JP2597968Y2 - Fluorescent lamp lighting device - Google Patents

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 for lighting two or more fluorescent lamps with the same ballast having a dimming function.

[0002]

2. Description of the Related Art In recent years, personal computers, word processors, and the like have been miniaturized steadily with the increase in the density of LSIs. Liquid crystal is often used as the display for such products, but this liquid crystal has a bright screen and can be colored, so the transmission type is becoming the mainstream, and fluorescent lamps are mainly used as backlights. Have been.

This liquid crystal display needs to have a dimming function for adjusting the brightness of the backlight according to the place of use. As the dimming method, a lamp current feedback method and a duty method are known. I have.
The lamp current feedback system is for dimming by continuously changing the lamp current, and the duty system is for providing a pause period for current supply and performing dimming by changing the width of this pause period. .

As described above, there are mainly two types of dimming methods for fluorescent lamps, but for those in which a relatively large current flows, the lamp current feedback method is more efficient than the duty method. Generally, the lamp current feedback method is used as a dimming method for a backlight of a liquid crystal display such as a personal computer or a word processor. This lamp current feedback system, as shown in FIG. 3, comprises a dimming circuit 1, a ballast 2, and a current detection circuit 3 for detecting the current of the lamp L by a feedback system in which an input is made from a DC power supply. The lamp current detected by the circuit 3 is returned to the dimming circuit 1, the current value is constantly adjusted by the dimming circuit 1, and the lamp is turned on.

[0005]

However, the dimming by the lamp current feedback method has a problem that two or more lamps cannot be connected in parallel and turned on at the same time. This is because even if the lamps are made in the same way, the lighting characteristics are slightly different, so if either lamp is lit first, the current detected by the current detection circuit
Therefore, the dimming circuit determines that the lamp is turned on and operates, so that the high voltage is not applied to the other lamp and the other lamp is not turned on. For this reason, conventionally, an independent lighting device has to be provided to light the lamp, which not only increases the number of components and increases the cost but also hinders miniaturization.

[0006] The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a dimming function for two or more lamps without providing an independent lighting device. It is an object of the present invention to provide a fluorescent lamp lighting device that can be turned on, the number of parts can be reduced, and the size can be reduced.

[0007]

The fluorescent lamp lighting device of the present invention is a device for lighting a plurality of fluorescent lamps with a dimming function of a lamp current feedback system, and is connected to a DC power supply. A dimming circuit, a ballast connected downstream of the dimming circuit, a plurality of fluorescent lamps having one electrode connected to the ballast in parallel, and the other of each of the plurality of fluorescent lamps. A plurality of current detection circuits independently connected to the electrodes, connected to the subsequent stage of the plurality of current detection circuits, comparing the magnitude of the current detected by each current detection circuit, the lowest current A current comparison circuit for returning to the dimming circuit, wherein the dimming circuit starts with the lowest current value.
Determined whether the fluorescent lamp was on or off, and determined that it was off
Sometimes a dimming cycle that keeps applying high voltage to all fluorescent lamps
It is a road .

[0008]

A current detection circuit is provided independently for each lamp, the magnitude of the detected current is determined by a current comparison circuit, and the lower current is returned to the dimming circuit to turn on or off the lamp.
Lighting is determined.
The high voltage is applied to the lamps so that even if one lamp is turned on first, the high voltage is applied to the other lamp and the dimming function is activated after all lamps are turned on. Become. Therefore, the dimming circuit and the ballast can be made common, and the lighting device is downsized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the lighting device of the present invention.
1 is a dimming circuit based on a lamp current feedback system, 2
Are ballasts, and L ₁ and L ₂ are 2 at the output side of ballast 2.
The fluorescent lamps 31 and 32 connected in parallel are the lamp L
Current detecting circuit connected independently to ₁ and L _2, 4 is a current comparator circuit for comparing the magnitude of the output current from the current detection circuits 31 and 32.

As the current detecting circuits 31 and 32 and the current comparing circuit 4, a circuit as shown in FIG. 2 can be used in a specific embodiment. That is, the lamp L
₁ and L ₂ current detection circuits 31 and 32 which are provided independently for the resistance R _1, R _2, R ₃ and a diode D _1, which is more and D ₂ and the capacitor C and the operational amplifier Op. Since the lamp current I _L which flows through the lamp L ₁ as shown in FIG. 2 flows through the resistor R ₁ of the current detection circuit 31, the voltage across the resistor R ₁ is from V = I _L R _1, rests voltage V is . That is, the voltage V is applied at the point. Here, the lamp current has an AC waveform shape. And so in terms that a voltage V which depends on the point through the diode D ₁ is half-wave rectified, the DC waveform is rectified by the condenser C at the point. And this waveform is the same at the point. The same applies to the current detection circuit 32.

The magnitudes of the voltages obtained at the points 'and' of the current detection circuits 31 and 32 are compared by a current comparison circuit 4.
This current comparison circuit 4 comprises a battery B, a resistor R and an operational amplifier O
p and are becoming more, the lamp L ₁ of V ₁ and the resulting voltage at the lamp current, the voltage obtained by the lamp current of the lamp L ₂ and V _2, when assumed to be V _1> V _2, the battery B To apply a voltage higher than V ₁ (at least V ₂ + the voltage of the voltage drop of the diode). In this example, DC12V was used. Although this way starts to flow a current i, since the low voltage direction of V ₂ than V _1, the current flows into. The voltages at this time are almost equal. That is, this circuit can obtain the lower one of the voltages. Yari out the voltage that the through operational amplifier Op neat current comparator circuit 4, the low operating voltage V ₂ dimmer circuit 2 with the person. As can be seen from the above description, these current detection circuits 31, 32
In the current comparison circuit 4, the current value is read by a change in voltage.

Accordingly, the voltage output from the comparator circuit 4 is a lower voltage, even if the lamp L ₁ is lit breakdown, towards the lamp L ₂ that is not broken down lamp current Is detected and returns to the dimming circuit 1.
The lamp is turned on or off,
And to confirm the presence of-flops L _2, lamp L ₁ and the lamp L ₂
Still have high voltage for breakdown,
This state continues until the lamp L ₂ is turned on. When the lamp L ₂ is turned on, so that the lamp L ₁ and L ₂ are turned on at a constant current value set (lower lamp current values of the lamp L ₁ and L _2). Therefore, as compared with the case where the lighting is performed by the conventional separate circuits, the number of the current comparing circuits 4 increases, but the dimming circuit 2 and the ballast 1 can be used in common, and the lighting device can be downsized.

[0013]

As described above, the fluorescent lamp lighting device of the present invention can simultaneously light two or more lamps simply by adding a current detection circuit and a current comparison circuit to a lighting device based on a lamp current feedback system. Since the dimming circuit and the ballast can be shared, the number of components of the lighting device can be reduced and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a fluorescent lamp lighting device according to the present invention.

FIG. 2 is a circuit diagram of a specific example of a current detection circuit and a current comparison circuit.

FIG. 3 is a block diagram of a conventional fluorescent lamp lighting device.

[Explanation of symbols]

1 ... light control circuit 2 ... ballast 3, 31, 32 ... current detection circuit 4 ... current comparator circuit L, L _1, L ₂ ... fluorescent lamp _{R 1, R 2, R 3} , R 4 ... resistance D _1, D ₂ ... diode C ... capacitor Op ... operational amplifier B ... battery

Continuation of the front page (56) References JP-A-52-93181 (JP, A) JP-A-60-74389 (JP, A) JP-A-60-74390 (JP, A) JP-A-60-74391 (JP, A) JP-A-60-74394 (JP, A) JP-A-1-231296 (JP, A) JP-A-4-50815 (JP, A) JP-A-5-135895 (JP, A) 61-15464 (JP, U) JP-A-3-118594 (JP, U) JP-A-4-81500 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 41/14 -41/42

Claims (1)

(57) [Scope of request for utility model registration] 1. A device for lighting a plurality of fluorescent lamps with a dimming function of a lamp current feedback system, comprising: a dimming circuit connected to a DC power supply; Ballast, a plurality of fluorescent lamps having one electrode connected in parallel to the ballast, and a plurality of current detection circuits independently connected to the other electrodes of the plurality of fluorescent lamps, respectively. And a current comparison circuit connected to the subsequent stage of the plurality of current detection circuits and comparing the magnitudes of the currents detected by the respective current detection circuits and returning the lowest current to the dimming circuit, The dimming circuit determines a point of the fluorescent lamp from the lowest current value.
Lights, not lighting, and when not
Make sure that the dimming circuit keeps applying high voltage to the fluorescent lamp
Characteristic fluorescent lamp lighting device.