JP2013065929A - Light-source driving device, image processing device, image readout device, and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the excess and shortage of supply power from a driving section side subjected to a constant and to allow performing stable operation.SOLUTION: A light-source driving device switches the driving number of LED light-source rows among a plurality of LED light-source rows constituting a light source 41, and selects one or a plurality of power-supply booster circuits according to the driving number of LED light-source rows (the magnitude of load). For example, when a light-source driver 42 drives only one LED light-source row, a drive control signal Sa is inputted to a booster circuit 50 and only a switch 53 is turned on. so that a power-supply booster circuit 51 performs boosting operation to generate small power by a supply voltage from a power supply 1. When the light-source driver 42 drives the two LED light-source rows, a drive control signal Sb is inputted to the booster circuit 50 and only a switch 54 is turned on, so that a power-supply booster circuit 52 performs boosting operation to generate large power by the supply voltage from the power supply 1.

Description

  The present invention relates to a light source driving apparatus for driving a plurality of light sources, an image processing apparatus including the light source driving apparatus, and an image reading apparatus including the light source driving apparatus or the image processing apparatus (images of a digital copying machine, a digital multifunction peripheral, a facsimile apparatus, etc. The present invention relates to an image reading apparatus such as a scanner apparatus mounted on a forming apparatus or an image reading apparatus such as a single scanner apparatus, and an image forming apparatus including the light source driving device, the image processing apparatus, or the image reading apparatus.

For example, as a light source of a scanner device, there is an LED light source using a plurality of light emitting diodes (LEDs). Since LEDs are semiconductor components, they are excellent in luminous efficiency and responsiveness. In addition, a large amount of light can be obtained with low power consumption. Furthermore, there is a merit that the light quantity stabilization wait time immediately after lighting is almost unnecessary.
Such an LED light source using a plurality of LEDs is used when the scanner device reads an image of a document which is a short subject (hereinafter also simply referred to as “document”) or detects the size of the document. There are cases involving changes in drive current and number of lighting.

However, in the case as described above, there is a difference in power supplied from the drive unit side to the LED light source as compared with a case where the drive unit fully turns on all LEDs of the LED light source in order to read an image of a long document. Therefore, depending on the constants on the drive unit side, the following problems (a) and (b) may occur, and as a result, there is a concern that the read image appears as a decrease in image quality due to fluctuations in the amount of light.
(A) Excessive generation of power (overvoltage boost)
The power supply becomes unstable because the drive unit repeatedly stops and drives the power generation operation (mainly the boosting operation).
(B) Insufficient supply of power If a plurality of LEDs, which are loads, are distributed in parallel and the drive unit does not involve a boosting operation, the above problem does not occur, but power with a large margin in advance is provided. Since supply is necessary, there is a problem that power consumption increases.

Therefore, in order to solve the problem, it is conceivable to use the technique disclosed in Patent Document 1.
In Patent Document 1, for the purpose of reducing power consumption and improving operational stability, when the battery voltage is higher than a predetermined voltage, a dummy load is connected in series with the load, and the battery voltage is equal to or lower than the predetermined voltage. Discloses a configuration in which a switching unit for short-circuiting the dummy load is provided.

However, since the device described in Patent Document 1 is configured to switch the load, as described above, the problem that the power supply becomes unstable and the operation becomes unstable cannot be solved.
The present invention has been made in view of the above points, and in a light source driving device, it is possible to avoid excessive or insufficient supply power from the driving unit side depending on a constant and perform stable operation. Objective.

In order to achieve the above object, the present invention provides a light source driving device, an image processing device, an image reading device, and an image forming device described below.
A light source driving device according to the present invention is a light source driving device for driving a plurality of light sources, and boosts a power supply voltage from a driving light source switching means for switching the number of light sources to be driven among the plurality of light sources. Boosting means for supplying to the light source to be driven, constant current driving means for making the driving current of the light source to which the boosted voltage is applied constant steadily, and the boosting means according to the number of the light sources to be driven And a boost switching means for switching between.

An image processing apparatus according to the present invention includes the above-described light source driving device, thereby illuminating a subject with irradiation light from the plurality of light sources, receiving reflected light from the subject, converting the image into an image signal, and performing image processing Is to do.
An image reading apparatus according to the present invention corresponds to the above-described image processing apparatus, and reads image data of the subject by the image processing.

  An image forming apparatus according to the present invention includes the above-described image reading device and an image forming unit that forms an image on a recording medium based on image data read by the image reading device. Image forming means for illuminating a subject with light emitted from a plurality of light sources and exposing the image carrier charged in advance with reflected light from the subject to form an image.

According to the light source driving device of the present invention, the number of light sources to be driven among the plurality of light sources is switched, and the boosting means (the power supply voltage from the power source is boosted) according to the number of the light sources to be driven (size of the load). The means for supplying to the light source to be driven is switched. That is, the optimum constant of the drive unit (actually the boosting means) corresponding to the magnitude of the load is selected. Therefore, excessive or insufficient supply power from the drive unit side depending on the constant can be avoided and stable operation can be performed, so that the light amount fluctuation of the light source can be prevented.
According to the image processing apparatus of the present invention, it is possible to achieve high image quality of a processed image.
According to the image reading apparatus of the present invention, it is possible to realize high quality of the read image.
According to the image forming apparatus of the present invention, high quality of the formed image can be realized.

It is a circuit diagram which shows the 1st example of the basic composition of the light source drive device which is 1st Embodiment of this invention. It is a circuit diagram which shows the 2nd example of the basic composition of the light source drive device which is 2nd Embodiment of this invention. It is a circuit diagram which shows the 1st example of a specific structure of the light source drive device which is 3rd Embodiment of this invention. It is a circuit diagram which shows the 2nd example of the specific structure of the light source drive device which is 4th Embodiment of this invention. It is a circuit diagram which shows the 3rd example of the specific structure of the light source drive device which is 5th Embodiment of this invention.

It is a circuit diagram which shows the 4th example of a specific structure of the light source drive device which is 6th Embodiment of this invention. It is a circuit diagram which shows the 5th example of a specific structure of the light source drive device which is 7th Embodiment of this invention. It is a circuit diagram which shows the 6th example of a specific structure of the light source drive device which is 8th Embodiment of this invention. It is a whole block diagram which shows the structural example of the mechanism part of the image reading apparatus which is 9th Embodiment of this invention. FIG. 10 is a block diagram illustrating a configuration example of a part of an image signal processing unit of the image reading apparatus 200 illustrated in FIG. 9.

It is a whole block diagram which shows the structural example of the mechanism part of the image forming apparatus which is 10th Embodiment of this invention. It is a circuit diagram which shows the structural example of the conventional light source drive device. It is a figure which shows the example of a waveform of switching operation | movement of step-up FET11 of FIG. FIG. 13 is a diagram illustrating a waveform example of a boosted output voltage of the booster circuit unit 10 of FIG. 12 and a current Ie flowing through the LED light source array 2.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. In this embodiment, an LED (LED light source) is used as the light source, but other light sources can also be used.
In the following embodiments, the light source driving device has the following characteristics when driving an LED light source accompanied by a change in the LED driving current and the number of lighting.

In other words, by providing a function for selecting an optimum constant of the drive unit, a mechanism that can always perform an optimum operation even when the load greatly changes is provided. This eliminates excess or deficiency of the power supplied from the drive unit side depending on the constant and enables stable operation, thereby eliminating the influence on the read image (light quantity fluctuation for each line, etc.). .
Therefore, the features thereof will be specifically described with reference to FIGS. 1 to 11. Before the description, the problems of the conventional light source driving device will be described with reference to FIGS. The description will be given with reference.

FIG. 12 is a circuit diagram showing a configuration example of a conventional light source driving device.
This light source driving device is constituted by a general boost type constant current LED driving circuit. In this example, two LED light source rows are used as the light source (LED light source).
In this light source driving device, the power supply voltage (input voltage) from the power source 1 is boosted (input voltage <boosted output voltage) by the booster circuit unit 10 and supplied to each LED light source array (load) 2, 3. The LED light source rows 2 and 3 can be turned on.

The step-up circuit unit 10 is a step-up unit that performs the step-up, and includes a step-up field effect transistor (FET) 11, a comparator 12, a lowest voltage detector 13, and an inductor (step-up coil). 14, a diode 15, and a capacitor 16.
The constant current circuit unit 20 is a constant current driving unit that constantly and constantly drives the driving current of the LED light source array 2 to which the voltage boosted by the boosting circuit unit 10 is applied, and includes a current detection resistor 21, an operational amplifier 22, and an FET 23. , And a power source 24.
The constant current circuit unit 30 is a constant current drive unit that constantly and constantly drives the drive current of the LED light source array 3 to which the voltage boosted by the boost circuit unit 10 is applied, and includes a current detection resistor 31, an operational amplifier 32, and an FET 33. , And a power source 34.

In each of the constant current circuit units 20 and 30, the current is sunk (sucked) for each of the LED light source arrays 2 and 3, and a constant current is passed through each of the LED light source arrays 2 and 3 to maintain the light quantity stability.
In the constant current circuit unit 20, the current flowing through the LED light source array 2 is detected by the current detection resistor 21 and converted into a voltage, and the operational amplifier 22 converts the voltage of the gate terminal G of the FET 23 according to the comparison with the reference voltage of the power supply 24. Control. As a result, a constant current predetermined by the reference voltage flows through the LED light source array 2.
In the constant current circuit unit 30, the current flowing through the LED light source array 3 is detected by the current detection resistor 31 and converted into a voltage, and the operational amplifier 32 converts the voltage of the gate terminal G of the FET 33 according to the comparison with the reference voltage of the power supply 34. Control. As a result, a constant current predetermined by the reference voltage flows through the LED light source array 3.

On the other hand, in order to continue to sink the specified current to the LED light source arrays 2 and 3, it is necessary to continuously supply a voltage exceeding a certain value to each LED light source array 2 and 3, which monitors the voltage on the cathode terminal side. Achieved by feedback.
The boosted voltage is obtained by driving (turning on / off) the boosting FET 11 with a general pulse width modulation (PWM) signal generator. In the example of FIG. 12, the PWM signal generator is configured by a comparator 12 and a lowest voltage detector 13.

Therefore, the lowest voltage (= the voltage of the column with the largest LED forward voltage in the column) among the cathode terminal voltages of the LED light source columns 2 and 3 is detected and picked up by the lowest voltage detection unit 13 to be an analog voltage. give feedback.
In the comparator 12, the analog voltage from the lowest voltage detector 13 input to the inverting input terminal (−) that is one input terminal, and the reference that is input to the non-inverting input terminal (+) that is the other input terminal. Is compared with a voltage (reference voltage) of a reference signal (for example, a signal indicating “sawtooth wave” or “triangular wave”) which is a periodic signal, and a signal indicating the comparison result is output as an FET drive signal. To the gate terminal G.

The FET drive signal output from the comparator 12 is high level “H” when the analog voltage is lower than the reference voltage, and low level “L” when the analog voltage is high. Therefore, the high level “H” is wide when the analog voltage is lowered and becomes a narrow signal when the analog voltage is raised, and the ON / OFF timing of the boosting FET 11 is controlled by the duty ratio.
While the boosting FET 11 is on, a short path between the power source 1 -inductor 14 -ground (GND) is established, so that the flowing current continues to rise and keeps the current as energy in the inductor 14. On the other hand, the voltage generated when the boosting FET 11 is turned off is proportional to the current energy.

Therefore, when the analog voltage decreases, the duty ratio of the FET drive signal output from the comparator 12 increases and the energy of the inductor 14 increases, so the level of the boosted voltage increases and the boosted voltage becomes constant. Realized.
As described above, constant voltage and constant current for driving the LED light source arrays 2 and 3 are realized. However, in the case of an LED light source that constitutes an image reading apparatus or an image forming apparatus, there is a case in which the load greatly fluctuates due to the size of a document to be read or a change in driving current, and the required boosted voltage level fluctuates. At this time, the driving condition may deviate from the optimum value, and voltage and current non-uniformity may occur.

FIG. 13 is a diagram showing a waveform example of the switching operation of the boost FET 11 of FIG.
The waveform Vm of the switching operation of the boosting FET 11 indicates the waveform of the input voltage to the drain D of the boosting FET 11. During the boosting operation, the voltage level and the GND level of the power source 1 are swung by the switching operation.
FIG. 14 is a diagram illustrating a waveform example of the boosted output voltage of the booster circuit unit 10 of FIG. 12 and the current (LED drive current) Ie flowing through the LED light source array 2. In this example, the LED drive current Ie is the current that flows through the LED light source array 2, but it may be the current that flows through the LED light source array 3.

  As can be seen from FIG. 14, when the boosted output voltage Vs becomes too high, the booster circuit unit 10 stops the boosting operation. After the stop, when the voltage is insufficient (= current drop), the boosting operation is resumed. When the boosting is resumed, an operation is performed to compensate for the insufficient voltage in a short time, so that much of the current is drawn into the boosting operation. As a result, the LED drive current Ie repeatedly varies.

I will explain the problem in more detail.
For example, when only the LED light source array 2 is driven, the load is reduced by reducing the number of LEDs to be driven, and when a necessary voltage level is reduced, a single boost operation (one cycle from ON to OFF of the boost FET 11) is performed. The voltage generated in (operation) becomes relatively large. Therefore, the cathode terminal voltage Vk of the LED light source array 2 rises more than necessary while repeating the boosting operation.

  As a result, the FET drive signal to the boosting FET 11 keeps the low level “L”, and the boosting operation is stopped for a certain time. When this state continues, the cathode terminal voltage Vk gradually decreases and the boosting operation is restored. At this time, the boosting FET 11 starts operating. However, the necessary generated voltage cannot be generated abruptly, resulting in instantaneous fluctuations in the boosted output voltage Vs and the LED drive current Ie. This causes a variation in the amount of light of the LED light source array 2, resulting in a variation for each line of the image, and appears as a horizontal stripe in the image.

  Accordingly, each embodiment for eliminating or reducing these fluctuations will be described below. In each of the embodiments, a case of selectively switching to driving one LED light source array or driving two LED light source arrays out of two LED light source arrays will be described as an example. However, among three or more LED light source arrays, selective switching to driving of N (“1” or more) LED light source arrays or driving of M (“N + 1” or more) LED light source arrays is performed. You can also.

[First Embodiment]
First, a first embodiment of the present invention will be specifically described with reference to FIG.
FIG. 1 is a circuit diagram showing a first example of the basic configuration of the light source driving apparatus according to the first embodiment of the present invention.
This light source driving device shows a configuration in which a power source booster circuit is switched according to the size of a load, and includes a light source 41 that is a load, a light source driver 42, and a booster circuit unit 50.
The light source 41 includes a plurality of light sources such as LEDs. In this example, it is assumed that the LED light source is composed of the LED light source rows 2 and 3 shown in FIG.

The light source driver 42 drives the LED light source arrays 2 and 3 constituting the light source 41 and has a function corresponding to the constant current circuit units 20 and 30 of FIG.
The booster circuit unit 50 includes power booster circuits 51 and 52 and switches 53 and 54. The power booster circuit 51 and the series circuit of the switch 53, the series circuit of the power booster circuit 52 and the switch 54, the power source 1 and the light source. 41 is connected in parallel.

The power boosting circuit 51 is a boosting unit that performs a boosting operation for boosting the power supply voltage from the power supply 1 and supplying the boosted voltage to the LED light source array that is driven. can do.
The power booster circuit 52 is a booster that performs a boosting operation for boosting the power supply voltage from the power supply 1 and supplying the boosted voltage to the LED light source array that is driven, and generates larger power (hereinafter referred to as “high power”) than the power booster circuit 51. can do. Note that “high power” is, for example, twice that of “low power”.

The switch 53 is an electrical switch such as an FET that turns on / off the boosting operation of the power boosting circuit 51. When the boosting operation of the power boosting circuit 51 is turned on, the power boosting circuit 51 is selected as the power boosting circuit that performs the boosting operation.
The switch 54 is an electrical switch such as an FET that turns on / off the boosting operation of the power boosting circuit 52. When the boosting operation of the power boosting circuit 52 is turned on, the power boosting circuit 52 is selected as the power boosting circuit that performs the boosting operation.

  The drive control signals Sa and Sb are signals for driving the LED light source rows 2 and 3 constituting the light source 41, respectively, and only the LED light source row 2 (one row) is driven, or the LED light source rows 2 and 3 are driven. It is possible to drive the LED light source rows 2 and 3 by switching to 3 (2 rows) driving. Accordingly, the power boosting circuit 51 constitutes a circuit for generating low power, and the power boosting circuit 52 constitutes a circuit for generating high power.

  When the light source driver 42 drives only the LED light source row 2 (one row), a drive control signal Sa (for example, a high level signal) is input to the booster circuit portion 50 by an external timing clock generator 254 (see FIG. 10) described later. Therefore, only the switch 53 is turned on (the switch 54 is turned off). As a result, the power boosting circuit 51 is selected, and a boosting operation is performed to generate a small amount of power using the power supply voltage from the power supply 1. That is, the power booster circuit is switched to generate a small electric power.

  On the other hand, when the light source driver 42 drives the LED light source columns 2 and 3 (two columns), the drive control signal Sb (for example, a high level signal) is input to the booster circuit unit 50 by the external timing clock generation unit 254. Only the switch 54 is turned on (the switch 53 is turned off). As a result, the power boosting circuit 52 is selected, and a boosting operation for generating a large amount of electric power by the power supply voltage from the power supply 1 is performed. That is, the power booster circuit is switched to generate a large amount of power.

Therefore, the light source driver 42 and the switches 53 and 54 function as drive light source switching means and boost switching means.
In addition, when a light source consists of 3 or more LED light source arrays, it is good to connect 3 or more sets of power supply booster circuits and switches in parallel between a power supply and a light source. In this case, it is assumed that the power booster circuits generate different amounts of power.

