JPH0544155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a light emission drive circuit for an electroluminescent element (hereinafter referred to as an EL element) that emits light by applying a pulse voltage.

Conventional technology Conventionally, a light emitting drive circuit for an EL element that applies a pulse voltage to the EL element to emit light has been developed, for example, by
Various methods are known, such as Japanese Patent No. 52-45466.

The light emitting drive circuit disclosed in the above publication has two switch elements, transistors Tr ₁ , Tr ₂ and
The first and second switch circuits 1 and 2 in which Tr ₃ and Tr ₄ are connected in series are connected in parallel to the power supply E, and the EL element 3 is connected to the first and second switch circuits 1 and 2 in series.
2 two transistors Tr ₁ , Tr ₂ and Tr ₃ ,
Control means _{4 and} 5 are connected between the connection points A and B of Tr 4 and further apply pulse voltages to the transistors Tr ₁ , Tr ₂ and Tr ₃ , Tr ₄ at appropriate timing. The conduction timing of the four transistors Tr ₁ to Tr ₄ is controlled by
The voltage of the power source E is supplied to the EL element 3 in a pulsed manner in the opposite direction to cause it to emit light.

Problems to be Solved by the Invention The above-described light emitting drive circuit can apply the output voltage of the power source E to both ends of the EL element 3 in the forward and reverse directions, which is generally advantageous, but the high voltage Considering the use of a device that can be easily obtained, that is, the case where it is desired to perform so-called DC pulse drive in which voltage is applied only in one direction, the so-called AC pulse drive configuration in which the power supply voltage is applied in forward and reverse directions is as follows.
On the contrary, it may become a cause of increased cost and complexity of the device.

Also, transistors Tr ₁ , Tr ₂ and Tr ₃ , Tr ₄
Depending on the supply timing of the pulse voltages applied from the control means 4 and 5, the four transistors Tr ₁ to _{Tr 4} may become conductive at the same time and be destroyed.

The present invention has been made in consideration of the above-mentioned points, and is a light emitting device of an EL element with a simple configuration suitable for direct current pulse drive of the EL element, without the switch element being directly connected to the power source. The purpose is to provide a drive circuit.

Means for Solving the Problems The light emission driving circuit for an EL element according to the present invention includes a switch circuit formed by connecting in series a first switch element, a diode, and a second switch element connected to both ends of a power supply, and the above-mentioned switch circuit. The gate means of the first switch element is connected between the power supply and the control pole of the first switch element, and the control pole is connected between the cathode of the diode, and the drop voltage generated across the diode is The circuit comprises a reverse bias means for reverse biasing the control pole, and a control circuit connected to the control pole of the second switch element to control conduction or non-conduction of the second switch element, It is characterized by connecting an EL element to both ends.

Function The light emitting drive circuit for the EL element according to the present invention has a simple configuration as described above, and when the second switch element of the switch circuit becomes conductive, the EL element
A current flows through the diode, causing the EL element to emit light. At this time, the control pole of the first switch element is reverse biased by the voltage drop generated across the diode, and is always in a non-conducting state.

Thereafter, when the second switch element becomes non-conductive, the first switch element becomes conductive due to the charge in the EL element, the charge in the EL element is discharged, and the EL element emits light.

Note that if the charge charged in the EL element is discharged, the first switch element cannot maintain conduction and becomes non-conductive.

Embodiment FIG. 1 is an electric circuit diagram showing an embodiment of the light emission driving circuit for an EL element according to the present invention.
The same figure numbers and symbols as in the figures indicate the same functional members.

As is clear from FIG. 1, in this embodiment, a switch circuit 6 consisting of a transistor 7 as a first switch element, a diode 8, and a transistor 9 as a second switch element is connected to both ends of a power supply E. has been done.

A gate means 10 of the transistor 7 consisting of a resistor 11 is connected between the control pole of the transistor 7, which is the first switch element of the switch circuit 6, and the power supply E.

Further, the control pole of the transistor 7 is connected to the cathode of a diode 8 connected in series with the transistor 7 through a power supply circuit 13. Therefore, when current flows through the diode 8, the resulting voltage drop reverse biases the control pole of the transistor 7 via the power supply path 13.

That is, the power supply path 13 forms the reverse bias means 12.

