JPH0550700U - EL drive circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress the change in the light emission luminance after startup so that the life of the EL display element is not shortened. In an EL drive circuit including an inverter circuit 13 driven by a power supply circuit 11 and an EL display element 14 connected to the inverter circuit, a DC-DC connected in series between the power supply circuit and the inverter circuit. The converter circuit 12 and the current detection circuit 15 for detecting the current flowing through the EL display element and feeding back the detection signal to the DC-DC converter circuit are included, and the current flowing through the EL display element is selected in advance. The EL drive circuit is configured so as not to exceed the predetermined value.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an EL drive circuit for lighting an EL display element by an inverter circuit.

[0002]

[Prior Art]

 Conventionally, such an EL drive circuit is configured as shown in FIG. 4, for example. That is, in FIG. 4, the EL drive circuit 1 includes a DC power supply circuit 2, an inverter circuit 3 that is drive-controlled by the DC power supply circuit 2, and an EL display element 4 connected to the inverter circuit 3. When the inverter circuit 3 supplies a drive voltage to the EL display element 4 on the basis of the drive voltage from the DC power supply circuit 2, the EL display element 4 emits light and can perform lighting display. It has become.

[0003]

[Problems to be solved by the device]

 However, in the EL drive circuit 1 configured in this way, there is a problem that the individual products have a difference when displayed and sold at the store due to the temporal change of the brightness as shown in FIG. there were.

In view of the above points, the present invention provides an EL drive circuit that suppresses a change in brightness during a certain period after startup, and at the same time, extends the life of an EL display element. It is intended for that.

[0005]

[Means for Solving the Problems]

 To achieve the above object, the present invention provides an EL drive circuit including a power supply circuit, an inverter circuit driven by the power supply circuit, and an EL display element connected to the inverter circuit. And a DC-DC converter circuit connected in series between the inverter circuit and a current detection circuit for detecting a current flowing in the EL display element and feeding back a detection signal to the DC-DC converter circuit. The EL display element is configured so that the current flowing through the EL display element does not exceed a predetermined value selected in advance.

[0006]

[Action]

 According to the above configuration, the drive voltage supplied from the power supply circuit is supplied to the inverter circuit via the DC-DC converter circuit, and the inverter circuit drives the EL display element based on the drive voltage to emit light. By doing so, a predetermined lighting display can be performed, and the drive current of the EL display element is detected by the current detection circuit, and the detection signal is fed back to the DC-DC converter circuit, whereby the DC -The DC converter circuit controls the input voltage based on the driving current value of the EL display element at that time so as to keep the drive current value at a predetermined current value or less, so that it is supplied to the EL display element. The drive current never exceeds a specified value. At this time, by setting the drive current of the EL display element to a small value in advance, the drive current of the EL display element can be stabilized until the output voltage of the DC-DC converter circuit becomes maximum, and thus the EL display element The change in brightness can be suppressed.

[0007]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 shows an embodiment of an EL drive circuit according to the present invention. The EL drive circuit 10 includes a DC-DC converter circuit 12 to which a drive voltage is supplied from a DC power supply circuit 11, and this DC-DC converter. An inverter circuit 13 driven and controlled by the circuit 12, an EL display element 14 connected to the inverter circuit 13, and a current flowing through the EL display element 14 are detected to output a detection signal to the DC-DC converter. A current detector 15 for feedback to the input circuit 12.

The EL drive circuit 10 according to the present invention is configured as described above, the drive voltage supplied from the power supply circuit 11 is controlled by the DC-DC converter circuit 12, and the output of the DC-DC converter circuit 12 is controlled. The inverter circuit 13 drives the EL display element 14 based on the voltage. At that time, a drive current flows through the EL display element 14, the drive current is detected by the current detector 15, and the detection signal is fed back to the DC-DC converter circuit 12. As a result, the DC-DC converter circuit 12 compares the detection signal with a predetermined value selected in advance, and controls the drive voltage from the power supply circuit 11 so that the drive current is kept below the predetermined value. To do.

Thus, the drive current of the EL display element 14 can be kept below a predetermined current value. As a result, as shown in FIG. 2, the emission brightness of the EL display element 14 can be stabilized for a certain period after activation.

FIG. 3 is a circuit diagram showing a specific configuration of the EL drive circuit 10 according to the present invention. The DC-DC converter circuit 12 is connected in series to the power supply line from the power supply circuit 11 to the inverter circuit 13. The inverter circuit 13 has a well-known configuration including a controlled transistor 21 and a control IC 22 such as a shunt regulator connected to the base of the transistor 21, and the input of the inverter circuit 13 is a single turn output via the transistor 23. It has a known structure connected to the primary terminal of the transformer 24. The current detector 15 includes a resistor 25 for current detection, which is connected in series to the negative output terminal of the inverter circuit 13, and a control IC 22 of the DC-DC converter circuit 12 from the output side of the resistor 25. It is composed of a rectifying diode 26 and a resistor 27 which are connected in series to a feedback line to the control input terminal.

According to such a configuration, the voltage generated across the resistor 25 based on the drive current flowing through the EL display element 14 is applied to the DC-DC converter circuit 12 via the diode 26 and the resistor 27 in the feedback line. It is input to the control input terminal of the control IC 22. As a result, the control IC 22 drives and controls the transistor 21 based on the signal input to the control input terminal so that the drive current of the EL display element 14 is maintained at a predetermined value or less.

[0012]

[Effect of the device]

 As described above, according to the present invention, the drive voltage supplied from the power supply circuit is supplied to the inverter circuit via the DC-DC converter circuit, and the inverter circuit displays the EL display based on the drive voltage. A predetermined lighting display is performed by driving the element to emit light. Further, the drive current of the EL display element is detected by the current detection circuit, and the detection signal is fed back to the DC-DC converter circuit, so that the DC-DC converter circuit drives the EL display element at that time. Based on the current value, the output voltage is controlled so that the drive current value is maintained below a predetermined current value. Therefore, the drive current supplied to the EL display element does not exceed a predetermined value and is maintained at a predetermined value or less, so that the drive current flowing through the EL display element is stable for a certain period after startup. The emission brightness of the EL display element is also stable. Further, generally, the brightness of the EL display element changes with time as shown in FIG. 5, but according to the present invention, the life of the EL display element becomes longer because the brightness does not increase after activation. Thus, according to the present invention, there is provided an extremely excellent EL driving circuit in which the luminance change is suppressed for a certain period after starting and the life of the EL display element is not shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an EL drive circuit according to the present invention.

FIG. 2 is a graph showing a change with time of a drive current value by the EL drive circuit of FIG.

FIG. 3 is a circuit diagram showing a specific configuration example of an EL drive circuit according to the present invention.

FIG. 4 is a block diagram showing an example of a conventional EL drive circuit.

5 is a graph showing a change over time of a drive current value by the EL drive circuit of FIG.

[Explanation of symbols]

 10 EL Drive Circuit 11 DC Power Supply Circuit 12 DC-DC Converter Circuit 13 Inverter Circuit 14 EL Display Element 15 Current Detector 21 Transistor 22 Control IC 23 Transistor 24 Output Transformer 25 Current Detection Resistor 26 Diode 27 Resistor

Claims (1)

[Scope of utility model registration request] 1. An EL drive circuit comprising an inverter circuit driven by a power supply circuit and an EL display element connected to the inverter circuit, further comprising a serial connection between the power supply circuit and the inverter circuit. And a current detection circuit for detecting a current flowing through the EL display element and feeding back a detection signal to the DC-DC converter circuit, and a current flowing through the EL display element. However, the EL drive circuit is characterized in that it does not exceed a predetermined value selected in advance.