JP3089072B2 - Semiconductor laser driver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a semiconductor laser.

[0002]

2. Description of the Related Art Semiconductor lasers are widely used as light sources for optical scanning devices using holograms and rotating polygon mirrors, and for electrophotographic printing devices such as laser beam printers. FIG. 3 shows an electrophotographic printing apparatus as an example of an apparatus using a semiconductor laser.

In FIG. 1, an electrophotographic printing apparatus includes a photosensitive drum 1 rotating at a predetermined speed and a photosensitive drum 1 rotating at a predetermined speed.
A pre-charger 2 for pre-charging the surface of the photosensitive drum 1, a semiconductor laser 3 as exposure means for exposing the charged photosensitive drum 1 to form an electrostatic latent image on the surface of the photosensitive drum 1, and a toner A developing unit 4 for developing, a transfer charger (not shown) for transferring a toner-developed image to a sheet 5, and a cleaner for removing electricity from the surface of the photosensitive drum 1 and removing residual toner in preparation for the next step 6 is provided. Reference numeral 7 denotes a supply source of a high DC voltage applied to the pre-charger 2, and reference numeral 8 denotes an optical system device for guiding a laser beam from the semiconductor laser 3 to the surface of the photosensitive drum 1.

[0004] Reference numeral 10 denotes a driving circuit for the semiconductor laser 3. When a digitized video signal is input, the drive circuit 10 supplies a drive current that modulates the video signal to the semiconductor laser 3. The semiconductor laser 3 includes a driving circuit 10
The photosensitive drum 1 is turned on / off by a drive current supplied from the printer, and forms a latent image on the surface of the photosensitive drum 1. In order to stably form a latent image on the drum, the driving circuit 10
Is configured to control the drive current of the semiconductor laser 3 so that the optical output of the semiconductor laser 3 is always constant. That is, the drive circuit 10 is configured to include an APC (constant optical output) circuit for detecting the optical output of the semiconductor laser and performing feedback control so as to match this with the set optical output.

Here, in such an electrophotographic printing apparatus, one cause of a change in the light output of the semiconductor laser 3 is a change in the ambient temperature. For example, as shown in FIG. 4, the temperature changes from T1 to T2. , The light output-current characteristic (IL characteristic) of the semiconductor laser changes from the straight line A to B, and if the drive current is left as it is, the light output decreases. Therefore, in order to maintain the optical output Ps, A
The drive current from If (T1) when the temperature is T1 is increased to If (T2) by using a PC circuit or the like. In the figure, Ith (T1) and Ith (T2) are threshold current values when the temperatures are T1 and T2, respectively.

Here, specific values of these currents applied to the semiconductor laser will be shown below as an example.

[0007]

Ith (T1) = 45 mA Ith (T2) = 60 mA If (T1) = 70 mA If (T2) = 85 mA By the way, the driving current of the semiconductor laser is a video current and a bias current based on a video signal. Therefore, the control of the drive current using the APC circuit or the like as described above is performed by either (a) changing the video current or (b) changing the bias current. .

That is, in the case of the method (a), as shown in the following equation, the bias current Ib is kept as it is, the video current is increased from Im1 to Im2, and the driving current If1 (= If
(T1)) is increased to drive current If2 (= If (T2)).

[0009]

## EQU2 ## If1 = Ib + Im1 If2 = Ib + Im2 As a result, the optical output Ps is maintained as shown in FIG.

On the other hand, in the case of the method (b), as shown in the following equation, the video current Im is kept as it is, the bias current is increased from Ib1 to Ib2, and the drive current If1 is increased to the drive current If2.

[0011]

## EQU3 ## If1 = Ib1 + Im1 'If2 = Ib2 + Im2' As a result, the optical output Ps is maintained as shown in FIG.
However, in this case, since the video current Im does not need to be strictly constant, Im1 'and Im2' (however, Im1 'and Im2'
Are almost equal).