The control pole of the transistor 9, which is the second switch element of the switch circuit 6, is connected to the control circuit 1, which includes an oscillator 15 that outputs a pulse signal, and resistors 16 and 17.
4 is connected. The EL element 3 is a transistor 7 which is the first switch element of the switch circuit 6.
connected to both ends.

The operation of one embodiment having the above configuration will be described below.

Now, when a predetermined voltage is output from the power supply E and a high level signal is output from the oscillator 15 of the control circuit 14, this high level signal is transmitted to the resistors 16 and 17.
is supplied to the control pole of transistor 9 via
EL element 3, diode 8, transistor 9
A current flows through the EL element 3, and the EL element 3 emits light.

At this time, the voltage drop generated by the current flowing through the diode 8 is applied to the control pole of the transistor 7 via the power supply line 13, which is a reverse bias means 12, and reverse biases this control pole, so that the transistor 7 is turned off. Conduction is controlled.

Further, at this time, although current flows through the resistor 11, no particular problem occurs as long as the resistance value of the resistor 11 is appropriately set.

On the other hand, when the signal level output from the oscillator 15 is reversed to a low level after an appropriate period of time taking into consideration the charging characteristics of the EL element 3, this low level signal is transmitted to the resistor 16,
17 to the control pole of transistor 9, transistor 9 becomes non-conductive.

Therefore, the connection to the power source E is cut off, and the reverse bias state of the transistor 7 due to the voltage drop generated across the diode 8 is released.

As a result, the transistor 7 becomes conductive through discharge between the base and emitter of the transistor 7 and the resistor 11 which is the gate means 10 for the charge charged in the EL element 3, thereby discharging the charge charged in the EL element 3. , at this time, the EL element emits light.

As the discharge of the charge in the EL element 3 progresses, the energy supplied to the gate means 10 decreases, and the transistor 7 is naturally controlled to be non-conductive at any given time. When the output signal level of the oscillator 15 is set to a high level after the transistor 7 is made non-conductive, the EL element 3 is charged and emitted light by the conduction of the transistor 9 as described above.

Thereafter, by switching the output level of the oscillator 15 to a low or high level, the above-described operation is repeated, that is, the EL element 3 is driven by a DC pulse and performs the desired light emitting operation.

As mentioned above, the embodiment shown in FIG.
Transistor 7 supplies energy to EL element 3
It has a simple configuration that is controlled by two switch elements, ie, transistor 9 and transistor 9. When transistor 9 is conductive by control circuit 14, transistor 7 is reverse biased by the voltage drop generated in diode 8, and is always non-conductive. conversely, when transistor 9 becomes non-conductive, transistor 7 becomes conductive for the first time due to the charge in EL element 3, and it is impossible for both transistors 7 and 9 to become conductive at the same time and to be connected to both ends of power supply E. do not have.

FIG. 2 is an electric circuit diagram showing another embodiment of the light emitting driving circuit for an EL element according to the present invention, and in the figure, the same numbers and symbols as in FIG. 1 indicate the same functional members.

As is clear from the drawings, this embodiment is an embodiment in which the first switch element, which used a transistor in the previous embodiment, is replaced with a thyristor 18. Therefore, its operation will be described below. Basically, it is the same as the previous embodiment.

Now, when a high level signal is output from the oscillator 15 of the control circuit 14, this high level signal is transmitted to the resistor 1.
6 and 17 to the transistor 9, and therefore, this transistor 9 becomes conductive and the power supply E
EL element 3, diode 8, transistor 9
A current flows through the EL element 3, and the EL element 3 emits light.

At this time, the voltage drop generated by the current flowing through the diode 8 is applied to the control pole of the thyristor 18 via the power supply line 13, which is the reverse bias means 12, and reverse biases this control pole, so that the thyristor 18 Controlled to be non-conductive.

At this time, the resistor 19 forming the gate means 10 of the thyristor 18, which is the first switch element,
Current flows through 20, but both resistors 19 and 20
No particular problem arises by appropriately setting the resistance value.

On the other hand, when the signal level output from the oscillator 15 is reversed to a low level after an appropriate period of time taking into consideration the charging characteristics of the EL element 3, the transistor 9 is controlled to be non-conductive.

