JPH0732071B2 - Lighting control device for EL element - Google Patents

Description

The present invention relates to a lighting control device suitable for lighting control of EL elements and the like.

[Conventional technology]

FIG. 4 is a diagram showing a schematic configuration of a conventional lighting control device of this type. This lighting control device is for lighting the EL element 1, and is composed of a lighting circuit 2 and a dimming circuit 3 connected to a DC power source of Vcc. The lighting circuit 2 is provided with a variable output inverter, the switching transistor Q ₁ is connected to the primary winding P of the inverter transformer T ₁ , and the EL element is connected to the secondary winding S via capacitors C ₁ and C _2. Element 1 is connected. Further, the dimming circuit 3 includes a switching regulator 4 composed of an IC and controls the transistor Q ₂ to control the primary winding P of the inverter transformer T _1.
The EL element 1 is dimmed by changing the input.

In the lighting control device configured as described above, when the EL element 1 causes dielectric breakdown due to overvoltage input or the like, or the EL element 1 is disconnected by mechanical vibration,
The load is open. In addition, when the terminals or lead wires of the EL element 1 are in contact with each other or the EL element 1 is extremely deteriorated by moisture absorption at high temperature, the load is short-circuited.

When the load becomes open, not only the EL element 1 does not light up, but also the load becomes extremely light, so the output voltage rises several times and the output frequency becomes several kHz, which is quite A harsh sound is produced. At this time, it exceeds the rated voltage of the switching transistor Q _1, transistor
Q ₁ is destroyed short-circuit current flows, heat generation, smoke or the like may occur. Further, even when the load is short-circuited, the transistor Q ₁ continues to be turned on, which may cause heat generation, destruction, and smoke generation, which may lead to a fire. Therefore, for example, as shown in FIG. 4, a current fuse or a temperature fuse F ₁ is inserted in the power supply input circuit, and when a load abnormality such as a load open or a load short circuit occurs, the fuse F ₁ is blown to cause an excessive load. It has been attempted to prevent a large amount of current from flowing. Also, a capacitor in parallel with EL element 1
It is also practiced to connect C ₁ and a capacitor C ₂ in series to prevent heat generation, destruction, and smoking. When these capacitors C ₁ and C ₂ are installed, E
Even when the L element 1 is open, the capacitor C ₁ acts as a load, so the output voltage and frequency will be higher than in the normal state, but the values will not cause circuit damage and will prevent heat generation and smoke generation. be able to. Further, even when the EL element 1 is short-circuited, the capacitors C ₁ and C ₂ work as a load, so that the oscillation can be continued without being stopped, and the heat generation and the smoke generation can be prevented.

On the other hand, the variable resistor VR ₁ is used to perform the dimming of the EL element 1, and the change of the resistance value is converted into the change of the voltage value by the switching regulator 4 to change the input voltage of the lighting circuit 2. Dimming is performed by.

Further, by making the lighting circuit 2 have a constant current characteristic or a characteristic that the current rises when the load impedance becomes high, the EL element 1 is kept at room temperature,
Even when it deteriorates due to normal humidity, the voltage is increased to prevent an apparent decrease in brightness.

[Problems to be Solved by the Invention]

However, in the conventional lighting control device as described above, or to set the dimming by the variable resistor VR _1, also prevents excess current by the current fuse or temperature fuse F _1, or a capacitor C _1, C ₂ Has been connected to a load circuit to prevent overcurrent, which causes the following problems.

a. It is difficult to set the current fuse because the circuit current at lighting and the circuit current at abnormal time change depending on the conditions such as size and deterioration state of EL element 1, set brightness, circuit constant, temperature, etc. It is difficult to select the fusing temperature depending on the installation location, and the reliable operation of the fuse F ₁ cannot be expected, resulting in a lack of safety.

b. Since a load abnormality is indirectly detected by a current change or temperature change, the responsiveness is poor, and some component parts operate after failure, so they may not be reused.

c. When the capacitors C ₁ and C ₂ are connected to the EL element 1, power is consumed by the capacitors C ₁ and C ₂ even during normal lighting, so the power consumption is large, the efficiency is reduced, and the inverter Components such as transformers are also large.

d. Since dimming is set by the variable resistor VR ₁ , dimming control cannot be performed in conjunction with other lighting devices.

e. When the capacitors C ₁ and C ₂ are connected to the EL element 1, changes on the load side are reduced and changes in voltage and frequency are reduced, so that the brightness assurance function is deteriorated and stable emission brightness cannot be obtained. When a brightness compensation function such as constant current characteristics is added,
When the EL element 1 deteriorates due to moisture absorption due to continuous lighting in a high-temperature and high-humidity environment, the load impedance decreases as opposed to deterioration at room temperature and normal humidity. Therefore, the applied voltage to the EL element 1 decreases due to moisture absorption deterioration. As a result, the brightness becomes low, and when moisture absorption further progresses, the oscillation stops and the lamp does not light up, and stable light emission cannot be obtained.

