JPH0328034B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electroluminescent device, and particularly to improvements in its driving circuit.

[Prior Art] Conventionally, a drive circuit for an electroluminescent device using an electroluminescent element called EL connects an AC power source to both ends of the electroluminescent element, and applies a voltage to the electroluminescent element. It is driven by In this case, the brightness of the electroluminescent device increases in proportion to the magnitude and frequency of the voltage applied to the light emitting device. For this reason, conventional drive circuits for electroluminescent devices use a transformer or the like to boost the voltage applied to the electroluminescent element and to convert the frequency.

[Problems to be Solved by the Invention] However, as described above, in the conventional electroluminescent device drive circuit using a transformer, the transformer itself is large and heavy, so the drive circuit inevitably becomes large. However, it has not been possible to satisfy the demands for thinness and low power consumption of electroluminescent devices.

For this reason, some driving circuits for electroluminescent devices that do not use transformers have been developed. for example,
There are those that use a multivibrator to apply voltage to the light emitting element, and those that use a voltage doubler rectifier circuit. However, the former has disadvantages in that extra power is consumed through a load resistor in addition to the electroluminescent element, and a double variable resistor is required to vary the frequency, making the configuration and operation complicated. On the other hand, the latter requires a large-capacity smoothing capacitor, and therefore is not necessarily suitable for miniaturization.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a drive circuit for an electroluminescent device that allows the electroluminescent device to be made smaller and thinner, and to reduce power consumption, and also allows easy frequency variation. purpose.

[Means for Solving the Problems] That is, the present invention provides a first DC power supply, a second DC power supply, and a DC power supply driven by the first DC power supply.
A variable frequency oscillation circuit, which is composed of a low power consumption logic element such as a CMOS Schmitt inverter, a capacitive element and a resistive element, and which oscillates a variable frequency signal, and which is driven by the first DC power supply and which is driven by the variable frequency Using the output of the oscillation circuit as a reference signal,
a timing generation circuit that generates a first timing signal that has an opposite phase to the reference signal and whose rise is delayed by a predetermined time; and a second timing signal that is in phase with the reference signal and whose rise is delayed by a predetermined time; The first and second DC power supplies have their respective collector-emitter paths connected in series to the second DC power source, and are bridge-connected in parallel to each other.
and third and fourth transistors, the bases and collectors of the first and third transistors are cross-connected, and the bases of the second and fourth transistors are connected to each other, respectively. a switch circuit connected correspondingly to each output terminal of the first and second timing signals of the timing generation circuit; and a midpoint between the collectors of the first and second transistors of the switch circuit; , and an electroluminescent element connected between the midpoints of the connections of the respective collectors of the third and fourth transistors.

[Function] To explain the function of the present invention, for example,
A reference signal is output from a variable frequency oscillation circuit using a low power consumption logic element such as a CMOS Schmitt trigger, and two types of signals, in-phase and anti-phase, are delayed by a predetermined time by a timing generation circuit. . Based on these two types of timing signals, a switch circuit made up of two pairs of bridge-connected transistors is driven, and by keeping this switch circuit in a high impedance state for a predetermined period of time, it is possible to disconnect from the DC power supply. A rectangular wave voltage with a predetermined period is applied to the electroluminescent element to drive it.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the circuit configuration of a driving circuit for an electroluminescent device according to an embodiment of the present invention, for example.
Both input terminals of a rectifier circuit (second DC power supply) 12 consisting of diodes 121 to 124 of the illustrated polarities connected in a bridge configuration are connected to both terminals of a commercial AC power supply 11 at 100 V, 50 or 60 Hz. A current limiting resistor 131 and a constant voltage diode 132 with the illustrated polarity selectable from 5 to 15 V, for example, are connected in series across the output of the rectifier circuit (second DC power supply) 12. And this constant voltage diode 13
A diode 133 and a capacitor 134 of the polarity shown in the figure are connected in series to both ends of the capacitor 2 to prevent an increase in ripple due to reverse current. A voltage Vcc is applied from the midpoint between the diode 133 and the capacitor 134 to each inverter (not shown), which will be described later, and these constitute the CMOS gate IC power supply circuit (first DC power supply) 13. are doing.

Further, the variable frequency oscillation circuit 14 has a first inverter 141, and a variable resistor 142 and a resistor 143 are connected in series between the input and output terminals of the first inverter 141. The input terminal of the first inverter 141, the rectifier circuit (second DC power supply) 12 and the power supply circuit (first DC power supply) 1
A capacitor 144 is connected between the three common lines 11a.

The signal output from the variable frequency oscillation circuit 14 is used as a reference signal for obtaining first and second timing signals delayed by a predetermined time, respectively, in a timing signal generation circuit 15 configured as follows. A diode ₁₅₁ and a resistor 152 of the polarity shown are connected between the output terminal of the first inverter 141 and the common line 11a.
A capacitor 153 is connected through a parallel connection with. Further, at the midpoint of the diode 151 and resistor 152 and the capacitor 153, a second
The input terminal of the inverter 154 is connected to the input terminal of the inverter 154.
_Two points P shown in the figure, that is, the second inverter 15
The output terminal of No. 4 is connected via a resistor 155 to the base of an npn transistor (fourth transistor) 171 constituting a switch circuit 17 to be described later.

