JP2001024273A - Optical output control circuit of multibeam laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the APC time necessary for APC control, and realize adequate APC control and high speed APC control, in an optical output control circuit (APC circuit) for controlling the optical output of each LD in a multibeam laser device provided with a plurality of semiconductor lasers (LD). SOLUTION: An I/V converter 210 obtaining a feedback voltage from a feedback current ID of a PD12 detecting optical outputs of a plurality of LD's 11A, 11B, a plurality of analog computing elements 221, 222 which are installed corresponding to the respective LD's and compare the feedback voltage from the l/V converter 210 with reference voltages Vref1, Vref2 set corresponding to each of the LDIs, a plurality of sample hold circuits 223, 224 which control driving currents to be supplied to the corresponding LD11A, 11B on the basis of the outputs of the analog computing elements 221, 222, and LD driving control circuits 225, 226, are installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam laser device using a plurality of semiconductor lasers as light sources, and more particularly to an optical output control circuit for controlling the optical output of a plurality of semiconductor lasers.

[0002]

2. Description of the Related Art In an LD scanning device using a semiconductor laser (hereinafter, referred to as an LD) as a light source, it is necessary to maintain a constant light intensity in order to form a uniform image pattern. APC for controlling light emission output
(Auto Power Control) circuit has been proposed. This A
In the PC circuit, light emitted from the LD is received by a light receiving element (hereinafter abbreviated as PD) such as a photodiode.
An output voltage obtained by receiving light at D is compared with a reference voltage, and based on the comparison result, a light emission current flowing through the LD is feedback-controlled so that the output voltage of the PD has a constant relationship with the reference voltage. By controlling the light emission of the LD, the light intensity of the LD can be controlled to be constant as a result.

In recent years, there has been proposed an LD scanning apparatus which includes a plurality of LDs and synchronously scans laser beams respectively emitted from the plurality of LDs, thereby improving the scanning speed of the entire LD scanning apparatus. Proposed. Such an LD scanning device is referred to as a multi-beam laser device.
In order to perform PC control, it is necessary to provide a PD for receiving light emitted from each LD. However, a one-chip type LD in which a plurality of LDs are integrally configured
In this case, the number of PDs corresponding to the number of LDs is not necessarily integrally mounted for reasons of element design. Therefore, light emitted from a plurality of LDs is
A light output control circuit has been proposed which receives light at D, and APC controls a plurality of LDs based on the result of the light reception.

FIG. 4 is a diagram showing a schematic configuration of the above-mentioned multi-beam laser device. The multi-beam laser scanning device 1 includes a plurality of LDs, here, two LDs 11A and 11A.
The laser beam LB emitted from each of the LDs 11A and 11B is converted into a parallel beam by a collimating lens 13 and shaped into a beam by a cylindrical lens 14, and then driven at high speed. The light is projected on the polygon mirror 15. The laser beam LB is deflected in the main scanning direction by being reflected by the reflection surface of the polygon mirror 15, and is main-scanned on the photosensitive surface of the photosensitive drum 17 through the fθ lens 16.
The photosensitive drum 17 has a rotating shaft 17a in the main scanning direction.
The laser beam LB is sub-scanned by being rotationally driven around the rotation axis 17a, and a predetermined pattern is drawn. Further, at one side position of the photosensitive drum 17, there is provided a synchronizing signal for receiving the laser beam LB to be scanned immediately before main scanning and outputting a horizontal synchronizing signal HSYNC as a timing reference for the main scanning and APC control. A PD 18 is provided. Here, each LD 11
A part of the laser light emitted from A and 11B is detected by the PD 12, and light for controlling the light output of the laser light in each of the LDs 11A and 11B at a timing before the main scanning is performed on the photosensitive drum 17. An output control circuit (APC circuit) 2 is provided.

