JP2005003849A - Organic el drive circuit and organic el display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL drive circuit capable of reducing electric power consumption of an organic EL display device and an organic EL display device. <P>SOLUTION: The organic EL drive circuit is equipped with a current source which is disposed in correspondence to display colors R, G and B for current driving of organic EL elements through terminal pins, a first power source line of a prescribed voltage which supplies electric power to the current source in correspondence to the organic EL elements of the display colors of the lower light emission efficiency among R, G and B, a second power source line lower than the prescribed voltage which supplies the electric power to the current source in correspondence to the organic EL elements of any of the remaining display colors among the R, G and B, and a switching regulator which stabilizes the voltage of the second power source line to the constant voltage lower than the prescribed voltage by receiving the electric power from the first power source line and supplying the electric power to the second power source line. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic EL drive circuit and an organic EL display device, and more particularly, to an improvement of an organic EL drive circuit and an organic EL display device that can reduce power consumption of the organic EL display device.
[0002]
[Prior art]
Organic EL display devices are capable of high-luminance display by self-light emission, and are therefore suitable for small-screen display and are currently being used as next-generation display devices mounted on mobile phones, DVD players, PDAs (portable terminal devices), etc. Attention has been paid. When this organic EL display device is driven by voltage like a liquid crystal display device, the luminance variation increases, and there is a difference in sensitivity between R (red), G (green), and B (blue). There is a problem that becomes difficult. Therefore, recently, an organic EL display device using a current-driven driver has been proposed.
[0003]
The ratio of the light emission efficiency to the drive currents of R, G, B is different from, for example, about R: G: B = 6: 11: 10. It depends on the material of the EL element.
Therefore, in the current drive circuit for color display, it is necessary to adjust the luminance according to the material used for R, G, and B and to take white balance on the display screen. For this purpose, an adjustment circuit for adjusting the brightness corresponding to R, G, and B is provided.
By the way, Patent Document 1 discloses an EL element drive circuit in which EL elements arranged in a matrix are driven by current and the anode and cathode of the EL element are dropped to the ground for resetting. Patent Document 2 discloses a technique for driving an EL element with low power consumption using a DC-DC converter.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-232974 [Patent Document 2]
Japanese Patent Laid-Open No. 2001-143867
[Problems to be solved by the invention]
In recent years, the number of drive pins tends to increase due to the demand for high resolution. For this reason, the drive frequency also increases and the power consumption tends to increase. Therefore, there is a strong demand for reducing power consumption.
FIG. 2 is a characteristic graph showing the relationship between the luminance and the applied voltage in the EL elements of R, G and B, and FIG. 3 is a characteristic graph showing the relationship between the luminance of the element and the drive current density.
As shown in FIGS. 2 and 3, the drive voltages for obtaining the same light emission luminance are usually lower for G and B than R if the drive current values are equal. Therefore, even if the G and B power supply voltages are lowered with respect to R, the luminance of the R, G, and B EL elements can be made comparable.
However, if two power supply lines of R power supply voltage and G power supply voltage are provided and power is supplied to each of them, the power consumed by the power supply circuit becomes large. For example, if a series regulator is provided to step down from a high voltage to generate two systems of power, a high voltage and a low voltage, power loss due to stepping down from a high power supply voltage increases. Even if two voltage outputs are obtained by the switching regulator, switching control is performed on the power lines of the respective voltages, so that the power consumption cannot be reduced sufficiently.
An object of the present invention is to solve such problems of the prior art, and to provide an organic EL driving circuit and an organic EL display device capable of reducing the power consumption of the organic EL display device. .
[0006]
[Means for Solving the Problems]
The characteristics of the organic EL drive circuit of the present invention and the organic EL display device using the same for achieving such an object are provided corresponding to the organic EL elements of display colors R, G, B of the organic EL panel. In an organic EL driving circuit that drives an organic EL element through a terminal pin (hereinafter referred to as a pin),
Corresponding to the current source provided corresponding to the display color of R, G, B that drives the organic EL element through a pin and the display color of the organic EL element of R, G, B with low luminous efficiency A first power supply line having a predetermined voltage for supplying power to the current source to be supplied and a predetermined power supply to the current source corresponding to the organic EL element of any one of the display colors of R, G, and B A second power line lower than the voltage of the first power line, and receiving power from the first power line and supplying power to the second power line to stabilize the voltage of the second power line to a constant voltage lower than a predetermined voltage And a switching regulator to be realized.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a first power supply line having a higher voltage and a second power supply line having a lower voltage are provided according to the luminous efficiency of the R, G, and B EL elements, and the respective EL elements are provided. The driving current source is operated at different voltages. The power to the second power supply line of the EL element with high light emission efficiency is supplied through the switching regulator from the first power supply line of the EL element with low light emission efficiency, and the second power supply line is supplied by the switching regulator. The voltage is stabilized to a predetermined voltage. Since this switching regulator only needs to operate at a voltage difference between the first power supply line and the second power supply line, power consumption can be reduced accordingly.