Further, the input terminal of a third inverter 156 is connected to the output terminal of the first inverter 141. There are _three points P in the figure, that is, between the output end of the third inverter 156 and the common line 11a,
A capacitor 159 is connected through a parallel connection with a diode 157 and a resistor 158 of the illustrated polarity. In addition, the diode 157 and the resistor 1
58 and the capacitor 159 are connected to the input terminal of a fourth inverter 160. illustration
_P4 point, that is, the output terminal of the fourth inverter 160, is connected via a resistor 161 to the base of an npn type transistor (second transistor) 172 constituting a switch circuit, which will be described later.

On the other hand, a switch circuit 17 is constituted by four bridge-connected transistors 171 to 174 and the like. A switch circuit 17 is connected to the output power line 11b of the rectifier circuit 12 via a connection 18.
First and third transistors 173 that are pnp type
and 174 emitters are commonly connected. The collectors of the first and third transistors 173 and 174 are connected to the collectors of the second and fourth transistors 172 and 171, respectively. The respective emitters of the second and fourth transistors 172 and 171 are commonly connected to the common line 11a. That is, the transistors 171 to 174
is connected to a bridge. Further, an npn transistor 17 is connected between the base and emitter of the first and third transistors 173 and 174.
In order to release leakage current from 1 and 172, resistors 177 and 178 are connected, respectively, and resistors 175 and 176 are connected across each base and collector, respectively.
Note that resistors 177 and 178 are npn transistors 1
It may be omitted when the leakage current from 71 and 172 is small.

Further, the first and second transistors 173
An electroluminescent element 19 is connected to a midpoint between the collectors of transistors 172 and 172 and a midpoint between collectors of the third and fourth transistors 174 and 171.

Here, each inverter 141, 154, 15
6,160 is a low power consumption logic element, for example.
It uses a Schmitt inverter consisting of a CMOS gate IC, and as mentioned above, although not shown in the diagram,
Power supply circuit for CMOS gate IC (first DC power supply)
A voltage Vcc from 13 is applied.

Figure 2 shows a pulse wave with period T obtained by the drive circuit of the electroluminescent device in Figure 1, where a represents the output waveform at point _P1 , and b represents the output waveform at point _P3 . This shows the output waveform at point P in the same figure, with the phase reversed from the waveform in a, and c shows the output waveform at _two points in the same figure, and the rise is delayed by Δt compared to b in the same figure. d is the same P ₄
This is the output waveform at point A, and represents a waveform whose rise is delayed by Δt compared to a in the same figure.

Furthermore, FIG. 3 is a diagram showing an example of the voltage applied to both ends of the electroluminescent element 19.

The drive circuit for the electroluminescent device configured as described above operates as follows.

First, activate the AC power supply 11, for example, 100V,
50 or 60Hz voltage is applied to the diodes 121-12
The voltage of the power supply circuit (first DC power supply) 13 is rectified into a DC voltage through the rectifier circuit (second DC power supply) 12 consisting of 4, and the divided voltage of this DC voltage is the voltage of the power supply circuit (first DC power supply) 13.
Each inverter 141, 154, 15 as Vcc
6,160. Here, the output of the variable frequency oscillation circuit 14 has a frequency that is different from that of the variable resistor 142,
It is determined by the values of the resistor 143 and capacitor 144, and becomes a rectangular wave with a duty cycle of approximately 50%. Also, the above frequency is the variable resistor 1
42 can be varied over a wide range. The rectangular wave obtained in this way is the second wave at point _P1 .
The waveform will be as shown in Figure a. Then, in order to obtain a waveform with an opposite phase to this waveform, the third inverter 156 inverts the waveform. As a result, a rectangular wave having a waveform as shown in b in the figure is obtained at point _P3 .

The rectangular waves obtained by the variable frequency oscillation circuit 14 and the third inverter 156 are respectively supplied to the timing generation circuit 15 for delaying the rise by a predetermined time Δt. By this timing generation circuit 15, the rise of the waveforms shown in FIGS. 2a and 2b is delayed by a predetermined time Δt, and
At P ₂ and P ₄ points, c and d in the same figure, respectively.
The timing signal will be as shown in . This is because both sides of the bridge connection of the switch circuit 17, which will be described later, are turned on and off by the timing signal, and are kept in a high impedance state for a predetermined time Δt each time they are switched. Note that the delay time Δt at this time is determined by the speeds of the resistors 152, 158, the capacitors 153, 159, and the gate elements in the second and fourth inverters 154, 160, but the value of the delay time Δt above Approximately 1 to 10 μsec.

