JP2000190563A - Drive circuit of multibeam semiconductor laser array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the necessity for providing photodetectors of which the number corresponds to the number of beams to the outside of a multibeam semiconductor laser array and to control the quantity of a plurality of beams within an effective scanning period. SOLUTION: A monitor current corresponding to the quantity of the emitted beams of LDs 9-1-9-3 flows to a PD 10 to be converted to monitor voltage by a current/voltage converter circuit 2 and the monitor voltage is integrated by an integration circuit 3 to be converted to an integral value S2. Input image data D1-D4 corresponding to four lines are added by an adder circuit 4 and the obtained voltage is integrated by an integration circuit 5 to be converted to an integral value S1. An error detecting amplifier 6 sets the integral value S1 to reference voltage to compare the same with the integral value S2 and calculates the difference corresponding to the light output fluctuation quantity caused by the LDs 9-1-9-4 themselves to output the same to a bias current supply circuit 7 and the bias current supply circuit 7 forms bias currents B1-B4 making the quantity of the emitted beams of the LDs 9-1-9-4 constant on the basis of this difference. The bias currents B1-B4 are added to LD driving pulse currents I1-I4 to be applied to the LDs 9-1-9-4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a multi-beam semiconductor laser array for controlling (APC) the respective light amounts of a plurality of beams.

[0002]

2. Description of the Related Art In recent years, a multi-beam semiconductor laser array which emits a plurality of beams as a laser beam light source for writing an image by modulating a light beam according to image data in a digital copying machine, a laser beam printer, a facsimile or the like. Is attracting attention. However, this type of multi-beam semiconductor laser array is provided with only a single photodetector and cannot independently monitor the respective light amounts of a plurality of beams.

Therefore, as a conventional example (1) in which the individual light amounts of a plurality of beams are controlled using this single photodetector,
For example, as disclosed in JP-A-5-19197, a method has been proposed in which a number of photodetectors corresponding to the number of beams are provided outside a semiconductor laser array. Further, as another conventional example (2), for example, as disclosed in Japanese Patent Application Laid-Open No. 7-235715, a method of turning on each light source independently within an ineffective scanning period has been proposed.

[0004]

However, in the conventional example (1), the number of photodetectors corresponding to the number of beams is provided outside the multi-beam semiconductor laser array. There is a problem that alignment is required. Further, in the above conventional example (2), since each light source is turned on independently during the non-effective scanning period, there is a problem that the beam light amount cannot be controlled during the effective scanning period (first problem). ).

Further, in the above conventional example (2), since each light source is turned on independently within the non-effective scanning period, there is a problem that a long non-effective scanning period is required as the number of beams increases. In order to prevent this, a method of shortening the lighting time per light source can be considered.
In this case, there is a possibility that APC cannot be sufficiently performed by one lighting, and in order to prevent this, the APs of all the light sources in one ineffective scanning period are set.
Instead of performing C, grouping multiple light sources into 1
For example, in a non-effective scanning period, A
A method is possible in which the number of APCs is reduced by performing the PC and performing the APC for the remaining light sources during the next ineffective scanning period. In this case, however, the amount of light may fluctuate. Therefore, it is desired to perform APC without thinning out the number of APCs even if the number of light sources is large and without lengthening the ineffective scanning period (second problem).

In general, the characteristic of the driving current I-output light quantity P of the semiconductor laser diode (LD) depends on the temperatures TA and TB as shown in FIG. Accordingly, there is a problem that the light intensity becomes unstable due to crosstalk caused by heat generation between the individual LD elements of the multi-beam semiconductor laser array (third problem).

In view of the above-mentioned first problem, the present invention does not require the provision of the number of photodetectors corresponding to the number of beams outside the multi-beam semiconductor laser array. A first object is to provide a driving circuit of a multi-beam semiconductor laser array capable of controlling the amount of light.

In view of the second problem, the present invention provides a multi-beam system capable of performing APC without thinning the number of APCs even if the number of light sources is large and without lengthening the ineffective scanning period. A second object is to provide a drive circuit for a semiconductor laser array.