FIG. 5 is a circuit diagram of an example of a conventional APC circuit of the APC circuit 2 for APC controlling the LDs 11A and 11B. The light emission output of the LDs 11A and 11B is controlled based on the currents of the first and second current source circuits 201 and 202, respectively. Laser light emitted from each of the LDs 11A and 11B is received by the PD 12, and is
A light receiving current corresponding to the light output of 11B, that is, a feedback current ID is output. The feedback current ID is selected by the analog switch 200, and the feedback current of the PD 12 when the laser beam of the LD 11A is received is changed by the first I / V converter 21.
After being converted into the feedback voltage VD1 at step 1, the first analog computing unit 221 detects a difference voltage from the reference voltage Vref of the reference voltage source 250. This difference voltage is sampled by the first sample-and-hold circuit 223, and based on the sampled difference voltage, the first LD drive control circuit 225
Controls the current of the first current source circuit 201 and, as a result, controls the LD 11A to an optical output corresponding to the reference voltage Vref by controlling the difference voltage of the first analog computing unit 221 to be zero. Similarly, for LD11B,
The feedback current ID of the PD 12 with respect to the LD 11B selected by the analog switch 200 is converted into a feedback voltage VD2 by a second I / V converter 212, and the second analog calculator 222 sets the difference voltage from the reference voltage Vref to zero. By controlling the second current source circuit 202 by the second sample / hold circuit 224 and the second LD drive control circuit 226,
The LD 11B is controlled to an optical output corresponding to the reference voltage Vref. Therefore, two LDs using one PD 12
APC control of 11A and 11B becomes possible.

Here, a timing chart of the operation of the multi-beam laser device is shown in FIG. The timing chart shows a timing when pattern writing by a laser beam is already being performed. The LDs 11A and 11B start emitting light based on the horizontal synchronization signal HSYNC, respectively, and the first and second LD drive control circuits 225 and 22 respectively.
6 is the drawing pattern data DA from the CPU 3 respectively.
Each of the LDs 11A and 11 receives the input of TA1 and DATA2.
The light emission output of B is modulated, and a pattern for one main scan is drawn on the photosensitive drum 17 in accordance with the data DATA1 and DATA2. Then, the drawing of the pattern for one main scan is completed and the first APC signal SAPC1 and the second APC signal
The PC signal SAPC2 is input and the first APC signal SAP
When C1 is in the active state “L”, the first analog operation unit 221, the first sample-and-hold circuit 223, and the first LD drive control circuit 225 perform the above-described operation on the LD 11A.
The PC control is executed, then the analog switch 210 is switched to the LD 11B side, and the second APC signal SAPC
2 is in the active state “L”, the second
Analog arithmetic unit 222, second sample and hold circuit 2
24, APC control by the second LD drive control circuit 226 is executed. The APC control is performed in the first
Since the second LD drive control circuits 225 and 226 are controlled by the held difference voltage, it is needless to say that the second LD drive control circuits 225 and 226 are also held during the next one-scan pattern drawing.

[0007]

SUMMARY OF THE INVENTION Such a conventional AP
In the C circuit, the output of the PD 12 is controlled by an analog switch 200 in order to APC-control the LDs 11A and 11B.
Therefore, the APC control is interrupted during the time required for switching the analog switch 200 (time tx in FIG. 6). Further, after the output after the switching of the analog switch 200 is stabilized, it takes time to control each of the analog calculators 221 and 222 with another control signal. Therefore, at least the LD11A, LD11A,
The APC control time distributed to 11B is shortened. In particular, when controlling with a large voltage width during APC control, sufficient APC control cannot be performed within the APC control time. In some cases, accurate APC control cannot be realized. In particular, when APC control is performed on a large number of LDs based on the light receiving current of one PD, the switching time in the analog switch 200 is generally longer, and the APC control time in each LD is correspondingly reduced. The above problem is likely to occur.

Since the LDs 11A and 11B do not always have the same characteristics, the feedback current ID of the PD 12
Even if the current values of the LDs 11A and 11B are the same, a difference may occur between the optical outputs of the LDs 11A and 11B. Therefore, LD11A, 11
In order to correct the variation in characteristics between B,
A and 11B have first and second IPCs in their respective APC circuits.
By interposing the I / V converters 211 and 212 and adjusting the coefficients of the I / V converters 211 and 212, for example, the gain, the LD 11A, 1
The light output of 1B is made equal. Therefore, the number of I / V converters corresponding to the number of LDs is required, and the number of components of the APC circuit is increased, which is a factor that complicates the circuit. Further, each of the I / V converters 211 and 212 needs to be configured as an element including a movable structure such as a variable resistor in order to perform the above-described adjustment, and the inductance and the capacitance parasitic on the movable structure are negative feedback. Responsiveness in the I / V converters 211 and 212 is degraded due to being in the loop, and as a result, high-speed followability of APC control is reduced, and it becomes impossible to realize APC control within the APC time as described above. It will help.

