JPS63273380A - Laser output controller - Google Patents

Abstract

PURPOSE:To obtain an image having no irregular concentration by detecting the quantity of light of a semiconductor laser to control a bias current and controlling a driving current. CONSTITUTION:The intensity of the output light of a semiconductor laser 1 is detected by a photodetector 9, and a detector 21 outputs an add/subtract signal of the application current of the laser 1 in response to the detection output. Bias current control means 22 made of bias current applying circuit 20 applies a bias voltage to the laser 1 in response to the output of the detector 21. A detector 24 outputs an add/subtract signal of the application current of the laser 1 in response to the output of the photodetector 9, and detects whether the output of the laser 1 is a predetermined value or not. Driving current control means 25 made of a driving circuit 23 applies a driving current to the laser 1 in response to the output of the detector 24.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a laser output control device, and more particularly to a laser output control device that can be applied to a laser beam printer that scans a semiconductor laser beam to form an image. be.

(Prior art) Since the output intensity of a semiconductor laser is extremely unstable with respect to temperature, the output intensity of the semiconductor laser must be stabilized using a semiconductor laser output control device, etc. in an environment where the ambient temperature of the semi-quadram laser changes. It is necessary to do so. There is a type of semiconductor laser output control device that uses a counter, and FIG. 8 shows an example of a laser printer that employs an example of this type of type.

A laser beam generated by a semiconductor laser 1 is collimated by a collimator lens 2, deflected by an optical scanning device 3 consisting of a rotating polygon mirror, and is imaged by an fθ lens 4 on the charged surface of a photoreceptor drum 5. As the spot moves repeatedly in the direction of arrow X by the rotation of the rotating polygon mirror 3, the photosensitive drum 5 rotates at the same time. A photodetector 6 is provided outside the information writing area, detects the laser beam deflected by the rotating polygon mirror 3, and generates a synchronization signal. The signal processing circuit 7 applies an information signal to the semiconductor laser drive circuit 8, and its timing is controlled by a synchronization signal from the photodetector 6. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 according to the information signal from the signal processing circuit 7, and therefore the laser beam modulated by the information signal is irradiated onto the photoreceptor drum 5 to form an electrostatic latent image. . This electrostatic latent image is developed by a developing device and transferred onto paper or the like by a transfer device. In addition, the laser beam emitted backward from the semiconductor laser l is detected by a photodetector 9.
The light intensity is detected by the control circuit 10, which controls the semiconductor laser drive circuit 8 in accordance with the output signal from the photodetector 9 to keep the output light amount of the semiconductor laser 1 constant.

FIG. 9 shows the semiconductor laser drive circuit 8 and the control circuit 10.
is shown in detail.

A laser beam emitted backward from the semiconductor laser 1 is incident on a photodetector 9 made of a photodiode, and the photodiode 9 outputs a current proportional to the intensity of the laser beam. This current is converted into a voltage by an amplifier 11, and a reference voltage 1. ．． compared to The output voltage of the comparator 12 becomes a high level or a low level depending on the magnitude relationship between both input voltages of the comparator 12, and controls the counting mode of the up/down counter 13. For example, when the intensity of the laser beam from the semiconductor laser 1 is weaker than the reference value, the output of the comparator 12 becomes a low level, and the up/down counter 13 enters a state in which it operates as an up counter. When the edge detection circuit 14 releases the enable signal to the up-down counter 13 in response to the timing signal T1, the up-down counter 13 increases its count value in response to the clock signal from the oscillator 15. The output is converted into an analog quantity by the digital/analog converter 16 and input to the semiconductor laser drive circuit 8. The semiconductor laser drive circuit 8 drives the semiconductor laser 1 based on the information signal from the signal processing circuit 7, and changes its drive current in accordance with the output of the digital/analog converter 16. Therefore up/down counter 1
As the count value of 3 gradually increases, the semiconductor laser 1
The intensity of the laser beam from the amplifier 11 increases gradually.
increase the output of When the output of the comparator δ12 is inverted from low level to high level, the edge detection circuit 14 detects the rising edge of the output of the comparator 12 and applies an enable signal to the up/down counter 13. Therefore, the up/down counter 13 is enabled and holds its count value, so that the magnitude of the driving current of the semiconductor laser I is maintained as it is. Next, when the edge detection circuit 14 releases the enable state of the up/down counter 13 by the timing signal T, if the output of the comparator 12 is at a high level (if the output intensity of the semiconductor laser 1 is strong), the up/down force is increased. 13 operates as a down counter, and the count value decreases by the clock signal from the oscillator 15. Therefore, the output of the digital/analog converter 16 decreases, and the driving current of the semiconductor laser 1 decreases.
output decreases. Then, the output of the amplifier 11 is set to the reference voltage V1. ．． When the output of the comparator 12 becomes smaller and the output of the comparator 12 is inverted from high level to low level, the edge detection circuit 14 detects the falling edge of the output of the comparator 12 and enables the up/down counter 13. Therefore, the up/down counter 13 holds the count value, and the magnitude of the driving current of the semiconductor laser 1 is maintained as it is. Here, in a laser printer, the environmental temperature changes slowly, and the output fluctuations of the semiconductor laser can be ignored in a short period of time due to the heat capacity of the semiconductor laser and its mounting hardware.