Further, in view of the above third problem, the present invention can prevent a light intensity from becoming unstable due to crosstalk between individual LD elements of a multi-beam semiconductor laser array due to heat generation. A third object is to provide a drive circuit for a beam semiconductor laser array.

[0010]

In order to achieve the first object, a first means comprises a plurality of light sources for emitting a plurality of beams, respectively, and one means for monitoring the plurality of beam light amounts collectively. A driving circuit for a multi-beam semiconductor laser array having a photodetector, wherein first calculating means for calculating a time average value of the plurality of beam light amounts based on a monitor current detected by the photodetector; Second calculating means for calculating a time average of the sum of the image data of a plurality of lines corresponding to the respective beams, based on the time average of the light amounts of the plurality of beams and the time of the sum of the image data of the plurality of lines. Negative feedback control means for performing negative feedback control so that the plurality of beam light amounts become constant.

A second means is the first means, wherein the negative feedback control means outputs a plurality of drive currents for modulating a plurality of light sources in accordance with a plurality of lines of image data respectively corresponding to the plurality of beams. A driving current generating circuit that generates
Generating a plurality of bias currents such that each of the plurality of beam light amounts becomes constant based on a time average value of the plurality of beam light amounts and a time average value of the sum of image data of a plurality of lines; And a bias current generation circuit for adding

A third means is a driving current for the negative feedback control means in the first means, wherein the negative feedback control means modulates a plurality of light sources according to image data of a plurality of lines respectively corresponding to the plurality of beams. A driving current generating circuit that generates a plurality of driving currents based on a time average value of the plurality of beam light amounts and a time average value of the sum of image data of a plurality of lines so that each of the plurality of beam light amounts is constant. There is a feature.

In order to achieve the second object, the fourth means comprises: a plurality of light sources each emitting a plurality of beams;
In a drive circuit of a multi-beam semiconductor laser array including one photodetector for monitoring the plurality of light beams collectively, detection is performed by the photodetector while the plurality of light sources are simultaneously turned on during an ineffective scanning period. Reference drive current control means for controlling a common reference drive current such that the light amounts of the plurality of light sources are constant based on the difference between the detected monitor current and the reference signal; and And a drive current correction means for generating a drive current for each of the plurality of light sources by multiplying the light source by a preset coefficient and adding a preset bias current value.

[0015] In order to achieve the third object, the fifth means comprises a plurality of light sources each emitting a plurality of beams;
In a drive circuit for a multi-beam semiconductor laser array including one photodetector for monitoring the plurality of light beams collectively, the photodetector is provided while the plurality of light sources are independently turned on during a non-effective scanning period. APC means for controlling the drive current so that the light amounts of the plurality of light sources are constant based on the monitor current detected by the computer, and calculating the amount of heat generated by the plurality of light sources based on the image data. Predict the temperature change of the plurality of light sources based on the, the calculated change in the threshold of the drive current of the plurality of light sources based on the predicted value of the temperature change, based on the change in the threshold of the plurality of light sources And a drive current correction means for correcting the drive current so that the light amount becomes constant.

A sixth means is the fifth means, wherein the drive current correction means corrects the drive current by pulse width modulation or power modulation.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a drive circuit for a multi-beam semiconductor laser array according to the present invention.

An LD (laser diode) array 1 shown in FIG. 1 has, for example, four LDs 9-1 to 9-4 and an LD
It has one PD (photo detector) 10 that monitors the light emission amounts of 9-1 to 9-4 collectively. The signal power supply circuit 8 is used to blink the LDs 9-1 to 9-4 in accordance with the input image data D1 to D4 for four lines, respectively.
D drive pulse currents I1 to I4 are generated, and LD9-1 to LD9-1 are generated.
9-4. When the LDs 9-1 to 9-4 are turned on, a monitor current corresponding to the amount of emitted light flows through the PD 10.

