JPS63218191A - Driving circuit of electroluminescence device - 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] [Field of Industrial Application] The present invention relates to a drive circuit for obtaining an initial luminance brightness for an electroluminescent device over a long period of time, and in particular, it relates to a drive circuit that has small frequency fluctuations and low energy loss. The present invention relates to an improvement of a drive circuit with a small amount of noise.

[Conventional technology]

Conventionally, in order to drive an electroluminescent element, four
0011z, it is common to supply alternating current of about 120 V using a triad combination type oscillation circuit.

FIG. 3 is a circuit diagram showing an example of the conventional drive circuit described above. In the figure, I is a transformer, and the -th winding 2. It has a secondary winding 3 and a feedback winding 4. - The main transistor 5 is connected to the secondary winding 2.

The base of the main transistor 5 is connected to the feedback winding 4 of the transformer 1 via resistors 6, 7 and a capacitor 8. A capacitor 9 is interposed between the base of the main transistor 5 and the primary winding 2. Note that an electroluminescent element 10 is connected to the secondary winding 3.

As described above, a positive feedback loop is constructed, and the negative side becomes an oscillation circuit, so that the alternating current voltage generated in the negative winding 2 is boosted by the secondary winding 3 to drive the electroluminescent element 10. Note that in this case, in order to adjust the brightness of the electroluminescent element 10, the transistor 31.
Zener diode 32. A stabilized power supply 34 consisting of a variable resistor 33 and other elements is connected to the input side. By changing the output voltage of the stabilized power source 34 via the variable resistor 33, the brightness of the electroluminescent element 10 is adjusted.

[Problem that the invention seeks to solve]

However, in the conventional electroluminescent element drive circuit described above, the inductance of the secondary winding 3 of the transformer 1 and the electroluminescent element 1 connected to the secondary winding 3 are
It oscillates at a resonant frequency determined by the capacitance of 0, and the frequency at which the electroluminescent element IO should be driven changes significantly as the characteristics of the electroluminescent element 10 change over time. The electric signal applied to the base of the main transistor 5 is also affected by the resonant circuit determined by the LC on the secondary side of the transformer 1.

Since the waveform is not a rectangular wave but close to a sine waveform, the main transistor 5 may perform an incomplete switching operation, resulting in large energy loss. Furthermore, as is clear from FIG. 3, since the electrical signal is obtained from the feedback winding 4, there is a problem that the winding of the transformer 1 becomes complicated and the work of winding the first winding becomes complicated. . Furthermore, since the stabilized power supply 34 is connected to the input side for adjusting the brightness of the electroluminescent element IO, there is also the problem that the power consumption is increased and the efficiency is significantly reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems existing in the above-mentioned prior art and to provide a drive circuit for an electroluminescent element with small frequency fluctuations and low energy loss.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the present invention has been made.

In a circuit that uses a transformer and a main switching element that is turned ON and OFF to convert DC input into AC to drive an electroluminescent element, a frequency is set in a positive feedback loop that applies positive feedback to the main switching element. A determining element and another switching element are used, and a current detecting element is connected in series with the electroluminescent element, and the current flowing through the luminescent element is detected via the electromotive force generated in the current detecting element. Controls the ON'M period of the main switching element. This technical method was adopted.

That is, as shown in FIG. 1 as a diagram explaining the principle, a current detection element such as a resistor 25 is connected in series with the electroluminescent element 10, and the electromotive force generated in the resistor 25 is used to detect the electroluminescent element. The feedback circuit 26 controls the ON period of a main switching element (not shown), which is a component of the DC/AC conversion circuit 27, by detecting the current flowing through the DC/AC conversion circuit 27.

[Effect]

With the above configuration, by interposing another switching element in the positive feedback loop configured on the primary side of the transformer,
It has the effect of amplifying the drive voltage of the main switching element and reducing energy loss generated in the main switching element. Further, by inserting a frequency determining element into the positive feedback loop, it is possible to control the two-oscillation frequency fluctuation. On the other hand, since the brightness of an electroluminescence-insensitive element is determined by the magnitude of its current, it is possible to maintain a constant brightness over a long period of time by detecting and controlling this current.

〔Example〕

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

Identical parts are designated by the same reference numerals as in FIG. 3 above.

In the figure, 11 is the main transistor, and the transformer 1
The 0th order 12 connected in series with the primary winding 2 and connected to the input DC power supply is another transistor, which is formed to be complementary to the main transistor 11.

A resistor 13 and a capacitor 14 are connected in series between the base and the secondary winding 2.

