JP2001068291A - Lighting device for light source, and irradiated document reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide desirable luminous energy in an eraly stage after lighting of a light source, and to reduce fluctuation of the luminous energy irrespective of moving positions of a carriage. SOLUTION: This lighting device is provided with a high-frequency voltage generating circuit HC, a switching circuit SW including a switching element Q1 connected to an input side of the circuit HC, a light source DL for irradiating a document connected to an output side of the circuit HC, and a luminous energy control circuit PC including a photo-sensor PD for detecting light from the light source DL, having a function for generating a driving signal PWM- controlled based on luminous energy detected by the photo-sensor PD, and for imparting the drive signal to the switching circuit SW. The switching element Q1 of the switching circuit SW is switching-controlled by the drive signal PWM-controlled based on a photo-detection signal by the photo-sensor PD from the luminous energy control circuit PC, and supply power supplied to the high-frequency voltage generating circuit HC is also controlled, so as to maintain the luminous energy of the light source DL at a substantially constant value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device of a light source and a document irradiation reading device, and more particularly to an improvement of a lighting device of a light source in a document irradiation reading device such as a facsimile, an image scanner, and a copying machine.

[0002]

2. Description of the Related Art In general, this type of document irradiation reading apparatus is configured as shown in FIGS. In the figure, PL is a document irradiation reading device, and a document table PH made of transparent glass disposed on an upper part of a box-shaped device main body;
A carriage CR arranged on the inner surface side of the platen PH so as to be able to move substantially in parallel in the direction of the arrow along the platen PH, a mirror M mounted on the carriage CR, and an apparatus body corresponding to the mirror M , A light source (for example, a cold cathode fluorescent lamp) DL mounted on the carriage CR, a lighting device TC of the cold cathode fluorescent lamp DL disposed at the bottom of the apparatus main body, It comprises an output line W connecting the cathode fluorescent lamp DL and the lighting device TC. The carriage CR has a slit S
L is formed, and a mirror M is fixed at an angle of approximately 45 ° on the non-document table side of the slit SL.

In this document irradiation reading device PL, the lighting device TC is, for example, a switching circuit (specifically, DC /
A DC converter CV) SW and a high-frequency voltage generating circuit (for example, an inverter circuit) HC for generating a high-frequency voltage are provided.
The C / DC converter CV is connected to the cold cathode fluorescent lamp DL on the output side using a flexible and long output line W.

The DC / DC converter CV in the lighting device TC includes a switching element Q1 such as a transistor, a coil L connected in series with the switching element Q1, and an input side of the coil L (switching element Q1).
1) and ground, a capacitor C1 connected between the output side of the coil L (inverter circuit HC) and ground, and a resistor R1 connected to the base of the switching element Q1. And a driving circuit DR for applying a driving signal through the driving circuit DR. In addition, this DC /
Although the DC converter CV is configured as a step-down type, it may be configured as a step-up type, a step-up / step-down type, a polarity inversion type converter, or the like.

[0005] The inverter circuit HC in the above-described lighting device TC has, for example, a primary coil T provided with an intermediate tap.
An oscillation transformer TR having an Rp, a secondary coil TRs, and a drive coil TRd; and a choke coil CH connected to an intermediate tap of the primary coil TRp in the oscillation transformer TR.
And switching elements Q2 and Q3 such as transistors connected to the winding start and winding end of the primary coil TRp.
And the output side of the choke coil CH and the switching element Q
2, R3 connected between the base of Q3 and R3
And a ballast capacitor C2 connected in series to the secondary coil TRs of the oscillation transformer TR, and a capacitor C4 connected in parallel to the primary coil TRp. The ends are connected to the bases of the switching elements Q2 and Q3, respectively. The cold cathode fluorescent lamp DL is connected in series to a secondary coil TRs of the oscillation transformer TR via a ballast capacitor C2 and an output line W.

The above-mentioned cold cathode fluorescent lamp DL is provided on the inner surface of a glass bulb whose outer diameter is reduced to, for example, 6 mm or less.
For example, a light-emitting layer is formed by a mixed phosphor obtained by mixing a plurality of phosphors that emit light in a blue region, a green region, and a red region, and an electrode is disposed at an end of a glass bulb.
In addition, a rare gas such as argon and mercury are sealed in the interior space of the glass bulb. A lead terminal LT extends from an end of the cold cathode fluorescent lamp DL, and an output line W is directly or indirectly connected to the lead terminal LT.

