JPH06225546A - Drive circuit of capacitive load - Google Patents

Abstract

PURPOSE:To improve the drive efficiency, making effective use of load and obviate conventional inductor for resonance so as to facilitate downsizing, by providing a capacitor for recovery of charge on the input side of a step-up circuit, and recovering the charge which fills up the charge period of the drive period of capacitive load in the next discharge period. CONSTITUTION:DC power source voltage Vin is boosted to DC high voltage with a step-up circuit 1, and the DC high voltage output Vout is applied to an EL light emitting element 3 through a switching circuit 2. At this time, the EL element 3 is charged with the high voltage output Vout by opening the switch 4, in condition that a switch 5 is open, by a control circuit 8, and next the charge with fills up the EL light emitting element 3 is discharged by closing the switch 5, in the condition that the switch 4 is open. And, the voltage applied to the EL light emitting element 3 changes in specified periods by repeating this switching operation, and the EL light emitting element 3 lights.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a capacitive load, and more particularly, to a capacitive EL light emitting device or a piezoelectric device for charging and discharging a high DC voltage obtained by boosting a DC power supply voltage. Drive circuit.

[0002]

2. Description of the Related Art For example, in a dispersion type EL light emitting device which is a kind of capacitive load, a light emitting body in which a special fluorescent material is dispersed and contained in a dielectric material is sandwiched between two electrodes. It has a structure of a capacitor, and when a voltage whose size changes with time is applied between its electrodes, an electric field whose size changes with time is applied to the fluorescent substance of the light-emitting body to emit light. In general, the EL light emitting element is generally turned on by using a drive circuit called an inverter.

[Prior Art 1] In a conventional inverter, a booster circuit for boosting a DC power supply voltage to a DC high voltage, a DC high voltage output of the booster circuit is charged into a capacitive load, and a capacitive load is charged. A switching circuit that discharges the generated electric charge to the ground potential and a control circuit that controls the switching circuit are provided, and the DC high voltage boosted by the booster circuit operates so that the capacitive load is periodically charged and discharged. The method was taken.

[Prior art example 2] In another conventional inverter, a booster circuit for boosting a DC power supply voltage to a DC high voltage and a DC high voltage output of the booster circuit are charged to a capacitive load and Equipped with a switching circuit that discharges the electric charge charged in the static load to the ground potential, a control circuit that controls the switching circuit, and a resonance inductor, and the DC high voltage boosted by the booster circuit is capacitive through the resonance inductor. A method of operating so that the load is periodically charged and discharged has been adopted. By forming a resonance circuit of an inductor and a capacitive load, the above-mentioned inverter has improved efficiency by mutually exchanging electric energy and magnetic energy based on its electric vibration.

[0005]

In the method according to [Conventional Example 1], the electric charge charged in the capacitive load during the charging period is discharged to the ground potential during the discharging period by the high DC voltage obtained by the booster circuit. Therefore, there is a problem that the charging efficiency is not recovered and the driving efficiency of the inverter is poor.

When the method according to [Conventional Example 2] is used to drive an EL light emitting element, the EL light emitting element is generally 500
Since it is driven at a relatively low frequency of ~ 1 KHz, a large inductance is required for the resonance inductor,
A large-sized inductor is also required, which makes it difficult to downsize the inverter.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to provide a drive circuit of a capacitive load which can easily realize miniaturization and improve drive efficiency. Especially.

[0008]

As a technical means for achieving the above object, the present invention provides a capacity for converting a DC power supply voltage into a DC high voltage and charging / discharging the high voltage to a capacitive load. In the drive circuit for the capacitive load, a capacitor for collecting the electric charge charged in the capacitive load is provided on the input side of the power supply voltage.

Further, in the above drive circuit, a diode is provided on the input side of the power supply circuit to prevent the charge charged in the capacitive load from flowing into the power supply side.

Further, in the above drive circuit, a booster circuit for boosting a DC power supply voltage to a DC high voltage, a switching circuit for charging a DC high voltage output of the booster circuit to a capacitive load, and a capacitive load. And a switching circuit that discharges the generated charges to a charge recovery capacitor provided on the input side.