For this reason, by using, for example, a print start signal at each start of recording or a power-on reset signal at power-on as the timing signal T+, it is possible to suppress fluctuations in the output light amount of the semiconductor laser and obtain high-quality recorded images. .

Incidentally, in addition to fluctuations in optical output due to ambient temperature as described above, semiconductor lasers often have problems with fluctuations in optical output due to self-heating, and as in the conventional example, the output of the photodetector 9 is monitored. Even if the drive current is controlled for each optical scan so that a predetermined output is obtained, the optical output fluctuates as shown by the solid line in the characteristic diagram of FIG. This appears as non-uniform density.

In order to reduce fluctuations in optical output due to self-heating of the semiconductor laser, as disclosed in JP-A-61-191083, a current of a predetermined value smaller than the threshold current is used as a bias current even when the semiconductor laser is turned off. A possible method is to promote self-heat generation by applying a voltage to the light, thereby reducing the amount of self-heat generated during lighting, thereby reducing the difference caused by blinking.

FIG. 11 is a circuit diagram showing one embodiment of the invention, and when the light is turned off, the transistor 17 causes a bias flow! .

is applied, and at the time of lighting, the bias current (8) and the current (11) of the semiconductor laser drive circuit 8 are changed to the drive current (2) of the semiconductor laser 1.

, and is applied. Further, in the figure, the same components as those in the circuit of FIG. 9 are given the same reference numerals, and the explanation thereof will be omitted. In the figure, 18 is a variable resistor for adjusting the bias current I8, and 19 is a limiting resistor for determining the upper limit of the bias current and preventing damage to the semiconductor laser due to overcurrent.

-S is the threshold voltage for the drive current TOP at the rated output of the semiconductor laser? The ratio of 1tTtb is I th/I
Since or=about 2/3, if the bias current 8 is approximately equal to the threshold current 1, the self-heating amount W8 due to the bias current 111 when the lights are turned off is equal to the drive current at the rated output. T. , about 2/ of the self-heating amount V7 op
It becomes 3. In other words, the amount of variation in optical output due to self-heating when lighting at rated output is bias current I.

Compared to not flowing! /3, and the optical output fluctuates as shown by the broken line in FIG.

However, there are variations in the luminous efficiency of semiconductor lasers, and as mentioned above, there are variations due to ambient temperature and self-heating. The threshold current is set to a safe value that does not exceed 0. On the other hand, in order to reduce fluctuations in optical output due to self-heating when the semiconductor laser is turned on, which is the objective of this device, the bias current is 1. It is better to make the value of the threshold current I closer to the threshold current I, and the effect of the device shown in FIG. 11 cannot be said to be sufficient.

(Purpose) The present invention was made to improve the above-mentioned drawbacks of the conventional device.The purpose of the present invention is to automatically adjust the value of the bias current in order to reduce fluctuations in the amount of light due to self-heating when the semiconductor laser is turned on. Is it possible to set the laser output side to an effective and efficient value and obtain an image with uniform density? a) to provide a device.

(Structure) In order to achieve the above object, the present invention includes a photodetection means for detecting the optical output of a semiconductor laser, and a laser output control that controls the driving current of the semiconductor laser according to the output of the photodetection means. In the apparatus, bias current control means monitors the output of the light detection means to detect a threshold current value of the semiconductor laser and applies a current smaller than the threshold current to the semiconductor laser; The present invention is characterized by comprising a drive current control means for monitoring the output of the detection means and controlling the drive current so that the optical output of the semiconductor laser becomes a predetermined value.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

