JPH07227088A - Inverter for el - Google Patents

Abstract

PURPOSE:To reduce a thickness and a size by so devising as to use a small-sized transformer and simplifying a circuit configuration. CONSTITUTION:The inverter for an EL comprises a booster converter 1, a first control circuit 2 for controlling ON/OFF of the converter 1, a second control circuit 3 for forming a voltage drop shunt circuit at an output side of the converter 1, a self-excited CR oscillator 4 for operating the circuits 2, 3, and a DC blocking capacitor 5 connected to the output side of the converter 1. An oscillating frequency of the oscillator 4 is set to a frequency adapted for firing an EL element to generate a pulselike voltage ON the output side of the converter 1, and an AC output is obtained by the capacitor 5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an EL (Electro Lumine
The present invention relates to an EL inverter device for lighting a scence element.

[0002]

2. Description of the Related Art Generally, a pager (pager),
An LCD (liquid crystal display) is used as an output display device of a notebook personal computer, a laptop word processor, etc., and an EL element (EL panel) or a cold cathode tube is used as a backlight of this LCD. In particular, EL elements have come to be built in small and thin devices such as pagers (pagers). An AC power supply in an appropriate frequency range is required to light this EL element, and an inverter device using a DC power supply such as a primary battery or a secondary battery as an input is usually used.

Conventionally, a general EL inverter device uses a blocking oscillation circuit to generate a drive voltage of 40 to 120 Vrms with an alternating current having a frequency of several 100 Hz to several kHz and directly apply it to an EL element to emit light. .

Further, a positive / negative DC voltage is generated by a DC / DC converter, an inductor is connected in series to the EL element, and a positive / negative DC voltage of the DC / DC converter is connected by an EL drive oscillation circuit and a switching circuit. An inverter device has been proposed that applies light to an EL element through an inductor to emit light [NEC Technical Report Vol.43 No.10 / 1990.
6 (EL switching application circuit)]. Further, a configuration similar to this is also proposed in Japanese Utility Model Laid-Open No. 3-37797.

[0005]

By the way, in the conventional general inverter device which directly drives the EL element by the oscillation output of the blocking oscillator circuit, the inverter is operated at the same frequency as the EL drive frequency. Became large, and it was very difficult to make the device smaller and thinner. In such an inverter device, a large transformer is a drawback especially when it is built in a device such as a pager which is required to be small and thin. Further, since the output voltage is proportional to the input voltage, it is difficult to control the output.

Further, in the conventionally proposed inverter device which generates positive / negative DC voltage and applies the voltage to the EL element via the inductor by switching, a positive / negative DC voltage is generated. Since extra circuits and parts are required, the circuits are complicated and disadvantageous in terms of cost.

In view of the above points, it is an object of the present invention to provide an EL inverter device which is devised so that a small transformer can be used, has a simple circuit configuration, and can be made thin and compact. .

[0008]

In order to achieve the above object, an EL inverter device of the present invention comprises a boost converter circuit and a first control circuit for controlling ON / OFF of the operation of the boost converter circuit. A second control circuit that forms a voltage drop shunt on the output side of the boost converter circuit, a self-excited CR oscillation circuit that operates the first and second control circuits, and an output side of the boost converter circuit And a DC blocking capacitor connected to.

Further, the oscillation output of the self-excited CR oscillator circuit is added to the control inputs of the first and second control circuits, and the first half of the cycle of the self-excited CR oscillator circuit is used for the first half cycle.
The control circuit turns on the operation of the step-up converter, and the second control circuit forms a voltage drop shunt on the output side of the step-up converter circuit in the latter half cycle of the cycle, thereby generating a pulsed output voltage. The configuration can be created.

FIG. 1 shows the basic structure of an EL inverter device according to the present invention. In the figure, 1 is an EL (Electro Lumi
2) is a first control circuit for controlling ON / OFF of the operation of the boost converter circuit 1;
Is a second control circuit that forms a voltage drop shunt 15 on the output side of the boost converter circuit 1, and 4 is a self-excited CR that operates the first control circuit 2 and the second control circuit 3.
An oscillating circuit, 5 is a DC blocking capacitor for removing a DC bias component of the output voltage from the boost converter circuit 1. Here, a DC voltage + V is applied between the DC input terminal Pin and the ground terminal COM1 from the primary battery or the secondary battery.
In is input, and the boosted output of the boost converter circuit 1 is output as an AC output voltage Vout between the output terminal Pout and the ground terminal COM2 through the DC blocking capacitor 5.

In the boost converter circuit 1, if the absolute value of the output voltage is larger than the absolute value of the input voltage, the positive / negative of the voltage between the input and the output may be inverted. For example, even if a negative voltage output is generated from a positive voltage input, there is no problem because the DC component is finally removed by the DC blocking capacitor 5.

