JPH0346789A - Light emitter - Google Patents

Abstract

PURPOSE:To miniaturize a transformer and prevent any generation of an audible noise by providing, in an electric power unit, a current source for operating the transformer at a frequency higher than a lighting frequency during a charg ing period to supply a charging current, and a discharge circuit for discharging a stored charge of a surface light emitting element during a discharging period. CONSTITUTION:During a period T1, a current source 1 is operative while a discharge circuit 2 is inoperative. Meanwhile, during a period T2, the current source 1 is inoperative while the discharge circuit 2 is operative. In an EL light emitter, an El lighting frequency corresponds to a basic period T; and an operative frequency of a transformer used in the current source 1, to a period (t) of a rectangular wave. Accordingly, only the operative frequency of the transformer can be sufficiently increased at the low EL lighting frequency, thereby miniaturizing the transformer. In addition, the operative frequency of the transformer can be set higher than that in an audible band, thus preventing any generation of an audible noise.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to 2, for example, E L (Hlectro Lum
The present invention relates to a light-emitting device that causes a surface-emitting element such as a sheet to emit light.

[Conventional technology]

A light emitting device using an EL receipt surface emitting element is used in a bank light of a liquid crystal display and the like.

Such light emitting devices employ a method of performing a light emitting operation by applying a sine wave AC voltage or an AC voltage having a waveform close to a sine wave AC voltage to the EL receipt.

In this system, the power supply device (DC-AC inverter) that generates alternating voltage for EL receipt operation from a DC voltage source mainly uses the EL receipt capacitance, which is a capacitive load, and the transformer built into the power supply device. A circuit that utilizes resonance with the inductance of the device is often used.

Therefore, in the conventional light emitting device, the operation of the transformer and the frequency of the applied voltage for frequency EL receipt light emission (hereinafter referred to as rEL lighting frequency) are necessarily equal.

On the other hand, a light emitting device that does not rely on such resonance has also been put into practical use, but even in this case, the EL lighting frequency and the operating frequency of the transformer are the same.

The main reason for this is the EL receipt characteristic in which when the EL lighting frequency is increased, the EL receipt current consumption increases exponentially and the luminous efficiency decreases.

Therefore, the operating frequency of the transformer in the power supply is
It was determined by the optimum EL lighting frequency for EL receipt luminous efficiency.

[Problem to be solved by the invention]

In any of the conventional light emitting devices described above, the operating frequency of the transformer used in the power supply device is equal to the EL lighting frequency.

As a result, the size of the transformer used in the power supply device is also limited by the EL lighting frequency, resulting in the problem that the transformer cannot be made smaller.

On the other hand, since the current EL lighting frequency is equal to the audible frequency range of one human being, there is a problem in that unpleasant audible noise is generated due to the magnetostrictive phenomenon of the magnetic components in the transformer.

This problem can be solved by increasing the operating frequency, but as mentioned above, in all conventional systems, the operating frequency of the transformer has to be equal to the EL lighting frequency. It is difficult to emit light effectively, and it is not a fundamental solution.

This invention was made in view of the above problems, and it is possible to reduce the size of the transformer used in the power supply device without reducing the luminous efficiency of the EL receipt, and also to reduce the generation of audible noise. It is an object of the present invention to provide a light emitting device with a capacitive load that can prevent such problems.

[Means to solve the problem]

In order to achieve the above object, the light emitting device according to claim 1 includes nine surface light emitting elements, supplying an alternating current for light emission to the surface light emitting elements, and charging the five surface light emitting elements corresponding to the lighting frequency of the surface light emitting elements. A power supply device that operates with a basic cycle consisting of a period and a discharge period, and this power supply device operates a transformer at a frequency higher than the lighting frequency during the charging period to periodically apply periodic power to the surface emitting element. This device includes a current source that supplies a charging current and a discharge circuit that discharges the accumulated charge of the surface emitting element during a discharge period.

Further, the light emitting device according to claim 2 includes a single surface light emitting element, an alternating current for light emission is supplied to the surface light emitting element, and a charging period and a discharging period corresponding to the lighting frequency of the surface light emitting element. A power supply device that operates at a basic cycle, and this power supply device operates a transformer at a frequency higher than the lighting frequency during the charging period to supply a periodic charging current to the surface emitting element. This device includes a power source and a power feedback circuit that periodically feeds back the accumulated charge of the surface emitting element to the current source at the operating frequency of the transformer during the discharge period.