  According to the light source driving device of the first embodiment, the number of LED light source arrays to be driven is switched among the plurality of LED light source arrays, and the power supply voltage is boosted according to the number of LED light source arrays to be driven (the size of the load). One or more circuits are selected (switching the power booster circuit). Therefore, the drive condition (constant) of the drive unit (actually the booster circuit unit 50) corresponding to the magnitude of the load is optimized. Therefore, excessive or insufficient supply power from the drive unit side depending on the constant can be avoided and stable operation can be performed, so that fluctuations in the light amount of the LED light source can be prevented.

[Second Embodiment]
Next, a second embodiment of the present invention will be specifically described with reference to FIG.
FIG. 2 is a circuit diagram showing a second example of the basic configuration of the light source driving apparatus according to the second embodiment of the present invention, and portions corresponding to those in FIG.

In this light source driving device, the number of switches is reduced by connecting the power boosting circuits 51 and 52 in series between the power source 1 and the light source 41. In this case, a circuit capable of generating the necessary power for driving the LED light source columns 2 and 3 (two columns) by simultaneously driving the power booster circuits 51 and 52 is provided.
When driving only the LED light source row 2 (one row), the drive control signal Sa is input to the booster circuit unit 50, so that the switch 55 is turned on, the power booster circuit 52 does not operate, and only the power booster circuit 51 is driven. Works.

  On the other hand, when the light source driver 42 drives the LED light source columns 2 and 3 (two columns), the drive control signal Sa is not input to the booster circuit unit 50, so the switch 55 is turned off and the power booster circuits 51 and 52 are simultaneously connected. Operate. In this embodiment, since the power boosting circuit 52 does not perform a boosting operation alone, the power boosting circuit 52 performs a boosting operation for generating small power similar to the power boosting circuit 51.

Therefore, the light source driver 42 and the switch 55 function as drive light source switching means and boost switching means.
When the light source is composed of three or more LED light source columns, a power booster circuit in which three or more power booster circuits are connected in series between the power source and the light source and the boosting operation needs to be switched on / off. It is recommended to connect a switch in parallel. In this case, all the power boosting circuits can generate the same low power.

  According to the light source driving device of the second embodiment, substantially the same function as that of the light source driving device of the first embodiment shown in FIG. 1 can be obtained, and the same effect can be obtained. In addition, each power booster circuit has a circuit configuration for generating low power, and the number of switches used for switching the power booster circuits is less than the number of power booster circuits, leading to space saving and cost reduction. .

[Third Embodiment]
Next, a third embodiment of the present invention will be specifically described with reference to FIG.
FIG. 3 is a circuit diagram showing a first example of a specific configuration of the light source driving apparatus according to the third embodiment of the present invention, and portions corresponding to those in FIGS. 1 and 12 are denoted by the same reference numerals.
The light source driving device of the third embodiment is an application example of the light source driving device of the first embodiment described with reference to FIG. 1, and constitutes a booster element switching type LED driving circuit.

The drive control signal Sa is a signal for driving only the constant current circuit unit 70 via the OR circuit 91 and the voltage regulator (REG) 92 and driving only the LED light source array 2 by the change to the high level “H”. It becomes.
The drive control signal Sb is driven by the change to the high level “H” to drive the constant current circuit unit 70 in the same manner as the drive control signal Sa and to turn on the switch 93 (electric switch such as FET). By supplying a voltage also to the current circuit unit 80 and driving the constant current circuit unit 80, a signal for driving the LED light source arrays 2 and 3 is obtained.

In the constant current circuit unit 70, the current flowing through the LED light source array 2 is detected by the current detection resistor 21 and converted into a voltage, and the operational amplifier 22 compares the output voltage (reference voltage) of the voltage regulator 92 with the gate of the FET 23. Controls the voltage at terminal G.
In the constant current circuit unit 80, the current flowing through the LED light source array 3 is detected by the current detection resistor 31 and converted into a voltage, and the operational amplifier 32 compares the output voltage of the voltage regulator 92 with the voltage at the gate terminal G of the FET 33. To control.

The inductor (boost coil) 61 that is a booster element in the power supply unit 60 is part of a circuit for generating low power in the power booster circuit 51 of FIG. 1, and the inductor 62 that is a booster element is in the power booster circuit 52. Respectively corresponding to a part of the circuit for generating large electric power. The relationship between the values of the inductors 61 and 62 (inductance) is such that the value of the inductor 61 <the value of the inductor 62.
A drive circuit (excluding the inductor 61) including the transistor 63 and the FET 64 in the power supply unit 60 is provided in the switch 53 of FIG. 1, and a drive circuit including the transistor 65 and FET 66 (excluding the inductor 62) is provided in the switch 54 of FIG. Correspondingly, an operation linked to ON (high level) / OFF (low level) of the drive control signals Sa and Sb is performed.

In this embodiment, only the inductors 61 and 62 are to be switched, and the boosting FET 11, the comparator 12, the minimum voltage detection unit 13, the oscillator (OSC) 94, and the like that constitute other boosting circuits are used in common. Thereby, space saving and cost reduction can be achieved.
The oscillator (OSC) 94 generates and outputs a reference signal input to the non-inverting input terminal (+) of the comparator 12.
According to the light source driving device of the third embodiment, in addition to the same effect as the light source driving device of the first embodiment, a general-purpose semiconductor is used as a switch used for switching the inductor constituting the power boosting circuit, By making only a plurality of inductors to be switched and using other booster circuits in common, it is possible to obtain an effect that space saving and cost reduction can be achieved.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 4 is a circuit diagram showing a second example of the specific configuration of the light source driving apparatus according to the fourth embodiment of the present invention. Parts corresponding to those in FIG.

The light source driving device of the fourth embodiment is an application example of the light source driving device of the second embodiment described with reference to FIG. 2, and constitutes a booster element switching type LED driving circuit.
Inductors 61 and 62, which are boosting elements in power supply unit 60, correspond to a part of a circuit for generating low power in power boosting circuits 51 and 52 in FIG.