The present invention has been made focusing on such a problem, and can detect load abnormality reliably and with good response, consumes less power, and can perform dimming control in cooperation with other lighting devices. It is an object of the present invention to obtain a lighting control device capable of achieving stable and stable light emission brightness.

[Means for Solving the Problems]

The lighting control device of the present invention includes a lighting circuit that has a variable output inverter and performs constant current control of an EL element, and a DC conversion circuit that converts a pulse signal for dimming control into a DC signal according to its duty ratio. A dimming circuit that performs dimming by changing the input to the transformer of the inverter according to the DC signal, and a detection circuit that detects a load abnormality from a change in the output of a switching element connected to the inverter transformer. A constant voltage power source is supplied from the light control circuit to the DC conversion circuit, and a non-lighting prevention circuit is provided for switching from constant current control to constant voltage control when the load impedance becomes small.

[Action]

In the lighting control device of the present invention, since the load abnormality is detected from the change of the input of the switching element connected to the inverter transformer of the lighting circuit, the load abnormality can be detected quickly and surely, and the dimming control Since the pulse signal is converted to a DC signal to control the inverter and the conversion circuit is supplied with a constant voltage power supply from the dimming circuit, dimming control linked with other lighting devices can be performed and stable. The emission brightness obtained is obtained.

〔Example〕

FIG. 1 is a block diagram showing a circuit configuration of a lighting control device according to an embodiment of the present invention. In the figure, 1 is an EL element that is a load, and 2 is a lighting circuit having a variable output self-exciting inverter, which performs constant current control of the EL element 1. 3 is a dimming circuit that performs dimming by changing the input voltage to the lighting circuit 2.
It has a switching regulator with a constant voltage function. Reference numeral 5 is a DC conversion circuit for converting a pulse signal for dimming control from an illumination controller (not shown) into a DC signal corresponding to its duty ratio. The dimming circuit 3 is a transformer of the inverter of the lighting circuit 2 according to the DC signal. Change the input to. 6a and 6b are a short-circuit detection circuit that detects a load short circuit and stops the oscillation of the lighting circuit 2, and an open detection circuit that detects a load open and stops the oscillation of the lighting circuit 2. These detection circuits 6a and 6b, respectively.
Both detect a load abnormality (a short circuit or an open state of the EL element 1) from a change in the output of the switching element connected to the transformer of the inverter. Reference numeral 7 is a non-lighting prevention circuit that switches the lighting circuit 2 from constant current control to constant voltage control when the load impedance becomes low.

FIG. 2 is a circuit diagram showing a specific configuration of the above lighting control device, and the same reference numerals as those in FIG. 4 denote the same components. A switching transistor Q ₁ is connected to the primary winding P of the inverter transformer T ₁ of the lighting circuit 2, and a resistor is used as a CR circuit for phase shift correction to prevent abnormal oscillation between the base and collector of the transistor Q _1. A series circuit of R ₁ and capacitor C ₃ is connected. Then, the change in the collector voltage of the transistor Q ₁ (the primary side input voltage of the inverter transformer T ₁ ) is detected by the detection circuits 6a and 6b. Further, since the feedback winding F of the inverter transformer T ₁ uses the intermediate tap of the secondary winding S, one transformer terminal is omitted. The primary winding P and the feedback winding F are connected so as to be positively fed back to the transistor Q ₁ .

Next, the operation will be described with reference to the waveform chart of FIG. Third
The figure shows the signal waveform of each part (a to g) in FIG.

The DC conversion circuit 5 is a pulse signal (a in FIG. 3) from a dimming illumination controller such as a light bulb in a vehicle.
Is input to the switching regulator 4 of the dimming circuit 3 after being amplified by the transistor Q ₃ and smoothed by the capacitor C ₄ (b in FIG. 3). The switching regulator 4 of the dimming circuit 3 controls ON / OFF of the transistor Q ₂ according to the input voltage (DC voltage), and the lighting circuit 2
Control the output voltage to. At this time, the input voltage to the dimming circuit 3 also changes depending on the duty ratio of the pulse signal, so that the output voltage of the dimming circuit 3 also changes accordingly.
Since the output voltage of the dimming circuit 3 is the input voltage of the lighting circuit 2, the applied voltage of the EL element 1 changes according to the above-mentioned pulse signal, and the dimming of the EL element 1 can be performed.

