JPS60147790A - El driving method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Application Fields □ This invention relates to a method for driving an EL display panel, particularly a matrix type 11J, E! , relates to a pulse drive method for an element. .

Problems to be Solved by the Prior Art and the Invention In general, pearlless driving of thin-film PL elements involves applying a single pulse of about 200 volts (V) to the EL element to charge the EL element and emit light, and then charging the EL element to emit light. The power consumption is the sum of the power required to cause the EL element to emit light with the required brightness (charging energy) and the power required for the light emitting current (light emitting energy). Here, the ratio (%) of charging energy and luminous energy that power consumption accounts for
Although it varies depending on the EL drive frequency and brightness, the charging energy is generally about 80%.

By the way, the driving voltage of the thin film EL*-F is quite high at around 200 (V), so the power consumption is much higher than that of the liquid crystal display.
This was quite a big deal compared to the distributed EL elements that are often used as clients. However, the iM type EL element is superior in terms of light and brightness. Recently, there has been a desire for long-life, high-performance thin-film EL elements to be used in the backlights of liquid crystal displays, and some of them are being put into practice, but as mentioned above, they consume a lot of power and are Reducing power consumption was a major issue.

C.1 Means for Solving Problems The present invention aims to provide a new method for driving an EL element with low power consumption. According to the present invention, a capacitor is connected to both electrodes of the EL single element, and when the charged charge of the EL single element that is charged and emitted by one pulse application is discharged, a part of this charge is collected by the capacitor, and when the next one pulse is applied, the An EL drive system is disclosed in which recovered charging energy is supplied as part of a predetermined charging energy to a single EL element. According to this method, the power consumption of a single EL element is recovered by the capacitor, and it is possible to save by the amount of charging energy supplied to the single EL element during the next EL drive.

Embodiment FIG. 1 shows the basic implementation circuit of the present invention.
L single elements (2a) and (2b) are electrodes of EL single element 1),
(3a) and (3b) are capacitors in which electrodes (2a) and (2b) are connected. (4a) and (4b) are EL
EL single element 1 on both electrodes (2a) and (2b) of single element 1)
), (5a), (5b
) is a drive circuit for the switching elements (4a) and (4b), and the electrodes (2a) and (2b) are in the application state of the drive voltage VEL, the open floating state, and the grounded state of 0 (V) set to the ground potential. Switch to three states. (6a
), (6b) are switching elements that selectively ground the open ends of each capacitor (3a), (3b), (7a),
(7b) is a drive circuit that switches the switching elements (6a) and (6b).

Now EL single element 1) and both capacitors (3a), (3b)
(7) The first one with the same capacity and VEL-200 (V)
The basic operation of the circuit shown in the figure will be explained from (a) to (d) in FIG. 2. First, as shown in Figure 2 (a), both capacitors (
3a), (3b) in open (floating) state,
One electrode (2b) of the EL single element 1) is grounded at 0 (V), and the other electrode (2a) is applied with a driving voltage of 200 (V).
) is applied to cause the EL single element 1) to emit light. Next, as shown in Fig. 2 (b), open the electrode (2a) (float?') and open one capacitor (3a).
Make the open end of the terminal O(V) grounded. Then, the capacitor (3a) becomes 100 (
V), and part of the charge is recovered. Then the second
As shown in (c) of the figure, the capacitor (3, a) is returned to the open state, the electrode (2a) is grounded, and the EL single element 1
) to 0 (v). In this state, when the next pulse of the same polarity is applied immediately before 9 and the electrode (2a) is opened and the capacitor (3a) is grounded as shown in (d) of Figure 2, the charge in the capacitor (3a) is reduced to EL. Element 1)
It becomes 50 (V) after being supplied to.

After this charge is supplied, VEL is applied as shown in (a) of Figure 2, but in this second time, the EL single element 1) is already at 50 (V).
It can be seen that the remaining 150 (V) is sufficient as the replenishment charge necessary for light emission, and that 50 (V) of pre-charging energy can be saved. Thereafter, the above operation is repeated.

Here, the capacitance of the EL single element (1) is C0% both capacitors (
The capacity of 3a) and (3b) is A times that of Co.

