JPH04229824A - Fluorescent lamp lighting device - Google Patents

Abstract

PURPOSE:To provide accurate photometry without being affected by a quantity of light of a fluorescent lamp by carrying out the photometry of the light quantity around a liquid crystal display within a turn-off period of the fluorescent lamp. CONSTITUTION:An external light detecting circuit 104 feeds a pulse width control circuit 105 with an output signal conformed to a quantity of ambient light, and outputs a pulse of pulse width conformed to the output signal. With an of-off period of this pulse width, a chopper circuit 102 makes a direct current of a DC power source 101 intermit, further it converts the direct current into an alternate current of yet higher frequency at an inverter circuit 10 at the next stage, thereby turning on or off a fluorescent lamp 106 according to the on-off period of the chopper circuit 102. Accordingly, during the lighting of the fluorescent lamp 106 by a control means, the external light detecting circuit 104 will not measure the quantity of ambient light, thus this circuit 104 measures the quantity of ambient light accurately within the off period of the chopper circuit 102, namely, within the turn-off period of the fluorescent lamp 106.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp lighting device used as a backlight for liquid crystal displays and the like.

0002

[Prior Art] Initially, liquid crystal displays were mainly reflective types that utilized the reflection of external light to display information such as characters on the screen, but recently, liquid crystal displays have become backlit types, that is, equipped with a backlight. things have come into use. For example, a backlight consisting of a fluorescent lamp, a lighting device, a reflector, a diffuser, etc. is incorporated into a liquid crystal display. The amount of light, that is, the brightness, of the fluorescent lamp is adjusted according to the detection result. However, since the amount of outside light is constantly detected by the optical sensor, if the optical sensor is attached to a lighting device or near a backlight, it will be affected by the amount of light from the fluorescent lamp, and the accurate amount of outside light will be inaccurate. There was a problem in that the amount of light could not be photometered, and therefore the brightness of the fluorescent lamp could not be adjusted appropriately depending on the brightness around the liquid crystal display.

0003

As described above, conventional backlights have a problem in that they cannot accurately measure the amount of light around the liquid crystal display, that is, the external light. The present invention was made in order to solve the conventional problems, and an object of the present invention is to provide a fluorescent lamp lighting device that can accurately measure the amount of light around a liquid crystal display without being affected by the amount of light from the fluorescent lamp. shall be.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fluorescent lamp, a DC power source for supplying power to the fluorescent lamp, an external light detection circuit for measuring the amount of surrounding light, and an external light detection circuit for measuring the amount of surrounding light. a pulse width control circuit that outputs a pulse with a pulse width corresponding to an output signal of the photodetection circuit; and a pulse width control circuit that turns on and off the DC of the DC power supply, the on-period of which is determined according to the pulse width of the pulse width control circuit. a controlled chopper circuit, an inverter circuit that converts the output from the chopper circuit into an alternating current of a higher frequency during its ON period to light the fluorescent lamp, and controls on/off the photometric operation of the external light detection circuit. A fluorescent lamp lighting device is provided, comprising a control means for turning on the photometric operation during a period when the fluorescent lamp is turned off.

[0005]

[Operation] The external light detection circuit supplies an output signal corresponding to the amount of surrounding light to the pulse width control circuit, and the pulse width control circuit outputs a pulse having a pulse width corresponding to the output signal. Subsequently, the chopper circuit intermittents the direct current of the DC power supply during an on/off period according to the pulse width of the pulse width control circuit, and further,
In the inverter circuit at the next stage, the direct current is converted to alternating current with a higher frequency, and the fluorescent lamp is turned on or off depending on the on/off period of the chopper circuit. At this time, the control means causes the external light detection circuit not to measure the amount of surrounding light while the fluorescent lamp is on, and the external light detection circuit does not measure the ambient light amount during the off period of the chopper circuit, that is, during the off period of the fluorescent lamp. Accurately measure the amount of light in the surrounding area.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a circuit diagram showing an embodiment of a fluorescent lamp lighting device according to the present invention, FIG. 2 is an explanatory diagram showing the level relationship between a sawtooth signal and a control signal, which will be described later, and FIG.
is the blinking of the fluorescent lamp 106 and the transistor Q, which will be described later.
1 is a timing chart showing the on/off relationship between Q1 and Q2.

[0007] This fluorescent lamp lighting device uses a DC power supply 10.
1, a step-down chopper circuit 102, a constant current push-pull inverter circuit 103, an external light detection circuit 104, a pulse width control circuit 105, and a fluorescent lamp 106. The positive terminal of the DC power supply 101, whose negative terminal is connected to the reference potential point, is connected to the base and emitter of the transistor Q3 via the resistor R1 in the step-down chopper circuit 102, and the collector of the transistor Q3 is connected to the base of the transistor Q3. It is connected to the base of transistor Q2 via resistor R2. A connection point between the base and the resistor R2 is connected to the emitter of the transistor Q2 via a resistor R3, and the connection point is connected to a reference potential point. Further, the collector of the transistor Q2 is connected to the anode of the diode D1, and its cathode is connected to the emitter of the transistor Q3 and the choke coil C.
Connected to one end of L.