An object of the present invention is to provide a multi-beam laser which simplifies the circuit configuration, secures APC time required for APC control, enables appropriate APC control, and realizes high-speed APC control. An object of the present invention is to provide a light output control circuit of a device.

[0010]

According to the present invention, a plurality of LDs are provided.
In a multi-beam laser device comprising:
D, which detects the light output of each D, a plurality of reference values set corresponding to each of the LDs, the received light output of the PD, and each of the reference values are compared, and the comparison result is a predetermined value. A light output control circuit (APC circuit) for controlling the light output of the corresponding LD so as to obtain a value is provided.

[0011] In a preferred embodiment of the present invention, the AP
The C circuit obtains a feedback voltage from the light receiving current of the PD,
A V converter; a plurality of analog operation units for comparing a reference voltage set corresponding to each of the plurality of LDs with a feedback voltage from the I / V converter; And a sample-and-hold circuit provided for each of the plurality of analog arithmetic units to sample and hold the output of each of the plurality of analog arithmetic units, and the sample-and-hold circuit provided for each of the plurality of semiconductor lasers. And a plurality of LD drive control circuits for controlling the drive current supplied to the corresponding LD based on the output of the circuit. In this case, the reference voltage set for each of the plurality of LDs is one reference voltage source and a plurality of reference voltages for adjusting the reference voltage of the reference voltage source for each of the LDs. Is set by a circuit composed of the voltage regulator of FIG. Further, the plurality of analog arithmetic units are time-divisionally operated based on the optical output control signal, and output a voltage difference between the feedback voltage and each reference voltage during the operation. Further, the conversion coefficient of the I / V converter is set to a fixed value.

In the present invention, the light receiving output of one PD is compared with a plurality of reference voltages set corresponding to each of the plurality of LDs, and the light output of the corresponding LD is determined based on the comparison result. Control the output. Therefore, an analog switch for selecting the light receiving output of the PD is not required, and the number of circuit components is reduced, and the time for switching the analog switch during the APC control is not required, and the time required for the APC control in each LD is secured. Becomes possible. In addition, the circuit component for processing the light receiving output of the PD can be set to a fixed value, and the variable structure element is not required in the APC loop for performing the APC control, thereby improving the responsiveness of APC control caused by the variable structure element. It is possible to do.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an APC circuit of an optical output control circuit of a multi-beam laser device according to the present invention, and is applied to the multi-beam laser device shown in FIG. 4 for comparison with the conventional APC circuit shown in FIG. 1 shows an embodiment according to the present invention. Note that parts equivalent to those of the conventional APC circuit in FIG. 5 are denoted by the same reference numerals. In FIG. 1, LD11
A and 11B denote first and second current source circuits 201,
The light emission output is controlled based on the current of 202. Each LD
The laser light emitted from 11A and 11B is
And a light receiving current corresponding to the light output of the LDs 11A and 11B, that is, a feedback current ID is output. This feedback current ID is converted into a voltage by the I / V converter 210, and then input to the negative input terminals of the first and second analog computing units 221 and 222. Each of the analog computing units 221,
The reference voltage source 25 is connected to the positive input terminal of the reference voltage source 222 via voltage regulators 241 and 242 each formed of a variable resistor.
0 is connected, and the first reference voltage Vref of the reference voltage source 250 is adjusted by a first voltage regulator 241 and a second voltage regulator 242, respectively.
The reference voltage Vref2 is applied to each of the analog computing units 221 and 222.
Input to the positive input terminal. Further, each of the analog arithmetic units 221 and 222 receives the voltage output from the I / V converter 210, that is, the feedback voltage VD and the first and second voltages.
Are detected from the reference voltages Vref1 and Vref2.