The document irradiation reading device P thus configured
L operates as follows. When the original irradiation reading device PL is driven with the original P set on the original platen PH,
A drive signal is applied from the drive circuit DR to the base of the switching element Q1 via the resistor R1.
1 is turned on. Then, the switching elements Q1,
DC / D by the cooperative action with the coil L and the capacitor C1
DC voltage is output from C converter CV. This DC voltage is applied to the bases of switching elements Q2 and Q3 via choke coil CH and resistors R2 and R3. In the initial state, one of the switching elements (Q2, Q3)
Is turned on, the switching elements Q2 and Q3 perform switching operations alternately by the voltage generated in the drive coil TRd, so that a high-frequency voltage is generated in the secondary coil TRs by the turn ratio with the primary coil TRp. Is applied to the cold cathode fluorescent lamp DL via the ballast capacitor C2. As a result, the cold cathode fluorescent lamp DL is turned on, so that the document P is irradiated. At the same time, the drive system of the carriage CR is driven, and the carriage CR moves from the right end to the dotted line position on the left end by a wire or the like, and moves substantially in parallel along the document table PH. At this time, the light emitted from the cold cathode fluorescent lamp DL
Is reflected by the mirror M, and the reflected light is refracted in the direction of 45 ° by the mirror M through the slit SL. The refracted light is incident on the sensor S, so that the original surface is read. When the reading is completed, the position returns to the position of the solid line at the right end to prepare for the next reading operation.

[0008]

According to the document irradiation reading apparatus PL, the output side of the inverter circuit HC has a frequency of 40 to 50 KHz and a voltage of 100, for example.
Since a high-frequency voltage of 0 to 1200 V is output, the cold cathode fluorescent lamp DL can be reliably turned on.
In the stable lighting state, the reading of the document surface can be appropriately performed.

However, since mercury is sealed in the glass bulb of the cold cathode fluorescent lamp DL, the amount of light of the cold cathode fluorescent lamp DL increases with the elapsed lighting time, for example, as shown by a solid line in FIG. , About 1 to 5 minutes, and reaches a stable light amount, which is larger than the light amount φ _OP required for reading the original surface.

[0010] This is because the mercury vapor pressure in the glass bulb is low immediately after the cold cathode fluorescent lamp DL is turned on, so that the efficiency of excitation of the light emitting layer by ultraviolet rays is insufficient.
This is because the mercury vapor pressure reaches the optimum vapor pressure in about 5 minutes, and the excitation efficiency of the light-emitting layer by ultraviolet rays becomes sufficient.

Therefore, even if the document irradiation and reading device PL is operated immediately after the cold cathode fluorescent lamp DL is turned on, the light amount of the cold cathode fluorescent lamp DL does not reach the light amount φ _OP required for reading. The document reading cannot be performed with high accuracy, and not only the reading quality is deteriorated, but also a long waiting time T _O of, for example, 30 seconds to 3 minutes is required before the document irradiation reading device PL can operate normally. is there.

In the above-mentioned document irradiation reading apparatus PL, the output side of the inverter circuit HC and the cold cathode fluorescent lamp D
The output line W connecting L and L is configured to be long so as not to hinder the movement of the carriage CR, and the area facing the bottom of the apparatus main body differs depending on the position of the carriage CR. That is, when the carriage CR is located at the right end, the facing area between the output line W and the bottom of the apparatus main body is relatively small, and when the carriage CR is located at the left end, the facing area becomes large, and the carriage CR moves from the right end to the left end. The area also changes.

In particular, since the high-frequency voltage is applied to the cold cathode fluorescent lamp DL as described above, a leakage current flows due to a stray capacitance existing between the output line W and the bottom of the apparatus body. In some cases, the leakage current increases as the area between the output line W and the bottom of the apparatus main body increases, and the leakage current tends to decrease as the area of the opposition decreases. When the leakage current flows between the output line W and the bottom of the apparatus main body, the lamp current flowing through the cold cathode fluorescent lamp DL decreases, and the light amount also decreases. Therefore, since the amount of light of the cold cathode fluorescent lamp DL varies depending on the moving position of the carriage CR, there is a problem that reading quality becomes unstable.