Furthermore, one end of the choke coil CL is
It is connected to the connection point of the resistors R4 and R5, which have one end connected to the bases of the transistors Q4 and Q5 in the constant current push-pull type inverter circuit 103, and the emitters of the transistors Q4 and Q5 are both connected to the base of the diode D1. connected to the anode. And each collector, respectively,
It is connected to one end of the primary winding of the transformer T, and a capacitor C1 is connected between these collectors in parallel with the primary winding. Note that a feedback winding L for self-excitation is connected between the bases of the transistors Q4 and Q5, and the primary winding of the transformer T, the capacitor C1, and the resistor R4,
The resonant circuit composed of R5 is excited. One end of the secondary winding of the transformer T is connected to one electrode of the fluorescent lamp 106 via the capacitor C2, and the other end is directly connected to the other electrode of the fluorescent lamp 106.

On the other hand, the other end of the resistor R6 in the external light detection circuit 104, which has one end connected to the reference potential point, is connected to the base of the transistor Q1.
The collector of is connected to pins 2, 14, 15 of the control integrated circuit IC in the pulse width control circuit 105, and
Connected to pin 3 via resistor R7. Moreover, the emitter is connected to one end of the light receiving sensor LS, and the emitter is connected to one end of the light receiving sensor LS.
The other end is connected to a reference potential point. Furthermore, the emitter is connected to the anode of the diode D2, and the cathode of the diode D2 is connected to the collector of the transistor Q1 via a resistor R8 and to pin 4 of the control integrated circuit IC.

Furthermore, the cathode of the diode D2 is connected to one end of a parallel circuit of a resistor R9 and a capacitor C3, and the other end of the parallel circuit is connected to the cathode of the light receiving sensor LS. Pin 5 of the control integrated circuit IC;
6 are connected to the reference potential point via a resistor R10 and a capacitor C4, respectively, while a pin 12 is connected to the DC power supply 10.
Connected to the positive terminal of 1. Pins 11 and 8 are connected to the base of the transistor Q3 through the resistor R11 in the step-down chopper circuit 102, and are also connected to the base of the transistor Q1 in the external light detection circuit 104.
Pins 1, 7, 9, 10, 13 and 16 are each connected to a reference potential point.

The control integrated circuit IC has a function as a control circuit that controls the on/off period of the step-down chopper circuit 102 by pulse width modulation. Pin 5 of the control integrated circuit IC
, 6 are not shown in the control integrated circuit IC.
It is connected to a sawtooth wave oscillation circuit, and the sawtooth wave oscillation circuit oscillates a sawtooth wave signal having a magnitude and period set by the resistor R10 and capacitor C4. The sawtooth wave signal and the current supplied to the pin 4 according to the amount of light measured by the light receiving sensor LS, that is, the control signal, are compared by a comparator circuit (not shown),
Next, an electronic circuit including a steering flip-flop circuit in the next stage generates a pulse width modulated output for each period, which has a pulse width proportional to the period during which the sawtooth signal is greater than the control signal. A pulse is generated.

In other words, in FIG. 2, the smaller the level of the control signal is than the level of the sawtooth signal, the more
The pulse width of the pulse within a certain period becomes large, and the period during which no pulse is generated, ie, the off period, becomes short. That is, the duty ratio becomes high. On the other hand, as the control signal becomes larger, the pulse width becomes smaller and the off period becomes longer. That is, the duty ratio becomes low. A transistor (not shown) connected between the pins 10 and 11 is turned on and off in a period depending on the magnitude of the pulse width. Further, the transistors Q1 and Q2 are
As shown in FIG. 3, the on-off periods are opposite to each other, and it functions as a control means for controlling the photometry of the light receiving sensor LS to be performed during the off period of the fluorescent lamp 106.

Next, the operation of the above embodiment will be explained with reference to FIGS. 1 to 3. The transistor Q1 in the external light detection circuit 104 is operated by being supplied with power from the DC power supply 101 via the pins 12 and 14 of the control integrated circuit IC. When the area around the display becomes dark, the light receiving sensor L
The resistance of S increases, the potential at point A increases, and the current flowing through diode D2 increases. The current is supplied as a control signal to pin 4 of the control integrated circuit IC. A sawtooth wave signal output from a sawtooth wave oscillation circuit (not shown) in the control integrated circuit IC, which is set by the control signal, an externally connected capacitor C4, and a resistor R10, is generated by a comparator circuit (not shown). compared (see Figure 2).

Next, from the comparator circuit, an output voltage corresponding to the period in which the level of the sawtooth signal exceeds the level of the control signal is supplied to an electronic circuit at the next stage, which is composed of a steering flip-flop circuit (not shown), etc. The electronic circuit generates an output pulse having a pulse width corresponding to the output voltage. The output pulse turns on a transistor (not shown) connected between the pins 10 and 11 for a period corresponding to the pulse width. That is,
The darker the surroundings, the larger the current supplied to pin 4, ie the control signal, and therefore the smaller the pulse width of the pulse generated within the control integrated circuit IC and the shorter the on-period of said transistor. .