The purpose of supplying a bias current to a semiconductor laser is to speed up a change in laser light output with respect to a change in laser drive current. Therefore, the semiconductor laser is MH like an electrophotographic printing device.
When operating in the order of z, the value of the bias current is not a problem, and any of the above methods may be used in this regard.

[0013]

Generally, in an optical scanning apparatus or an electrophotographic printing apparatus using such a semiconductor laser, it is desired to perform optical scanning and image formation with higher accuracy.

However, in general, a semiconductor laser has the property that the oscillation wavelength changes according to the value of a current to be injected, and a video current corresponding to a change in the ambient temperature during the operation of the above-described semiconductor laser is generated. If the laser beam changes, the oscillation wavelength also changes, so that, for example, when the laser beam is deflected by a diffraction grating or the like, the deflection direction also changes. Particularly, in the case of a laser beam printer using a hologram, a change in video current appears as a change in spot position, so that highly accurate optical scanning, image formation, detailed printing, and the like cannot be performed.

Therefore, in such a case, the method (a) for changing the video current cannot be used, and the light output is controlled by the method (b) for changing the bias current. The video current does not change with temperature or the like, and needs to be exactly constant.

Conventionally, however, there has been no semiconductor laser driving device capable of controlling the light output to a predetermined value while maintaining the video current accurately constant regardless of the temperature change.

Further, since the conventional semiconductor laser driving device controls the light output even in the state where the video current is supplied, the light output is set depending on what video signal is input. There is a problem that the output changes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide a semiconductor laser driving device capable of accurately controlling the optical output of a semiconductor laser while keeping the oscillation wavelength of the semiconductor laser constant. The task is to provide

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a semiconductor laser driving device according to the first invention of the present application has a temperature change.
First driving means for supplying a constant first current regardless of
And a current having a current value necessary to obtain a desired light output.
And second driving means for supplying a second current.
The second power supply is driven to drive the driving means to obtain a desired light output.
The current value of the current was set, and the current value of the second current was set.
While maintaining the current value, the data signal consisting of the pulse train
In the semiconductor laser drive apparatus characterized by modulating a first current in response, the first driving means is a current mirror
-Current output section of the current mirror circuit
Is connected to the output terminal of the second drive means and is connected to the semiconductor
The laser is connected to the current input of the current mirror circuit.
Is a switch for switching the current mirror circuit.
The switching device is characterized in that a switching means is connected .

In order to solve the above-mentioned problem, the semiconductor laser driving device according to the second aspect of the present invention has a constant laser drive regardless of a temperature change.
A first driving means for supplying a current of 1
The current value of the first current from the current value required to obtain
A second providing a second current having a subtracted current value;
Driving means, and the first and second
The second driving means is driven to obtain a desired light output.
Set the current value of the current and set the modulation time zone following the non-modulation time zone.
Then, do not hold the current value of the second current at the set current value.
Meanwhile, the first current according to the data signal composed of the pulse train
Semiconductor laser drive device characterized by modulating
And the first driving means comprises a current mirror circuit.
The current output of the current mirror circuit is
Connected to the output terminal of the
The current input of the current mirror circuit is
Switching means for switching the
It is characterized by being connected .

[0021]

According to the semiconductor laser drive device of the first invention of the present application, the first drive means is provided with a constant first drive regardless of a temperature change.
Supplying current and the second driving means obtaining a desired light output
To supply a second current having a current value necessary for this. This
Here, the desired light output is obtained by driving the second driving means.
Thus, the current value of the second current is set, and the current value of the second current is set.
While maintaining the value at the set current value,
The first current is modulated according to the data signal. The first drive
The driving means is composed of a current mirror circuit.
The current output part of the mirror circuit is connected to the output terminal of the second driving means.
Is connected and the semiconductor laser is connected.
A current mirror circuit is connected to the current input section of the
Switching means for switching is connected.
You . As a result, even if the ambient temperature of the semiconductor laser changes during the driving of the semiconductor laser, the first current is determined by the first driving means and its value does not change depending on the temperature or the like.
It is possible to accurately control the light output of a semiconductor laser while keeping the oscillation wavelength constant.

According to the semiconductor laser drive device of the second invention of the present application, the first drive means is provided with a constant first drive regardless of a temperature change.
And the second driving means obtains a desired light output.
Subtract the current value of the first current from the current value required for
And supplying a second current having the same current value. Where non
The first and second driving means are driven during the modulation time zone.
Set the current value of the second current to obtain the desired light output
During the modulation time period following the non-modulation time period, the second current is supplied.
While maintaining the current value at the set current value,
The first current is modulated according to the data signal. First
The driving means is composed of a current mirror circuit.
The current output part of the mirror circuit is connected to the output terminal of the second driving means.
Is connected and the semiconductor laser is connected.
A current mirror circuit is connected to the current input section of the
Switching means for switching is connected.
You. As a result, even if the ambient temperature of the semiconductor laser changes during the driving of the semiconductor laser, the first current is determined by the first driving means and its value does not change depending on the temperature or the like.
It is possible to accurately control the light output of a semiconductor laser while keeping the oscillation wavelength constant.

The operation of the present invention will be more apparent from the following examples of the present invention, and further other effects of the present invention will be apparent.

[0024]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a semiconductor laser driving device according to a first embodiment of the present invention.

In the figure, the semiconductor laser driving device is
A current driver 11 constituting an example of a second driving unit;
And a current driver 12 which constitutes an example of a first driving means. The current driver 11 supplies a drive current If to the semiconductor laser 3. On the other hand, the current driver 12 generates a video current Im that is turned on / off in response to a video signal composed of a pulse train. Here, in the first embodiment, the current driver 12 is configured to add a video current Im having a direction opposite to the drive current If to the drive current If, that is, one of the drive currents If from the current driver 11. The driving current If is modulated by sucking the section as the video current Im. Therefore, if the video current Im is zero, the current ILD, high equal to the drive current If from the current driver 11 causes the semiconductor laser 3
Oscillates. On the other hand, when the video current Im takes a predetermined value, the semiconductor laser 3 stops oscillating by subtracting the video current Im from the drive current If. Therefore, the semiconductor laser 3 is turned on / off by the video current Im. can do. Further, when the semiconductor laser 3 is not oscillating in this way, the current ILD, low obtained by subtracting the video current Im from the drive current If can be supplied to the semiconductor laser 3 as a bias current.

In the first embodiment, the current driver 12
Is configured to turn on / off the video current Im in response to the video signal in a periodically repeated modulation time period. The current driver 11 controls the semiconductor laser 3 in a non-modulation time period following the modulation time period. The value of the drive current If is determined on the basis of the optical output of the control signal, and the value of the drive current If in the modulation time period following the non-modulation time period is maintained at the determined value as described later.

Next, the configuration of the current driver 11 will be described in detail.

In FIG. 1, the photoelectric element 14 is constituted by a photodiode or the like, and converts a monitor light output of the semiconductor laser 3 into a current. Current-voltage conversion circuit (I / V
The conversion circuit 15 converts the output current of the photoelectric element 14 into a voltage and outputs a monitor voltage Vm. The comparison circuit 16 is configured so that a reference voltage Vs according to the set light output can be set. The comparison circuit 16 compares the monitor voltage Vm from the current-voltage conversion circuit 15 with the reference voltage Vs. If the monitor voltage Vm is higher, it outputs a low-level signal, and the monitor voltage Vm is lower. In this case, a high level signal is output.

The counter 17 is an up / down counter. When a high-level signal is input from the comparison circuit 16, the counter 17 counts the clock CK and increases the count value by one, while the low-level signal is input. In this case, the count value is decreased by one each time the clock CK is input. The controller 19 is for controlling the counter 17, and outputs a predetermined control signal to the counter 17 when a control signal is input. The counter 17 operates only when the control signal is input to increase or decrease the count value. When the control signal is not input, the counter 17 holds the previous count value. The D / A converter 18 converts the count value of the counter 17 into an analog signal and outputs the analog signal to the constant current source 20 as a current control signal. The constant current source 20 outputs a drive current If corresponding to the current control signal from the D / A converter 18. As described above, in the first embodiment, an example of the control means is constituted by the controller 19 and the counter 17.

Next, the operation of the current driver 11 configured as described above will be described. When a control signal is given to the controller 19 during the non-modulation time period of the semiconductor laser 3, the controller 19 outputs a predetermined control signal to the counter 17, whereby the counter starts operating. The photoelectric element 14 receives monitor light from the semiconductor laser 3 and outputs a current corresponding to the output. Conversion circuit 15
Converts the current into a voltage and outputs it to the comparison circuit 16 as a monitor voltage Vm. The comparison circuit 16 compares the voltage Vm with the reference voltage Vs. Here, assuming that the output of the monitor light is low and therefore the voltage Vm is lower than the voltage Vs,
The comparison circuit 16 outputs a high-level signal, and as a result,
The counter 17 performs a count-up operation and the clock C
Each time K is input, the count value is increased by one.
The output of the counter 17 is converted into an analog voltage by the D / A converter 18 and supplied to the constant current source 20 as a current control voltage. Therefore, when the count value of the counter 17 increases, the constant current source 20 also outputs the drive current as its output current. Increase If. As a result, the light output of the semiconductor laser 3 is enhanced.
That is, when the optical output of the semiconductor laser 3 decreases, the output current of the constant current source 20 increases so as to increase it.

Conversely, when the output of the monitor light is high, the comparison circuit 16 outputs a low-level signal, so that the counter 17 performs a countdown operation, and the count value is incremented by 1 every time the clock CK is input. Decrease by one. As a result, the output current of the constant current source 20 decreases, and the semiconductor laser 3
The light output also decreases. That is, when the optical output of the semiconductor laser 3 becomes strong, the constant current source 2
The output current of 0 decreases. Therefore, the light output of the semiconductor laser 3 is kept constant irrespective of the change of the ambient temperature.
When the control signal is not input to the controller 19, the controller 19 does not output the control signal, so that the counter 17 does not perform the counting operation and holds the count value up to that time. Therefore, in this case, the constant current source 20
Is maintained at a constant value determined by the count value held by the counter 17. During the APC operation, the current driver 12 is off.

Next, the configuration of the current driver 12 will be described.
This will be described in detail with reference to the circuit diagram of FIG.

In FIG. 2, a current driver 12 is a constant current source constituted by using a constant current circuit, for example, a current mirror circuit, and more specifically, transistors 30b and 30.
c constitutes a current mirror circuit. The bases of the transistors 30b and 30c are connected together, and are connected to the collector of the transistor 30b. The emitter of each of the transistors 30b and 30c has a resistor 3
1b and 31c (resistance values are Rb and Rc, respectively) are connected to the ground. And the transistor 30
The collector of c is the output of the current driver 12.
On the other hand, a video signal is input to the base of the transistor 30a, and its collector is connected to the power supply Vcc, and its emitter is connected to the collector of the transistor 30b through a resistor 31a (resistance value is Ra).

Next, the current driver 1 configured as described above
Operation 2 will be described. First, the video signal turns on,
When the level becomes low, the transistor 30a turns off, and as a result, both the transistors 30b and 30c turn off. Therefore, the collector current I2 of the transistor 30c
Becomes zero, and the driving current If of the current driver 11 becomes the current I
All flows into the semiconductor laser 3 as LD, high. Therefore, the semiconductor laser 3 is driven to generate a laser beam having an optical output Ps.