Then, the reverse bias state of the control pole of the thyristor 18 due to the voltage drop generated in the diode 8 is released.

Therefore, the thyristor 18 becomes conductive by discharging through the gate means 10 of the EL element 3, that is, the resistors 19 and 20, and rapidly transfers the charge of the EL element 3 between its anode and cathode. Discharge occurs, and the EL element 3 emits light at this time.

When the current flowing through the thyristor 18 becomes equal to or less than the holding current due to discharge of the charge in the EL element 3, the thyristor 18 becomes non-conductive.

Thereafter, by switching the output level of the oscillator 15 to a high or low level, the above-described operation is repeated, that is, the EL element 3 is driven by a DC pulse, and performs the desired light emitting operation.

Note that the high-level inversion operation of the oscillator 15
Assuming that this occurs while the charge in the EL element 3 is discharging through the thyristor 18, the gate of the thyristor 18 is reverse biased by the diode 8, and the thyristor 18 attempts to reverse to a non-conducting state. cannot be completely inverted, and as with the conventional device, there is a possibility that the thyristor 18 and the transistor 9 become conductive at the same time, but in reality,
Since the discharge period through the thyristor 18 is shorter than the drive cycle required for stable light emitting operation of the EL element 3, no particular problem arises in conjunction with the fact that it is reverse biased. Further, it is also possible to use a gate turn-off thyristor as the thyristor 18.

As is clear from the above explanation, like the previous embodiment, this embodiment has a simple configuration in which the energy supply to the EL element 3 is controlled by two switch elements, and the transistor 9 is turned on by the control circuit 14. When the transistor 9 is turned off, the thyristor 18 is reverse-biased by the voltage drop generated across the diode 8 and is always controlled to be non-conductive.On the other hand, when the transistor 9 becomes non-conductive, the thyristor 18 becomes conductive for the first time due to the charge in the EL element 3. The transistor 9 and the thyristor 18 become conductive at the same time, and the power supply E
is not connected to both ends.

Furthermore, in this embodiment, since the thyristor 18 is used as the first switch element, the discharge characteristic of the charge charged in the EL element 3 is steeper than in the previous embodiment due to the difference in switching characteristics between the transistor and the thyristor. becomes.

FIG. 3 shows still another embodiment of the light emitting driving circuit for an EL element according to the present invention, in which the same figure numbers and symbols as in FIGS. 1 and 2 indicate the same functional members.

As is clear from FIG. 3, this embodiment includes a constant voltage transistor 22, a Zener diode 23 which is a constant voltage element, and a resistor 24 forming a gate means of the transistor 22 in addition to the embodiment shown in FIG. A means 21 is added.

The transistor 22 is connected between the power supply E and the switch circuit 6, the Zener diode 23 is connected between the base of the transistor 22 and the cathode of the diode 8, and the resistor 24 is connected between the power supply E and the base of the transistor 22. It is connected to the.

The operation of the embodiment shown in FIG. 3 having the above configuration will be described below. Note that the operations other than the constant voltage means 21 described above are the same as those in the embodiment shown in FIG. 2, and the explanation of those parts will be simplified.

Now, when a predetermined voltage is output from the power supply E and a high level signal is output from the oscillator 20 of the control circuit 19, the transistor 9 becomes conductive.

Therefore, a current flows from the power supply E through the loop of the resistor 24, the Zener diode 23, and the transistor 9, making the transistor 22 conductive, and the constant voltage generated across the Zener diode 23 is applied to the emitter side of the transistor 22. Output.

This constant voltage will be applied to the EL element 3 and the diode 8 or the resistors 19 and 20, etc.
As a result, a current flows through the EL element 3 and the diode 8, causing the EL element 3 to emit light.

At this time, the voltage drop generated in the diode 8 is applied to the control pole of the thyristor 18 via the power supply line 13, which is the reverse bias means 12, and the thyristor 18 is always controlled to be non-conductive. . At this time, current also flows through the resistors 19 and 20, but this does not cause any particular problem by appropriately setting the resistance values of both resistors 19 and 20.

On the other hand, when the signal level output from the oscillator 15 is reversed to a low level after an appropriate period of time taking into consideration the charging characteristics of the EL element 3, the transistor 9 is controlled to be non-conductive, and the current from the power source E to the Zener diode 23 is Since the supply loop is interrupted, transistor 22 is also non-conducting.