The emitter of the transistor 12 is connected to one end of the DC input power supply via a resistor 15, the collector of the transistor 12 is connected to the base of the main transistor 11, and a capacitor 1 is connected between the base and collector of the transistor 12.
6, and a resistor 17 is connected between the base and the other end of the DC input power source. Next, the base of the transistor 12 is connected to the collector of a control transistor 24. On the other hand, the emitter of the transistor 24 is connected to the DC input power supply, and the emitter of the transistor 24 is connected to the DC input power source.
The output sides of the resistor 18 for detecting the tt load current, the diode 20 for rectification, the resistors 21, 22 and the capacitors 19, 23 for the smoothing circuit are connected to the base of the transistor. Note that the primary winding 2 and secondary winding vA3 of the transformer 1 are connected in series.

With the above configuration, the alternating current voltage generated in the primary winding 2 by the switching action of the main transistor 11 is superimposed on the alternating current voltage generated in the secondary winding 3 and is applied to the electroluminescent element 10.

On the other hand, the alternating current voltage generated in the primary winding 2 is applied to the base of a transistor 12 formed complementary to the main transistor 11 via a high-pass circuit constituted by a resistor 13 and a capacitor 14. This AC voltage is amplified by the transistor 12 and applied to the base of the main transistor 11 in the form of a rectangular wave. In this case, the resistor 15 is
It acts to limit the maximum value of the base current of the main transistor 11. On the other hand, the resistor 17 is connected to the transistor 12.
is the bias resistance. Further, the capacitor 16 becomes a negative feedback capacitance of the transistor 12, and if considered including the resistor 13, a low-pass circuit is formed.

In other words, a frequency determining element is provided. Here, when the current flowing through the electroluminescent element 10 increases,
The electromotive force generated in the resistor 18 increases.

Turn on the control transistor 24 connected to its output side
act in the direction of Therefore, it is the main switching element. Since the ON period of the main transistor 11 is reduced,
It acts to reduce the current flowing through the electroluminescent element 10 and keeps the current flowing through the electroluminescent element 10 constant. As described above, sufficient base current is supplied to the main transistor 11, so the ON loss in the main transistor 11 is reduced, and there is no loss in the stabilized power supply required in the conventional one. Since the current flowing through the electroluminescent element IO can be controlled, energy efficiency is increased.

Furthermore, since the high-frequency and low-frequency pass circuits are interposed in the feedback loop constructed on the primary side of the transformer l, it can be expected that fluctuations in the single oscillation frequency will be extremely small.

In this embodiment, an example is shown in which a resistor and a capacitor each having a fixed value are used as one frequency determining element, but if at least one or more of them is made variable, it is possible to drive the electroluminescent element. The frequency can be made variable. In this case, fine adjustment of the brightness or color tone of the electroluminescent element is possible. Further, although an example has been shown in which a resistor is used as a current detection element of an electroluminescent element for controlling the ON period of the main switching element, the same effect can be obtained even if a current detection element other than a resistor is used.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
It is possible to control the fluctuation of the oscillation frequency due to aging of electroluminescent elements, which has been a problem in the past, and to ensure switching operation, which reduces energy loss and enables highly efficient driving, and to use a stabilized power supply. This has the effect that the brightness of the electroluminescent element can be efficiently adjusted without any problems.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing the principle of the present invention. FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional one. 1: transformer, S, tt: main transistor, 10: electroluminescent element, 12, 24:) transistor, 13,
15, 18, 21.22: Resistance. 14.16.19=Capacitor.

Claims (5)

[Claims] (1) In a circuit that uses a transformer and a main switching element that is turned ON and OFF to convert DC input into AC to drive an electroluminescence element, a positive feedback loop that applies positive feedback to the main switching element. A frequency determining element and another switching element are used in the switching element, and a current detecting element is connected in series with the electroluminescent element, and the current flowing through the luminescent element is detected via the electromotive force generated in the current detecting element. 1. A driving circuit for an electroluminescent element, characterized in that the ON period of the main switching element is controlled by: (2) The driving circuit for an electroluminescent element according to claim 1, wherein the frequency determining element comprises at least one set of a resistor and a capacitor. (3) The driving circuit for an electroluminescent element according to claim 2, wherein the resistor or the capacitor is variable. (4) A drive circuit for an electroluminescent device according to any one of claims 1 to 3, wherein the main switching element and the other switching elements are complementary. (5) The driving circuit for an electroluminescent element according to any one of claims 1 to 4, wherein the switching element is a transistor.