[0011]

In the capacitive load driving circuit according to the present invention, the charge charged during the charging period of the driving period of the capacitive load is not discharged to the ground potential in the next discharging period, and the input side of the power supply voltage is not discharged. Is collected by the charge collection capacitor provided in
Used to supply voltage for the next charging period. Further, the diode provided on the input side of the power supply voltage can prevent the current from flowing into the power supply side. At this time, the voltage charged in the capacitive load is sufficiently higher than the voltage across the charge recovery capacitor, and the capacitance of the charge recovery capacitor is set sufficiently higher than the equivalent capacitance of the capacitive load, thereby The same effect as when the electric charge of the sexual load is discharged to the ground potential is obtained. Due to the above action, effective use of electric charges can be achieved and drive efficiency can be improved.

Further, according to the drive circuit described above, the drive efficiency can be improved without using the resonance inductor, so that the miniaturization can be easily realized.

[0013]

EXAMPLE An example of the present invention will be described with reference to FIGS.

As shown in FIG. 1, the inverter, which is the drive circuit of the embodiment of the present invention, boosts a DC power supply voltage Vin from a dry battery or the like to a DC high voltage by a booster circuit (1), and the booster circuit (1). The DC high voltage output Vout is applied to the dispersion type EL light emitting element (3) which is a capacitive load through the switching circuit (2).

The switching circuit (2) has a first switch (4) whose one end is connected to the output side of the booster circuit (1) and a second switch whose one end is connected to a charge recovery capacitor (6). And the other end of each of the first switch (4) and the second switch (5) is connected to the EL light emitting element (3) which is a load.

As a feature of the present invention, the input side of the power supply voltage,
That is, the charge recovery capacitor (6) is grounded to the input side of the booster circuit (1). This charge recovery capacitor (6)
May also serve as a bypass capacitor used for the purpose of lowering the input impedance of the power supply. Further, the diode (7) may be connected to the input side of the power supply voltage. The diode (7) prevents the current due to the discharge of the electric charge charged in the EL light emitting element (3) from flowing to the power supply side.

In the figure, (8) is a control circuit for controlling the switching circuit (2) and the like.

In the inverter having the above structure, when the DC power supply voltage Vin is supplied to the booster circuit (1), the booster circuit (1) boosts it to a DC high voltage, and its DC high voltage output Vout is a switching circuit. It is applied to the EL light emitting element (3) via (2). At this time, by the control circuit (8),
The switching circuit (2) is switched to charge the EL light emitting element (3) with a DC high voltage output. That is, in the switching circuit (2), when the first switch (4) is closed while the second switch (5) is open, the high voltage output Vout becomes (a) of the EL light emitting element (3). The side is charged as +. Next, when the second switch (5) is closed with the first switch (4) opened, the electric charge charged in the EL light emitting element (3) passes through the second switch (5). Are discharged to the charge recovery capacitor (6).

By repeating the above switching operation, the voltage applied to the EL light emitting element (3) changes in a predetermined cycle, and the EL light emitting element (3) lights up.

Here, when the second switch (5) is grounded as in the conventional case, the electric charge charged in the EL light emitting element (3) during the charging period is discharged to the ground during the next discharging period. Will be lost. Therefore, in the drive circuit of the present invention, the charge charged during the charging period is collected in the charge collecting capacitor (6) provided on the input side of the power supply voltage via the second switch (5). The capacity of the charge recovery capacitor (6) is sufficiently larger than the equivalent capacity of the EL light emitting element (3), and the power supply voltage Vin is the high voltage output V.
If it is sufficiently smaller than out, the decrease in the peak value of the AC voltage after switching can be suppressed, and the same effect as when the second switch (5) is grounded can be obtained, and the brightness of the EL light emitting element (3) is It never drops. Thus, by collecting the charge charged in the EL light emitting element (3) during the charging period into the charge recovery capacitor (6) during the discharging period, the charge is used for the voltage supply in the next charging period. To be done. At this time, the diode (7) provided on the input side of the power supply voltage can prevent the current from flowing into the power supply side and prevent malfunction due to noise.