Therefore, the reverse bias state of the control pole of the thyristor 18 by the diode 8 is released, and as a result,
The thyristor 18 is the resistance 1 for charging the EL element 3.
9 and 20, conduction occurs and the above EL
The charge charged in the element 3 is rapidly discharged, and of course the EL element 3 emits light at this time.

Thereafter, by switching the output level of the oscillator 15 to a high or low level, the above-described operation is repeated, that is, the EL element 3 is driven with a DC pulse at a stable voltage value, and the desired light emitting operation is performed. become.

As described above, the above embodiment has a simple configuration in which the timing of energy supply to the EL element 3 is controlled by two switch elements, and the stabilization of the supply voltage, that is, the voltage reduction is controlled by the transistor 22 and the Zener diode 23. At the same time, when the transistor 9 is conductive, the thyristor 18 is controlled to be non-conductive due to the voltage drop generated in the diode 8, and at the same time, a constant voltage is supplied to the EL element by a constant voltage configuration such as the Zener diode 23, and vice versa. When the transistor 9 is non-conducting, the constant voltage configuration is inactive and the voltage supply to the EL element 3 is cut off, and at the same time the thyristor 1 is
8 becomes conductive for the first time.

Although the embodiment shown in FIG. 3 uses a thyristor as the first switch element, it goes without saying that a transistor as shown in FIG. 1 may also be used.

Effects of the Invention The light emitting driving circuit for an EL element according to the present invention includes a switch circuit including a series connection body of a first switch element connected to a power supply, a diode, and a second switch element. to EL
The gate means and the reverse bias means for supplying the voltage drop of the diode when the second switch element is conductive are connected to the control pole of the first switch element, resulting in an extremely simple structure. In addition, the first and second switch elements are not rendered conductive at the same time and are not connected to both ends of the power supply, which has the effect of preventing damage caused by simultaneous conduction of both switch elements.

Furthermore, since the conduction operation of the first switch element is performed using the charged charges of the EL elements connected in parallel, it also has the effect of reducing power consumption in the entire circuit system.

Furthermore, by providing a constant voltage means between the power supply and the switch circuit that operates only when the second switch element is conductive and supplies a constant voltage to the EL element, variations in the luminance of the EL element due to voltage fluctuations in the power supply are prevented. You can also expect some positive effects.

Furthermore, by using a thyristor as the first switch element, the discharge characteristics of the charged charges of the EL element can be made better than those of a transistor due to the difference in switching characteristics between a transistor and a thyristor. It also has an advantageous effect.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the light emitting drive circuit for an EL element according to the present invention, and FIGS.
The figure is an electric circuit diagram showing another embodiment, and FIG. 4 is a schematic electric circuit diagram of an example of a conventional light emission driving circuit for an EL element. 3...EL element, 6...Switch circuit, 7,9
...Transistor, 8...Diode, 10...
Gate circuit, 11, 16, 17, 19, 20...
Resistor, 12... Reverse bias means, 13... Power supply path, 14... Control circuit, 15... Oscillator, 18...
...thyristor.

Claims (1)

[Scope of Claims] 1. A switch circuit in which a first switch element, a diode, and a second switch element connected in series are connected to both ends of a power supply, and between the power supply and a control pole of the first switch element. a gate means of the first switch element connected to the first switch element; a reverse bias means connecting the control pole and the cathode of the diode and reverse biasing the control pole with a voltage drop generated across the diode; a control circuit for controlling conduction and non-conduction of a switch element, and an EL element light emission drive circuit that connects an EL element to both ends of the first switch element. 2 Transistors connected to both ends of the power supply, the first
a series connection body consisting of a switch element, a diode, and a second switch element, and the first switch element connected between the power source and the control pole of the first switch element via the collector-emitter of the transistor. gate means for the switch element; reverse bias means for connecting the control pole and the cathode of the diode and reverse biasing the control pole with a voltage drop generated across the diode; A constant voltage element connected, a gate means of the transistor connected between the base and the power source, and a conduction or non-conduction of the second switch element connected to the control pole of the second switch element. and a control circuit for controlling an EL element, the EL element being connected to both ends of the first switch element.