The drive control signal Sa becomes high level “H” when only the LED light source row 2 (one row) is driven. Therefore, the transistor 67 and the FET 68 constituting the drive circuit corresponding to the switch 55 in FIG. 2 are operated. . That is, when the transistor 67 is turned on, the FET 68 is also turned on. Therefore, since the inductor 62 is not used, the boost level becomes small.
The drive control signal Sa becomes low level “L” when driving the LED light source columns 2 and 3 (two columns), and the transistors 67 and FET 68 are turned off, so that the inductors 61 and 62 are used simultaneously. . In this embodiment, since the inductor 62 is not used alone, a boosting operation for generating low power is performed. In this case, the relationship between the values of the inductors 61 and 62 is the value of the inductor 61 = the value of the inductor 62.

  According to the light source driving device of the fourth embodiment, the same effect as that of the light source driving device of the first embodiment can be obtained. In addition, any of the plurality of inductors in the power supply unit may be used for generating low power, and the number of components of the drive circuit used for switching the inductor is smaller than that of the light source driving device of the third embodiment shown in FIG. This leads to further space saving and cost reduction.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 5 is a circuit diagram showing a third example of the specific configuration of the light source driving apparatus according to the fifth embodiment of the present invention. The same parts as those in FIG.
The light source driving device of the fifth embodiment is an example in which a general-purpose LED driver IC is applied to a part of each circuit constituting the light source driving device of the third embodiment described with reference to FIG.

The LED driver IC 100 includes the boosting FET 11, the comparator 12, the minimum voltage detecting unit 13, the oscillator (OSC) 94, the OR circuit 91, the voltage regulator (REG) 92, the switch 93, and the constant current circuit units 70 and 80 shown in FIG. Therefore, the same operation as each part is performed internally.
According to the light source drive device of the fifth embodiment, by using a general-purpose integrated circuit (general-purpose IC), in addition to the same effects as the light source drive device of the third embodiment, further space saving and The effect of leading to higher accuracy can be obtained.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 6 is a circuit diagram showing a fourth example of the specific configuration of the light source driving apparatus according to the sixth embodiment of the present invention. The same parts as those in FIG.
The light source driving device of the sixth embodiment is an example in which a general-purpose LED driver IC is applied to a part of each circuit constituting the light source driving device of the fourth embodiment described with reference to FIG.

The LED driver IC 100 includes the boosting FET 11, the comparator 12, the minimum voltage detecting unit 13, the oscillator (OSC) 94, the OR circuit 91, the voltage regulator (REG) 92, the switch 93, and the constant current circuit units 70 and 80 shown in FIG. Therefore, the same operation as each part is performed internally.
According to the light source driving device of the sixth embodiment, using a general-purpose IC leads to further space saving and higher accuracy in addition to the same effects as the light source driving device of the fourth embodiment. An effect can be obtained.

[Seventh Embodiment]
Next, a seventh embodiment of the present invention will be specifically described with reference to FIG.
FIG. 7 is a circuit diagram showing a fifth example of the specific configuration of the light source driving apparatus according to the seventh embodiment of the present invention. Components identical with those shown in FIGS.

The light source driving device of the seventh embodiment is a configuration example in the case of switching the boosting system by switching the switching frequency instead of switching the boosting element (inductor) from the light source driving device of the sixth embodiment described with reference to FIG. The step-up frequency switching type LED driving circuit is configured.
In addition to the same function as the LED driver IC 100 of FIG. 6, the LED driver IC 110 converts the voltage generated by the external transistor 121 and the resistors 122 and 123 constituting the voltage generation unit 120 into a switching frequency for the boost operation. It has a VF conversion (voltage-frequency conversion) function.

  In the LED driver IC 110, when only the LED light source column 2 (one column) is driven, only the drive control signal Sa becomes the high level “H”, so that the transistor 121 is turned on and the resistors 122 and 123 are combined in parallel. The voltage corresponding to the resistance value is converted into a switching frequency (switching frequency lower than the switching frequency for generating high power) corresponding to the boosting operation for generating low power. When driving the LED light source columns 2 and 3 (two columns), only the drive control signal Sb is at the high level “H”, so that the transistor 121 is turned off and a voltage corresponding to the resistance value of the resistor 123 is increased. It converts into the switching frequency corresponding to the pressure | voltage rise operation | movement for producing | generating electric power. Therefore, a boosting operation corresponding to the converted switching frequency is performed.

Specifically, it is as shown below.
Although the specifications differ depending on the LED driver IC 110, the internal configuration and operation of many terminals FSW are as shown in any of the following (a) and (b).
(A) There is a constant current source inside the FSW terminal, and the level of the voltage generated at the terminal FSW varies depending on the value of the external resistor. This voltage level is further converted into a frequency (VF conversion) inside. That is, the boost switching frequency is switched.
(B) There is a constant voltage source inside the terminal FSW, and the current flowing out from the terminal FSW varies depending on the value of the external resistor. This current is further internally converted from voltage conversion to frequency. That is, the boost switching frequency is switched.

Thus, in any case, the boost switching frequency can be switched by changing the value of the external resistor.
Therefore, in FIG. 7, when only the drive control signal Sa becomes “H”, the enable signal to the terminal EN1 becomes “H”, and only the LED light source row 2 (one row) is driven. Further, since the transistor 121 is turned on, the value of the resistor connected to the terminal FSW terminal becomes a parallel combined resistance value of the resistors 122 and 123.

On the other hand, when only the drive control signal Sb becomes “H”, the enable signal to the terminal EN2 becomes “H”, and the LED light source rows 2 and 3 (2 rows) are driven. Further, since the transistor 121 is turned off, the value of the resistor connected to the terminal FSW becomes the resistance value of the resistor 123.
As described above, the boosting switching frequency can be switched according to the drive signals Sa and Sb (depending on the magnitude of the driven load), and the boosting operation corresponding to the switching frequency is performed.

  Here, by decreasing the switching frequency corresponding to the boosting operation, an instantaneous voltage increase width can be suppressed, and a stable boosting operation can be continued at all times. If the voltage increase range is large, the voltage applied to the constant current circuit unit in the LED driver IC 110 increases instantaneously, causing a change in on-resistance of the switch and a change in current, leading to instability of the light amount.