Therefore, an object of the present invention is to provide a light source lighting device and a document illuminating device which can obtain a desired light amount at an early time after the light source is turned on, and can reduce the fluctuation of the light amount irrespective of the moving position of the carriage. A reading device is provided.

[0015]

SUMMARY OF THE INVENTION Therefore, in order to achieve the above-mentioned object, the present invention provides a high-frequency voltage generating circuit for generating a high-frequency voltage, and a switching device including a switching element connected to an input side of the high-frequency voltage generating circuit. A circuit and a light source for document irradiation connected to the output side of the high-frequency voltage generation circuit;
A light sensor that detects a light from the light source, has a function of generating a PWM-controlled drive signal based on the detected light amount of the photosensor, and includes a light amount control circuit that applies the drive signal to a switching circuit. Then, based on the light detection signal of the photo sensor from the light amount control circuit, PW
The switching element of the switching circuit is controlled by the M-controlled drive signal, and the power supplied to the high-frequency voltage generation circuit is controlled to maintain the light amount of the light source at a substantially predetermined value.

A second invention of the present invention is characterized in that the switching circuit is constituted by a DC / DC converter including a switching element, a coil, and a capacitor. , A switching element, a capacitor, and a diode.

According to a fourth aspect of the present invention, the light amount control circuit includes an error amplifier for amplifying at least an error between a photosensor for detecting light from a light source and an output voltage of the photosensor with respect to a reference voltage. An error amplifier section, a comparison circuit section including a comparison circuit that outputs a signal subjected to PWM control based on the output signal of the error amplifier section and the triangular wave signal, and a switching element that performs a switching operation by a signal from the comparison circuit section. According to a fifth aspect of the present invention, the switching circuit and the switching element of the light quantity control circuit are constituted by transistors, and the light quantity control circuit is connected between a base of the transistor of the switching circuit and ground via a resistor. Are connected.

Further, according to a sixth aspect of the present invention, there is provided a light source for irradiating a document surface, a light source lighting device, a light source, and substantially parallel movement along the document surface when the light source is lit. And a switching circuit including a switching element connected to an input side of the high-frequency voltage generating circuit, and a light source. A photosensor for detecting light, having a function of generating a PWM-controlled drive signal based on the detected light quantity of the photosensor, and a light quantity control circuit for applying the drive signal to a switching circuit; A photosensor in the light quantity control circuit is arranged on the carriage so as to be able to detect light of the light source. Location and configured to implement such circuit components on a printed circuit board, characterized by being equipped with the lighting device to the carriage.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a first embodiment of a document irradiation reading apparatus provided with a light source lighting device according to the present invention will be described with reference to FIGS. The same parts as those in the conventional example shown in FIGS. 8 and 9 are denoted by the same reference numerals, and detailed description thereof will be omitted. This embodiment is characterized in that a lighting device TCA for a light source DL includes a light quantity control circuit PC including a photosensor PD such as a photodiode for detecting light from the light source DL.
And that the lighting device TCA including the light amount control circuit PC is mounted on the carriage CR of the document irradiation reading device PL together with the light source DL.

The carriage CR has a lamp housing DLB at one end of a frame CRF made of, for example, a metal member.
On the other end side, a lighting circuit TCA having circuit components mounted on a printed circuit board PR is arranged and mounted, respectively, and a slit SL is formed between the lamp housing portion DLB and the printed circuit board PR. The mirror M is fixed to the non-document surface side at an angle of 45 °. In particular,
The light source (for example, a cold cathode fluorescent lamp) DL is formed in a U-shape and is housed in a lamp housing DLB, and its lead terminals LT, LT are directly connected to conductive lands of the printed circuit board PR by soldering or the like. I have. A slit SL1 is formed in an arbitrary portion (preferably, a central portion) of the lamp housing portion DLB, and a photo sensor PD for detecting the amount of light from the cold cathode fluorescent lamp DL is provided on the non-document side of the slit SL1. Are located. The lamp housing portion DLB is formed of a resin member so as to have a U-shaped groove, but the frame CRF and the lamp housing portion DLB are formed.
Can be formed integrally with a resin member or integrally formed with a metal member.