As a result, the power consumption of the organic EL display device can be reduced.
[0008]
【Example】
FIG. 1 is a block diagram centering on a power supply circuit of a column driver of an organic EL panel according to an embodiment to which the organic EL drive circuit of the present invention is applied.
In FIG. 1, 10 is a column IC driver (hereinafter referred to as a column driver) as an organic EL drive circuit in an organic EL panel, and 1 is a DC / DC converter that supplies power to the column driver 10, and R (red) ), For example, a power supply circuit that outputs power of DC 12V to the power line 2 of + Vcc via the input terminal 10a.
In the column driver 10, reference numeral 3 denotes a power supply line corresponding to G (green) and B (blue), for example, with a voltage of DC 9V. Reference numeral 4 denotes a supply power control circuit that receives power from the power supply line 2 and stabilizes and supplies the reduced power to the power supply line 3.
Reference numerals 5G, 5R, and 5B denote output stage current sources corresponding to R, G, and B of the column driver 10, respectively, and are configured by current mirror circuits that receive a predetermined drive current in the input side transistors. The output stage current source 5R is connected to the power supply line 2 and operates by receiving power supply therefrom, and the output stage current sources 5G and 5B are connected to the power supply line 3 and operate by receiving power supply therefrom.
Output stage current sources 5R, 5G, and 5B receive drive currents from D / A conversion circuits (not shown) provided in the preceding stage corresponding to each. This D / A conversion circuit D / A converts the received luminance display data with reference to the received current, and generates a drive current corresponding to the display data corresponding to the terminal pin. The converted drive currents drive the output circuits of the current mirrors of the output stage current sources 5R, 5G, 5B, and generate drive currents for the organic EL elements corresponding to the terminal pins.
6G, 6R, and 6B are EL elements corresponding to R, G, and B, respectively, and the anode side is connected to each of the output stage current sources 5G, 5R, and 5B via the terminal pins 8, and the cathode side is , And grounded via the low-side scanning circuit 7.
[0009]
The supply power control circuit 4 is a regulation circuit that performs switching control of PWM (Pulse Wide Modulation), and controls the power supply line 3 to be maintained at a constant voltage value 3V lower than the power supply line 2. Therefore, the voltage of the output power with respect to the power line 3 is detected by the detection circuit 50 with respect to the voltage of the power line 2 as a reference. Then, power corresponding to the potential difference between the power supply lines 2 and 3 is supplied to the power supply line 3 via the transistor Q62.
The supply power control circuit 4 includes a reference voltage generation circuit 40, a detection circuit 50, a switching regulation circuit 60, and a smoothing circuit 70.
The smoothing circuit 70 is a circuit provided outside the column driver 10.
[0010]
The switching regulation circuit 60 is a circuit inserted between the power supply line 2 (+ Vcc) and the power supply line 3. This comprises a control voltage value generation circuit 65 and a switching circuit 66. The control voltage value generation circuit 65 includes a transistor Q61 and an amplifier 61, and generates a control voltage value for switching control. The switching circuit 66 includes a comparator 62, a PNP-type switching transistor Q62, and a triangular wave generation circuit 63. The transistor Q62 turns on / off the power supply line connected from the power supply line 2 (+ Vcc) to the power supply line 3. The resulting electric power is sent to the power supply line 3 through the smoothing circuit 70.
[0011]
The voltage of the power supply line 3 is stabilized to 9V by the control of the supply power control circuit 40. At this time, since the power consumption in the transistor Q62 is supplied from the power supply line 2 to the power supply line 3 by switching control, the power consumption is reduced by a step-down transistor or the like. Further, since the operating voltage of the supply power control circuit 40 is 3V which is a potential difference between the power supply line 2 (+ Vcc) and the power supply line 3, it is consumed more than the case where a switching regulator for generating 9V is provided independently as a power supply circuit. Power is reduced. In addition, the detection circuit 50 detects a potential difference between the power supply line 2 (+ Vcc) and the power supply line 3. In this respect as well, power consumption can be suppressed.
The switching frequency of the transistor Q62 is a high frequency of about 50 kHz to 800 kHz, for example.