[0012]

The basic operation of the EL inverter device shown in FIG. 1 will be described. Since the output of the boost converter circuit 1 is a DC output (pulsating current) as it is, the self-excited CR oscillation circuit 4
By the following, exchange is made. The self-excited CR oscillation circuit 4 operates the first control circuit 2 to turn on the operation of the boost converter 1 in the first half cycle of the oscillation cycle, and the second control circuit 3 in the latter half cycle of the oscillation cycle. To form a voltage drop shunt 15 on the output side of the boost converter circuit 1 [shunt the output voltage]. That is, in the first half cycle of the oscillation cycle, a positive voltage is output from the boost converter circuit 1 through the capacitor 5 to between the output terminal Pout and the ground terminal COM2. Further, in the latter half cycle of the oscillation cycle, the output side of the boost converter circuit 1 and the ground terminals COM1, CO.
Voltage drop shunt 1 between earth lines 10 connected to M2
5 is formed, the output side of the boost converter circuit 1 is substantially short-circuited to the ground line 10, the converter output voltage becomes substantially zero voltage level, and the DC blocking capacitor 5 causes the output terminal Pout and the ground terminal. An inversion potential is applied between COM2. By repeating the above cycles, a pulsed output voltage (AC voltage) is output between the output terminal Pout and the ground terminal COM2.

As described above, in the present invention, since the output voltage is made alternating by the oscillation output of the self-excited CR oscillation circuit 4, the oscillation frequency of the self-excited CR oscillation circuit 4 is optimal for lighting the EL element. Frequency (several 100 Hz to several kHz)
By doing so, the frequency for boosting in the boost converter circuit 1 can be set independently of the EL element drive frequency, and by setting the boost frequency to a high frequency (for example, several hundred kHz), the transformer used in the converter can be downsized. be able to. Therefore, downsizing of the inverter device for EL,
The thickness can be reduced. Further, the circuit configuration is relatively simple, and the number of necessary parts can be reduced, so that the cost can be reduced.

[0014]

Embodiments of an EL inverter device according to the present invention will be described below with reference to the drawings.

In FIG. 2, the boost converter circuit 1 is
A DC / DC converter of a self-exciting step-up chopper system for generating a power supply voltage of several 10V to several hundreds of 10V required to light an EL element, including a primary winding Np, a boosting winding Ns, and a feedback winding. A transformer T having a line Nd, a transistor Q1 as a switching element, resistors R1 and R2,
It is composed of capacitors C1 and C2 and a diode D1. Then, a DC voltage + Vin is supplied from a primary battery, a secondary battery or the like between the DC input terminal Pin and the ground terminal COM1, and the series circuit of the primary winding Np and the transistor Q1 is connected to the DC input terminal Pin and the ground terminal. It is connected between the earth line 10 leading to COM1. A capacitor C1 is provided between the supply line 11 connected to the primary winding Np and connected to the DC input terminal Pin and the ground line 10. A starting resistor R1 is connected between the base of the transistor Q1 and the supply line 11, and a resistor R2 is connected between the base of the transistor Q1 and one end of the feedback winding Nd.
And a series circuit of the capacitor C2 is connected. The other end of the feedback winding Nd is connected to the ground line 10. Further, one end of the boosting winding Ns (that is, the windings Np, N
The anode side of the rectifying diode D1 is connected to one end of a secondary winding composed of s connected in series.

A DC blocking capacitor C5 (see FIG. 1) is provided between the cathode of the diode D1 from which the boosted output voltage after rectification of the boost converter circuit 1 is obtained and the output terminal Pout.
(Corresponding to the DC blocking capacitor 5) is connected.

An astable (unstable) multivibrator 4A as a self-excited CR oscillator circuit is composed of a pair of transistors Q.
3, Q4, resistors R4, R5, R6 and R7, and capacitors C3 and C4, and resistors R4, R5, R6.
One end of R7 is connected to the supply line 11, and the emitters of the transistors Q3 and Q4 are connected to the ground line 10. This astable multivibrator 4A has an operating frequency of several 100 Hz to several kH which is the optimum lighting frequency of the EL element during operation.
It oscillates at z (for example, 500 Hz to 3 kHz) and outputs a square wave from the output end 16 on the collector side of the transistor Q3. The oscillation output becomes low level which is substantially zero voltage in the first half cycle of the oscillation cycle, and becomes high level of positive voltage in the second half cycle of the cycle.

