JPH0516157B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a DC-AC inverter for lighting an EL lamp.

[Prior Art] EL lamps are lit using alternating current. The alternating current for lighting EL lamps usually has a voltage of several tens to hundreds of volts.
The frequency is adjusted to several hundred to several KHz. In addition, the inverter for lighting the EL lamp is 100V.
It is powered by -60Hz alternating current or several volts direct current. Therefore, the inverter for lighting the EL lamp needs to convert the supplied power into the lighting voltage and frequency of the EL lamp. The inverters commonly used for lighting EL lamps currently use the well-known RCC type booster circuit or Royer type booster circuit to supply the AC voltage generated on the secondary side of the transformer to the EL lamp. This is what I did. By the way, EL lamps deteriorate over time and their brightness gradually decreases. This is because the light emitter deteriorates and the brightness decreases. Furthermore, as the EL lamp deteriorates, the current also decreases. This also causes a decrease in brightness. The reason for the current drop is that the capacitance of the EL lamp decreases over time. Therefore, when an EL lamp is driven by a constant voltage, constant frequency power source, the brightness decreases significantly in a short period of time. To prevent this drawback, inverters have been developed that increase the frequency of the power supply applied to the EL lamp as it is used. This inverter makes effective use of the characteristic of EL lamps, which become brighter when the frequency of the supplied power is increased. This inverter generates electricity over time by increasing the frequency supplied to the EL lamp as it is used.
Prevents the brightness of the EL lamp from decreasing. An inverter that achieves this is shown in Patent Application Publication No. 502009 of 1988. This inverter connects a reactor to an EL lamp,
An EL lamp is used as an oscillation element. Therefore, as the EL lamp deteriorates and its capacitance decreases,
The oscillation frequency is adjusted higher. This type of inverter adjusts the power frequency of the EL lamp to a higher level as the EL lamp deteriorates, so it has the advantage of allowing the EL lamp to remain brightly lit for a long period of time. However, with this type of inverter, when the capacitance of the EL lamp decreases, the voltage applied to the EL lamp becomes extremely high.
EL lamps have the disadvantage of easily causing dielectric breakdown.
This is because when the EL lamp deteriorates, the Q of the series resonant circuit between the EL lamp and the reactor increases. The Q of the series resonant circuit composed of the EL lamp and the reactor increases in proportion to the frequency. Furthermore, as the equivalent parallel resistance of the EL lamp increases, Q also increases. As the equivalent parallel resistance of the EL lamp increases and the frequency increases, the Q of the series resonant circuit increases. The voltage applied across the EL lamp increases in proportion to the Q of the resonant circuit composed of the EL lamp and the reactor. As an EL lamp is used, its capacitance decreases and the resistance connected in parallel in the equivalent circuit increases. Therefore, as the EL lamp deteriorates, the oscillation frequency of this inverter increases, the resistance increases, and the Q value gradually increases. As a result, the voltage applied to both ends of the EL lamp becomes extremely high, causing dielectric breakdown. Furthermore, the current or capacitance of the EL lamp is detected, and the detection signal is used to control the voltage-controlled oscillator circuit.
Inverters for adjusting the supply frequency of EL lamps have also been developed (Japanese Patent Application Laid-open Nos. 55-28247 and 61-277192). The inverters described in these publications have deteriorated EL lamps,
When the capacitance decreases or the current decreases,
The oscillation frequency of the voltage controlled oscillation circuit is adjusted high. When the frequency of the alternating current used to light an EL lamp increases, the current increases and the lamp becomes brighter. For this reason,
It has the advantage of reducing the decrease in brightness.

[Problem to be solved by the invention]

However, the inverters described in these publications convert the current and capacitance of the EL lamp into a detected voltage, compare this detected voltage with a reference voltage using a comparator, and control the voltage based on the difference between the reference voltage and the detected voltage. It is input to the oscillation circuit to adjust the oscillation frequency. The inverter of this circuit has the disadvantage that the circuit configuration is complicated and the cost of parts is high. Furthermore, there is a drawback that the circuit for adjusting the amount of change in the oscillation frequency becomes complicated in response to deterioration of the EL lamp. With a simple circuit configuration, the EL lamp cannot be lit brightly for a long time. This invention was developed with the aim of solving these shortcomings of conventional inverters for EL lamps.An important objective of this invention is to provide a simple circuit configuration that allows EL lamps to operate for long periods of time. An object of the present invention is to provide an inverter for an EL lamp, which can light up brightly over a long period of time and can control the AC voltage supplied to the EL lamp.