The difference voltage detected by the first analog computing unit 221 is applied to a first sample and hold circuit (S /
H) The sample and hold is performed in 223, and the held difference voltage is input to the first LD drive control circuit 225. The first LD drive control circuit 225 is connected to the LD 11
By controlling the current of the first current source circuit 201 of A, and controlling the difference voltage of the first analog computing unit 221 to be zero as a result, the LD 11A is turned into an optical output corresponding to the first reference voltage Vref1. APC control is performed. Similarly, also for the LD 11B, the difference voltage in the second analog arithmetic
The sample-and-hold circuit 224 samples and holds, and the held difference voltage is input to a second LD drive control circuit 226.
By controlling the second current source circuit 202 of D11B, the LD voltage of the second analog operation unit 222 is reduced to zero.
11B to the optical output corresponding to the second reference voltage Vref2
Control. The first and second analog computing units 2
Reference numerals 21 and 222 denote first and second APCs from the CPU 3.
The APC based on the control signals SAPC1 and SAPC2
Control will be executed.

FIG. 2 is a flowchart for explaining the operation of the APC control. This flowchart is based on L
The operation common to D11A and 11B is shown, and the LD may be applied to LD11A and 11B, respectively. First,
When the LDs 11A and 11B are turned on (S101), each LD
The PD 12 receives the laser light emitted from the
That is, the feedback current ID is output (S102, S10
3). The feedback current ID is converted as a feedback voltage VD by the I / V converter 210 (S104), and the analog operation unit (first or second analog operation unit) 221 and 221 respectively.
22 is input to the negative input terminal. Then, in the analog calculators 221 and 222, the reference voltage from the reference voltage source 250 input to the positive input terminal, here, the first voltage adjusted by the first or second voltage adjuster 241 or 242.
Alternatively, it is compared with the second reference voltages Vref1 and Vref2 (S1
05).

Then, the analog computing units 221 and 222 determine whether or not the feedback voltage VD is lower than the reference voltages Vref1 and Vref2.
In e), the difference voltage becomes a positive voltage, and this difference voltage is sampled by the sample and hold circuits 223 and 224 (S1).
06), each LD is obtained by the sampled positive difference voltage.
The drive control circuits 225 and 226 control the first current source circuit 201 and the second current source circuit 202 so that the LD drive current supplied to the LDs 11A and 11B increases (S10).
7). As a result, the light emitting outputs of the LDs 11A and 11B increase, and the feedback current ID of the PD 12 increases accordingly.
Reference voltage Vref in analog arithmetic units 221 and 222
1, the difference voltage from Vref2 is reduced. Step S
In the comparison between the analog arithmetic units 221 and 222 at 105, when the feedback voltage VD is higher than the reference voltages Vref1 and Vref2 (False), the difference voltage becomes a negative voltage. 224 (S108), and the LD drive control circuits 225 and 226 use the sampled negative voltage to control the LD 1
The first current source circuit 201 and the second current source 202 are controlled so that the LD drive current supplied to 1A and 11B is reduced (S109). As a result, the light emitting outputs of the LDs 11A and 11B decrease, the feedback current ID of the PD 12 decreases,
The difference between the analog arithmetic units 221 and 222 and the reference voltage is reduced.

As described above, the difference between the reference voltage and the feedback voltage finally becomes zero, and the optical outputs of the LDs 11A and 11B follow the reference voltages Vref1 and Vref2, thereby realizing APC control. Therefore, in the APC circuit of FIG.
The APC control in the LD 11A results in an optical output that follows the first reference voltage Vref1, and the APC control in the LD 11B produces an optical output that follows the second reference voltage Vref2. For this reason,
Even when the characteristics of the LDs 11A and 11B vary, the first and second voltage regulators 241 and 242 can be used.
By adjusting each of the reference voltages Vref1 and Vref2, PD1
It is possible to APC-control the optical outputs of the LDs 11A and 11B to the same value for the feedback current of 2. When the APC control is completed, the sample and hold circuit 22
3 and 224 hold the difference voltage respectively, and APC
Keep the state stable.