FIG. 1 is a block circuit diagram showing an embodiment of a laser output control device according to the present invention for applying a bias current more effectively. This circuit includes a semiconductor laser l, a photodetector 9, a negative output circuit 21 for detecting the threshold current value of the semiconductor laser 1, a bias current application circuit 20, a bias current control means 22, a detection circuit 24, and a drive circuit 23. and drive current control means 25. The detection circuit 21 outputs a signal for adjusting the current applied to the semiconductor laser 1 in accordance with the output of the photodetector 9 which receives the optical output of the semiconductor laser 1 and detects the light intensity. A bias current control means 22 consisting of a bias current application circuit 20 applies a bias to the semiconductor laser 1 according to the output of the detection circuit 21. The detection circuit 24 outputs a signal for adjusting the current applied to the semiconductor laser 1 in accordance with the output of the photodetector 9, and detects whether the output of the semiconductor laser 1 is a predetermined value. Drive '71. consisting of drive circuit 23.
The current controller 5 applies a drive current to the semiconductor laser 1 according to the output of the detection circuit 24.

The operation of the embodiment will be described with reference to the na+ circuit shown in FIG. This circuit consists of an amplifier 26, comparators 27 and 28
, a D flip-flop (F/F) 29°30, a NOR circuit 31, and a J- flip-flop (F/F) 32.
A detection circuit, bias current control means constituted by a bias current application circuit consisting of an up/down counter 33, a digital/analog (D/A) converter 34, an amplifier 35, 36, and a transistor 37, and comparators 39, 40, and D. It consists of a detection circuit consisting of flip-flops 41, 42, a NOR circuit 43 and a JK flip-flop 44, and a drive current control means consisting of an up/down counter 46, a D/A converter 47, amplifiers 48, 49 and a transistor 50.

In such a circuit, up/down counter 33.
When the signal PR for initializing the value of 46 is input,
The up/down counters 33 and 46 are set to predetermined values, for example, the maximum value of the counters. As a result, the maximum value is input to the D/A converter 34.47, the maximum value limited by the variable resistor 38.45 that limits the maximum output value is output, and the maximum value is output to the amplifiers 35.36 and 48.47. j9 applies an inverted voltage signal to the base of transistor 37.50. That is, the lowest voltage level signal is applied. Note that variable resistors 51 and 52 connected to amplifiers 36 and 49 are transistors 37 and 52, respectively. '
The upper limit value of the voltage signal applied to the voltage signal 50 is regulated. In this manner, the bias current I flowing through the transistor 37 is set to the minimum value by the PR signal, and the drive current I flowing through the transistor 50 is set to the minimum value. Note that the minimum value of the bias current (2) here does not necessarily have to be zero, but may be a value sufficiently smaller than the previously assumed threshold current of the semiconductor laser. Similarly, the drive current 11 flowing through the transistor 50
is not necessarily zero, and the bias current 1. The sum of the drive current ■1 and the output of the semiconductor laser described later should be a predetermined value ←Current value ■. Note that at this point, the modulation signal video of the semiconductor laser 1 is at a low level, so the differential transistor 53 is off, and the drive current ! + flows from the transistor 54, so the current I of the semiconductor laser 1. P is 1op” Ibuki.

Next, bias current 1. Signals B and S for setting
When ET is input, the J- flip-flop 32 is cleared and the up/down counter 33 is enabled from the Q output terminal. The output signal of the comparator 28 is latched by the D flip-flop 29 using the clock signal CLK.
The output signal of the D flip-flop 29 is applied to the up/down counter 33 as a counting mode signal to control its counting mode, and at the same time is latched by the D flip-flop 30 using the clock CLK. The non-inverted output Q of the D flip-flop 29 and the inverted output of the D flip-flop 30 are input to a NOR circuit 31, and the output signal of the NOR circuit 31 sets the flip-flop 32 to J-. Since the output of the comparator 28 is now at a low level (there is no optical output from the semiconductor laser I), the up/down counter 33 operates as a down counter. As a result, D/
The output of the A converter 34 decreases and thus increases the base voltage signal of the transistor 37, which causes the bias current I of the semiconductor laser 1 to increase and produce an optical output when a threshold is reached. semiconductor laser l
When more light output is generated, the photodetector 9 receives this light and generates an output according to the light intensity. This causes comparator 27 to detect the occurrence of a light output and invert and therefore go high.

