applied between the base emitters of the corresponding PNP transistor 22b, and the corresponding transistor 22b is turned off. Then, the corresponding first transistor 24a is also turned off. Therefore, this causes the base voltage of the transistor 24b in the output stage to be approximately VDD, and the transistor 24b is turned on.

  Since the emitters of the four transistors 24b are wired-or connected, if there is at least one transistor 24b that is turned on, the voltage is approximately VDD.

Accordingly, when there is no short-circuited organic EL element 14a, the voltage at the output terminal TA is at the ground level regardless of the presence or absence of energization. On the other hand, when even one organic EL element 14a with a short circuit fault exists, the voltage at the output terminal TA becomes VDD when the energization is stopped.

  Next, on the premise of the operation of the above-described short failure detection circuit 20, the operation of the lighting fixture 10 shown in FIGS. 1 and 2 will be described with reference to FIG.

  When the lighting apparatus 10 is turned on, the constant current circuit 12 starts energizing the series circuit of the organic EL elements 14 a of the organic EL panel 14. Thereby, each organic EL element 14a lights up.

  On the other hand, when the power is turned on, the control unit 18 starts the process shown in the flow of FIG. 5 and switches the switch 16 at a duty ratio according to the dimming degree instructed by operating a dimming knob (not shown). Turn on and off. That is, the organic EL panel 14 is PWM-controlled.

  For example, when the dimming degree is instructed to be high (bright), the control unit 18 increases the ratio of the period during which the switch 16 is turned on to increase the total amount of current (energy) supplied to the organic EL element 14a. If the dimming degree is instructed to be low (dark), the ratio of the period during which the switch 16 is turned on is reduced to reduce the total amount of current (energy) supplied to the organic EL element 14a. (Step S1).

  The control unit 18 determines whether or not it is time to detect a short failure while performing the above-described lighting operation (step S2).

  The detection timing of a short circuit failure is the timing at which the switch 16 that repeatedly turns on and off in order to perform PWM dimming is off.

  If it is determined that the short failure detection timing has not come (step S2; No), the process returns to step S1 and continues the PWM control.

  On the other hand, if the control unit 18 determines that the short failure detection timing has come (step S2; Yes), the switch 16 is off and the current flowing through the organic EL element 14a becomes 0 (step S3).

  Then, as described above, the applied voltage of the normal organic EL element 14a is maintained substantially at Vf, while the applied voltage of the organic EL element 14a having a short circuit failure is substantially zero.

  Due to this difference, as described above, a voltage is generated at the output terminal TA.

  The control unit 18 determines the voltage appearing at the output terminal TA, and determines that there is no failure if it is approximately ground level, and that at least one short failure exists if it is approximately VDD (step S4). When it is determined that there is no short failure (step S4; No), the control unit 18 returns the process to step S1 and continues the lighting operation.

  On the other hand, when it is determined that there is a short circuit failure (step S4; Yes), the control unit 18 turns on the display unit 28 (step S5) and notifies that a short circuit failure has occurred.

  Thereafter, it is optional to stop or continue the lighting operation.

  According to the lighting apparatus 10 of the present embodiment, by stopping energization to the organic EL element 14a, there is almost no effect on the normal lighting process, and the organic EL element in which no short failure has occurred is not energized. The presence / absence of a short circuit failure in the organic EL panel is detected by utilizing the characteristic of the organic EL element that the forward direction applied voltage is different from the forward direction applied voltage when the organic EL element in which the short circuit failure occurs is not energized. be able to.

  Also, since the dimming switching function is used to cut off the energization to the organic EL element, it is not necessary to provide a configuration for cutting off the current exclusively for short-circuit failure, and the circuit configuration is also highly efficient. .

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation and application are possible.

  For example, the circuit configurations shown in FIGS. 1 and 2 are examples, and can be arbitrarily changed as long as the same function can be obtained.

  For example, although the example which connected the four organic EL elements 14 in series was shown, the number of organic EL elements is arbitrary.

  Moreover, although the electric current was interrupted | blocked using the dimming function, the electric current which flows into the organic EL panel 14 may be interrupted | blocked by another structure, and you may make it bypass so that it may not flow into the organic EL panel 14 .

  Moreover, although the configuration in which the applied voltage when the organic EL element 14a is not energized is detected by the base emitter voltage of the transistor 22b connected in parallel is exemplified, other detection methods may be used.