In order to smoothly move the carriage CR, a plurality of guide insertion portions GA for inserting the guide rods GR, GR are provided at both ends of the carriage CR.
Are formed. Accordingly, in a state where the guide rods GR, GR are inserted through the plurality of guide insertion portions GA, GA at both end portions, the carriage CR is guided by the guide rods GR, GR, for example, by a wire interlocking with a drive system such as a stepping motor. Then, it is reciprocated substantially in parallel along the document table PH.

In particular, the lighting device TCA of the cold cathode fluorescent lamp DL is mounted on the carriage CR, so that the power line DW is connected to the lighting device TCA with a length that allows the carriage CR to move. ing. As shown in FIG. 1, when the carriage CR is located at the right end, the power supply line DW has a relatively small area facing the bottom of the apparatus main body as shown by the solid line in the drawing, and the carriage CR is located at the left end. In this case, the area facing the bottom of the apparatus main body becomes large as shown by the dotted line in the figure.

The lighting device TCA of the cold cathode fluorescent lamp DL mounted on the carriage CR is a switching circuit including a DC / DC converter (for example, a DC / DC converter is a specific example).
The circuit includes a converter CV) SW, a high-frequency voltage generation circuit (specifically, an inverter circuit) HC, and a light quantity control circuit PC. This DC / DC converter CV includes, for example, a switching element Q1 such as a transistor, a coil L connected in series to the switching element Q1, and a reverse direction between an input side (switching element Q1 side) of the coil L and ground. , A capacitor C1 connected between the output side of the coil L (the inverter circuit HC side) and the ground, and a resistor R1 connected to the base of the switching element Q1.

In the lighting device TCA, the light amount control circuit PC includes, for example, a photosensor PD and a photosensor P.
A series circuit of resistors R4 and R5 connected in series to D;
A capacitor C3 connected in parallel to the resistor R5 for reducing ripples, a series circuit of resistors R6 and R7 connected in series to the reference power supply Eref, and resistors R4 and R5 connected to the non-inverting input terminal (+). Are an error amplifier (error amplifier) OP1 in which the connection points of the resistors R6 and R7 are respectively connected to the inverting input terminal (-), and an error amplifier O
A resistor R8 connected between the inverting input terminal (-) of P1 and the output terminal, and an error amplifier O connected to the non-inverting input terminal (+).
Comparison circuit (comparator) to which the output terminal of P1 is connected
OP2, a triangular wave oscillator OSC connected to the inverting input terminal (-) of the comparison circuit OP2, a driver circuit Dr connected to the output side of the comparison circuit OP2, and a driver circuit D
and a switching element Q4 such as a transistor whose base is connected to the output terminal of r. The collector of the switching element Q4 is connected to the base of the switching element Q1 in the DC / DC converter CV via the resistor R1. . Incidentally, the resistor R5 is constituted by a variable resistor.

The document irradiation reading apparatus P thus configured
L operates as follows. When the original irradiation reading device PL is driven with the original P set on the original platen PH,
Since the switching element Q4 of the light quantity control circuit PC is on, the switching element Q1 also turns on.
Then, a DC voltage is output from the DC / DC converter CV by the cooperation of the switching element Q1, the coil L, and the capacitor C1. This DC voltage is applied to the switching element Q via the choke coil CH and the resistors R2 and R3.
2, Q3. In the initial state, when one of the switching elements (Q2, Q3) is turned on, the switching elements Q2, Q3 alternately perform a switching operation (self-excited oscillation operation) by a voltage generated in the drive coil TRd. A high-frequency voltage is generated in the secondary coil TRs by a winding ratio with respect to the primary coil TRp, and is applied to the cold cathode fluorescent lamp DL via the ballast capacitor C2.

As a result, the cold cathode fluorescent lamp DL is turned on, so that the document P is irradiated. At the same time, the drive system of the carriage CR is driven, and the carriage C
R moves from the right end to the dotted line position on the left end by a wire or the like, and moves substantially in parallel along the document table PH. At this time, the light emitted from the cold cathode fluorescent lamp DL
Is reflected by the mirror M, and the reflected light is refracted in the direction of 45 ° by the mirror M through the slit SL. The refracted light is incident on the sensor S, so that the original surface is read. When the reading is completed, the position returns to the position of the solid line at the right end to prepare for the next reading operation.