[Means to solve problems]

The inverter of the present invention has the following configuration in order to achieve the above-mentioned object. In other words, the inverter for EL lamps of the present invention changes the input voltage
Equipped with a voltage adjustment circuit that changes the voltage to a voltage that can light the EL lamp and converts it to DC, an oscillation circuit and an output circuit, and converts the output of the voltage adjustment circuit to AC.
-This is an improved inverter that includes an AC conversion circuit and a frequency control circuit that adjusts the frequency of AC supplied to the EL lamp, and changes the supply frequency when the EL lamp deteriorates. The inverter of the present invention has an extremely simple circuit configuration, and the frequency control circuit is composed of a reactor and a feedback element in order to prevent a decrease in brightness due to deterioration of the EL lamp. The reactor is
It is connected between the EL lamp and the output side of the DC-AC conversion circuit to form a series resonant circuit with the EL lamp. Feedback elements are reactor and EL
It is connected between the connection point with the lamp and the oscillation circuit of the DC-AC conversion circuit. The feedback element feeds back a trigger signal from the series resonant circuit of the EL lamp and the reactor to the oscillation circuit. The amount of change in the oscillation frequency of the oscillation circuit of the DC-AC conversion circuit is controlled by the amount of feedback from the feedback element. In the feedback element, when the impedance is lowered, the amount of feedback increases, and when the impedance is increased, the amount of feedback is decreased. When the amount of feedback is increased, the oscillation frequency of the oscillation circuit is strongly pulled from the free-running oscillation frequency to the resonance frequency of the EL lamp and the reactor. Therefore, the amount of change in the oscillation frequency of the oscillation circuit can be easily adjusted by adjusting the impedance of the feedback element.

[Preferred embodiment]

Embodiments of the present invention will be described below based on the drawings. However, the embodiments shown below illustrate an inverter for embodying the technical idea of the present invention, and the inverter of the present invention is not limited to the following circuit configuration. The inverter of this invention has the following features within the scope of the claims:
Various changes are made. The inverter for lighting the EL lamp shown in Figure 1 is
It is equipped with a voltage adjustment circuit that boosts the input voltage to a voltage that can be used to light the EL lamp and converts it to DC. The voltage adjustment circuit includes a booster circuit and a rectifier circuit. A booster circuit and a rectifier circuit are transistors Q ₁ ,
Q ₂ , oscillation transformer T ₁ , rectifier diode D ₁ ,
D ₂ , reactor L ₁ , L ₂ , resistor R ₁ , capacitor
It uses a Royer circuit consisting of _C3 . The boost circuit converts the supply voltage V ₁ to the EL lamp lighting voltage
Other well known circuits capable of boosting to V ₂ can also be used. This circuit boosts the supply voltage V ₁ to V ₂ . The boosted alternating current is rectified by diodes D ₁ and D ₂ and converted into smooth direct current by reactor L ₂ and capacitor C ₃ . The DC-AC conversion circuit includes an oscillation circuit and an output circuit. The output circuit is controlled by the output signal of the oscillation circuit to switch and convert the output voltage _V2 of the voltage regulation circuit into alternating current that is supplied to the EL lamp. The oscillation circuit for lighting the EL lamp is a transistor.
It consists of a multivibrator consisting of Q ₃ , Q ₄ , resistors R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , and capacitors C ₄ and C ₆ . The free-running oscillation frequency of the multivibrator is determined by resistors R ₄ and R ₅ and capacitors C ₄ and C ₅ . The oscillation circuit, which is a multivibrator, oscillates a square wave. This oscillation circuit oscillates at a free-running oscillation frequency when no feedback is applied from the resonant circuit of the EL lamp and reactor. The output circuit is composed of transistors Q ₅ , Q ₆ , Q ₇ , Q ₈ which are switching elements, and resistors R ₈ , R ₉ , R _10,11 . In this circuit, when transistor _Q4 in the oscillation circuit turns on and off repeatedly, the transistor in the output circuit
Q ₅ and Q ₆ are turned on and off alternately, and then transistors Q ₇ and Q ₈ are turned on by resistors R ₈ , R ₉ , R ₁₀ , and R ₁₁ .
will be turned on and off alternately. A reactor is installed at the connection point of transistors Q ₇ and Q _8.
L ₃ is connected, and the EL lamp is connected to this. That is, the EL lamp and the reactor _L3 are connected in series, and this is connected as a load of the output circuit. Transistors Q ₇ and Q ₈ of the output circuit alternately repeat on/off operations. The output circuit therefore provides a square wave output to the resonant circuit of the EL lamp and reactor _L3 . The square wave pulse voltage supplied from transistors Q ₇ and Q ₈ is connected to the capacitive EL lamp and reactor.
Series resonance occurs with L ₃ , and a sine wave is applied to the EL lamp. Feedback is applied to the oscillation circuit from the voltage generation point of the resonant circuit between the EL lamp and the reactor _L3 in order to pull the oscillation frequency of the oscillation circuit into the resonant frequency of the resonant circuit. The inverter shown in Figure 1 applies feedback to the oscillation circuit from the connection point between reactor _L3 and the EL lamp via resistor _R12 and capacitor _C6 . Resistor _R12 adjusts the amount of feedback from the resonant circuit of the EL lamp and reactor _L3 . resistance
If R ₁₂ is small, the feedback will be strong and the oscillation frequency of the oscillator circuit will be more strongly pulled to the resonant frequency. On the other hand, if the resistor _R12 is large, the amount of feedback from the resonant circuit between the EL lamp and the reactor _L3 will be small, the pull from the resonant circuit will be small, and the oscillation circuit will oscillate at a frequency close to the free-running oscillation frequency. . Adjust resistor R ₁₂ , EL lamp and reactor L ₃
The amount of feedback from the resonant circuit to the oscillation circuit can be adjusted. As the EL lamp deteriorates and changes over time, the capacitance component decreases, and along with this change, the resonant frequency increases and moves to a new optimal point. For this reason, EL
The lamps have progressively higher frequencies and voltages, allowing for less brightness loss over longer periods of time.