In the above embodiment, the case where the switching circuit (2) is composed of the first and second switches (4) and (5) has been described, but the present invention is not limited to this. It is also possible to configure the circuit as shown in FIG.

That is, the inverter of this embodiment has the first to fourth switches (4) (5) (9) (1) as shown in FIG.
A switching circuit (2) consisting of 0) is used. Specifically, the switching circuit (2) is connected to the output of the booster circuit (1), and has a first switch (4) and a fourth switch (4).
Switch (10) series circuit and the third switch (9)
And a series circuit of the second switch (5) are connected in parallel to form a circuit. The EL light emitting element (3) includes a first switch (4) and a fourth switch (10).
Connection point, the third switch (9) and the second switch (1
0) connection point.

A switching circuit (2) having the above configuration
In the inverter having, when the DC power supply voltage Vin is supplied to the booster circuit (1), the booster circuit (1) boosts the DC high voltage, and the DC high voltage output Vout is passed through the switching circuit (2). Are applied to the EL light emitting element (3).
At this time, the control circuit (8) causes the switching circuit (2)
Is switched to charge the EL light emitting element (3) with a DC high voltage output. That is, in the switching circuit (2), when the first and second switches (4) and (5) are closed while the third and fourth switches (9) and (10) are opened, a high voltage output is generated. Vout is charged with the (a) side of the EL light emitting element (3) as + and the (b) side as −. Next, when the third and fourth switches (9) and (10) are closed while the first and second switches (4) and (5) are open, the high voltage output Vout is EL The light-emitting element (3) is charged with (b) side as + and (a) side as −. By repeating this switching operation, the polarity of the high voltage output Vout applied to the EL light emitting element (3) is converted in a predetermined cycle to become alternating current, and the EL light emitting element (3) is turned on.

Here, the fourth and second switches (10)
If the connection point of (5) is grounded as in the past,
The charges charged during the half cycle of the driving period of the EL light emitting element (3) are discharged to the ground and lost in the next half cycle.
Therefore, in the drive circuit of the present invention, the charge recovery capacitor provided on the input side of the power supply voltage through the fourth switch (10) or the second switch (5) is used for the charge charged every half cycle. It is collected in (6) and the collected charges are used for charging the EL light emitting element (3) every next half cycle.

[0025]

According to the drive circuit of the capacitive load of the present invention, the electric charge charged during the charging period of the capacitive load is not discharged to the ground during the next discharging period, and the power supply voltage is input. Since it is recovered by the charge recovery capacitor provided on the side, the charge utilization rate is good, and the driving efficiency can be greatly improved. Further, as compared with the conventional method using the resonance inductor used as another means for improving the driving efficiency, the miniaturization is easier to realize and its practical value is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a drive circuit for a capacitive load according to the present invention.

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

[Explanation of symbols]

 1 Booster circuit 2 Switching circuit 3 Capacitive load [Distributed EL light emitting element] 6 Charge recovery capacitor 7 Diode 8 Control circuit

Claims (3)

[Claims] 1. A drive circuit for a capacitive load, which converts a DC power supply voltage into a DC high voltage and charges and discharges the high voltage into a capacitive load, wherein the capacitive load is charged to the input side of the power supply voltage. A drive circuit for a capacitive load, which is provided with a capacitor for collecting the accumulated electric charge. 2. The drive circuit according to claim 1, further comprising a diode provided on an input side of the power supply circuit, the diode preventing the electric charge charged in the capacitive load from flowing into the power supply side. Drive circuit. 3. The drive circuit according to claim 1, further comprising a booster circuit for boosting a DC power supply voltage to a DC high voltage, and a switching circuit for charging a DC high voltage output of the booster circuit to a capacitive load. And a switching circuit for discharging the electric charge charged in the capacitive load to a charge recovery capacitor provided on the input side.