By the way, when the cold cathode fluorescent lamp DL is turned on, a part of the light emitted therefrom enters the photosensor PD through the slit SL1 of the lamp housing DLB. However, this cold cathode fluorescent lamp DL
Means that the mercury vapor pressure in the glass bulb does not reach the optimum value immediately after lighting, and the light intensity is lower than the rated value at the beginning of lighting, and the light intensity increases to the rated value and stabilizes.
It has the characteristic that it takes about 5 minutes. Therefore, when the cold cathode fluorescent lamp DL is turned on, weak light is emitted from the lamp housing D.
The light is incident on the photosensor PD through the slit SL1 of the LB, and a current corresponding to the light amount flows through the resistors R4 and R5 and the capacitor C3, and a small voltage Vp corresponding to the current is generated in the resistor R5.

This voltage Vp is applied to the non-inverting input terminal (+) of the error amplifier OP1. In the error amplifier OP1, the difference (error) between the reference voltage Vf applied to the inverting input terminal (-) and the small voltage Vp applied to the non-inverting input terminal (+) is amplified and input to the comparison circuit OP2. .
In the comparison circuit OP2, the output signal of the error amplifier OP1 is compared with the triangular wave signal from the triangular wave oscillator OSC, and a drive signal having a large PWM pulse width related to the magnitude of the output signal is switched via the driver circuit Dr. Applied to the base of element Q4, switching element Q4 is turned on, and switching element Q1 is also turned on.

In particular, since the amount of light is small when the cold cathode fluorescent lamp DL is turned on, the pulse width of the PWM-controlled drive signal applied to the switching element Q4 is large.
As a result, the on-duty ratio of switching element Q4 increases, and the on-duty ratio of switching element Q1 also increases. Therefore, the DC / DC converter C
The power supplied from V to the high-frequency voltage generation circuit HC is increased, and a large lamp current flows through the cold cathode fluorescent lamp DL.
At 0, it is forcibly increased as shown by the dotted line.

When the light quantity of the cold cathode fluorescent lamp DL is forcibly increased in this manner, the voltage Vp applied to the non-inverting input terminal (+) of the error amplifier OP1 necessarily increases. Then, the difference between the voltage Vp and the reference voltage Vf becomes smaller, so that P
The pulse width of the WM-controlled drive signal is also reduced, and the on-duty ratio of the switching elements Q4 and Q1 is also controlled. Eventually, when the pulse width of the PWM-controlled drive signal becomes a normal state, DC /
The power supplied from the DC converter CV to the high-frequency voltage generation circuit HC is reduced as compared with the transition period at the beginning of lighting, and is almost in a rated state, and the light amount of the cold cathode fluorescent lamp DL is also controlled in a substantially rated state.

According to this embodiment, since the light amount control circuit PC is incorporated in the lighting device TCA, even if the light intensity of the cold cathode fluorescent lamp DL is insufficient at the initial stage of lighting, the light amount is controlled by the light intensity control circuit PC. The on-duty ratio of the switching elements Q4 and Q1 is controlled by the drive signal detected by the photosensor PD in the circuit PC and subjected to PWM control based on the light amount, so that a large current flows through the cold cathode fluorescent lamp DL. The flow and the light amount φ are forcibly increased as shown by the dotted line in FIG. Accordingly, the light amount φ _OP required for reading can be secured from an early point (elapsed time Tn shorter than T _{O in the} conventional example) after the operation of the document irradiation reading device PL, and the reading operation can be performed with high accuracy.

The carriage CR includes a DC / DC converter CV, a high-frequency voltage generation circuit HC, and a light quantity control circuit PC.
Is mounted together with the cold cathode fluorescent lamp DL, the output line connecting the lighting device TCA and the cold cathode fluorescent lamp DL is installed and wired in a short length on the printed circuit board PR, and The wiring length is fixed. Therefore, even if the carriage CR reciprocates along the document table PH during operation of the document irradiation reading device PL,
Since the output line connecting the lighting device TCA and the cold cathode fluorescent lamp DL does not cause a stray capacitance between the output line and the bottom of the device main body as in the conventional example shown in FIG. The amount of light is independent of the movement of the carriage CR.
It is possible to always maintain the same constant, and to improve the reading quality of the original.