Here, since the LDs 9-1 to 9-4 are substantially in the same condition both in the manufacturing process and in the use environment, it is considered that there is little difference in the characteristics between the LDs 9-1 to 9-4. . Therefore, the monitor current is converted into a monitor voltage by the current-voltage conversion circuit 2, and the monitor voltage is integrated by the integration circuit 3 and converted into an integrated value S2.
This integral value S2 is a voltage corresponding to the time average value of the total light output of the LDs 9-1 to 9-4. Further, the input image data D1 to D4 for four lines are added by the adding circuit 4,
Next, the added voltage is integrated by the integration circuit 5 and converted into an integrated value S1. This integral value S1 is a voltage corresponding to the time average value of the sum of the input image data D1 to D4 for four lines.

The error detection amplifier 6 compares the integrated value S1 with the integrated value S2 by using the integrated value S1 as a reference voltage.
The difference according to the optical output variation caused by 9-4 itself is calculated and output to the bias current supply circuit 7. The bias current supply circuit 7 generates bias currents B1 to B4 such that the light emission amounts of the LDs 9-1 to 9-4 become constant based on the difference. The bias currents B1 to B4 are
LD9-1 to LD9-1 are added to the driving pulse currents I1 to I4.
9-4.

Therefore, according to the above embodiment, the LD
Based on the difference between the time average value of the total light output of 9-1 to 9-4 and the time average value of the sum of the input image data D1 to D4 for four lines, the light emission amounts of the LDs 9-1 to 9-4 are made constant. Since such bias currents B1 to B4 are generated and added to the LD drive pulse currents I1 to I4, it is necessary to provide a number of photodetectors corresponding to the number of beams outside the multi-beam semiconductor laser array. In addition, the light amounts of a plurality of beams can be controlled within the effective scanning period.

It should be noted that the present invention is not limited to the above configuration, and for example, the bias current supply circuit 7 (and the bias currents B1 to B1)
B4) is omitted, and instead, the error detection amplifier 6 outputs the difference between the integrated values S1 and S2 to the signal power supply circuit 8 as indicated by a broken line, and the signal power supply circuit 8 outputs the LD 9-1 based on the difference. LD where the amount of emitted light of ~ 9-4 becomes constant
The driving pulse currents I1 to I4 may be generated. Further, in the configuration shown in FIG.
D4 is added by an adder circuit 4, and this voltage is integrated by an integrating circuit 5 to obtain input image data D1 for four lines.
Is converted to a time average value of the sum of the input image data D1 to D4.
Next, the integration value may be added by the addition circuit 4.

<Second Embodiment> Next, a second embodiment will be described. FIG. 2 shows the second embodiment, and FIG. 3 shows the main parts of the APC circuit and the LD driver in FIG. 2 in detail. An image processing unit (IPU) 10 converts image data input for each line into image data of four lines and outputs the image data to a pulse width modulation (PWM) unit 11. PWM unit 1
1 performs pulse width modulation of this image data to perform power modulation (P
M) unit 12, and the PM unit 12 power-modulates this data and outputs it to the LD driver 13. LD driver 1
3 is based on this data and each of LDs 9-1 to 9-4
The driving pulse currents I1 to I4 are generated.

The LD driver 13 simultaneously turns on the LDs 9-1 to 9-4 during the ineffective scanning period,
The monitor current detected by D10 is fed back to the LD driver 13 via the APC circuit 15, and the LD drive pulse currents I1 to I4 of the LDs 9-1 to 9-4 are controlled so that the output light amount becomes constant. .

Here, suppose that the LD 9-1 in the LD array 1 is
Assuming that the ambient temperature and characteristics are exactly the same, a drive current is applied to all the LDs 9-1 to 9-4 from the same current source, and the current source is determined based on the monitor current detected by the PD 10. By performing APC on the LD array 1
Can be APC as if it were one LD. Since the LDs 9-1 to 9-4 in the LD array 1 are placed in substantially the same environment, the ambient temperatures are considered to be substantially the same. The reason why the optical output of the LD fluctuates is that the temperature change occurs mainly due to the heat generated by the light emission of the LD, and the threshold current Ith shown in FIG. 7 changes. Each LD in LD array 1
Since 9-1 to 9-4 generate heat according to the input signal,
Actually, the temperatures are different, but if a certain time elapses after the lamps are turned on at the same time, it is considered that the temperature in the LD array 1 is saturated, and the temperatures of the LDs 9-1 to 9-4 are all in the same steady state. Can be