Here, when smoothing the pulse signal, the transistor Q ₃
If it is directly input to the integrating circuit of the capacitor C ₄ and the resistor R ₃ without passing through, the level of the DC voltage that smoothed the pulse signal changes due to the fluctuation of the power supply voltage (Vcc), and the change in the emission brightness of the EL element 1 and the flicker. Occurs. However, in the present embodiment is carried out the pulse signal inputted to the integration circuit of a capacitor C ₄ via the transistor Q _3, and the power supply to the transistor Q ₃ from the constant-voltage power supply of the switching regulator 4. Therefore, even if the power supply voltage fluctuates and the voltage level of the pulse signal from the illumination controller fluctuates, it can be smoothed in the form of a pulse signal having a constant voltage level, and can be smoothed to the dimming circuit 3. The output voltage also does not change. Therefore, the change in brightness and the flicker due to the change in the power supply voltage are prevented, and it is not necessary to separately provide the stabilizing power supply.

Next, the operation of the lighting circuit 2 having an inverter will be described. First, when the base current is supplied to the transistor Q ₁ through the primary winding P of the transformer T ₁ and the resistor R ₅ , the current amplified by the transistor Q ₁ flows through the primary winding P of the transformer T ₁ . Then, a voltage is induced in the feedback winding F of the transformer T ₁ , a positive feedback current is supplied to the base of the transistor Q ₁ through the resistor R ₆ and the capacitor C ₅ , and the transistor Q ₁ rapidly turns on. Then, the positive feedback is further applied to the base of the transistor Q ₁ ,
Q ₁ is fully on. As a result, the current flowing in the primary winding P becomes saturated, the magnetic flux change generated in the transformer T ₁ disappears, and at the same time, the voltage induced in the feedback winding F and the secondary winding S also disappears. The base current of transistor Q ₁ begins to decrease. Then, the collector current also begins to decrease, and the current flowing in the primary winding P also decreases, so that a voltage opposite to that generated before is generated in the feedback winding F and the base current of the transistor Q ₁ rapidly increases. Head in the direction of turning off. When the transistor Q ₁ is made completely turned off, the transistor Q ₁ again through resistor R ₅
The base current begins to flow to. By repeating the above operation, the transistor Q ₁ is repeatedly turned on and off, and the inverter of the lighting circuit 2 continues stable oscillation.

Here, the case where the load is opened will be described. Open detection circuit 6b is a frequency change upon open load detected from the collector of the transistor Q _1, has a function of turning off the base of the transistor Q _1. that time,
In general, the EL element 1 is a parallel circuit of a capacitor C and a resistor R, of which the C component is the majority. Then, normally, oscillation is performed at the resonance frequency of the C component of this load and the inductance L of the secondary winding S of the transformer T ₁ . However, when the load is opened, the C component of the load disappears, and oscillation occurs at an extremely high frequency that resonates with the inductance L of the secondary winding S of the transformer T _{1 and} the interwinding capacitance. This difference in frequency
A high-pass filter composed of C ₆ and resistor R ₇ is used to detect by extracting only high-frequency components,
Transistor Q converted to direct current with D ₁ and capacitor C ₇
Supply to base of ₄ . As a result, the transistor Q ₄ is turned on, and the base of the transistor Q ₁ connected to the collector of the transistor Q ₄ is turned off, so that the oscillation is stopped. Therefore, the transistor Q ₁ even when the load open never exceed the voltage rating, since the transistor Q ₁ is substantially off, breakdown, heating, situation that smoke can be avoided.