【Effect of the invention】

The inverter for an EL lamp of the present invention forms a series resonant circuit with an EL lamp and a reactor, and feeds back a trigger signal from the resonant circuit to an oscillation circuit of a DC-AC conversion circuit via a feedback element. A trigger signal fed back to the oscillator circuit causes the oscillator circuit to shift its frequency from the free-running frequency and operate at a new frequency. The amount of feedback can be easily changed by adjusting the values of the resistors and capacitors that are the feedback elements. When the amount of feedback is increased, the frequency of the oscillation circuit is strongly pulled into the resonant frequency of the EL lamp.
In other words, the oscillation frequency approaches more closely the resonant frequency of the EL lamp and reactor. The frequency of the oscillator circuit can also be approximately equal to the resonant frequency of the EL lamp. In this case, the reduction in brightness of the EL lamp can be minimized, but when the EL lamp deteriorates, the supply voltage becomes abnormally high, causing dielectric breakdown. In order to prevent this from happening, the inverter of the present invention adjusts the impedance of the feedback element to adjust the amount of feedback. Increasing the amount of feedback reduces the reduction in brightness of the EL lamp, and reducing the amount of feedback effectively prevents dielectric breakdown. The inverter of the present invention reduces the reduction in brightness of the EL lamp by adjusting the values of the resistance and capacitor of the feedback element to optimal values.
In addition, it is possible to easily adjust to the optimum conditions that do not cause dielectric breakdown. Furthermore, a noteworthy feature of the present invention is that the circuit configuration can be made extremely simple in spite of realizing such excellent features. This is because the frequency control circuit that lights up the deteriorated EL lamp brightly is composed of a reactor and a feedback element. The reactor is connected to the EL lamp to form a series resonant circuit, and the oscillation frequency is directly controlled by inputting a trigger signal from this resonant circuit to the oscillation circuit. Therefore, the inverter of the present invention has the advantage of being able to be mass-produced at low cost with an extremely simple circuit, and also capable of lighting EL lamps in ideal conditions.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a specific example of an inverter.

Claims (1)

[Claims] 1. A DC-AC device that includes a voltage adjustment circuit that changes the input voltage to a voltage that can light the EL lamp and converts it into DC, an oscillation circuit, and an output circuit, and converts the output of the voltage adjustment circuit into AC. In an inverter that includes a conversion circuit and a frequency control circuit that adjusts the frequency of alternating current supplied to the EL lamp, and is configured to change the supply frequency when the EL lamp deteriorates, the frequency control circuit connects the EL lamp and the DC- A reactor is connected between the output side of the AC conversion circuit and forms a series resonant circuit with the EL lamp, and a trigger signal is input from the connection point between the reactor and the EL lamp to the oscillation circuit of the DC-AC conversion circuit to oscillate. and a feedback element that controls the frequency, and is configured such that the amount of change in the oscillation frequency of the oscillation circuit of the DC-AC conversion circuit is controlled by the amount of feedback fed back from the feedback element to the oscillation circuit. An inverter for EL lamps featuring: