JPS61208359A - Driving device for fluorescent tube - Google Patents

Abstract

PURPOSE:To make even the quantity of light in the lengthwise direction uniform by applying alternately a prescribed DC voltage alternately across filament and flowing alternately a prescribed level of currents in opposite direction to each other to the filament for each prescribed time so as to light the fluorescent tube in a stable state without flickering. CONSTITUTION:After a control circuit 25 turns on switching elements 301, 304 at the same time for a prescribed time and then they are turned off, and at the next moment, switching elements 302, 303 are turned on at the same time and then turned doff after a prescribed time and the switching elements 301, 304 are turned on; The operations above are repeated at a prescribed period. When the elements 301, 304 are turned on and the other elements 302, 303 are turned off, a DC current flows to a filament 8 by a DC power supply 22. Thus, thermo electrons are generated, they go to an anode 9 while being driven by a DC voltage and collide with the fluorescent body coated on the anode.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a drive device for a fluorescent tube used in a light source of an image reading device or the like.

"Prior Art" An image line sensor is one of the devices that reads an image drawn on a document and converts it into an electrical signal. this is,
For example, as shown in FIG. 9, light 1□ emitted from the light source II and reflected on the surface of the document 2 is guided to the light receiving surface of the image line sensor 3 using the converging lens 13, and the document 2 is moved in the direction of the arrow 4. The image on the original 2 is photoelectrically converted while moving the original 2.

The light source used in such a device must not only be able to obtain a sufficient amount of light, but also have characteristics such as emitting light at a wavelength within the range for which the image line sensor is sensitive. .

Consideration has been made to employ a fluorescent tube as this light source.

As shown in FIG. 10, the fluorescent tube 5 uses a transformer 7 to reduce the voltage of a commercial power supply 6 to about 6.3V to 8V, heats the filament 8, generates thermoelectrons, and A DC power supply 10 is connected between the anode 9 and the anode 9 to cause these thermoelectrons to collide with the anode 9, causing the phosphor coated on the anode 9 to emit light. In the present invention, a lamp that emits light based on this principle is referred to as a fluorescent tube.

This phosphor 5 has the advantage that the wavelength of the light can be appropriately selected by selecting the phosphor material, the amount of light can be increased or decreased by changing the voltage applied to the anode 9, and it generates relatively little heat. There were various problems that prevented it from being immediately adopted for use in image reading devices.

``Problems to be solved by the invention'' One of the problems is that light emission flickers. This flickering tends to be felt more strongly as the length of the light emitting section, that is, the filament 8 is increased.

If there is flicker that can be felt with the naked eye, there is a risk that the photoelectric conversion level will fluctuate during the reading operation of the image line sensor.

The reason for this is that when the wiring is connected as shown in Figure 10,
This is considered to be because the potential difference between the anode voltage 11 and the filament voltage 12 varies depending on the power supply frequency, as shown in FIG.

On the other hand, it is conceivable to ignite the filament 8 with direct current.

However, when a voltage is applied to the filament 8 using the DC power supply 14 as shown in FIG. 12(a), a potential gradient occurs in the longitudinal direction of the filament 8, and this gradient remains as it is as shown in FIG. 12(b). As shown, the potential difference V between the anode 9 and the filament 80 has a slope as shown in FIG. The potential difference between the filament 8 and the anode 9 determines the speed at which thermionic electrons generated from the filament 8 impinge on the anode 9, which determines the amount of light emitted by the phosphor. That is, in this case, the amount of light emitted is non-uniform in the longitudinal direction of the light source, which is not suitable for image reading.

In addition, the conventional device as shown in FIG. 10 uses a transformer and the like, making it large in size, resulting in an increase in cost.

The present invention has been made in view of the above points, and an object of the present invention is to provide a fluorescent tube drive device that suppresses flickering in the amount of light emitted.

Another object of the present invention is to provide a fluorescent tube drive device with little change in light amount in the longitudinal direction.

"Means for Solving the Problems" The fluorescent tube driving device of the present invention applies a first voltage to one end of the filament and a second voltage to the other end, thereby moving the filament from one end to the other end. After passing a current at a nearly constant level for a predetermined period of time, the second voltage is applied to one end of the filament and the first voltage is applied to the other end, so that the current flows from the other end of the filament to one end. The device is characterized by having a power supply section that causes a current at a constant level to flow for a predetermined period of time, and repeats the above operation alternately and periodically.

For this purpose, for example, the power supply section includes a switching element inserted between one end of the filament and the high potential side of the DC power supply, and a switching element inserted between the other end of the filament and the low potential side of the DC power supply. By turning on simultaneously, a current flows from one end of the filament to the other,
The filament is turned on by simultaneously turning on a switching element inserted between the other end of the filament and the high potential side of the DC power supply, and a switching element inserted between one end of the filament and the low potential side of the DC power supply. The current flows from one end to the other end.

"Effect" In this way, by applying a constant DC voltage alternately to both ends of the filament and causing currents of a constant level in opposite directions to flow through the filament alternately for a predetermined period of time, the filament potential with respect to the anode becomes stable. However, flickering of light emission can be suppressed.

Furthermore, by repeating this at a fast cycle, it is possible to suppress differences in light amount from occurring in the longitudinal direction of the filament.

If this repetition period is increased to about the commercial frequency or higher, flickering caused by reversal of the direction of the current becomes almost negligible.

If the voltage applied to both ends of the filament is a negative voltage, the potential difference between the anode and the filament increases, so that the overall amount of light emission can be increased.

As the power supply section of such a fluorescent tube drive device, it is preferable to use a semiconductor switching element such as a transistor or SIRISK which has a fast switching operation.

This allows a stable, constant level of current to be passed through the filament in alternating rapid cycles.

Embodiment (Explanation of Principle of Drive Device) FIG. 1 is a wiring diagram showing the operating principle of the fluorescent tube drive device of the present invention, and FIG. 2 is a wiring diagram showing a modification thereof.

In the figure, the anode 9 of the fluorescent tube 5 is connected to the anode of a DC power supply 21 that applies a constant voltage. The cathode of this DC power supply 21 is grounded.

Furthermore, two switching elements 30. are attached to one end 8I of the filament 8. ．． 303 is connected.

In this figure, each switching element is represented by an on/off switch symbol to make it easier to understand its operation.

This one switching element 30. The other end is grounded. and the other switching element 30. The other end is connected to the anode of the DC power supply 22. The cathode of this DC power supply 22 is grounded.

Similarly, two switching elements 30. ．． 30. are connected, the other end of one switching element 304 is grounded, and the other switching element 30. The other end is connected to the anode of the DC power supply 22.

In the example shown in FIG. 2, a switching element 30 is connected to both ends of a filament 80. ．． 30. The other ends of the switching elements 308 and 30 are respectively grounded, and the other ends of the switching elements 308 and 30 are grounded to the cathode of the DC power supply 23, and the anode of the DC power supply 23 is grounded.

This is essentially the switching element 30. in the wiring diagram of FIG. ．． 30. It has exactly the same function as the DC type 122 connected to the DC type 122 with the polarity reversed. In both the device of FIG. 1 and the device of FIG. 2, the switching element 30. A control circuit 25 is provided to control the on/off timing of the circuits 304 to 304.

(Description of operation of drive device) The above circuit operates as follows. □In FIG. 1, first, the control circuit 25' controls the switching elements 30. and switching element 30° are simultaneously turned on for a contact time and then turned off, and the next moment, switching element 302 and switching element 303 are turned on at the same time and turned off again after a certain period of time, and switching element 30 is turned off again. ．． The operation of turning on the switching element 304 and the switching element 304 is repeated at a constant cycle. As shown in FIG. 1, the switching element 30. and switching element 30. is turned on, and the other switching elements 30,
．． 30. When the filament 8 is turned off, a direct current flows through the filament 8 from the left to the right in the figure (from one end 8. of the filament 8 to the other end 8□) by the DC power supply 22. This generates thermoelectrons, which fly toward the anode 9 due to the DC voltage applied to the anode 9, collide with the phosphor coated on the anode, and emit light.

At the next timing, the switching element 302 and the switching element 303 are turned on, and the other switching element 30 is turned on.
．． ．． 30. When the filament 8 is turned off, a direct current flows in the opposite direction from the other end 82 of the filament 8 to the one end 8, and the same operation is performed.

During such operation, as shown in FIG. 1, current flows through filament 8 in either direction, either through switching element 303 or switching element 30. One end 8. of the filament 8 is on because either one of them is on. Alternatively, the other end 8□ is grounded, and the potential difference between this grounded side and the anode 9 is a constant voltage determined by the DC power supply 21.

That is, as shown in FIG. 3, the potential difference (2) between the grounded terminal of the filament 8 and the anode 9 is always kept almost constant except around 410 when the switching operation is changed. Further, FIG. 4 shows the state of the filament current I at that time, and although the direction of this current I also periodically reverses, its absolute value is always approximately constant.

At this time, looking at the filament 8 in FIG. 1 in the longitudinal direction,
The potential difference between the anode 9 and the filament 8 is shown in FIG. In this figure, the horizontal axis indicates the longitudinal position of the filament, and the vertical axis indicates this potential difference.