Furthermore, the light emitting device according to claim 3 is provided in claim 1 or 2.
The light emitting device described in 2 is provided with a polarity reversal switch that switches the charging polarity of the surface light emitting element every basic cycle.

That is, this invention uses the light emitting device according to claim 1 as a basic invention, and the invention according to claim 2.

In place of the discharge circuit in the light emitting device according to claim 1,
It is equipped with a power feedback circuit that periodically feeds back the accumulated charge of the surface emitting element to the current source at the operating frequency of the transformer during the discharge period.

Furthermore, the invention according to claim 3 is based on the invention according to claim 1 or 2.
The light emitting device described in 2 is provided with a polarity reversal switch that switches the charging polarity of the surface light emitting element every basic cycle.

[For production]

According to the light emitting device of the present invention, in any light emitting device, the charging period and the discharging period are repeated at a basic cycle corresponding to the lighting frequency for optimal operation of the surface emitting element to be driven, so that one luminous efficiency is reduced. The surface emitting device is driven at the optimum operating point.

In addition, the current source can operate the transformer at a frequency higher than one lighting frequency to periodically charge the surface emitting device, so the operating frequency of the transformer.

The lighting frequency can be set sufficiently higher than the optimum lighting frequency of the surface emitting element.

As a result, the capacity of the transformer can be reduced, and the transformer can be made smaller.

Further, since the operating frequency of the transformer can be set to a value exceeding the audible frequency, generation of audible noise can be prevented.

〔Example〕

Embodiments of the light emitting device of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an EL device according to an embodiment of the light emitting device according to claim 1.
1 is a block diagram showing the configuration of a light emitting device, and this EL light emitting device includes an EL receipt which is a nine-sided light emitting element, and this EL
It is composed of a current source 1 connected in parallel with the receipt, and a power supply device IO consisting of a discharge circuit 2.

The current source 1 supplies the EL receipt with an output current value that changes periodically during the charging period of the basic cycle, which will be described later. The AC voltage thus obtained is stepped up by a transformer and supplied to the EL receipt.

The discharge circuit 2 periodically generates a discharge path from the EL receipt during a basic cycle discharge period to be described later, and is composed of a resistor, a switch circuit, and the like.

FIG. 2 is a diagram showing a current waveform flowing at point A in this EL light emitting device.

Although the current waveform is a rectangular wave in this example, this is for the purpose of simplifying the explanation, and it goes without saying that the current waveform is not limited to a rectangular wave.

As shown in FIG. 2, this EL light emitting device operates according to a basic period T consisting of two periods T1 and T2. This basic period T corresponds to the EL lighting frequency and is 1
The period t of each square wave is.

It corresponds to the operating frequency of the transformer used in the current source 1.

The operation of this EL light emitting device will be explained below. During one period TI, the current source 1 is in an operating state.

The discharge circuit 2 becomes inactive.

As a result, a charging current intermittently flows into the EL receipt at a period indicated by t in FIG.

This charging current causes the EL receipt to emit light.
Because EL receipts have capacitance.

Charge is accumulated.

Next, during the second period TI, the current source 1 is in the non-operating state,
The discharge circuit 2 becomes operational.

As a result, the charges accumulated in the EL receipt during the period T1 are intermittently discharged at a period indicated by t.

During this discharge, the EL receipt emits light due to the discharge current.

According to this EL light emitting device, since the output current of the current source 1 is discontinuous with respect to time, the amount of energy required for one period t may be equal to the energy required for the basic period T divided, so that the current If the internal elements of the source 1 include a power converter.

This means that the power conversion device only needs to have the ability to convert only the energy required for nine periods t.

Generally, a transformer is used in this power converter, so the shorter the 9-period t, the more compact the transformer can be.

On the other hand, in this EL light emitting device, the EL lighting frequency corresponds to the fundamental period T, and the operating frequency of the transformer used in the current source 1 corresponds to the period t of the rectangular wave.

Therefore, since only the operating frequency of the transformer can be sufficiently increased while the EL lighting frequency is kept low, the transformer can be made smaller.

Furthermore, since the operating frequency of the transformer can be set higher than the audible band, generation of audible noise can be prevented.