Therefore, during the ineffective scanning period, the LD 9
APC is performed on the basis of the saturation temperature in the LD array 1 when -1 to 9-4 are simultaneously turned on. LD9-1
9-4 are performed collectively, not independently.
However, each of the LDs 9-1 to 9-4 in the LD array 1 is
There is a variation in the characteristics such as the threshold current I _th, and the light transmission efficiency varies depending on the optical path of each laser beam of the LDs 9-1 to 9-4 until reaching the photosensitive drum. It is necessary to adjust in advance so that each laser beam on the drum is uniform.

Therefore, as shown in FIG.
Multipliers 22-1 to 22-4 (22-i) are provided so that the drive signals I1 to I4 for 9-4 can be output at different magnifications (coefficients) with respect to the common reference drive signal I0. _{1 to} α ₄ (α _i ) are adjusted at the time of shipment from the factory. A bias current value B1 set in advance for each of the drive signals I1 to I4.
B1 to B4 are applied, and B1 to B4 are also adjusted at the time of factory shipment.

When performing APC, the LDs 9-1 to 9-4 are simultaneously turned on during the ineffective scanning period, and the PD1 is turned on.
The monitor current I _m which is detected by the 0 is converted to the monitor voltages V ₁ = R ₁ · I _m by the resistor R _1, and applies the monitor voltage V ₁ and the reference voltage V _ref to the comparator 21. During the ineffective scanning period, the APC circuit 15 enters the sampling mode and the switch SW is turned on, and the comparator 21 charges the capacitor C via the switch SW when the monitor voltage V ₁ <the reference voltage _Vref . On the other hand, the monitor voltage V
_{If 1} <the reference voltage _Vref , the capacitor C is discharged. For this reason, since the charging voltage of the capacitor C is controlled, the reference drive signal I ₀ is controlled so that the light amount of the LD array 1 becomes constant. Then, I _i = α _i × I ₀ is generated by the multipliers 22-i. When the APC is completed, the switch SW is turned off and the APC circuit 15 shifts to the hold mode.

<Third Embodiment> Next, a third embodiment will be described with reference to FIGS. An image processing unit (IPU) 10 converts image data input for each line into image data of four lines and performs pulse width modulation (PW).
M) Output to the unit 11. The PWM unit 11 performs pulse width modulation of the image data and outputs the image data to a power modulation (PM) unit 12. The PM unit 12 performs power modulation of the data and outputs the data to an LD driver 13. The LD driver 13 generates pulse currents I1 to I4 for driving the LDs of the LDs 9-1 to 9-4 based on the data. Here, the LD driver 13 turns on the LDs 9-1 to 9-4 independently during the ineffective scanning period, and the monitor current detected by the PD 10 is set to the AP.
The LDs 9-1 to 9-4 are fed back to the LD driver 13 via the C circuit 15 so that the output light amount becomes constant.
, The LD drive pulse currents I _{1 to} I ₄ are controlled.

The LD drive pulse currents I _{1 to} I ₄ are I
The voltage is converted into a voltage V by the V conversion circuit 14 and fed back to the IPU 10, and the temperature T _M of the heat sink of the LDs 9-1 to 9-4 is detected by the thermocouple 16 and
This is fed back to U10. Then, as shown in FIG. 5, the IPU ₁₀ writes the image data (drive currents I _{1 to} I ₄₎ based on the image data, the pulse currents I _{1 to} I ₄ for LD driving of the LDs 9-1 to 9-4, and the temperature T _M. ) Is corrected. This correction is roughly divided into the following four steps S1 to S4.

<Step S1: LD9-1 based on the written image data sent to the PM unit 12 or the PWM unit 11
9-4 are calculated. > LD9-1 to 9-4
Assuming that each heat value is Q _i , the power applied to the LDs 9-1 to 9-4 is W _i , and the light emission amounts of the LDs 9-1 to 9-4 are P _i , the heat value Q _i is expressed as follows. .