Between the base of the transistor Q1 of the boost converter circuit 1 and the ground line 10, there is provided a first control circuit 2 for controlling ON / OFF of the operation of the boost converter circuit 1.
Are connected. The first control circuit 2 controls on / off of the transistor Q1, and includes a transistor Q2 as a control element and a resistor R3 connected to its base. The resistor R3 is provided between the output end 16 of the astable multivibrator 4A and the base of the transistor Q2, and limits the current applied to the base as the control input end of the first control circuit 2. The transistor Q2 is turned on (conducted) by the output of the astable multivibrator 4A, so that the base of the transistor Q1 and the ground line 10 are substantially short-circuited.

The second control circuit 3 connects the cathode side of the diode D1 which is the output terminal of the boost converter circuit 1 and the capacitor C5 in order to bring the output voltage of the boost converter circuit 1 to the zero voltage level. And earth line 1
It is for forming a voltage drop shunt 15 between 0, and is composed of a transistor Q5 as a control element for controlling ON / OFF of the connection of the shunt 15 and a resistor R8 connected to its base. . The transistor Q5 is turned on by the output of the astable multivibrator 4A to short-circuit the connection point between the diode D1 and the capacitor C5 and the ground line 10. The resistor R8 is provided between the output end 16 of the astable multivibrator 4A and the base of the transistor Q5, and limits the current applied to the base as the control input end of the second control circuit 3.

The on / off timings of the transistors Q2 and Q5 of the first and second control circuits 2 and 3 are synchronized.

The DC blocking capacitor C5 removes the DC bias component of the boosted output (voltage on the cathode side of the rectifying diode D1) of the boost converter circuit 1 and outputs the AC output voltage Vout between the output terminal Pout and the ground terminal COM2. The voltage is applied to the connected EL element. It is desirable to use a capacitor (for example, 10 times or more) larger than the electrostatic capacitance of the EL element as the capacitor C5.

Next, the overall operation of the embodiment shown in FIG. 2 will be described.

First, the transistor Q1 is connected to the starting resistor R1.
When a minute current starts to flow into the base of the transistor, the transistor Q1
Collector current starts to flow, and the primary winding Np of the transformer T
An induced voltage is generated in the feedback winding Nd through. Feedback winding N
When an induced voltage is generated in d, a current is caused to flow to the base of the transistor Q1 through the capacitor C2 and the resistor R2, and oscillation (for example, several hundreds of kHz) is started by the positive feedback action. (For example, number 1
0V to a few hundreds of 10V is generated (in this case, the secondary winding can be considered equivalent to the series connection of the windings Np and Ns, and a voltage corresponding to the primary / secondary winding ratio is obtained. ).
Then, this high voltage is rectified by the rectifying diode D1 and applied to the EL element through the DC blocking capacitor C5. However, since only the DC output (pulsating current) is applied to the EL element as it is, the astable multivibrator 4A Exchange as follows.

The astable multivibrator 4A outputs a square wave (pulse signal) which becomes a low level (substantially zero voltage) in the first half cycle of the oscillation cycle and a positive high level in the latter half cycle. The oscillation output is applied from the output terminal 16 to the control input terminals of the first control circuit 2 and the second control circuit 3, respectively. In the first half cycle of the oscillation cycle, since the output signal is at the low level, the transistor Q2 of the first control circuit 2 is in the off state (cutoff state),
The operation of the boost converter circuit 1 is turned on. Also,
The transistor Q5 of the second control circuit 3 is also turned off, and the output of the boost converter circuit 1 passing through the diode D1 is output as a positive voltage between the output terminal Pout and the ground terminal COM2 through the capacitor C5. In the latter half cycle of the oscillation cycle, since the output signal changes to the high level, the transistor Q2 of the first control circuit 2 is turned on (conducting state), and the base of the transistor Q1 and the ground line 10 are substantially short-circuited. Then, the transistor Q1 is turned off (cut-off state) to stop the operation of the boost converter circuit 1. Further, the transistor Q5 of the second control circuit 3 is also turned on to form a voltage drop shunt 15 that substantially short-circuits the connection point between the diode D1 and the capacitor C5 and the ground line 10 (shunt). , The output voltage from the boost converter circuit 1 is reduced to substantially zero voltage. Therefore, the potential of the output terminal Pout becomes negative due to the capacitor C5, and the inverted potential is applied to the EL element connected between the output terminal Pout and the ground terminal COM2. The operations of the first half cycle and the second half cycle described above are repeated, and the EL inverter device outputs the output terminal Pou.
An AC pulsed output voltage as shown in FIG. 3 is output between t and the ground terminal COM2. That is, an AC voltage regulated by the oscillation frequency of the astable multivibrator 4A is applied to the EL element.

FIG. 3 shows the output voltage Vout and the output current Iout between the output terminal Pout and the ground terminal COM2 of the above embodiment.
Shows the waveform of.