Next, when the video signal turns off and goes to a high level, the transistor 30a turns on, so that the emitter potential VE becomes Vcc-VBE, and a current I1 substantially equal to VE / (Ra + Rb) flows through the transistor 30b. . Therefore, since Rb = Rc, a current of I2 = I1 flows into the transistor 30c. as a result,
A current ILD, low obtained by subtracting the video current I2, ie, Im, from the drive current If of the current driver 11 flows through the semiconductor laser 3.

Therefore, when the video signal is off, the current ILD, low flows through the semiconductor laser 3 as the bias current Ib, and when the video signal is on, the semiconductor laser 3 receives the bias current Ib and the video current Im. Will flow. Since the video current Im is an output current of a constant current source constituted by a current mirror circuit, its value does not fluctuate due to the ambient temperature of the semiconductor laser, the drive current If, and the like, and is extremely stable. .

The current ILD, low (ie, the bias current Ib
) Is determined by the laser light output at that time and the characteristics of the photosensitive drum, and is generally set to a threshold current value Ith or less. However, in order to reduce the change in the laser oscillation wavelength, the video current Since it is preferable to reduce Im, the value of the current ILD, low is preferably as high as possible.

As described above, in the semiconductor laser driving device according to the first embodiment, the driving current If of the semiconductor laser is supplied by the current driver 11, and the value thereof is set to a predetermined value when the control signal is input to the controller 19. Is controlled so as to obtain the light output. Therefore, when applied to a laser printer or the like, a period from the end of scanning for one line to the start of scanning for the next line, or the end of printing for one page and starting printing for the next page. In a non-modulation time period of the semiconductor laser, such as the period, a control signal is supplied to the controller 19 at a timing when a video signal is not input, so that the optical output can be controlled. As a result, the video signal is affected. It is possible to control the light output to a predetermined value without any problem.

In the first embodiment, the video current Im supplied to the semiconductor laser 3 is determined by the current driver 12 which is a constant current circuit. It is extremely stable without being changed by the change of If. Therefore, even in the case of an optical scanning device, a laser beam printer, or the like configured to deflect laser light by a diffraction grating, a hologram, or the like, it is possible to prevent a change in spot position due to a change in video current.

Next, FIG. 7 shows a configuration of a semiconductor laser driving device according to a second embodiment of the present invention. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals.

In FIG. 7, the semiconductor laser driving device comprises:
A current driver 51 constituting an example of a second driving unit;
And a current driver 52 which constitutes an example of a first driving means. The current driver 51 supplies the drive current Ib to the semiconductor laser 3. On the other hand, the current driver 52 generates a video current Im that is turned on / off in response to an INV video signal composed of a pulse train (that is, an inverted video signal). Here, in the second embodiment, the current driver 52
The video current Im in the same direction as the drive current Ib is applied to the drive current I.
b, and thus the video current I
When m takes a predetermined value, the semiconductor laser 3 has I = I
Since a current of b + Im flows, the semiconductor laser 3 oscillates. On the other hand, if the video current Im is zero, only the drive current Ib by the current driver 51 flows through the semiconductor laser 3 and the current Ib is set to be equal to or smaller than the threshold current value Ith of the semiconductor laser 3. The semiconductor laser 3 stops oscillating. As described above, the semiconductor laser can be turned on / off by the video current Im. Also,
Thus, when the semiconductor laser 3 is not oscillating, the drive current Ib from the current driver 51 functions as a bias current.

Next, the configuration of the current driver 51 will be described in detail.

In FIG. 7, the photoelectric element 14 is constituted by a photodiode or the like, and converts the monitor light output of the semiconductor laser 3 into a current. Current-voltage conversion circuit (I / V
The conversion circuit 15 converts the output current of the photoelectric element 14 into a voltage and outputs a monitor voltage Vm. The comparison circuit 16 is configured so that a reference voltage Vs according to the set light output can be set. The comparison circuit 16 compares the monitor voltage Vm from the current-voltage conversion circuit 15 with the reference voltage Vs. If the monitor voltage Vm is higher, it outputs a low-level signal, and the monitor voltage Vm is lower. In this case, a high level signal is output.