Q _i = W _i -P _i where i represents the channel number of the LDs 9-1 to 9-4.

Here, the light emission amounts P _i of the LDs 9-1 to 9-4.
Is assumed to be substantially constant by performing the following correction with APC. Therefore, since the applied voltage of the LDs 9-1 to 9-4 can be considered to be substantially constant from the diode characteristics thereof, the heat generation amount Qi is changed to the LDs 9-1 to 9-4.
A constant value corresponding to the light emission amount P _i may be subtracted from the drive current value. Therefore, for the signal sent to the PM unit 12,
Multiplying a signal to be sent to the PWM unit 11 ( "0" or "1"), a value obtained by subtracting a predetermined value corresponding to the light emission amount P _i as the calorific value Q _i.

[0033] <Step S2: calorific value Q _i variation ΔQ _i of
Is calculated based on the temperature change ΔT _i of each of the LDs 9-1 to 9-4. > If the heat capacity of each LD 9-1 to 9-4 is Ci and the heat value of each channel is Qi, the temperature change Δ of each channel
Ti can be calculated by ΔT _i = Q _i / Ci, where Qi uses the calorific value calculated in step S1.

Next, the temperature change Δ of each of the LDs 9-1 to 9-4.
The T _i, heat as shown in FIG. 6 LD9-1～9-4
The temperature is further transmitted to the LDs 9-1 to 9-4 and the following calculation is performed. LD thermal resistance between the channels of the array 1 R _ij, each temperature T _i of LD9-1～9-4, or heat sink of the LD array 1 LD9-1
The heat capacities of the mounts 9 to 9-4 are C _M and LD 9-1 to 9-9.
-4, the thermal resistance between the heat sink and the temperature of the LD 9-1 to 9-4 due to conduction inside the LD array 1, where R _iM , the temperature of the heat sink is T _M , and the pulse lighting time is Δt.
Let T _j be ΔT _j = Σ (1 / R _ij C _i ) (T _i −T _j ) Δt− (1 / R
_iM C _M) (calculated by T _i -T _M) Δt.

Thereafter, the temperatures T _{i of the} LDs 9-1 to 9-4 are further obtained by adding ΔT _j . However, since the calculated value T _i is the error with time is increased, LD9-1～9-4 all lit in a non-effective scanning period LD9-1
To equalize the respective temperatures T _i of ～9-4, the temperature difference T _i -T _j in homogenized time to "0". Then, the value of the subsequent temperature difference T _i -T _j is obtained from the temperature change ΔT _j . Further, the temperature TM of the heat sink is detected by the thermocouple 16 (step S8).

<Step S3: The change ΔI _th of the threshold value of the drive current accompanying the temperature change ΔT _i of each of the LDs 9-1 to 9-4 is calculated. In general, it is known that the threshold current I _th of the LD has a large temperature dependency, is exponentially proportional to the temperature change at the junction of the laser oscillation section, and has the following relationship.

I _thB = I _thA · exp (ΔT _i / T ₀ ) where I _thB and I _thA are the temperatures T _B and T _A shown in FIG. 7, respectively.
(T _B <T _A ), where ΔT _i = T _B −T
_A and T ₀ are characteristic temperature constants.

From this equation, the change Δ of the threshold currents I _thB and I _thA
I _th is obtained from the temperature difference ΔT _i by ΔI _th = I _thA {exp (ΔT _i / T ₀ ) −1}. Here, the value I _thA threshold current at temperature T _A as a reference but is necessary, flow through LD9-1~9-4 at that time as a reference temperature when performing the APC in a non-effective scanning period The drive current is monitored, a threshold current is obtained based on the current value, and the threshold current is set as a reference value I _thA (step S7).