As explained earlier, when a direct current is passed through the filament as shown in this figure, a certain gradient of potential difference occurs in the longitudinal direction of the filament 8, but the state of the straight line 42 and the state of the straight line 43 are different from each other. When repeated alternately at a fast cycle, the potential distribution appears to be uniform in the horizontal direction as shown by the broken line 44.

According to experiments, this repetition period needs to be at least equal to or higher than the commercial frequency, that is, 50 times per second or more, and a repetition rate of 2000 times or more per second (2000 times or more) to obtain a satisfactory result.
KH2).

In addition, if the wiring is connected as shown in FIG. 2, the potential of the filament is changed so as to widen the potential difference between the filament 8 and the anode 9 as shown by the broken line 45 in FIG. 5 while maintaining such good characteristics. can be moved in parallel.

This makes it possible to increase the amount of light emitted from the fluorescent tube.

(Explanation of an Actual Circuit Example of a Power Supply Unit) The power supply unit of a fluorescent tube drive device that operates on the principle as described above can actually be realized using a circuit as shown in FIG.

In FIG. 6, each switching element 3 shown in FIG.
0. 304 are switching transistors 50. to 304 each having switching current adjustment resistors 481 to 484 inserted in series. ~50. It consists of

Drive transistors 52 and 1522 are connected to the bases of the switching transistors 501 and 502, respectively, via resistors 513 and 512 for base current control. This driving transistor 52. ．． 52□
Also, the DC power supply 2 is connected through collector resistors 531 and 532.
It is connected to the anode of No. 2 and performs switching operation with its emitter grounded.

These transistors 52I, 522 and switching transistors 503, 50 . are provided with drivers 541-54., which supply base currents necessary for switching, respectively. are connected one by one.

Each driver 54. ~54. is composed of a so-called AND circuit. That is, when a constant positive voltage is applied to both of the two input terminals, the switching transistor 52. ．． 5
2□, 50. ．． 50. Outputs current to turn on.

Each driver 54. An enable signal 56 for controlling on/off of the fluorescent tube 5 is input to one input terminal of the fluorescent tubes 544 to 544. This enable signal 56 is a signal that becomes a constant level of positive voltage only when the fluorescent tube 5 is turned on. Further, a clock signal 59 output from an oscillator (O3C) 58 is input to the other terminal of each of the drivers 54° to 544.

This clock signal 59 has a duty ratio of 1/2,
For example, it is a pulse signal with a frequency of 5 CKHl) kilohertz.

This clock signal 59 is applied to the driver 54. and 544 are input as they are, and the inverter 60. is input to drivers 54□ and 543. ．． 602 and is inverted and input.

As a result, switching operations similar to those described in FIG. 1 are performed alternately.

The enable signal 5G, the clock signal 59, and the timing of the switching operation of each transistor are shown in the chart of FIG. Now, while the enable signal 56 is being applied, the switching transistors 50, . 50. and a switching transistor 50. ．． It is clearly seen that 504 turns on and off alternately.

In this way, direct current is alternately passed through the filament 8 of the fluorescent tube 5 of this circuit at the frequency of the clock signal 59 output from the oscillator 58.

The circuit shown in FIG. 8 is a circuit that embodies the principle of operation shown in FIG. 2.

In this circuit, the same parts as in FIGS. 2 and 6 are given the same reference numerals, and redundant explanation of the operation will be omitted.

In FIG. 8, unlike the switching elements 711 and 712 in FIG. 6, PNP transistors are used with their emitters grounded. In order to flow the switching base current from the emitter to the base, the base is connected to the negative power supply (E
+ (shown in the diagram). Drive transistor 73
．． 1732 increases and decreases this base voltage to operate the transistor 71. ．． Controls the switching of 71□. This transistor 73. ．． The collector of 732 is resistor 74. ．． 74
It is connected to a driving power source, for example, a +5.degree. Driver 541 or 542 is transistor 731, 732
When transistor 71. is turned on, transistor 71. ．． The 7120 pace voltage drops and turns on these transistors. Of course, when either one is on, the other is off.
□ On the other hand, transistors 713 and 714 have their emitters connected to a negative power supply (-E, shown).

In order to control switching by raising and lowering this base voltage, two transistors 78 . ~784 is used. These connect the collector to transistor 713.
A PNP transistor 782.783 is connected to the base resistor 804.80□ of 71- and the other end is connected to a driving power supply, for example, a +5■ DC power supply, and for driving the switching element 711.712 described earlier. The driving transistors 73, . NPN transistor 78.732 connected similarly to NPN transistor 732. ．． 78. It is made up of.