The voltage between the capacitor terminals due to the recovered charge in (3b) is Vd
, from capacitors (3a) and (3b), EL single element 1)
Assuming that the voltage between the terminals of the EL element for the nth time when charge is supplied to is v2n, the operation of the circuit in Figure 1 after the nth time is as follows.
This is done by repeating steps (a) to (c) in the figure, and at this time,
The light emission pulse waveform is expressed as shown in FIG. '4. That is,
(A) in Figure 3 is the nth state of (D) in Figure 2, and the voltage across the terminals of the EL single element 1) is the capacitor (3a).
The charge □ supply i becomes Vpn. In this state, as shown in Figure 3 (b), when capacitor (3a) is opened and VIAL is applied to the electrode (2a), the EL single element 1) is charged only by the charging energy of VIAL-Vpn. □The electrode (2) lights up and shows the charging energy of Vpn
Open a) and ground the capacitor (3a) to E.
'A part of the charge charged in the L element (1) is recovered by the capacitor (
, %a), and then, as shown in FIG. 3(d), the capacitor (3a) is opened and the electrode (2a) is grounded. The light emission pulse waveform during this period is shown at PI in FIG.

Next, operations using pulses of opposite polarity from (d) in FIG. ff13 are performed in the steps shown in (e) to (h) in FIG. This reverse polarity pulse drive is performed on the other capacitor (3b) side in the same manner as described above, and the light emission pulse waveform at this time is P in Fig. 4.
Shown in 2. Then, the process returns from (H) in FIG. 3 to (B) in FIG. 3, and the above-mentioned operations are repeated.

In the above pulse drive, the n-th inter-terminal voltage Vpn of the PL element (1) is calculated from the following equation.

=-1-go Vpn+i stone-Vl! L (A+1) ... (1) Bn, t+ =Vp (n↑+) -Vpn ... (2
), where B o −Vp+ −Vpo= −m−1(,′, V
PO=O)(A+1) From equation (2), n-■ From equation (3), the actual EL drive frequency is 5082 or more, so Vpn can be instantaneously determined as shown in equation (4). Also Vp
n increases the capacitance of capacitors (3a) and (3b) (
The larger A), the larger the amount of power consumption (charging energy) that can be saved. Specifically, Vpn
The upper limit of is 'AVEL, and when this upper limit is set, the power consumption W is as follows, which shows that the power consumption can be reduced by about 25%.

Next, another example of an implementation circuit of the present invention will be explained with reference to FIG. This figure 5 shows both electrodes (2a) and (2b) of EL element 7 (1).
), a plurality of m capacitors (3al) to (3a
m), (3bl) ~ (3b+*) are connected,
When supplying charge to the ELa element (1), use a capacitor (
3al) to (3am) or (3bl) to (3bs
), and conversely, the charge recovery of the IEL element (1) is performed from the capacitor (3as+) to (3al) or (3ha
4 sequential lines from +') to (3bl). In this way, even lower power consumption can be achieved. For example, each capacitor (2al) ~ (2am), (2bl) ~ (2b
m) capacity as 100Co (A = 100),
Above, charge energy for m when driven in the above sequence -
When the savings rate (%) was determined, the results shown in the graph of FIG. 6 were obtained. In other words, it is possible to save about 25% in mml, about 409≦strong when m=2, and about 90% when m-20.

Theoretically, if m = bell, charging energy can be reduced by 100%, but in reality, m = about 20, and the total EL power consumption at this level is about 50 to 70% even if the luminous energy cannot be reduced. It was found that savings could be achieved.

E1 Effects of the Invention As described above, the present invention makes it possible to reduce power consumption, and in particular, Will! 50 in EL display panel
Power consumption can be reduced by ~70%, Wf, l5IE
It is possible to expand the use of L elements, for example, to make them effective as backlights for liquid crystals.

[Brief explanation of the drawing]

Fig. 1 is a basic implementation circuit diagram of the effect method of the present invention, Fig. 2 (a) to (d) are circuit diagrams showing the basic operation of the circuit in Fig. A) to (H) are circuit diagrams showing the n-th and subsequent operations of the circuit in FIG. 1, FIG. 4 is a light emission pulse waveform diagram in the operation in FIG. 3, and FIG. Another implementation circuit diagram, FIG. 6, is a graph showing the relationship between the number of capacitors (m>) and the charging energy saving rate (%) in the circuit of FIG. 5. (1) - E L element - (2a), (2b ) −electrode, (
3a), (3b), (3al) ” (3am), (3
bl) ~ (3bm) - capacitor.

Claims (1)

[Claims] , (l) A capacitor is connected to the terminal of the EL element, and the EL element is heated for one hour by applying a pulse to emit light. When the charged charge is discharged, a part of this charge is collected and stored in the capacitor, and the next pulse is generated. An EL driving method characterized in that the energy accumulated in the capacitor is applied to the EL element as part of the charging power required for its light emission.