In particular, the high frequency voltage generating circuit HC and the cold cathode fluorescent lamp DL in the lighting device TCA including only the cold cathode fluorescent lamp DL and the photosensor PD mounted on the carriage CR and including the light quantity control circuit PC are shown in FIGS. Can be configured by connecting with an output line W as in the conventional example shown in FIG. In this case, the output line W
Leakage current occurs due to stray capacitance generated between the device and the bottom of the apparatus body, and the light amount fluctuates. However, the changed light amount is detected by the photo sensor PD, and the light amount control circuit P
In C, since the switching of the switching element Q1 is controlled by the PWM-controlled drive signal in accordance with the light quantity, the light quantity of the cold cathode fluorescent lamp DL can always be kept substantially constant.

FIG. 6 shows a second embodiment of the present invention. The basic configuration is the same as that of the embodiment shown in FIG. The difference is that the coil L in the switching circuit SW in the lighting device TCB is omitted. Therefore, this switching circuit SW is DC / DC shown in FIG.
The function as a converter CV cannot be expected.

In this embodiment, since the output side of the switching circuit SW outputs a rectangular wave voltage having a power supply voltage substantially on the positive side and a forward voltage of the diode D on the negative side, the oscillation transformer in the high-frequency voltage generation circuit HC is output. The step-up ratio of the secondary coil TRs to the primary coil TRp of the TR can be set large. Therefore, the cold cathode fluorescent lamp DL
When it is necessary to reduce the lamp current to a small value, the lamp voltage required for maintaining the discharge can be secured, so that a stable discharge state with little fluctuation in the amount of light can be maintained, and sufficient reading quality can be secured.

FIG. 7 shows a third embodiment of the present invention, and the basic configuration is the same as the embodiment shown in FIGS. The difference is that the carriage CR has a photosensor P in the high-frequency voltage generation circuit HC and the light quantity control circuit PC.
D and the cold cathode fluorescent lamp DL.
The switching circuit SW including the DC / DC converter CV and the light amount control circuit PC excluding the photo sensor PD are arranged on the apparatus main body side, and are connected to each other by a flexible wire.

According to this embodiment, since the mounting circuit on the carriage CR is restricted, the weight of the carriage CR can be reduced, and the carriage CR can be moved smoothly.

Although the present invention has been described with reference to a cold cathode fluorescent lamp as an example of a light source without being limited to the above-mentioned embodiment, only a rare gas is sealed inside and a light emitting layer is formed on the inner surface. It is also possible to use a rare gas discharge lamp or the like in which a pair of band-shaped external electrodes are arranged on the outer peripheral surface of a glass bulb having the same. Further, the high-frequency voltage generating circuit in the lighting device of these light sources may be constituted by a circuit that generates a pulse-like high-frequency voltage in addition to a circuit that generates a sine wave or a rectangular wave voltage. Further, the switching circuit in the lighting device can be omitted. Further, only the light source and the photo sensor are mounted on the carriage, and the lighting device including the light amount control circuit can be arranged on the apparatus main body side. further,
The light source may be formed in an I shape (straight tube) in addition to the U-shape.

[0039]

As described above, according to the present invention, since the light quantity control circuit including the photo sensor is incorporated in the lighting device, even if the light quantity is insufficient at the initial stage of lighting the light source, the light quantity control circuit including the photo sensor can be used. The light amount is detected by a photo sensor in the light amount control circuit, and the drive signal subjected to PWM control based on the light amount is controlled so that the on-duty ratio of the switching element becomes longer. As a result, a large current flows through the light source and the light amount is forcibly increased. Will be increased. Therefore, the light amount required for reading can be secured from an early point in time after the operation of the document irradiation reading apparatus, and the reading operation can be performed with high accuracy.