According to the above embodiment, the DC output voltage of the boost converter circuit 1 is converted into an alternating current by the oscillation output of the astable multivibrator 4A, and the optimum frequency for lighting the EL element by the astable multivibrator 4A is obtained. Therefore, the operating frequency for boosting in the boost converter circuit 1 can be set independently of the EL element driving frequency, and the boost converter circuit 1 can be set by setting the operating frequency to a high frequency (frequency higher than the EL element driving frequency). The transformer used can be made smaller and thinner. Therefore, the EL inverter device can be made smaller and thinner.

Further, the step-up converter circuit does not need to generate positive and negative DC voltages and does not need an inductor or the like, so that the circuit configuration is relatively simple and the number of necessary parts can be reduced, so that the cost can be reduced. You can

Further, if a circuit configuration capable of changing the duty of the output waveform of the astable multivibrator 4A is adopted (for example, at least one of R4 to R7 is a variable resistor), the square wave of the output terminal 16 becomes high. By prolonging the level state, the ON state of the transistor Q2 of the first control circuit 2 is prolonged, that is, the transistor Q2.
It is possible to lengthen the OFF state of No. 1 to prolong the operation stop time of the boost converter circuit 1 and reduce the output voltage. Conversely, by shortening the high-level state of the square wave at the output terminal 16, the on-state of the transistor Q2 of the first control circuit 2 is shortened, that is, the off-state of the transistor Q1 is shortened, and the boost converter circuit 1 of the boost converter circuit 1 is shortened. The operation stop time can be shortened and the output voltage can be increased. That is, the output voltage can be controlled regardless of the input voltage.

In the above embodiment, the first control circuit 2
Although bipolar transistors are used as the transistors Q2 and Q5 of the second control circuit 3, FETs or other control elements may be used. Similarly, an FET or other control element may be used for the transistor Q1 of the boost converter circuit 1.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to these and various modifications and changes can be made within the scope of the claims. Let's do it.

[0031]

As described above, in the EL inverter device of the present invention, the boost converter circuit boosts the input voltage, and the oscillation output of the self-excited CR oscillator circuit is controlled by the first control circuit and the second control circuit. In addition to the circuit, the first control circuit controls ON / OFF of the operation of the boost converter circuit, and operates the second control circuit to form a voltage drop shunt on the output side of the boost converter circuit. Then, a pulsed voltage is generated, and an AC output voltage for lighting the EL element is obtained from the output side of the boost converter circuit through a DC blocking capacitor, and the output voltage is AC by the oscillation output of the self-excited CR oscillation circuit. Since it has been converted to
The oscillation frequency of the self-excited CR oscillation circuit can be set to the optimum frequency for lighting the EL element. Further, as a result, the operating frequency of the boost converter circuit can be set independently of the EL element driving frequency, and by setting the operating frequency of the boost converter circuit higher than the EL element driving frequency, the transformer used in the boost converter can be set. The size can be reduced. Further, the circuit configuration is relatively simple, the number of required parts is small, and it is advantageous in terms of cost. Therefore, it is possible to obtain an EL inverter device which realizes miniaturization and thinning, is inexpensive, and is particularly suitable for lighting an EL element incorporated in a small device such as a pager.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an EL inverter device according to the present invention.

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

FIG. 3 is a waveform diagram showing an output voltage and an output current in the operation of the example.

[Explanation of symbols]

 1 Boost Converter Circuit 2 First Control Circuit 3 Second Control Circuit 4 Self-Excited CR Oscillation Circuit 4A Astable Multivibrator 5 DC Blocking Capacitor 10 Earth Line 11 Supply Line 15 Voltage Drop Shunt 16 Output Terminals C1 to C5 Capacitor D1 Diode R1 to R8 Resistance T Transformer Np Primary winding Nd Feedback winding Ns Step-up winding Q1 to Q5 Transistor Pin DC input terminal COM1, COM2 Ground terminal Pout Output terminal

Claims (2)

[Claims] 1. A boost converter circuit, a first control circuit for controlling ON / OFF of an operation of the boost converter circuit, and a second control for forming a voltage drop shunt on the output side of the boost converter circuit. Inverter device for EL, comprising a circuit, a self-excited CR oscillation circuit for operating the first and second control circuits, and a DC blocking capacitor connected to the output side of the boost converter circuit. . 2. An oscillation output of the self-excited CR oscillation circuit is added to control inputs of the first and second control circuits,
In the first half cycle of the cycle of the self-excited CR oscillator circuit, the operation of the boost converter is turned on by the first control circuit, and in the second half cycle of the cycle, the voltage is applied to the output side of the boost converter circuit by the second control circuit. The EL inverter device according to claim 1, wherein a pulsed output voltage is created by forming a shunting path.