The counter 17 is an up / down counter. When a high-level signal is input from the comparison circuit 16, the counter 17 counts the clock CK and increases the count value by one, while the low-level signal is input. In this case, the count value is decreased by one each time the clock CK is input. The controller 19 is for controlling the counter 17, and outputs a predetermined control signal to the counter 17 when a control signal is input. The counter 17 operates only when the control signal is input to increase or decrease the count value. When the control signal is not input, the counter 17 holds the previous count value. The D / A converter 18 converts the count value of the counter 17 into an analog signal and outputs the analog signal to the constant current source 60 as a current control signal. The constant current source 60 outputs a drive current Ib corresponding to the current control signal from the D / A converter 18. As described above, in the second embodiment, an example of the control means is constituted by the controller 19 and the counter 17.

Next, the operation of the current driver 51 configured as described above will be described. When a control signal is applied to the current driver 52 during the non-modulation time period of the semiconductor laser 3, the current driver 52 is turned on and outputs a video current Im to the semiconductor laser 3. At this time, since the control signal is also given to the controller 19 of the current driver 51, the controller 19 outputs a predetermined control signal to the counter 17, whereby the counter 17 starts operating. I do. The photoelectric element 14 receives monitor light from the semiconductor laser 3 and outputs a current corresponding to the output. The conversion circuit 15 converts the current into a voltage and outputs it to the comparison circuit 16 as a monitor voltage Vm. Comparison circuit 16
Compares the voltage Vm with the reference voltage Vs. here,
The output of the monitor light is low, so that the voltage Vm is higher than the voltage Vs
If it is lower, the comparison circuit 16 outputs a high-level signal. As a result, the counter 17 performs a count-up operation and increases the count value by one each time the clock CK is input. The output of the counter 17 is converted into an analog voltage by the D / A converter 18 and supplied to the constant current source 60 as a current control voltage. Therefore, when the count value of the counter 17 increases, the constant current source 60 also outputs the drive current as its output current. Increase Ib. As a result, the light output of the semiconductor laser 3 is enhanced. That is, when the optical output of the semiconductor laser 3 decreases, the output current of the constant current source 60 increases so as to increase it.

Conversely, when the output of the monitor light is high, the comparison circuit 16 outputs a low-level signal, so that the counter 17 performs a countdown operation, and the count value is incremented by 1 every time the clock CK is input. Decrease by one. As a result, the output current of the constant current source 60 decreases, and the semiconductor laser 3
The light output also decreases. That is, when the optical output of the semiconductor laser 3 becomes strong, the constant current source 6
The output current of 0 decreases. Therefore, the light output of the semiconductor laser 3 is kept constant irrespective of the change of the ambient temperature.
When the control signal is not input to the controller 19, the controller 19 does not output the control signal, so that the counter 17 does not perform the counting operation and holds the count value up to that time. Therefore, in this case, the constant current source 60
Is maintained at a constant value determined by the count value held by the counter 17.

As described above, in the drive device of the second embodiment, the drive current Ib (T) of the current driver 51 is controlled so that If (T) = Im + Ib (T).

Next, regarding the configuration of the current driver 52,
This will be described in detail with reference to the circuit diagram of FIG.

In FIG. 8, a current driver 52 is a constant current source constituted by using a constant current circuit, for example, a current mirror circuit, and more specifically, transistors 30b and 30.
c constitutes a current mirror circuit. The bases of the transistors 30b and 30c are connected together, and are connected to the collector of the transistor 30b. The emitter of each of the transistors 30b and 30c has a resistor 3
1b and 31c (resistance values are Rb and Rc, respectively) are connected to the ground. And the transistor 30
The collector of c is the output of the current driver 52.
On the other hand, an INV video signal (that is, an inverted video signal) is input to the base of the transistor 30a, its collector is connected to the power supply Vcc, and its emitter is connected to the collector of the transistor 30b through the resistor 31a (the resistance value is Ra). I have.