  Further, the voltage of the output terminal TA is controlled by the OR circuit 24 when there is a short fault in at least one organic EL element 14a. However, an output terminal for each organic EL element 14 is provided. Also good. In this case, for example, an output terminal may be individually connected to the emitter of each second transistor 24b.

  Although an example in which an organic EL panel is used as a light emitting element has been shown, a configuration in which a plurality of organic EL diodes are arranged may be used.

  In addition, the example in which the energization is stopped for a period of time that cannot be recognized by the user during the lighting operation and the presence or absence of a short failure is determined has been described. However, the short failure may be determined only when the light is on or off. Good.

  A part or all of the above embodiments can be described as in the following supplementary notes, but is not limited thereto.

(Appendix 1)
Energize the organic EL element, then stop energization,
Detecting the forward applied voltage of the organic EL element after energization is stopped,
Based on the detected applied voltage, it is determined whether or not a short failure has occurred in the organic EL element,
A method for detecting a short circuit failure in an organic EL element.

(Appendix 2)
When the detected applied voltage is higher than the reference voltage, it is determined that no short-circuit failure has occurred,
When the detected applied voltage is equal to or lower than the reference voltage, it is determined that a short fault has occurred.
The method for detecting a short circuit failure in an organic EL element according to Supplementary Note 1, wherein:

(Appendix 3)
An energization control unit for energizing the organic EL element and subsequently stopping energization;
A voltage detector for detecting a forward applied voltage of the organic EL element after energization is stopped;
A determination unit for determining whether or not a short failure has occurred in the organic EL element, based on the detected applied voltage;
A short failure detection circuit for an organic EL element, comprising:

(Appendix 4)
The determination unit determines that a short-circuit failure has not occurred when the detected applied voltage is higher than the reference voltage, and determines that a short-circuit failure has occurred when the detected applied voltage is equal to or lower than the reference voltage. To
The short circuit failure detection circuit of the organic EL element according to Supplementary Note 3, wherein

(Appendix 5)
The energization control unit
Dimming means for controlling the duty of energizing the organic EL element;
Means for interrupting the current for a predetermined period during energization;
The short circuit failure detection circuit of the organic EL element according to appendix 3 or 4, characterized by comprising:

(Appendix 6)
The voltage detection unit includes a transistor including a base connected to one of an anode and a cathode of an organic EL element, and an emitter or a collector connected to the other,
The short circuit failure detection circuit for an organic EL element according to any one of appendices 3 to 5, wherein the determination unit determines whether or not a short circuit failure has occurred based on on / off of the transistor.

14 Organic EL panel 14a Organic EL element 16 Switch (energization controller)
18 Control unit (discrimination unit, discrimination means)
20 Short failure detection circuit 22 Forward voltage detector (voltage detector)
22a First resistor 22b PNP transistor (transistor)
24 OR circuit 24a first NPN transistor 24b second NPN transistor TA output terminal

Claims (6)

Energize the organic EL element, then stop energization,
Detecting the forward applied voltage of the organic EL element after energization is stopped,
Based on the detected applied voltage, it is determined whether or not a short failure has occurred in the organic EL element,
A method for detecting a short circuit failure in an organic EL element. When the detected applied voltage is higher than the reference voltage, it is determined that no short-circuit failure has occurred,
When the detected applied voltage is equal to or lower than the reference voltage, it is determined that a short fault has occurred.
The organic EL device short failure detection method according to claim 1. An energization control unit for energizing the organic EL element and subsequently stopping energization;
A voltage detector for detecting a forward applied voltage of the organic EL element after energization is stopped;
A determination unit for determining whether or not a short failure has occurred in the organic EL element, based on the detected applied voltage;
A short failure detection circuit for an organic EL element, comprising: The determination unit determines that a short-circuit failure has not occurred when the detected applied voltage is higher than the reference voltage, and determines that a short-circuit failure has occurred when the detected applied voltage is equal to or lower than the reference voltage. To
The short circuit failure detection circuit for an organic EL element according to claim 3. The energization control unit
Dimming means for controlling the duty of energizing the organic EL element;
Means for interrupting the current for a predetermined period during energization;
The short failure detection circuit of the organic EL element according to claim 3 or 4, characterized by comprising: The voltage detection unit includes a transistor including a base connected to one of an anode and a cathode of an organic EL element, and an emitter or a collector connected to the other,
6. The short circuit failure detection circuit for an organic EL element according to claim 3, wherein the determination unit determines presence or absence of a short circuit failure based on on / off of the transistor.

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