The D flip-flop 29 uses this high level as the clock CL.
Latch with K and up/down counter 33 with Q output
Switch to up-count operation. This in turn causes the base voltage signal of transistor 37 to decrease and therefore become less than the threshold because the bias current decreases. When the output of the comparator 28 becomes low level again, it is latched by the D flip-flop 29 using the clock CLK, and the Q output is made high level. At this time, the D flip-flop 30 uses the high level output of the D flip-flop 29 in the previous stage as the clock (LK), so the inputs of the NOR circuit 31 both become low level, and the high level of the output changes to J. − is input to the flip-flop 32, latched by the clock CLK, and output to the up/down counter 33.
Disable. As a result, the counting operation ends and the bias current is fixed. In this way, the bias current is lower than the threshold voltage at the D/A converter.
It will be fixed at a value smaller by the bit resolution.

Next, in order to set the optical output of the semiconductor laser 1 to a predetermined value, the Video signal is first set to a high level, and the semiconductor laser 1
Assuming that the current 10F flowing through the transistor 37 is the sum of the bias current (3) flowing through the transistor 37 and the drive current (2) flowing through the transistor 50, the CL of the flip-flop 44 is connected to J-.
By inputting the P, SET signal (low level) to the K terminal, the flip-flop 44 at J- is cleared and the up/down counter 46 is enabled. The output signal of the comparator 40 is latched by the clock CLK in a D flip-flop 41, and the output signal of this D flip-flop 41 is applied as a counting mode signal to the up/down counter 46 to control its counting mode, and at the same time, the D flip-flop 42 It is latched by the clock CLK.

The inverted outputs of the D flip-flops 41 and 42 are input to the NOR circuit 43, and the output signal of the NOR circuit 43 causes the J
The flip-flop 44 is set to -. If the output of the comparator 40 is now at a low level (the optical output of the semiconductor laser 1 is smaller than a predetermined value), the up/down counter 4
6 operates as a down counter. Therefore, D/
The output of A converter 47 is decreasing, and therefore the base signal of transistor 50 is increasing. As a result, the drive current 1 of the semiconductor laser 1 increases, and when the optical output reaches a predetermined value, the comparator 40 is inverted and becomes a high level. D flip-flop 41 uses this high level as clock C
Latch with LK and use Q output to create up/down counter 4
6 to up count operation. This in turn causes the base voltage signal of transistor 50 to decrease, thus reducing its drive current and thus its light output to be less than a predetermined level. As a result, the output of the comparator 40 is again inverted to a low level, which is latched by the D flip-flop 41 using the clock CLK, thereby setting the Q output to a high level.

At this time, the D flip-flop 42 outputs the high level output from the previous stage D flip-flop 41 to the same clock CL.
Since it is latched at K, the inputs of the NOR circuit 43 are both at low level, and the high level output is input to the flip-flop 44 at J-, which is latched at clock CLK and disables the up/down counter 46. As a result, the counting operation ends and the drive current it is fixed.The current I flows through the semiconductor laser 1 due to one or more.

P is bias current I, and drive current! , and is fixed at a value such that the optical output becomes a predetermined value.

After that, when resetting the bias current, apply the B, SET signal to the flip-flop 32 at J-, and apply the P, SET signal to the J- flip-flop 44 with the Video signal at high level when resetting the drive current. It can be reset by giving

As described above, the bias current Im can maintain the relationship of r*<I, which is close to the threshold current, by giving reset No. 43 as necessary, and the drive current 1
0F is also controlled so that the optical output becomes a predetermined value.

The variable resistor 55 connected to the amplifier 27 is used to cancel the dark current level of the photodetector 9, and the variable resistor 56 connected to the amplifier 39 is used to adjust the optical output to a predetermined value. This is for setting.

FIG. 3 is a circuit diagram showing an embodiment that is a modification of the circuit shown in FIG. 2, in which the same parts as those in FIG. 2 are given the same reference numerals and detailed explanations are omitted. In FIG. 3, by inputting the signal B and SET for setting the bias current Im, the output of the NOR circuit 31 becomes high level after the operation described in FIG. 2. This is connected to J- by flip-flop 32 and clock C
It is latched by LK and the up/down counter 33 is disabled. With this bias current II fixed, the amplifier 36 is opened by opening the switch 57 by the output signal of the flip-flop 32 at J-.
The base voltage signal of the transistor 37 is switched to Rr/R++Rz by reducing the gain of the transistor 37. According to this, for example, when the cycle of resetting the bias current is long, and when there is a possibility that the bias current exceeds the threshold current due to temperature fluctuations, etc., It becomes possible to set the bias current at a constant rate with safety in mind.