When the load is short-circuited, the collector voltage waveform of transistor Q ₁ is almost constant during normal lighting.
Oscillation continues between GND and 2Vcc, but when the load is shorted, the collector voltage of transistor Q ₁ rises to Vcc. Short detection circuit 6a has the function of the transistor detects a change in the collector voltage of Q _1, to turn off the base of the transistor Q _1. At that time, when the load is short-circuited first, the output voltage becomes 0, so that no voltage is generated also in the feedback winding F of the transformer T _{1 and} the feedback to the base of the transistor Q ₁ is lost, so that the oscillation stops, The collector voltage of the transistor Q ₁ rises to almost the input voltage of the lighting circuit 2. Therefore, resistor R ₈ and diode D ₂
The base current of the transistor Q ₄ flows through the transistor Q ₄ is turned on, the base potential of the transistor Q ₁ which is connected to the collector of the transistor Q ₄ is lowered. Therefore, the DC base current almost does not flow through the transistor Q ₁ through the resistor R ₅ , and the transistor Q ₁ is turned off, so that the heat generation, the destruction, and the smoke generation can be similarly avoided.

However, considering the case of normal lighting, the collector voltage waveform of the transistor Q ₁ is as shown in c of Fig. 3 (peak value of about 18 V), and the resistor R ₉ , the capacitor C ₈ , and the transistor Q ₅ are in the absence of the resistor. Sufficient voltage will be applied to the base of transistor Q ₄ through diode D ₂ to turn on transistor Q ₄ even after passing through the integrating circuit of R ₈ and capacitor C ₉ . Therefore, the transistor Q ₄ is turned on, the potential of the base of the transistor Q ₁ connected to the collector of the transistor Q ₄ is lowered, the transistor Q ₁ is turned off, and the oscillation is stopped. That is, the short-circuit detection circuit 6a is activated. The short detection circuit 6a may be able to work only when the load short, since usually do not work when the lighting, the resistor R _9, capacitor C
₈ 、 Use transistor Q ₅ to prevent oscillation from stopping. At that time, the capacitor C ₉ is charged by the collector voltage of the transistor Q ₁ through the resistor R _8, but since the collector of the transistor Q ₁ normally oscillates between GND and 2Vcc, the capacitor C ₈ The AC component with the DC cut (d in Fig. 3: peak value about 4V) is the current limiting resistor R ₉
Through the base of transistor Q ₅ through the transistor
It means that the collector of Q ₅ is repeatedly turned on and off. Then, since the electric charge of the capacitor C ₉ is the voltage reset of the capacitor C ₉ that discharged to GND through the collector of the transistor Q ₅ is continued every one cycle of oscillation during the on period of the collector of the transistor Q _5, the capacitor The terminal voltage of C ₉ does not rise (e in Fig. 3: peak value of about 0.3V), so transistor Q ₄ remains off and transistor Q ₁ continues to oscillate stably. become.

However, when the load is short-circuited and the collector voltage of the transistor Q ₁ rises, the direct current component is cut off to the base of the transistor Q ₅ by the capacitor C _{8 and} no current flows, so that the transistor Q ₅ is not turned on. Therefore, the transistor Q ₄ is turned on and the transistor Q ₁ is turned off. The peak value in FIG. 3f is about 1.4V. Here, in both the open detection circuit 6b and the short detection circuit 6a, after once detecting a load abnormality and stopping the oscillation, the oscillation does not recover and remains stopped even if the abnormality is removed. By turning off the power once, the above stopped state is released, and the device is extremely safe.

Next, the operation of the non-lighting prevention circuit 7 will be described. In this circuit, when the lighting circuit 2 is a circuit with excellent brightness compensation such as constant current characteristics, the collector voltage of the transistor Q ₁ rises when the load impedance becomes low due to moisture absorption deterioration of the EL element 1. Detect transistor Q ₆
Is turned on and the resistor R ₁₀ is short-circuited, so that the lighting circuit 2 is changed from a constant current characteristic to a characteristic close to a constant voltage.

That is, if the EL element 1 is lit for a long time in an atmosphere of high temperature and high humidity, it will deteriorate due to moisture absorption. When the EL element 1 is considered in the parallel circuit of the capacitor C and the resistor R as described above, it can be seen from the actual measurement value that the R component decreases when moisture absorption deteriorates. From a circuit perspective, this means that the load impedance decreases when moisture absorption deteriorates. vice versa,
It is known that the R component increases and the load impedance increases during normal deterioration at room temperature. And
Since the EL element 1 is almost always lit at room temperature, when the EL element 1 deteriorates and the load impedance becomes high, the voltage is increased to suppress the luminance drop,
That is, the lighting circuit 2 is provided with the constant current characteristic or the current rising characteristic. However, when the EL element 1 is provided with such constant current characteristics and the like, when the EL element 1 deteriorates by absorbing moisture in a high temperature and high humidity atmosphere and the load impedance becomes low, on the contrary, the EL element 1
If the applied voltage of is decreased, and further deterioration due to moisture absorption progresses, the oscillation will stop.