FIG. 3 shows a timing chart of the operation of the multi-beam laser device. The timing chart shows a state in which a required pattern by the laser beam is already being performed. LD11A, 11B
Starts emitting light in response to the horizontal synchronization signal HSYNC, respectively, and the first and second LD drive control circuits 22
5, 226, the first and second data DAT from the CPU 3
A1 and DATA2 are input, the light emission output of each of the LDs 11A and 11B is modulated, the main scan is performed on the photosensitive drum 17, and a pattern for one main scan corresponding to each data is drawn. Next, the writing of the pattern for one main scan of each of the LDs 11A and 11B is completed, and the first and second APCs are sent from the CPU 3 until the timing of the next main scan cycle.
Signals SAPC1 and SAPC2 are input. here,
First, the first APC signal SAPC1 enters the active state “L” (sampling state), and the first analog operation unit 221, the first sample / hold circuit 223,
The APC control described above is executed by the first LD drive control circuit 225. Thereafter, the first APC signal SAPC1 becomes inactive state "H" (hold state), and the APC state is maintained. Next, the second APC signal SAPC2 goes to the active state “L” (sampling state), and the LD 11
B, the second analog arithmetic unit 222 and the second sample
The APC control is executed by the hold circuit 224 and the second LD drive control circuit 226, and the APC state is held at "H" (hold state). After the APC control ends, the LD 11A, 1
After the light emission of 1B is stopped, the LD 11A is forcibly turned on again to perform light detection by the synchronous PD 18 to obtain the horizontal synchronization signal HSYNC of the next main scanning. Then, in the subsequent pattern writing for one main scan, the first and second LD drive control circuits are based on the difference voltages held in the first and second sample and hold circuits 223 and 224, respectively. 225, 226 are LD11A, 11
A light emission output of B is held at the output of the APC control.
Pattern drawing with a controlled and suitable light intensity is ensured.

As described above, in this APC circuit, the PD
The feedback current ID of the first and second analog calculators 22 is always used as the feedback voltage VD through the I / V converter 210.
1 and 222, and each analog arithmetic unit 2
The first and second voltage regulators 24 and 22 simultaneously
Since the reference voltages Vref1 and Vref2 are input from the first and second APC signals SAPC1 and SAPC,
When 2 becomes active, the operation is immediately executed,
In addition, APC control is executed. For this reason, LD
An analog switch for switching the APC control of 11A and 11B is not required, and a time for switching the analog switch and a standby time until the output becomes stable after the switching are not required. Therefore, as can be seen from FIG.
The preset APC time is not reduced by the time for switching the analog switch. Therefore, the APC time for each of the LDs 11A and 11B can be secured longer than that of the conventional circuit, and stable APC control can be realized even when the voltage change width in the APC control is large. In particular, even when the number of LDs increases, no time is required for switching the analog switches, so that the degree to which the APC time of each LD is reduced can be minimized.

In the APC circuit, the LD 11A,
11B for performing APC control on each of
To obtain the reference voltages Vref1 and Vref2 of
Are provided, and these voltage regulators 241 and 242 are constituted by variable resistors. As a result, the characteristics of the LDs 11A and 11B fluctuate.
When there is a difference between the optical outputs of D11A and 11B,
By individually adjusting the first and second reference voltages Vref1 and Vref2 by the voltage adjusters 241 and 242, the optical outputs of the LDs 11A and 11B can be adjusted to the same output. Therefore, in the circuit of FIG.
2 connected to the I / V converter 2, ie, the I / V converter 210 connected in the negative feedback loop of the APC circuit.
Can be configured as an element whose coefficient (gain) is set to a fixed value, and does not need to be configured as a movable structure such as a variable resistor as in a conventional circuit, and the capacitance and inductance are reduced. The response of the APC control is not degraded due to the inductance or the inductance. Meanwhile, on the other hand, two different reference voltages V
In order to obtain ref1 and Vref2, each voltage regulator 241, 24
2 has a structure including a movable structure, but this movable structure simply converts the reference voltage Vref into the first and second reference voltages Vref.
1, Vref2, and does not exist in the negative feedback loop for performing the APC control. However, the responsiveness of the APC control is not affected, and the high-speed tracking performance of the APC control is not reduced.

Here, in the above embodiment, an example is shown in which APC control is performed on two LDs based on the feedback current of one PD. However, three or more LDs are controlled by the feedback current of one PD. It goes without saying that the APC circuit of the present invention can also be applied to APC control based on the APC circuit. As described above, when the number of LDs increases, the time required for switching the analog switch increases in the conventional circuit, and the APC time allocated to one LD is further reduced. Regardless of the number, the time required for switching the analog switches is zero, so that the APC time allocated to one LD can be secured longer, and APC control in each LD can be performed appropriately.