Next, the current driver 5 configured as described above
Operation 2 will be described. First, when the INV video signal turns on and goes to a low level, the transistor 30a turns off, and as a result, both the transistors 30b and 30c turn off. Therefore, the collector current I2 of the transistor 30c becomes zero, and the semiconductor laser 3 has a current driver 5
Only one drive current Ib flows as ILD, low.

Next, when the INV video signal turns off and goes to a high level, the transistor 30a turns on, so that the emitter potential VE becomes Vcc-VBE, and the transistor 3a
0b has a current I substantially equal to VE / (Ra + Rb).
1 flows. Therefore, Rb =
Since Rc, a current of I2 = I1 flows. As a result, a current ILD, high obtained by adding the video current Im to the drive current Ib of the current driver 51 flows through the semiconductor laser 3, so that the semiconductor laser 3 is driven and the laser light having the optical output Ps is generated. Occur.

Therefore, when the INV video signal is on, the current ILD, low is applied to the semiconductor laser 3 by the bias current I.
When the INV video signal is off, a current obtained by adding the video current Im to the bias current Ib flows through the semiconductor laser 3. Since the video current Im is an output current of a constant current source constituted by a current mirror circuit, its value does not fluctuate due to the ambient temperature of the semiconductor laser, the drive current Ib, and the like, and is extremely stable. .

The current ILD, low (ie, the bias current Ib
) Is determined by the laser light output at that time and the characteristics of the photosensitive drum, and is generally set to a threshold current value Ith or less. However, in order to reduce the change in the laser oscillation wavelength, the video current Since it is preferable to reduce Im, the value of the current ILD, low is preferably as high as possible. The value of the current Im is determined by the resistance Ra, Rb, or R
c, and further, can be adjusted by the value of Vcc.

As described above, in the semiconductor laser driving apparatus according to the second embodiment, the driving current Ib of the semiconductor laser is supplied by both the current driver 51 and the current driver 52, and the value of the control current is transmitted to the controller 19 by the control signal. When input, it is controlled so as to obtain a predetermined light output. Therefore, when applied to a laser printer or the like, 1
Non-modulation of the semiconductor laser, such as the period from the end of scanning for one line to the start of scanning for the next line, or the period from the end of printing for one page to the start of printing on the next page. In a time zone, a control signal is given to the controller 19 at a timing when a video signal is not input, so that the light output can be controlled. As a result, the light output can be controlled to a predetermined value without being affected by the video signal. Becomes possible.

In the second embodiment, the video current Im supplied to the semiconductor laser 3 is determined by the current driver 52 which is a constant current circuit.
It is extremely stable without being changed by the ambient temperature of the laser 3 or the change of the driving current Ib. Thus, for example, a diffraction grating,
Also in the case of an optical scanning device configured to deflect laser light by a hologram, a laser beam printer, etc.
It is possible to prevent a change in spot position due to a change in video current.

[0056]

As described in detail above, according to the semiconductor laser driving device of the first invention of the present application, one device is not affected by a temperature change.
A first driving means for supplying a constant first current;
A second current having a current value necessary to obtain an output is provided.
And second driving means for driving the second driving means.
So that the current value of the second current is
Set and maintain the current value of the second current at the set current value
While the first signal according to the data signal consisting of the pulse train
Semiconductor laser drive device characterized by modulating current
, The first driving means comprises a current mirror circuit.
And the current output of the current mirror circuit is the second drive
Connected to the output terminal of the means and to the semiconductor laser
The current input to the current mirror circuit
Switching means for switching a mirror circuit
Is connected, even if the ambient temperature of the semiconductor laser changes during driving of the semiconductor laser, it is possible to accurately control the optical output while keeping the oscillation wavelength of the semiconductor laser constant.