<Step S4: The signal (drive current) sent to the PM unit 12 or the PWM unit 11 is corrected according to the change ΔI _th of the threshold currents I _thB and I _thA . > Here, the threshold current I _thB, can be corrected crosstalk by increasing by [Delta] I a drive current I in response to a change [Delta] I _th of I _thA, a new cross-talk is generated by this correction. Therefore, a secondary correction is added to the crosstalk (step S6). When the heat generated by the current is increased for correction to DerutaQi, temperature change delta ² T _j newly generated is represented by _{^{Δ 2 T j = Σ (1}} / R ij C i) ΔQ i dt.

Therefore, it is considered that a secondary correction is added, and the temperature change Δ ² _{Tj is applied} to step S 2 again.
The calculation in S3 is performed, and the calculation result Δ ² I _th is 2
Consider adding it to ΔI _th as the next correction amount. However, as a result, a new crosstalk is generated again. Therefore, in order to correct it, a third-order Δ ³ I _th must be considered. That is, ΔI _th + Δ ² I _th + Δ ³ I _th +... However, since the amount of correction for crosstalk is small and the higher-order correction term can be completely ignored, the processing in steps S2 to S4 and S6 is repeated a few times (step S5), for example, ΔI _th + Δ ² I _th + ^{Δ 3} I _th by correcting the drive current (step S9).

Therefore, according to the third embodiment, it is possible to prevent the light intensity from becoming unstable due to crosstalk caused by heat generation. The present invention is not limited to the above configuration. For example, the polarity of the LD array 1 is as shown in FIG.
May be reversed.

[0042]

As described above, according to the first aspect of the present invention, the plurality of beam light amounts are made constant based on the time average value of the plurality of beam light amounts and the time average value of the sum of image data of a plurality of lines. Negative feedback control is performed so that the number of photodetectors corresponding to the number of beams does not need to be provided outside the multi-beam semiconductor laser array, and the amount of light of multiple beams is controlled within the effective scanning period. can do.

According to the second aspect of the present invention, a bias current is generated based on the time average value of a plurality of beam light amounts and the time average value of the sum of image data of a plurality of lines so that the plurality of beam light amounts become constant. The number of photodetectors corresponding to the number of beams does not need to be provided outside the multi-beam semiconductor laser array, and the amount of light of multiple beams is controlled within the effective scanning period. can do.

According to the third aspect of the present invention, a drive current is generated such that the plurality of beam light amounts are constant based on the time average value of the plurality of beam light amounts and the time average value of the sum of image data of a plurality of lines. Therefore, it is not necessary to provide the number of photodetectors corresponding to the number of beams outside the multi-beam semiconductor laser array, and it is possible to control the light amounts of a plurality of beams within the effective scanning period.

According to the fourth aspect of the present invention, a plurality of light sources are detected based on a difference between a monitor current detected by one photodetector and a reference signal while the plurality of light sources are simultaneously turned on during the ineffective scanning period. Since a common reference drive current is generated, and the reference drive current is multiplied by a preset coefficient for each of the plurality of light sources to generate respective drive currents for the plurality of light sources, the APC is performed even if the number of light sources is large. APC can be performed without thinning out the number of times and without lengthening the ineffective scanning period.

According to the fifth aspect of the invention, the amount of heat generated by the plurality of light sources is calculated based on the image data, and the temperature change of the plurality of light sources is predicted based on the calorific value. A change in the threshold value of the drive current of the plurality of light sources is calculated based on the predicted value, and the drive current is corrected based on the change in the threshold value so that the light amounts of the plurality of light sources are constant. It is possible to prevent the light intensity from becoming unstable due to crosstalk between the individual LD elements of the semiconductor laser array due to heat generation.

According to the sixth aspect of the present invention, it is possible to prevent light intensity from becoming unstable due to crosstalk between individual LD elements of the multi-beam semiconductor laser array due to heat generation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a driving circuit for a multi-beam semiconductor laser array according to the present invention.

FIG. 2 is a block diagram illustrating a drive circuit of a multi-beam semiconductor laser array according to a second embodiment.

FIG. 3 is a block diagram showing in detail main parts of an APC circuit and an LD driver in FIG. 2;

FIG. 4 is a block diagram illustrating a drive circuit of a multi-beam semiconductor laser array according to a third embodiment.