In the above embodiment, the configuration of the APC circuit for one PD is shown. However, there are two or more PDs, and a plurality of LDs are connected to each PD. In the case of a multi-beam laser device having such a configuration, the circuit configuration shown in FIG. 1 may be provided by the number of PDs.

[0023]

As described above, according to the present invention, one P
Since the light receiving output of D is compared with a plurality of reference voltages set corresponding to each of the plurality of LDs, and the light output of the corresponding LD is controlled based on the comparison result, P
An analog switch for selecting the light receiving output of D is not required, which reduces the number of circuit components and eliminates the time for switching the analog switch during APC control, thus ensuring the time required for APC control in each LD. Becomes In addition, the circuit component for processing the light receiving output of the PD can be set to a fixed value, and the variable structure element is not required in the APC loop for performing the APC control, thereby improving the responsiveness of APC control caused by the variable structure element. Can be
High-speed APC control can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a light output control circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining an operation flow of APC control in the light output control circuit of FIG. 1;

FIG. 3 is a timing chart showing operation timings of the light output control circuit of FIG. 1;

FIG. 4 is a schematic configuration diagram of a multi-beam laser device to which the present invention is applied.

FIG. 5 is a circuit diagram of an example of a conventional light output control circuit.

FIG. 6 is a timing chart showing operation timings of the light output control circuit of FIG. 5;

[Explanation of symbols]

 Reference Signs List 1 laser scanning device 2 light output control circuit 3 CPU 11 one-chip LD 11A, 11B LD (semiconductor laser) 12 PD (photodiode) 13 collimating lens 14 cylindrical lens 15 polygon mirror 16 fθ lens 17 photosensitive drum 18 synchronous PD (synchronous photo) Diode) 200 Analog switch 201, 202 Current source circuit 210 I / V converter 221, 222 Analog operation unit 223, 224 Sample / hold circuit 225, 226 LD drive control circuit 241, 242 Voltage regulator 250 Reference voltage source

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/113 B41J 3/00 D 1/23 H04N 1/04 104A

Claims (6)

[Claims] 1. A multi-beam laser device comprising a plurality of semiconductor lasers and synchronously scanning a laser beam emitted from each of the semiconductor lasers to draw a desired pattern, wherein each of the plurality of semiconductor lasers A light-receiving element for detecting light output, a plurality of reference values set corresponding to each of the semiconductor lasers, a light-receiving output of the light-receiving element and each of the reference values are compared, and the comparison result is a predetermined value. An optical output control circuit for a multi-beam laser device, comprising: an optical output control circuit for controlling an optical output of a corresponding semiconductor laser so as to obtain a value. 2. An optical output control circuit comprising: an I / V converter for obtaining a feedback voltage from a light receiving current of the light receiving element; a reference voltage set corresponding to each of the plurality of semiconductor lasers; A plurality of analog arithmetic units for respectively comparing feedback voltages from an I / V converter, a sample and hold circuit for sampling and holding the output of each of the plurality of analog arithmetic units, and each of the plurality of semiconductor lasers And a plurality of laser drive control circuits for controlling a drive current supplied to the corresponding semiconductor laser based on an output of each of the sample and hold circuits. Light output control circuit of multi-beam laser device. 3. A reference voltage set corresponding to each of the plurality of semiconductor lasers, wherein one reference voltage source and a reference voltage of the reference voltage source are adjusted in voltage corresponding to each of the semiconductor lasers. 3. The light output control circuit according to claim 2, wherein the light output control circuit is set by a circuit including a plurality of voltage regulators. 4. The plurality of analog arithmetic units are time-divisionally operated based on an optical output control signal, and output a voltage difference between the feedback voltage and each reference voltage during the operation. 4. An optical output control circuit of the multi-beam laser device according to 2 or 3. 5. The optical output control circuit according to claim 2, wherein the conversion coefficient of the I / V converter is set to a fixed value. 6. The laser drive control circuit according to claim 2, wherein the plurality of laser drive control circuits function as modulators for modulating and controlling the corresponding semiconductor lasers based on data of a pattern to be drawn. 3. An optical output control circuit for a multi-beam laser device according to claim 1.