[0012]
The detection circuit 50 is mainly composed of an NPN transistor Q50 having a detection terminal between the base and the emitter. The detection signal E is output to the transistor Q61 of the switching regulation circuit 60 to turn on / off the transistor Q62. The emitter of the transistor Q50 is connected to the power supply line 3 which is an output line of electric power, and receives the voltage of this at the emitter. The base is connected to one end of the resistor R50. One end of the resistor R50 to which the base is connected is connected to the power supply line 2 via the reference voltage generation circuit 40, and the other end of the resistor R50 is connected to the power supply line 3.
The reference voltage generation circuit 40 is a circuit that generates a voltage lower than this line by using the power line 2 as a reference, and is a series circuit of diodes 41, 42, and 43 connected to the power line 2 and inserted in the forward direction. The cathode side of the diode 43 is connected to the base of the transistor Q50 via a resistor R51. A resistor R50 is provided between the base and emitter of the transistor Q50, and the voltage between both terminals of the resistor R50 is substantially when the voltage difference between the power supply line 2 and the power supply line 3 is substantially 3V. Is set to 1 Vf (≈0.7) or in the vicinity thereof, and the transistor Q50 is turned from ON to OFF or from OFF to ON. As such, the resistance values of the resistors R51 and R50 are selected. Therefore, when the voltage of the power supply line 3 is 3 V or less with respect to the voltage of the power supply line 2, the transistor Q50 is OFF.
Further, the reference voltage generation circuit 40 sets the voltage on the cathode side of the diode 42 with respect to the power supply line 2 to a potential that is reduced by 3 Vf (≈2.1 V). This voltage is output as a reference voltage signal G to other circuits described later.
Note that when the transistor Q50 is OFF, the transistor Q61 is also OFF, and the output of the amplifier 61 becomes a level equal to or lower than the triangular wave signal of the triangular wave generating circuit 64. At this time, the comparator 62 generates a HIGH level (hereinafter, “H”) output, and turns off the transistor Q62.
As a result, the power supply line 3 is held at a constant voltage that is 3V lower than the power supply line 2, and at this time, the operation of the switching regulation circuit 60 is stopped.
[0013]
The detection circuit 50 uses the power supply line 2 as a reference, and when the power supply line 3 exceeds 3 V and drops below that, the transistor Q50 is turned on, and the transistor Q50 generates a detection signal E corresponding to the difference. To do. The transistor Q61 generates a voltage obtained by amplifying it in accordance with the error voltage E as a divided voltage F on the collector side, and outputs it to the amplifier 61. Upon receiving this, the amplifier 61 generates an output signal P (comparison voltage value P) in the comparator 62.
As a result, the control voltage value generation circuit 65 receives the detection signal E from the detection circuit 50 and generates a comparison voltage value P for the comparator 62.
[0014]
More specifically, when the power supply line 3 drops below 3V and the transistor Q50 is turned on, a detection signal E (= error voltage) indicating a difference voltage exceeding 3V is generated, and a current corresponding thereto is generated. Applied to the base of transistor Q61. In response to the detection signal E from the detection circuit 50, the transistor Q61 is turned ON, and the voltage value between the potential of the power supply line 2 (+ Vcc) and the potential of the power supply line 3 is connected in series to the collector side of the transistor Q61. A divided voltage F is generated at a connection point N between the series-connected resistance circuits R62 and R63. However, the resistance value of the resistor R62 <the resistance value of the resistor R63. As a result, even if the voltage on the power supply line 3 side slightly decreases, the divided voltage F substantially becomes a voltage value determined by the internal impedance of the transistor Q61 at that time. That is, as the current value of the detection signal E increases, the divided voltage F increases.
The amplifier 61 receives this divided voltage F, amplifies the signal of the difference between this and the potential on the cathode side of the diode 42 (reference voltage signal G), and generates the comparison voltage value P. Then, this is outputted to the (−) input (reference terminal side) of the comparator 62.
The comparison voltage value P increases as the divided voltage F increases. Therefore, it increases as the current value of the detection signal E increases.
[0015]
The comparator 62 receives a triangular wave signal S having a constant frequency exceeding the audible frequency from the (+) input from the triangular wave generating circuit 63. Then, the voltage of the comparison voltage value P and the voltage of the signal S are compared, and when the voltage of the signal S exceeds the voltage of the comparison voltage value P, an “H” signal that turns off the PNP transistor Q62 is set as the drive pulse H. This drive pulse H is applied to the transistor Q62.
However, the triangular wave signal S here is based on the reference voltage signal G (the potential on the cathode side of the diode 42), and the reference voltage signal G and the signal S are combined before being input to the comparator 62. It is synthesized by the circuit 64.