The switch circuit 17 is driven based on the two types of timing signals obtained in this way.
In other words, P ₂ points and P ₄ points alternately repeat the state in which one is at a high level and the other is at a low level,
When the _P4 point side is at a high level, current flows in the order of third transistor 174 → electroluminescent element 19 → second transistor 172. On the contrary
When the _P2 point side is at a high level, current flows in the order of first transistor 173 → electroluminescent element 19 → fourth transistor 171. Then, the electroluminescent element 19 is always at a high level except for the delay time Δt at the rise of the timing signal. For this reason, the electroluminescent element 1
9, the third signal is amplitude modulated with the power supply frequency and pulse width modulated with the timing signal.
A voltage as shown in the figure is applied. This doubly modulated applied voltage has a substantially higher frequency than a normal alternating current voltage, thereby increasing the brightness of the device.

In this way, the timing generation circuit 15 sets the time Δt during which all transistors are in the off state, and a high impedance state is ensured, so that the circuit configuration of the driving portion can be simplified. Moreover, since no circuit that consumes extra power is added to the circuit of this driving part, the current flowing without passing through the electroluminescent element 19 is extremely reduced, and the current flowing from the first transistor 173 to the second transistor 173 is The leakage current disappears while flowing from the transistor 172 or the third transistor 174 to the fourth transistor 171. Therefore, the power consumption of these transistors is also reduced, and smaller transistors can be used. Furthermore, the frequency can be easily varied by the variable resistor 142.

Furthermore, since a transformer is not used in the drive circuit of this electroluminescent device, it can be made smaller and thinner, and it can also be integrated into an IC. Furthermore, it is used for low voltage generation circuits. CMOS gate IC
The diode 133 and capacitor 134 in the power supply circuit (first DC power supply) 13 mainly affect stability, and therefore are not necessarily necessary depending on the application and may be omitted.

In addition, in this example, in terms of circuit simplicity and stability,
Although it was configured using a CMOS Schmitt inverter, a NAND circuit or a NOR circuit, which can be used equivalently and can turn off/off oscillation and synchronize, can be used in place of the inverter, as shown in Figure 4. It's also good. The figure shows an example in which a NAND circuit 145 is used in place of the first inverter 141.

Furthermore, although a smoothing capacitor is not provided in the rectifier circuit (second DC power supply) 12 in the same embodiment, if flicker of twice the commercial frequency is allowed, miniaturization can be achieved. There is no need to provide it.

[Effects of the Invention] As described above, according to the present invention, the time during which all transistors are in the male state is set, and the high impedance state is ensured for this set time, thereby simplifying the circuit configuration of the driving part. Since no extra power consuming circuitry is added, the current flowing without passing through the electroluminescent element is significantly reduced. This reduces the power consumption of these transistors, allows the use of smaller transistors, and allows the frequency to be easily varied using a variable resistor.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the circuit configuration of a driving circuit of an electroluminescent device according to an embodiment of the present invention, FIG.
b, c, d are P ₁ , P ₃ , P ₂ ,
P A diagram showing an example of each output waveform at ₄ points, Figure 3 is a diagram showing an example of the applied voltage across both ends of the electroluminescent element in Figure 1, and Figure 4 is a diagram showing an example of the voltage applied to both ends of the electroluminescent element in Figure 1. FIG. 7 is a diagram showing an example in which a NAND circuit is used as another example of the circuit. 11... AC power supply, 12... Rectifier circuit, 13...
CMOS gate IC power supply circuit, 14... variable frequency oscillation circuit, 15... timing generation circuit, 17... switch circuit, 19... electroluminescent element.

Claims (1)

[Claims] 1 Consisting of first and second DC power supplies, a low power consumption logic element, a capacitive element, and a resistive element driven by the first DC power supply,
A variable frequency oscillation circuit that oscillates a variable frequency signal; and a variable frequency oscillation circuit that is driven by the first DC power supply, uses the output of the variable frequency oscillation circuit as a reference signal, and has a reverse phase with respect to the reference signal and rises only for a predetermined time. a timing generation circuit that generates a delayed first timing signal and a second timing signal that is in phase with the reference signal and whose rise is delayed by a predetermined time; and respective collector-emitter paths for the second DC power supply. have first and second transistors and third and fourth transistors connected in series and bridge-connected in parallel to each other,
The bases and collectors of the first and third transistors are cross-connected, and the bases of the second and fourth transistors are respectively connected to the first and second timing signals of the timing generation circuit. a switch circuit connected to each output terminal in a corresponding manner; a midpoint between the collectors of the first and second transistors of the switch circuit; and a connection between the collectors of the third and fourth transistors; What is claimed is: 1. A drive circuit for an electroluminescent device, comprising: an electroluminescent element connected between the midpoints of . 2. The driving circuit for an electroluminescent device according to claim 1, wherein the second DC power source is a rectified commercial AC power source. 3. The drive circuit for an electroluminescent device according to claim 1, wherein the first DC power source is a voltage-divided version of the second DC power source.