  According to the light source drive device of the seventh embodiment, the number of LED light source examples to be driven is switched among a plurality of LED light source arrays, and the switching frequency is changed according to the number of LED light source arrays to be driven (the size of the load). To change. Therefore, since only one inductor is required and it is not necessary to use an FET, in addition to the same effect as that of the light source driving device of the sixth embodiment, an effect of further space saving can be obtained.

[Eighth Embodiment]
Next, an eighth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 8 is a circuit diagram showing a sixth example of the specific configuration of the light source driving apparatus according to the eighth embodiment of the present invention. Parts corresponding to those in FIG.
The light source driving device of the eighth embodiment is different from the light source driving device of the seventh embodiment described with reference to FIG. 7 only in the internal configuration of the voltage generation unit 120.

In the LED driver IC 110, when driving only the LED light source column 2 (one column), only the drive control signal Sa becomes high level “H”, so that the transistor 121 is turned off, and the series combined resistance of the resistors 124 and 125 The voltage corresponding to the value is converted into a switching frequency (switching frequency lower than the switching frequency for generating large power) corresponding to the boosting operation for generating small power. When driving the LED light source columns 2 and 3 (two columns), only the drive control signal Sb is at the high level “H”, so that the transistor 121 is turned on and a voltage corresponding to the resistance value of the resistor 124 is increased. It converts into the switching frequency corresponding to the pressure | voltage rise operation | movement for producing | generating electric power. Therefore, a boosting operation corresponding to the converted switching frequency is performed.
According to the light source driving device of the eighth embodiment, the same effect as that of the light source driving device of the seventh embodiment can be obtained.

  In the above 1st-8th embodiment, the optimal operation | movement according to the magnitude | size of load is constructed | assembled by constructing | assembling the system which switches a drive condition according to the electric power (size of load) of LED light source row | line | column (load). It has a mechanism to realize. As a result, the voltage or current change can be minimized even with large load fluctuations. In the following ninth and tenth embodiments, examples in which the characteristics are applied to an image reading apparatus and an image forming apparatus which are image processing apparatuses will be described. Note that the image processing device illuminates the image surface of a document, which is a subject, with light emitted from an LED light source array by a light source driving device, and receives reflected light from the image surface with a CCD (or other image sensor). Then, it is converted into an image signal and image processing is performed.

[Ninth Embodiment]
Next, a ninth embodiment of the present invention will be specifically described with reference to FIGS.
FIG. 9 is an overall configuration diagram showing a configuration example of a mechanism portion of an image reading apparatus according to the ninth embodiment of the present invention. Parts (light sources 41) corresponding to FIG. 1 and FIG. .

  The image reading device is a scanner device or a single scanner device mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine, and has a light source driving unit (shown in any of FIGS. 1 to 8). Equivalent to a light source driving device) and an image signal processing unit. Then, the original that is the subject is illuminated by the light emitted from the light source (LED light source) by the light source driving unit, the reflected light from the original is received by the CCD, and converted into an image signal by the A / D conversion unit to perform image processing. The image data of the original can be read. Since the image signal converted by the A / D converter is an analog signal, it is converted to a digital signal.

  As shown in FIG. 9, the image reading apparatus 200 includes a contact glass 201 on which a document is placed, and a light source 41 for document exposure (LED light source arrays 2 and 3 shown in any of FIGS. 1 to 8). A first carriage 206 composed of a first reflection mirror 203 and a second carriage 207 composed of a second reflection mirror 204 and a third reflection mirror 205. Also, a CCD linear image sensor (hereinafter simply referred to as “CCD”) 209, a lens unit 208 for forming an image on the CCD 209, a white reference plate 210 for correcting various distortions due to a reading optical system, and a sheet through A reading slit 211 is also provided.

An automatic document feeder (hereinafter abbreviated as “ADF”) 220 as an automatic document feeder is mounted on the upper part of the image reading apparatus 200, so that the ADF 220 can be opened and closed with respect to the contact glass 201. Are connected via a hinge or the like (not shown).
The ADF 220 includes a document tray 221 as a document placement table on which a document bundle composed of a plurality of documents can be placed. In addition, separation / feeding means including a feeding roller 222 that separates documents one by one from a bundle of documents placed on the document tray 221 and automatically feeds them toward the sheet-through reading slit 211 is also provided.

In the image reading apparatus 200 configured as described above, the following reading operation is performed in the scan mode in which the image surface of the document is scanned (scanned) to read the image of the document.
That is, the first carriage 206 and the second carriage 207 are moved in the arrow A direction (sub-scanning direction) at different speeds so that the optical path length is not changed by a stepping motor (not shown).

  At the same time, the image surface which is the lower surface of the document set on the contact glass 201 is illuminated (exposed) by the light source 41 (the LED light source composed of the LED light source rows 2 and 3) of the first carriage 206. Then, the reflected light image from the image surface is sequentially sent to the CCD 209 via the first reflecting mirror 203 of the first carriage 206, the second reflecting mirror 204 and the third reflecting mirror 205 of the second carriage 207, and the lens unit 208. The image of the original is read.

On the other hand, in the sheet-through mode in which an original is automatically fed and an original image is read, the following reading operation is performed.
That is, after the first carriage 206 and the second carriage 207 move to the lower side of the sheet-through reading slit 211, the document placed on the document tray 221 is moved in the direction indicated by the arrow B (sub-scanning direction) by the feed roller 222. ) Is automatically fed.

  Since the lower surface (image surface) of the automatically fed document is illuminated by the light source 41 of the first carriage 206 at the position of the sheet-through reading slit 211, the reflected light image from the image surface is the first carriage. The image is sequentially sent to the CCD 209 via the first reflection mirror 203, the second reflection mirror 204 and the third reflection mirror 205 of the second carriage 207, and the lens unit 208, and the image of the original is read. The document whose reading has been completed is discharged to a discharge port (not shown).

Note that the image of the white reference plate 210 is read by illumination by the light source 41 started before the image reading in the scan mode or the sheet through mode, and shading correction at the time of image reading is performed based on the reading result. Since this shading correction is a known technique, a detailed description thereof will be omitted.
Further, when the ADF 220 is provided with a conveyance belt, the document can be automatically fed to the reading position on the contact glass 201 by the ADF 220 and the image of the document can be read even in the scan mode.