FIG. 5 is a flowchart illustrating a process of the drive circuit of FIG. 4;

FIG. 6 is an explanatory diagram showing heat conduction between a plurality of laser diodes.

FIG. 7 is an explanatory diagram showing a characteristic of a driving current-output light amount of a laser diode.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 LD array 2 current-voltage conversion circuit 3, 5 integration circuit 4 addition circuit 6 error detection amplifier 7 bias current supply circuit 8 signal power supply circuit 9-1 to 9-4 LD 10 image processing unit (IPU) 11 pulse width modulation ( PWM) section 12 Power modulation (PM) section 13 LD driver 15 Automatic power control (APC) section 16 Thermocouple 21 Comparator 22-1 to 22-4 Multiplier

Claims (6)

[Claims] 1. A plurality of light sources for emitting a plurality of beams, respectively, and a plurality of light amounts of the plurality of beams are monitored collectively.
A driving circuit for a multi-beam semiconductor laser array including two photodetectors, wherein first calculating means for calculating a time average value of the plurality of beam light amounts based on a monitor current detected by the photodetectors; A second calculating means for calculating a time average value of the sum of the image data of the plurality of lines respectively corresponding to the plurality of beams; and a time average value of the sum of the image data of the plurality of lines and the time average value of the plurality of beam light amounts. And a negative feedback control means for performing negative feedback control so that the plurality of beam light amounts are constant on the basis of the plurality of beam light amounts. 2. A drive current generating circuit for generating a plurality of drive currents for modulating a plurality of light sources according to a plurality of lines of image data respectively corresponding to the plurality of beams, A plurality of bias currents are generated such that each of the plurality of beam light amounts becomes constant based on a time average value of a plurality of beam light amounts and a time average value of a sum of image data of a plurality of lines, and the plurality of drive currents are generated. 2. The driving circuit for a multi-beam semiconductor laser array according to claim 1, further comprising: a bias current generating circuit for adding. 3. A driving current for modulating a plurality of light sources in accordance with a plurality of lines of image data respectively corresponding to the plurality of beams, the negative feedback control means comprising: 2. The multi-function circuit according to claim 1, wherein the circuit is configured to generate a plurality of driving currents so that each of the plurality of beam light amounts is constant based on a value and a time average value of a sum of image data of a plurality of lines. Drive circuit for beam semiconductor laser array. 4. A plurality of light sources for emitting a plurality of beams, respectively, and a plurality of light sources for monitoring the plurality of light beams collectively.
In the drive circuit of the multi-beam semiconductor laser array having two photodetectors, based on a difference between a monitor current and a reference signal detected by the photodetectors while the plurality of light sources are simultaneously turned on during an ineffective scanning period. Reference drive current control means for controlling a common reference drive current so that the light amounts of the plurality of light sources are constant; multiplying the reference drive current by a coefficient preset for each of the plurality of light sources, and presetting And a drive current generating means for generating drive currents for the plurality of light sources by adding the bias current values thus obtained, to a drive circuit for a multi-beam semiconductor laser array. 5. A plurality of light sources for emitting a plurality of beams, respectively, and a plurality of light sources for monitoring the plurality of light beams collectively.
In the driving circuit of the multi-beam semiconductor laser array having one photodetector, the plurality of light sources are independently turned on within an ineffective scanning period, and the plurality of light sources are independently turned on based on the monitor current detected by the photodetector. APC means for controlling the drive current so that the light amount of the light source is constant, calculating the amount of heat generated by the plurality of light sources based on image data, and predicting a temperature change of the plurality of light sources based on the amount of heat Then, a change in a threshold value of the drive current of the plurality of light sources is calculated based on the predicted value of the temperature change, and the drive current is corrected based on the change in the threshold value so that the light amounts of the plurality of light sources become constant. A driving circuit for a multi-beam semiconductor laser array, comprising: 6. The drive circuit for a multi-beam semiconductor laser array according to claim 5, wherein said drive current correction means corrects the drive current by pulse width modulation or power modulation.