According to the semiconductor laser driving device of the second invention, a constant first current is supplied irrespective of a temperature change.
The first driving means to obtain the desired light output
Current obtained by subtracting the current value of the first current from the appropriate current value
Second driving means for supplying a second current having a value.
The first and second driving means are driven during the non-modulation time period.
So that the current value of the second current is
The second current is set during the modulation time period following the non-modulation time period.
Pulse train while maintaining the current value of
Modulating the first current in response to a data signal comprising
In the semiconductor laser driving device, the first drive
The driving means is composed of a current mirror circuit.
The current output section of the error circuit is connected to the output terminal of the second drive means
Is connected and a semiconductor laser is connected.
-A current mirror circuit is connected to the current input of the circuit.
Switching means for switching the semiconductor laser, even if the ambient temperature of the semiconductor laser changes during driving of the semiconductor laser, the optical output of the semiconductor laser can be accurately maintained while keeping the oscillation wavelength constant. Can be controlled.

Therefore, according to the present invention, for example, even in the case of a laser beam printer or the like configured to deflect a laser beam by a hologram or the like, a change in the spot position due to a change in the video current is prevented while keeping the light output constant. Thus, highly accurate image formation, detailed printing, and the like can be performed.

As a result, a high-quality laser beam printer or the like can be realized using the semiconductor laser driving device of the present invention.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a semiconductor laser driving device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a part of the semiconductor laser driving device of FIG. 1 in detail.

FIG. 3 is a main part configuration diagram showing an example of an electrophotographic printing apparatus using a semiconductor laser.

FIG. 4 is a graph showing characteristics of a semiconductor laser.

FIG. 5 is one graph for explaining control of laser light output.

FIG. 6 is another graph for explaining control of laser beam output.

FIG. 7 is a block diagram showing a configuration of a semiconductor laser driving device according to a second embodiment of the present invention.

8 is a circuit diagram showing a part of the semiconductor laser driving device of FIG. 7 in detail.

[Explanation of symbols]

 Reference Signs List 3 semiconductor laser 11, 12, 51, 52 current driver 14 photoelectric element 15 current-voltage conversion circuit 16 comparison circuit 17 counter 18 D / A converter 19 controller 20, 60 constant current source 30a, 30b, 30c transistor 31a, 31b, 31c resistance

Claims (2)

(57) [Claims] 1. A constant first current is supplied regardless of a temperature change.
The first driving means to supply the light and the
A second driver for supplying a second current having a required current value
And a step for driving the second driving means to obtain a desired light output.
The current value of the second current,
While maintaining the current value of
Modulating the first current in accordance with a data signal comprising
In the semiconductor laser driving device , the first driving means is constituted by a current mirror circuit.
The current output of the current mirror circuit is connected to a second drive
Connected to the output terminal of the means and to the semiconductor laser
The current input section of the current mirror circuit has
Switch for switching the current mirror circuit
A semiconductor laser driving device to which a driving means is connected . 2. A constant first current is supplied regardless of a temperature change.
The first driving means to supply the light and the
The current obtained by subtracting the current value of the first current from the required current value
Second driving means for supplying a second current having a current value.
Driving the first and second driving means during a non-modulation time period
So that the desired light output is obtained.
Set the value, and set the value to the modulation time period following the non-modulation time period.
Holding the current value of the second current at the set current value;
While the first signal according to a data signal composed of a pulse train.
Semiconductor laser driving device for modulating current
In location, the first driving means is composed of a current mirror circuit
The current output of the current mirror circuit is connected to a second drive
Connected to the output terminal of the means and to the semiconductor laser
The current input section of the current mirror circuit has
Switch for switching the current mirror circuit
A semiconductor laser driving device to which a driving means is connected .