Here, looking at the change in the collector voltage waveform of the transistor Q _1, the transistor Q ₁ is turned on as described above, are repeated off, the collector voltage waveform before the deterioration of the EL element 1 of c in Figure 3 However, as moisture absorption deterioration progresses, it changes like g in Fig. 3 and the voltage does not drop to GND. Therefore, the non-lighting prevention circuit 7 is operated by detecting the voltage change.

Also, as a method of providing constant current characteristics, a transistor
There is a method to insert a resistor R ₁₀ between the emitter of Q ₁ and GND.
In this case, if the collector current Ic of the transistor Q ₁ , that is, the load current increases, the voltage across the resistor R ₁₀ increases and the increase in the current is suppressed. If the collector current Ic, that is, the load current decreases, the resistance of the resistor R ₁₀ decreases. The voltage at both ends is reduced to compensate for the decrease in current. Therefore, the resistance
If R ₁₀ is short-circuited, this function will be stopped, and this will bring it closer to the constant voltage characteristic. The circuit operation, first Although the capacitor C ₁₀ through the resistor from the power supply R ₁₁ is charged, charge diode D ₃ of the capacitor C ₁₀ to the on-period of the transistor Q _1, the transistor Q _1, G through a resistor R ₁₀
Since the voltage reset of the capacitor C ₁₀ that is discharged to the ND is continued for each one period of oscillation, the capacitor
The terminal voltage of C ₁₀ does not rise, therefore the transistor Q ₆ passing through the Zener diode ZD ₁ does not turn on, and the transistor Q ₁ repeats normal oscillation. However, as the moisture absorption contact deterioration of the EL element 1 progresses, the applied voltage decreases, and the voltage across the primary winding P connected by the transformer T ₁ also decreases. At this time, the amplitude of the collector voltage of the transistor Q ₁ becomes small, and the voltage waveform becomes as shown by g in FIG. In this way, when the collector voltage of transistor Q ₁ rises without dropping to GND, capacitor C
The discharge of ₁₀ decreases and the terminal voltage of the capacitor C ₁₀ rises. Then, the base potential of the transistor Q ₆ passing through the Zener diode ZD ₁ also gradually rises, and the transistor Q ₆ turns on at a certain point. As a result, the resistor R ₁₀ is short-circuited and approaches a constant voltage characteristic, so that it is possible to prevent a decrease in applied voltage due to moisture absorption deterioration of the EL element 1 and to continue stable oscillation.

〔The invention's effect〕

As described above, according to the present invention, the load abnormality is detected from the change in the output of the switching element of the inverter, the pulse signal for dimming control is converted into the DC signal to control the inverter, and the conversion circuit thereof is provided. Since the power source of is a constant voltage power source from the dimming circuit, the following effects can be obtained.

I. The load abnormality can be detected reliably and with good responsiveness, the operation is safe, the operation of the detection circuit is stable, and the components can be reused.

B. It can be controlled in conjunction with other lighting devices.

C. Low power consumption and small component parts can be used.

D. Stable emission brightness can be obtained.

Further, by providing the constant current characteristic, brightness compensation can be easily obtained, and further, stable lighting can be obtained by switching to the constant voltage characteristic when the load impedance becomes small.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a lighting control device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a concrete example of the device of FIG. 1, and FIG. 3 is a signal of each part of FIG. Waveform diagrams and FIG. 4 are circuit diagrams showing a conventional example. 1 ...... EL element 2 ...... lighting circuit 3 ...... dimming circuit 4 ...... switching regulator 5 ...... DC converter 6a ...... short detection circuit 6b ...... open detector circuit 7 ...... unlighted preventing circuit T ₁ ...... Inverter transformer Q ₁ …… Switching transistor

Claims (1)

[Claims] 1. A lighting circuit having a variable output inverter for constant current control of an EL element, a DC conversion circuit for converting a pulse signal for dimming control into a DC signal according to its duty ratio, and a DC circuit thereof. A dimming circuit that performs dimming by changing an input to the transformer of the inverter according to a signal, and a detection circuit that detects an abnormality of the EL element from a change in the output of a switching element connected to the transformer of the inverter, A constant voltage power supply is supplied from the dimming circuit to the DC conversion circuit, and a non-lighting prevention circuit is provided for switching the lighting circuit from constant current control to constant voltage control when the load impedance becomes small. Element lighting control device.