By the way, during the ON period of the above transistor, the potential at point B drops to the reference potential point, and the transistor Q
3 becomes conductive, and therefore transistor Q2 becomes conductive, thereby operating the step-down chopper circuit 102, and during the on-period, DC power supply 101 supplies direct current to constant current push-pull type inverter circuit 103 at the next stage. The constant current push-pull inverter circuit 103 has a self-exciting feedback winding L that provides positive feedback from the collectors of the transistors Q4 and Q5 to the bases of the transistors Q4 and Q5, and automatically switches the transistors Q4 and Q5. The direct current is made into a square wave alternating current with a higher frequency. The alternating current is transformed by a transformer T, set to a predetermined voltage, and supplied to the fluorescent lamp 106, so that the fluorescent lamp 106 is turned on. In other words, the darker the surroundings, the shorter the period during which the transistor Q2 is conductive, and therefore the shorter the period during which the fluorescent lamp 106 is lit, and the longer the fluorescent lamp 1 is turned on.
The brightness of 06 decreases depending on the surrounding darkness. At this time, the potential at point B drops to the reference potential point, so the transistor Q1 is turned off, and no current flows through the light receiving sensor LS, so side illumination of the surrounding area is not performed (times t1 to t2 in Figure 3).
.

On the other hand, during the OFF period of the pulse generated within the control integrated circuit IC, the pins 10 and 11
The transistor connected between them is turned off, the potential at point B becomes high, and the transistor Q3 is turned off. Therefore, the transistor Q2 is turned off, the step-down chopper circuit 2 does not operate, and the fluorescent lamp 106 is turned off. At this time, the potential at point B becomes high, so the transistor Q1 becomes conductive, and therefore, a current flows through the light receiving sensor LS to perform side illumination of the surroundings (times t2 to t3 in FIG. 3).

Next, when the area around the liquid crystal display becomes brighter, the resistance of the light receiving sensor LS decreases, the potential at point A decreases, and the current flowing through the diode D2 decreases. Then, the current supplied to the pin 4, that is, the level of the control signal, becomes smaller than the level of the sawtooth signal, and the pulse width of the pulse generated within the control integrated circuit IC increases, and the pulse width of the pulse generated in the control integrated circuit IC increases. The on-period of the transistor connected between them becomes longer. Therefore, the on period of the step-down chopper circuit 102 and the constant current push-pull type inverter circuit 103 becomes longer, the period during which the fluorescent lamp 106 is lit becomes longer, and the brightness of the fluorescent lamp 106 increases according to the surrounding brightness. do. In this case, as in the above case, side lighting of the light receiving sensor LS is performed during the off period of the pulse generated within the control integrated circuit IC, that is, during the period when the fluorescent lamp 106 is turned off.

In the above embodiment, the light receiving sensor L is activated during the period from immediately after the fluorescent lamp 106 is turned off to immediately before the next lighting.
Although the case where side lighting of S is performed is shown, the fluorescent lamp 106
The outside light may be measured more accurately by delaying the side light for a predetermined period of time after the fluorescent lamp 106 is turned off until the afterglow of the fluorescent lamp 106 disappears. Furthermore, the light amount of the fluorescent lamp 106 may be controlled more precisely by photometrically measuring the light amount of the fluorescent lamp 106 itself during the lighting period of the fluorescent lamp 106.

[0019]

[Effects of the Invention] As detailed above, according to the present invention,
By measuring the amount of light around the LCD display while the fluorescent lamp is off, accurate photometry is possible without being affected by the amount of light from the fluorescent lamp, and the amount of light from the fluorescent lamp can be accurately controlled according to the surrounding brightness. . Therefore, an excellent effect is achieved in that the power consumption of the fluorescent lamp is reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a fluorescent lamp lighting device according to the present invention.

FIG. 2 is an explanatory diagram showing the level relationship between a control signal and a sawtooth signal.

FIG. 3 is a timing chart showing the relationship between blinking of a fluorescent lamp and on/off of a transistor.

[Explanation of symbols]

101... DC power supply, 102... Step-down chopper circuit, 103... Constant current push-pull type inverter circuit, 104
...External light detection circuit, 105...Pulse width control circuit, 106...Fluorescent lamp, Q1, Q2...Transistor.

Claims (1)

[Claims] 1. A fluorescent lamp, a DC power source that supplies power to the fluorescent lamp, an external light detection circuit that measures the amount of surrounding light, and outputs a pulse with a pulse width corresponding to the output signal of the external light detection circuit. a pulse width control circuit that turns on and off the DC of the DC power source, the on-period of which is controlled according to the pulse width of the pulse width control circuit; and an output from the chopper circuit, an inverter circuit that converts the alternating current into a higher frequency during the on period to light the fluorescent lamp; and controls on/off the photometric operation of the external light detection circuit, and the photometric operation is performed during the off period of the fluorescent lamp. 1. A fluorescent lamp lighting device, comprising: a control means for turning on the fluorescent lamp.