FIG. 10 is a block diagram illustrating a configuration example of a part of the image signal processing unit of the image reading apparatus 200 illustrated in FIG. 9.
In the image signal processing unit 250, the analog image signal photoelectrically converted by the CCD 209 is output to the analog processing circuit unit 251 as shown in FIG.
The analog processing circuit unit 251 performs various image processing such as sample hold processing and black level correction on the analog image signal input from the CCD 209, and then outputs the analog image signal to the A / D conversion circuit unit 252.

The A / D conversion circuit unit 252 converts the analog image signal input from the analog processing circuit unit 251 into a digital image signal (image data), and outputs the digital image signal to the subsequent image signal processing unit via the LVDS interface 253.
The timing clock generation unit 254 receives various timing clock signals to be input to the CCD 209, the analog processing circuit unit 251, the A / D conversion circuit unit 252, the LVDS interface 253, and a stepping motor (not shown) and the light source driving device in the image reading apparatus 200. It is generated and supplied based on the reference clock from the oscillator 255.

  According to the image reading apparatus of the ninth embodiment, the light source driving apparatus according to any one of the first to eighth embodiments is provided, and the original is illuminated with light emitted from a plurality of LED light sources by the light source driving apparatus. The following effects can be obtained by reading the image data of the original by receiving the reflected light from the image and converting it into an image signal to perform image processing. That is, since fluctuations in the amount of light of the light source 41 (LED light source) can be prevented, deterioration in image quality due to fluctuations in the amount of light of the read image (processed image) can be avoided. That is, it is possible to achieve high image quality of the read image.

[Tenth embodiment]
Next, a tenth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 11 is an overall configuration diagram showing a configuration example of a mechanism portion of an image forming apparatus according to the tenth embodiment of the present invention. The same reference numerals are given to the same portions as those in FIG.
The image forming apparatus 300 is a digital copier equipped with the image reading apparatus 200 shown in FIG. 9 (including a light source driving unit corresponding to the light source driving apparatus shown in any of FIGS. 1 to 8).

As shown in FIG. 11, the image forming apparatus 300 is provided with an ADF 400 on an upper part of a contact glass 201 on which an original is placed. A hinge or the like (not shown) is provided so that the ADF 400 can be opened and closed with respect to the contact glass 201. It is connected through.
The ADF 400 includes a document tray 401 as a document placement table on which a document bundle composed of a plurality of documents can be placed. Further, when a print key on an operation unit (not shown) is pressed, the originals are separated one by one from the original bundle placed on the original tray 401 with the image surface facing upward, and automatically fed, and the sheet through reading slit 211 is provided. Alternatively, separation / feeding means including a feeding roller 402 and a conveying belt 403 that are conveyed toward the contact glass 201 is also provided.

The document fed by the feeding roller 402 or the conveyance belt 403 is read out as described with reference to FIG. 9 and then discharged onto the upper surface of the ADF 400 by the conveyance belt 403 and the discharge roller 404.
Here, the operation of the controller (not shown) and the ADF 400 when the document is conveyed to the reading position of the contact glass 201 by the ADF 400 will be described.

  The feed motor of the ADF 400 is driven by an output signal from the controller. When the feed start signal generated by pressing the print key on the operation unit is input, the controller corrects the feed motor.・ Reverse drive. When the feeding motor is driven to rotate forward, the feeding roller 402 rotates clockwise to automatically feed the document located at the highest position from the bundle of documents toward the sheet-through reading slit 211 or the contact glass 201. Be transported. When the leading edge of the document is detected by the document set detection sensor 405, the controller drives the feed motor in reverse based on the output signal from the document set detection sensor 405. This prevents subsequent documents from entering and prevents separation.

  When the document set detection sensor 405 detects the trailing edge of the document, the controller also counts a rotation pulse of a conveyance belt motor (not shown) from this detection point, and when the rotation pulse reaches a predetermined value, the conveyance belt 403. Is stopped and the conveying belt 403 is stopped, whereby the document is stopped at the reading position on the contact glass 201. Further, when the trailing edge of the document is detected by the document set detection sensor 405, the feeding motor is driven again, and the subsequent document is separated and automatically fed as described above. Then, the sheet is conveyed toward the contact glass 201, and when the pulse of the feeding motor from the time when this document is detected by the document set detection sensor 405 reaches a predetermined pulse, the feeding motor is stopped and the next document is detected. To wait first.

  When the document stops at the reading position on the contact glass 201, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveying belt motor in the normal direction by this signal, and the document is discharged from the contact glass 201 by the conveying belt 403 to the discharge roller. Unload to 404.

As described above, the document bundle placed on the document tray 401 in the ADF 400 with the image surface of the document facing up is automatically fed from the top document by pressing the print key. For example, the reading position on the contact glass 201 It is conveyed to.
The original that has been conveyed to the reading position and stopped is discharged from the discharge port by the conveying belt 403 or the like after the image is read. Further, when it is detected that there is a next document on the document tray 401, the next document is automatically fed and conveyed onto the contact glass 201 in the same manner as the previous document.

  The transfer sheets (paper sheets) stacked on the first tray 301, the second tray 302, and the third tray 303, which are sheet feeding trays, are a first sheet feeding unit 311, a second sheet feeding unit 312, and a third sheet feeding unit, respectively. The sheet is fed by 313 and conveyed by the vertical conveyance unit 314 to a position where it abuts on a drum-shaped photosensitive member (photosensitive drum) 315 as an image carrier. Actually, any one of the trays 301 to 303 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

On the other hand, the image data read by the image reading apparatus 200 is written onto the surface of the photoreceptor 315 that has been charged in advance by a charging unit (not shown) by a laser beam from a writing unit 350 in the printer that is an image forming unit (that When the surface is exposed), the portion passes through the developing unit 327, and a toner image is formed there. The developing unit 327 that performs the image formation, the charging unit, and the like constitute image forming means.
The transfer sheet fed from the selected paper feed tray is transferred by the transfer belt 316 at the same speed as the rotation of the photoconductor 315, and the toner image on the photoconductor 315 is transferred. Further, the toner image is fixed by the fixing unit 317, and is discharged by a paper discharge unit 318 to a paper discharge tray 319 outside the apparatus.