Transistor 781 by driver 543.544
, or when 784 is turned on, transistor 78□
, or the base voltage of 783 becomes zero and the collector current flows, causing these transistors 782, 78.
is turned on, which causes the pace voltage of transistor 713 or 714 to rise, causing these transistors 713 or 71 . Turn on. Of course, transistor 71. ．． 71. When one is on, the other is always off.

By using such a circuit, the potential at both ends of the filament 80 of the fluorescent tube 5 can be made lower than the ground potential. This widens the potential difference between the filament 8 and the anode 9, and the thermoelectrons generated from the filament are repelled by the filament 8 and head toward the anode 9, so as mentioned above, the thermoelectron emission effect can be enhanced. .

Using the circuit shown in FIG. 6, the voltage of the DC power supply 22 is set to 15 (V) volts, and the voltage of
A direct current of 00 (mA) milliamperes was applied. At this time, the frequency of the clock signal is 51: KH2: 1 kilohertz,
The anode current is 180-200 CmA], and the DC voltage applied across the filament is 7.5 milliamperes (
V) It was a bolt.

Under these conditions, no variation in the fluorescent tubes 5 was perceptible to the naked eye. Furthermore, the amount of light emitted in the longitudinal direction of the fluorescent tube was also uniform.

"Modifications" The present invention is not limited to the above embodiments. Fluorescent tubes of various configurations can be used as long as they operate on the same principle. For example, the same effect can be obtained even if the device has two or more filaments or uses a transparent electrode stuck to the face glass as an anode.

Further, the switching element can be replaced with a combination of various elements such as a field effect transistor (FET) or a SIRISC (SCR) instead of a transistor.

Further, even if at least one of the filaments is made negative, the voltage difference between the filament and the anode can be widened, so the connection can be changed as appropriate.

"Effects of the Invention" According to the fluorescent tube driving device of the present invention described above, the fluorescent tube can be caused to emit light in a stable and flicker-free state, and the amount of light in the longitudinal direction can also be made uniform. can.

Therefore, it can be used as a linear light source with a stable constant light amount in an image reading device or the like.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing the operating principle of the fluorescent tube drive device of the present invention, Fig. 2 is a wiring diagram of a modification thereof, Figs. 3 to 5 are explanatory diagrams of its operation, and Fig. 6 is the A wiring diagram showing a more specific example of the power supply unit in the wiring diagram in Figure 1, Figure 7 is a timing chart explaining its operation, and Figure 8 is a more specific implementation of the power supply unit in the second wiring diagram. A wiring diagram showing an example, FIG. 9 is a diagram explaining the reading operation of an image reading device, FIG. 10 is a wiring diagram of a conventional fluorescent tube drive device, and FIGS. 11 and 12 are connections between the filament and the anode. FIG. 3 is an explanatory diagram showing changes in potential difference. 5... Fluorescent tube, 8... Filament, 81... One end of filament, 82...
...Other end of filament, 9...Anode, 22...DC power supply, 30, ~30. ...Switching element. Applicant: Fuji Xerox Co., Ltd. Representative
People Patent Attorney Yudai Ume Yamauchi
1 Figures 〒～n Figure 2 萬 3 Figure 6 Figure 7 Tr50*-1, Roe-7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. Applying a first voltage to one end of the filament and applying a second voltage having a higher potential than the first voltage to the other end,
After passing a current at a substantially constant level from one end of the filament to the other end for a predetermined period of time, a second voltage is applied to one end of the filament, and a first voltage is applied to the other end of the filament. 1. A fluorescent tube driving device comprising a power supply section that causes the current at the constant level to flow for a predetermined period of time and alternately and periodically repeats the above operation. 2. The fluorescent tube driving device according to claim 1, wherein the repetition cycle of the operation is set to 50 times or more per second. 3. The fluorescent tube driving device according to claim 1, wherein at least the first voltage is a negative voltage. 4. The fluorescent tube driving device according to claim 1, wherein the first voltage and the second voltage are both negative voltages. 5. The power supply section simultaneously turns on the switching element inserted between one end of the filament and the high potential side of the DC power supply and the switching element inserted between the other end of the filament and the low potential side of the DC power supply. By doing so, a current flows from one end of the filament to the other end, and a switching element inserted between the other end of the filament and the high potential side of the DC power supply connects one end of the filament with the low potential side of the DC power supply. Claim 1, characterized in that current is caused to flow from the other end of the filament to one end by simultaneously turning on a switching element inserted between the filaments.
A fluorescent tube driving device according to items 1 to 4.