JPS6091594A - Circuit for firing el - Google Patents

Abstract

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

Description

TECHNICAL FIELD The present invention relates to a KL lighting circuit, and more particularly to a KL lighting circuit that has little difference in brightness between the beginning and end of its life.

Background Art There are various types of ML such as inorganic type (enamel type), organic type (plastic type or dispersion type), and thin film type, but basically the entire light emitting layer is placed between a pair of opposing electrodes, at least one of which is transparent. It has a clamping structure, and the counter electrode is generally connected to an alternating current power source for lighting. however,
As the lighting time elapses, the phosphor that makes up the entire light-emitting layer deteriorates, resulting in a decrease in brightness, which causes inconvenient noise in various applications.

Therefore, as shown in Japanese Patent Publication No. 33-10096, for example, it has been considered to detect the brightness using a photoelectric conversion device M and feed back the detection output to change the frequency to make the brightness completely constant. However, the disadvantage is that the equipment is extremely expensive.

DISCLOSURE OF THE INVENTION [Objective] Therefore, the entire purpose of the present invention is to provide an inexpensive IcL lighting circuit that exhibits as little luminance change as possible during its life.

〔composition〕

To summarize, the present invention is configured such that the EL is turned on by supplying all of the AC voltage of a constant frequency to the EL through all resistors, and the brightness of the EL at the initial stage of lighting is all Bo.

The present invention is characterized in that when the brightness at the end of the life is the total Bt, the resistance value of the resistor is set so that Bo-Bt becomes the minimum.

〔effect〕

In other words, it was found that the luminance deterioration of EL is mainly due to the deterioration of the phosphor that makes up the entire light emitting layer, and that the capacitance between the opposing electrodes decreases as the phosphor deteriorates. . For this reason, when a resistor is connected in series with the EL, the time constant of charging and discharging changes as the capacitance decreases, so by setting the resistance value of the resistor appropriately, the KL at the end of the lifespan is lower than that at the beginning of lighting. By increasing the total applied voltage, it is possible to compensate for the decrease in brightness due to life by increasing the brightness due to an increase in the total applied voltage, and it is possible to reduce the change in brightness of the EL between the initial stage of lighting and the end of life.

Embodiments of the present invention will be described below with reference to all drawings.

FIG. 1 shows a complete circuit diagram of an EL lighting circuit according to an embodiment of the present invention. In the figure, 1 is +V. 0 positive voltage terminal, 2 -
The negative voltage terminal 3.4 of Voo is connected in series between the positive voltage terminal 1 and the negative voltage terminal 2. The NPN transistors 1 and 5 as an example of the second switching element are the first and second switching elements. In the drive circuit for the second transistors 3 and 4, the illustrated example includes a third NPN transistor 6 whose flipter is connected to the base of the first transistor 3 and whose emitter is connected to the negative voltage terminal 2, a resistor 7 connected between the voltage terminal l and the base of the first transistor 30;
a resistor 8 connected to the base of the second transistor 4;
and an input signal terminal 9 to which the other end of this resistor 8 is connected,
It consists of a resistor lO connected between the base of the third transistor 6 and the input signal terminal 9. Said 1st. KL12 is connected between the connection point of the second transistors 3 and 4 and the ground via a resistor 11').

The resistance value r of this resistor 11 is set according to the luminance and capacitance of the EL 12, as will be described later.

In the above configuration, when a constant frequency pulse voltage IE 13' (r is applied to the input signal terminal 9, the pulse voltage 13 becomes L
In the case of L/H, no bias voltage is applied between the base and emitter of the second transistor 4, and this transistor 4 is turned off. Further, no bias voltage is applied between the base and emitter of the third transistor 6, and this transistor 6 is also turned off.

On the other hand, when the second transistor 6 is turned off, a predetermined bias voltage is applied between the base and emitter of the first transistor 3, and this transistor 3 is turned on. Therefore, a positive current 1 flows through the EL 12 through the path of the positive voltage terminal 1 - the first transistor 3 - the resistor 11 - 11: L12, and the EL 12 lights up. This FiL12
K L12 is charged to the polarity shown while it is lit.

Further, the pulse voltage 13 applied to the input signal terminal 9 is H
When the level is reached, the first transistor 3 is turned off and the second transistor 4 is turned on, contrary to the above. As a result, the reverse current 11 flows through the path KL12--resistor 115--second transistor 4, and KL lights up.

Therefore, the pulse voltage 1 applied to the input signal terminal 9
Depending on the level of 1. second transistor 3.4
Since one of them is on and the other is off, they are in mutually different operating states and are alternately inverted, so a high frequency current flows through 11iL12 and InL12 lights up.

By the way, as described above, the phosphor in the light emitting layer of the 1CL12 gradually deteriorates as the lighting time elapses, the brightness decreases, and the capacitance between the opposing electrodes decreases. Therefore, if the capacitance at the beginning of lighting is Co, the total capacitance at the end of the life is 0t((Oo), and the resistance value of the resistor 11 is R, then the charging time constant to at the beginning of lighting of KL12 is t(, -0oR Therefore, the charging time constant t at the end of life is t
-OtR. In other words, 0t(Oo, so to
It becomes a lot. Therefore, the voltage applied to EL12 at the end of its life is +■. 0 or -V. If the resistance value R'ft of the resistor 11 is set to 0, the applied voltage 1±v16- of the EL 12 at the initial stage of lighting will naturally become smaller than the applied voltage 1±vaa+ at the end of the life.

Therefore, in the early stage of lighting when the phosphor does not deteriorate and emits light at high brightness, the applied voltage of EL12 is relatively small, and at the end of the life when the luminescent layer emits low brightness due to deterioration of the phosphor, the applied voltage of KL12 becomes relatively large, and the change in brightness of EL 12 is suppressed to a small level during its life.

Figure 2 shows the applied voltage waveform diagram of EL12 at the initial stage of lighting L1
FIG. 3 shows the entire applied voltage waveform diagram of EL12 at the end of its life.

It is a diagram.

FIGS. 2 and 3 are applied voltage waveform diagrams at the initial stage of KL lighting and at the end of its life.

11...Resistance, 12...KL.

dA'J-

Claims (1)

[Claims] A full alternating current voltage of a constant frequency is supplied to KL through a resistor to light it, and the brightness of the EL at the initial stage of lighting is set to BO. A KL lighting circuit characterized in that the resistance value R of the resistor is set so that BO-Bt is the minimum when the brightness at the end of the life is Bt.