  At this time, for example, in order to reverse the transfer paper on which the toner image is formed on one side in order to discharge face-down (the image surface faces downward in order to align the transfer paper in the page order), the transfer paper is discharged. The paper is conveyed to the double-sided paper conveyance path 320 by the unit 318, switched reverse by the reversing unit 321, and then discharged to the paper discharge tray 319 through the reverse paper conveyance path 322.

When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is conveyed to the double-sided input conveyance path 320 by the paper discharge unit 318 and is switched back by the reverse unit 321. After that, it is sent to the duplex conveying unit 323.
The transfer paper sent to the double-sided conveyance unit 323 is fed again from the double-sided conveyance unit 323 to transfer the toner image formed on the photoconductor 315 again, and is again applied to the photoconductor 315 by the vertical conveyance unit 314. After the toner image is transferred to the other surface and transferred to the other surface, the toner image is fixed by the fixing unit 317 and discharged to the paper discharge tray 319 by the paper discharge unit 318.

  The photoconductor 315, the conveyance belt 316, the fixing unit 317, the paper discharge unit 318, and the development unit 327 are driven by a main motor (not shown), and the driving force of the main motor is transmitted to each of the paper feed units 311 to 313 by a paper feed clutch. Driven. The vertical conveyance unit 314 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 350 includes a laser output unit 351, an imaging lens 352, and a mirror 353. Inside the laser output unit 351, a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) that scans the laser light. Or it has a vibrating mirror. The laser light emitted from the laser output unit 351 is deflected by a polygon mirror or a vibrating mirror, passes through an imaging lens 352, is folded by a mirror 353, and is focused on the surface of the photoreceptor 315.

  According to the image forming apparatus (digital copying machine) of the tenth embodiment, the image reading apparatus of the ninth embodiment is provided, and image formation is performed on a recording medium based on image data read by the image reading apparatus. Therefore, it is possible to avoid the deterioration of the image quality of the formed image. That is, it is possible to achieve high image quality of the formed image.

In the tenth embodiment, the present invention is applied to a digital copying machine. However, the present invention is not limited to this, and other image forming apparatuses such as a digital multi-function peripheral and a facsimile machine as well as an analog copying machine. It can be applied. In the case of a digital image forming apparatus such as a digital copying machine, an image reading device including a light source driving device and an image forming unit that forms an image on a recording medium based on image data read by the image reading device. I have. However, in the case of an analog image forming apparatus such as an analog copying machine, an image reading device is not provided, and an original (subject) is illuminated by light emitted from an LED light source by a light source driving device, and the original is read from the original. An image forming means for forming an image by exposing the image carrier charged in advance by reflected light is provided.
Moreover, this invention is not limited to each embodiment mentioned above, It cannot be overemphasized that all the technical matters contained in the technical idea described in the claim are object.

DESCRIPTION OF SYMBOLS 1: Power supply 2, 3: LED light source row | line | column 11: Boosting FET 12: Comparator 13: Minimum voltage detection part 14, 61, 62: Inductor 15: Diode 16: Capacitor 21, 31: Current detection resistor 22, 32: Operational amplifier 23 , 33, 64, 66, 68: FET (field effect transistor)
41: Light source (LED light source) 42: Light source driver 50: Booster circuit unit 51, 52: Power booster circuit 53-55, 93: Switch 60: Power supply unit 63, 65, 67, 121: Transistor 70, 80: Constant current Circuit unit 91: OR circuit 92: Voltage regulator (REG) 94: Oscillator (OSC)
100, 110: LED driver IC 120: Voltage generator 122-125: Resistor 200: Image reading device 209: CCD 220, 400: ADF
251: Analog processing circuit unit 252: A / D conversion circuit unit 253: LVDS interface 300: Image forming apparatus 315: Photoconductor 317: Fixing unit 327: Development unit 350: Writing unit

JP 2008-187816 A

Claims (10)

A light source driving device for driving a plurality of light sources,
Drive light source switching means for switching the number of light sources to be driven among the plurality of light sources;
Boosting means for boosting a power supply voltage from a power source and supplying the boosted voltage to the driving light source;

Constant current driving means for making the driving current of the light source to which the voltage boosted by the boosting means is applied constantly constant;
A light source driving apparatus comprising: a boost switching unit that switches the boost unit according to the number of the light sources to be driven. The boosting means has a plurality of booster circuits connected in parallel or in series,
2. The light source driving device according to claim 1, wherein the boosting switching unit selects one or a plurality of boosting circuits according to the number of light sources to be driven.   3. The light source driving device according to claim 2, wherein the step-up switching unit controls one or more of the plurality of step-up circuits by controlling a field effect transistor. Each of the plurality of booster circuits has an inductor,
4. The light source driving device according to claim 2, wherein the step-up switching unit selects one or a plurality of inductors of the plurality of step-up circuits. 5. The boosting means is a means for boosting a power supply voltage from the power source according to a switching frequency,
The light source driving apparatus according to claim 1, wherein the boost switching unit changes the switching frequency according to the number of the light sources to be driven.   6. The light source driving device according to claim 1, wherein the driving light source switching unit, the constant current driving unit, and the boost switching unit are configured by one integrated circuit.   7. A light source driving apparatus according to claim 1, comprising: illuminating a subject with light emitted from the plurality of light sources by the light source driving device; receiving reflected light from the subject; An image processing apparatus that performs image processing by converting the image into an image. The image processing apparatus according to claim 7 is an image reading apparatus,
An image reading apparatus that reads image data of the subject by the image processing.   9. An image forming apparatus comprising: the image reading apparatus according to claim 8; and image forming means for forming an image on a recording medium based on image data read by the image reading apparatus.   The light source driving device according to claim 1, and an image carrier that illuminates a subject with irradiation light from the plurality of light sources by the light source driving device and is pre-charged with reflected light from the subject An image forming apparatus comprising image forming means for forming an image by exposing the body.