Note that the current source 1 changes the output current value over time using a circuit that is realized by a combination of a voltage source, a power supply source such as a power source, active elements such as semiconductor elements, and passive elements such as resistors, capacitors, inductors, and transformers. It is something that can be changed along with the transition of.

In the example of the current waveform shown in FIG. 2, this current source is
It can be constructed from a constant current source and an element that performs a switching operation at an arbitrary period.

FIG. 3 is a block diagram showing an EL light emitting device according to an embodiment of the light emitting device according to claim 2 of the present invention.

In this circuit, a power feedback circuit 4 is provided in place of the discharge circuit 2 shown in FIG.

This power feedback circuit 4 has EL during period T1 in FIG.
This circuit feeds back the charges accumulated on the receipt to the current source 1 during nine periods T2.

According to this EL light emitting device, the energy stored in the EL receipt is fed back to the current source 1, so there is no energy loss caused by the energy stored in the EL receipt being consumed during discharging. Efficiency can be increased.

FIG. 4 is a block diagram showing an EL light emitting device according to an embodiment of the light emitting device according to claim 3 of the present invention.

This EL light emitting device has a polarity reversal switch 5a on the picture electrode side of the EL receipt of the EL light emitting device shown in FIG.

5b are provided respectively.

The common terminal of the polarity reversing switches 5a and 5b is.

Each electrode is connected to the EL receipt.

Further, the selection terminals of the polarity reversing switches 5a and 5b are connected to the first
The connection is such that the polarity of the current supplied to the EL receipt is reversed between the state and the second state.

In this EL light emitting device, the polarity reversal switches 5a and 5b are switched every basic cycle T in FIG.

As a result, the EL receipt electrode where charge is accumulated is switched each time charging and discharging are performed.
It is possible to perform the conventional AC operation (the EL receipt terminal voltage has positive voltage and negative voltage states).

Note that in each of the above embodiments, an EL receipt is used as a surface emitting device, but the present invention is not limited thereto, and can be applied to other surface emitting devices without departing from the gist of the invention. It is something that can be done.

〔Effect of the invention〕

As described above, in the light emitting device of the present invention, the operating frequency of the transformer constituting the current source can be set higher than the lighting frequency of the nine surface light emitting elements in any case, so the capacity of the transformer This makes it possible to reduce the amount of noise and to downsize the J transformer.

Furthermore, in any case, the light emitting device of the present invention allows the operating frequency of the transformer to be set higher than the audible frequency, thereby preventing the generation of audible noise and providing a light emitting device free from unpleasant noise. It is something that can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an EL light emitting device according to an embodiment of the light emitting device according to claim 1 of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the light emitting device. FIG. 3 is a block diagram of an EL light emitting device according to an embodiment of the light emitting device according to claim 2 of the present invention, and FIG. 4 is a block diagram of an EL light emitting device according to an embodiment of the light emitting device according to claim 3 of the present invention. FIG. 2 is a block diagram of the device. 1... Current source 2... Discharge circuit 3... EL receipt 4... Power feedback circuit 5a, 5b... Polarity reversal switch 10... Power supply device

Claims (3)

[Claims] (1) A surface emitting device and a power supply device that supplies alternating current for light emission to the surface emitting device and operates in a basic cycle consisting of a charging period and a discharging period corresponding to the lighting frequency of the surface emitting device. This power supply device includes a current source that operates a transformer at a frequency higher than the lighting frequency during the charging period to supply periodic charging current to the surface emitting device, and a current source that supplies periodic charging current to the surface emitting device during the discharging period. 1. A light emitting device comprising: a discharge circuit for discharging accumulated charge of the light emitting device. (2) A surface emitting device and a power supply device that supplies alternating current for light emission to this surface emitting device and operates in a basic cycle consisting of a charging period and a discharging period corresponding to the lighting frequency of this surface emitting device. This power supply device includes a current source that operates a transformer at a frequency higher than the lighting frequency during the charging period to supply periodic charging current to the surface emitting device, and a current source that supplies periodic charging current to the surface emitting device during the discharging period. 1. A light emitting device comprising: a power feedback circuit that periodically feeds back the accumulated charge of the above to a current source at the operating frequency of a transformer. (3) The light emitting device according to claim 1 or 2, further comprising a polarity reversal switch that switches the charging polarity of the surface emitting element every basic cycle.