As a result, the transistor Q62 is PWM-controlled according to the error voltage of the detection signal E from the transistor Q50. The error voltage of the detection signal E is generated according to the difference between the power supply line 2 and the power supply line 3. As a result, when the voltage of the power supply line 3 is greatly reduced, a large amount of power is supplied from the power supply line 2 to the power supply line 3, and when the voltage of the power supply line 3 is slightly reduced, the corresponding power is supplied from the power supply line 2 to the power supply line. 3 is supplied.
[0016]
When the voltage of the power supply line 3 becomes 3V lower than the power supply line 2, the transistor Q50 is turned off. When the detection signal E at this time is received from the detection circuit 50, the transistor Q61 is turned OFF, and when this is turned OFF, the difference between the voltage of the power supply line 3 and the voltage on the cathode side of the diode 42 (voltage of the reference voltage signal G), that is, A voltage signal that is about 0.7 V (≈1 Vf) lower than the terminal voltage of the resistor R50 is input to the amplifier 61. This is amplified by the amplifier 61 to generate a comparison voltage value P. At this time, the comparison voltage value P becomes a constant voltage value, and takes a value lower than the triangular wave signal level as described above. As a result, the output of the comparator 62 becomes “H”, and the transistor Q62 remains OFF.
Therefore, the voltage of the power supply line 3 is maintained at a constant voltage 3V lower than that of the power supply line 2, and during this time, power is supplied from the capacitor C of the smoothing circuit 70 to the power supply line 3.
[0017]
The smoothing circuit 70 is connected to the output of the transistor Q62 of the switching circuit 66 and smoothes the output power. This circuit includes a coil L70 inserted in series between the output of the transistor Q62 and the power supply line 3, and a capacitor C for storing power connected between the power supply line 3 and the ground GND.
Through this coil L70, the switched power is smoothed, and the smoothed power is sent to the power supply line 3 and stored in the capacitor C.
A flywheel diode D70 is connected between the input end of the coil L70 and the ground GND. The diode D70 forms a return path for the current flowing through the coil L70. Thereby, when the power supply line is cut off by the switching transistor Q62, the energy stored in the coil L70 is supplied to the amplifier 3 side as an inertial current and returns to the coil L70.
[0018]
As a result, when the output stage current sources 5G and 5B operate and power is supplied to the EL elements 6G and 6B, the charge of the power capacitor C is discharged and the voltage of the capacitor C decreases, the voltage of the power supply line 3 decreases. The voltage drops to over 3 V with respect to the power line 2. At this time, the transistor Q50 of the detection circuit 50 is turned on, the switching regulation circuit 60 operates to supply power to the power supply line 3, the power capacitor C is charged, and the output stage current sources 5G and 5B are charged. Power is supplied. When the voltage of the power capacitor C rises and the difference between the potential of the power supply line 3 and the potential of the power supply line 2 becomes 3V, the transistor Q50 of the detection circuit 50 is turned off, and the output of the comparator 62 becomes “H”. Thus, the transistor Q62 remains OFF, and the operation of the switching regulation circuit 60 is stopped.
In this way, the voltage of the power supply line 3 is stabilized at 9V, which is 3V lower than the power supply line 2.
[0019]
By the way, in the active matrix organic EL panel, since the drive current value is small, the output itself of the preceding stage D / A conversion circuit for driving the output stage current sources 5R, 5G, 5B can be used as the drive current. In this case, the D / A conversion circuit becomes an output stage current source. Therefore, the output stage current source of the present invention includes such a D / A conversion circuit used as an output stage.
[0020]
As described above, the switching regulation circuit 60 according to the embodiment is a PWM-controlled switching regulator. However, the present invention can be operated in accordance with the detection signal E and the switching control is performed so as to stop the operation. Any control circuit may be used. For example, a switching regulator that turns ON / OFF at a characteristic frequency may be used. In the case where the switching transistor Q62 is turned on / off at the characteristic frequency, a ring oscillator can be used.
In the embodiment, power is supplied to G and B through the same power supply line 3, but power may be supplied individually by providing a power supply line for each of G and B. In this case, a switching regulation circuit may be provided for supplying power to each power supply line.
Further, in the embodiment, R is a power supply line having a high voltage and G and B are power supply lines having a lower voltage. This is because the EL element of R has lower luminous efficiency than other EL elements. is there. In the present invention, the voltage of the power supply line is determined by the light emission efficiency of the EL element, and the power supply line is not necessarily a voltage having a high R.
In the embodiment, the bipolar transistor is mainly used. However, the MOSFET transistor may be mainly used. Further, the npn type transistor (or N channel type) in the embodiment can be replaced with a pnp type (or P channel type) transistor, and the npn type transistor can be replaced with an N channel (or P channel type) transistor. In this case, the power supply voltage is negative, and the transistor provided upstream is provided downstream.