In particular, when the light source and the photo sensor are mounted on the carriage, and the high frequency voltage generating circuit in the lighting device including the light amount control circuit is connected to the light source by an output line through which high frequency is applied, the movement of the carriage may occur. Even if leakage current occurs due to stray capacitance generated between the output line and the bottom of the apparatus main body due to the change in the light amount, the changed light amount is detected by the photo sensor, and the light amount control circuit In the above, the switching of the switching element is controlled by a drive signal that is PWM-controlled according to the amount of light.
The light amount of the light source can always be kept substantially constant, and sufficient reading accuracy can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a first embodiment of the present invention.

FIG. 2 is a plan view of the carriage shown in FIG.

FIG. 3 is a sectional view taken along line XX of FIG. 2;

FIG. 4 is a bottom view of FIG. 1;

5 is an electric circuit diagram of the lighting device shown in FIG.

FIG. 6 is an electric circuit diagram of a lighting device according to a second embodiment of the present invention.

FIG. 7 is a plan view of a carriage showing a third embodiment of the present invention.

FIG. 8 is a schematic side view of a conventional example.

9 is an electric circuit diagram of the lighting device shown in FIG.

FIG. 10 is a diagram illustrating a change characteristic of a light amount with respect to an elapsed time of a light source.

[Explanation of symbols]

 PL Document irradiation reader CR Carriage PH Document table DL Light source (Cold cathode fluorescent lamp) LT Lead terminal DW Power line TC, TCA, TCB Lighting device HC High-frequency voltage generation circuit SW Switching circuit CV DC / DC converter PC Light control circuit Q1 Q4 Switching element TR Oscillation transformer PD Photo sensor OP1 Error amplifier OP2 Comparison circuit OSC Triangular wave oscillator

Continued on the front page F-term (reference) 2H109 AB04 AB18 AB23 3K072 AA19 BA05 CA16 DE01 GB14 GC03 HA09 HA10 5C072 AA01 BA13 CA04 CA12 CA14 CA20

Claims (7)

[Claims] A high-frequency voltage generating circuit for generating a high-frequency voltage, a switching circuit including a switching element connected to an input side of the high-frequency voltage generating circuit, and a light source for document irradiation connected to an output side of the high-frequency voltage generating circuit. A light sensor that detects a light from a light source, has a function of generating a PWM-controlled drive signal based on the detected light amount of the photosensor, and a light amount control circuit that applies the drive signal to a switching circuit. By controlling the switching of the switching element of the switching circuit by a drive signal PWM-controlled based on the photodetection signal of the photosensor from the light quantity control circuit, and controlling the power supplied to the high frequency voltage generation circuit. And a lighting device for the light source, wherein the light amount of the light source is maintained at a substantially predetermined value. 2. The lighting device for a light source according to claim 1, wherein the switching circuit comprises a DC / DC converter including a switching element, a coil, and a capacitor. 3. The lighting device for a light source according to claim 1, wherein the switching circuit comprises a switching element, a capacitor, and a diode. 4. An error amplifier, comprising: a photosensor for detecting light from a light source; and an error amplifier for amplifying an error between an output voltage of the photosensor and a reference voltage. A comparison circuit unit including a comparison circuit that outputs a signal subjected to PWM control based on an output signal of the unit and a triangular wave signal, and a switching element that performs a switching operation by a signal from the comparison circuit unit. Item 2. A lighting device for a light source according to item 1. 5. The switching circuit and the switching element of the light quantity control circuit are constituted by transistors, and the transistor of the light quantity control circuit is connected between the base of the transistor of the switching circuit and ground via a resistor. The lighting device for a light source according to claim 4. 6. A light source for irradiating a document surface, a light source lighting device, and a carriage configured to dispose the light source and to be able to move substantially in parallel along the document surface when the light source is turned on. The lighting device includes at least a high-frequency voltage generation circuit that generates a high-frequency voltage, a switching circuit including a switching element connected to an input side of the high-frequency voltage generation circuit, and a photosensor that detects light from a light source, A light quantity control circuit for generating a PWM-controlled drive signal based on the light quantity detected by the photo sensor, and applying the drive signal to a switching circuit; And a document irradiation reading device arranged to detect light of a light source. 7. The document irradiation and reading device according to claim 6, wherein the lighting device of the light source is configured by mounting a circuit component or the like on a printed circuit board, and the lighting device is mounted on a carriage.