[0021]
【The invention's effect】
As described above, in the present invention, the first power supply line having a higher voltage and the second power supply line having a lower voltage are provided in accordance with the light emission efficiency of the R, G, and B EL elements. Thus, the current sources for driving the EL elements are operated with different voltages. The power to the second power supply line of the EL element with high light emission efficiency is supplied through the switching regulator from the first power supply line of the EL element with low light emission efficiency, and the second power supply line is supplied by the switching regulator. The voltage is stabilized to a predetermined voltage. Since this switching regulator only needs to operate at a voltage difference between the first power supply line and the second power supply line, power consumption can be reduced accordingly.
As a result, the power consumption of the organic EL display device can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram centering on a power supply circuit of a column driver of an organic EL panel according to an embodiment to which an organic EL driving circuit of the present invention is applied.
FIG. 2 is a characteristic graph showing the relationship between luminance and applied voltage in R, G, and B EL elements.
FIG. 3 is a characteristic graph showing the relationship between the luminance of the element and the drive current density.
[Explanation of symbols]
1 ... DC / DC converter,
2, 3 ... Power line,
4 ... Supply power control circuit,
5G, 5R, 5B ... output stage current source,
6G, 6R, 6B ... organic EL elements,
7: Low side scanning circuit, 8 ... Terminal pin,
4 ... Supply power control circuit, 40 ... Reference voltage generation circuit,
41, 42, 43 ... diodes,
50. Detection circuit,
60 ... switching regulation circuit, 65 ... control voltage value generation circuit,
61 ... Amplifier, 62 ... Comparator, 63 ... Triangle wave generating circuit,
66 ... switching circuit, 70 ... smoothing circuit,
Q50, Q61, Q62 ... transistors.

Claims (6)

In an organic EL driving circuit that drives the organic EL element through a terminal pin provided corresponding to each of the organic EL elements of display colors R, G, and B of the organic EL panel,
A current source provided corresponding to the display colors of R, G, B for driving the organic EL element through the terminal pin;
A first power supply line having a predetermined voltage for supplying power to the current source corresponding to the organic EL element having a display color with low luminous efficiency among R, G, and B;
A second power supply line lower than the predetermined voltage for supplying power to the current source corresponding to the organic EL element of the remaining display color of R, G, B;
A switching regulator that receives power from the first power supply line and supplies power to the second power supply line to stabilize the voltage of the second power supply line at a constant voltage lower than the predetermined voltage. Organic EL drive circuit. And a detection circuit that generates a detection signal according to a potential difference between the first power supply line and the second power supply line, the first power supply line corresponding to the display color of R. The power is supplied to the current source, the second power supply line supplies power to the current source corresponding to the display color of G or the display color of B, and the switching regulator is 2. The organic EL drive circuit according to claim 1, wherein the organic EL drive circuit operates or stops operating in accordance with a detection signal of the detection circuit. The second power supply line supplies power to each of the current sources corresponding to the G display color and the B display color, and the switching regulator responds to a detection signal of the detection circuit. The organic EL drive circuit according to claim 2, which is a circuit that performs PWM switching control. In an organic EL display device having an organic EL drive circuit that current-drives the organic EL element through a terminal pin provided corresponding to each of the organic EL elements of the display colors R, G, and B of the organic EL panel,
A current source provided corresponding to the display colors of R, G, B for driving the organic EL element through the terminal pin;
A first power supply line having a predetermined voltage for supplying power to the current source corresponding to the organic EL element having a display color with low luminous efficiency among R, G, and B;
A second power supply line lower than the predetermined voltage for supplying power to the current source corresponding to the organic EL element of the remaining display color of R, G, B;
A switching regulator that receives power from the first power supply line and supplies power to the second power supply line to stabilize the voltage of the second power supply line at a constant voltage lower than the predetermined voltage. Organic EL display device. And a detection circuit that generates a detection signal according to a potential difference between the first power supply line and the second power supply line, the first power supply line corresponding to the display color of R. The power is supplied to the current source, the second power supply line supplies power to the current source corresponding to the display color of G or the display color of B, and the switching regulator is 5. The organic EL display device according to claim 4, wherein the organic EL display device operates or stops in response to a detection signal of the detection circuit. The second power supply line supplies power to each of the current sources corresponding to the G display color and the B display color, and the switching regulator responds to a detection signal of the detection circuit. 6. The organic EL display device according to claim 5, which is a circuit that performs PWM switching control.

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