Next, an embodiment of a laser scanning device using the laser driving device shown in the embodiment of FIG. 3 will be described with reference to FIG. 4. Referring to FIGS. 1, 3, and 4, first,
When the power is turned on, a signal PR for initializing the bias current I and the drive current I is sent from the signal processing circuit 7 to the control circuit 21 of the bias current control means 22 and the control circuit 24 of the drive current control means 25. As a result, as described above, the up/down counters 33 and 46 are set to initial values, for example, the maximum value, and the up/down counters 33.4
6, the D/A converter 3447 outputs the maximum value set by the variable resistor 38.45. As a result, the base voltage signal of the transistor 370 is set so that the bias current flowing to the semiconductor laser 1 via the transistor 37 has a value sufficiently smaller than the threshold current level of the semiconductor laser 1.

Further, the base voltage signal of the transistor 50 is a bias current I flowing through the transistor 37.

The bias current 8 and V flowing through the semiconductor laser 1 through the transistor 37 are set to a predetermined value smaller than the threshold current level of the semiconductor laser 1. When the 1deo signal is set to a high level, the transistors 53 and 50 The sum of the driving current (1) flowing through the semiconductor laser 1 via the drive current (1). P
The setting is such that when the light output from the rotary polygon mirror 3 is scanned by the scanning means made up of the rotating polygon mirror 3, it can be detected by the scanning light detection means made up of the photodetector 9. In addition, in the initial state, V
Since the ideo signal is at a low level, the drive current (1) flows through the transistors 54 and 50, and the semiconductor laser 1 receives a bias current (2). only flows.

Next, when signals B and SET for setting the bias current are sent from the signal processing circuit 7, the threshold current level of the semiconductor laser 1 is detected by the above-described operation, and the Q output of the flip-flop 32 is sent to J-. The bias current is 1. At the same time, the switch 57 is opened and the bias current! .

is fixed at a predetermined value smaller than the threshold current of the semiconductor laser l. Note that the value of the bias current (2) at this time is set at a value within the range of 80 to 90 It may be about %.

When the bias current I3 is set, the signal processing circuit 7 inputs a bias set completion signal to, for example, J- from the Q output of the flip-flop 32, and then sets the V1deo signal to high level to turn on the transistor 53. By turning off the transistor 54, the I transistor 5
Drive current to the semiconductor laser 1 via 3 and 50! Apply 1. As a result, the semiconductor laser 1 has a bias current of 1
l which is the sum of m and drive current 11; P is applied. As a result, the semiconductor laser 1 generates a light output of a predetermined level that allows its scanning light to be detected by the photodetector 9, as described above. The signal processing circuit 7 receives a detection signal BD from the photodetector 9.
When input, a signal P, SET for setting the drive current I is sent to the control circuit 24 of the drive current control means at a predetermined timing.

As a result, the drive current (1) is the sum of the bias current (1) and the bias current (I), as described above. The optical output by P is adjusted to a predetermined level, and when it reaches the predetermined level, the adjustment operation is completed and fixed to J- by the Q output of the flip-flop 44. As a result, the signal processing circuit 7 inputs a power set completion signal to, for example, J- from the Q output of the flip-flop 44, and knows that the setting of the drive current is completed. As a result, it is determined that image data can be scanned, the video signal is set to a low level, a signal is output to a peripheral device, and image data is scanned using an information signal such as an image scan start signal. At the same time, signals P and SET for setting the drive current II are outputted at predetermined timing based on the detection signal of the photodetector 9, and therefore the drive current control means sets the drive current II for each double scan. I will do it.

According to this, the ratio of the period required for scanning image data (scanning period ratio) to one scanning period (scanning period of one surface) by the scanning means consisting of the rotating polygon mirror 3 is high, and the semiconductor laser is driven for each scanning period. The timing chart in FIG. 5 shows the operation of 0 or more, which allows the drive current to be set to generate stable optical output even in a scanning device where the period allowed for setting the current is short. In the figure, α indicates the degree of threshold current level, and as mentioned above, 80 to 90%
It is.

In addition, if the ratio of the period required for scanning image data to one scanning period (scanning period ratio) is low and the period allowed for setting the semiconductor laser drive current for each scanning period is relatively long, the photodetector Based on the detection signal 9, signals B and SET for bias current setting and signals P and SET for drive current setting are sequentially sent from the signal processing circuit 7 at a predetermined timing for each double scan. In this case, it is possible to set the bias current and drive current close to the threshold current level. Therefore, the bias current and drive current can be controlled more effectively, and the self-heating during lighting of the target semiconductor laser 1 can be further reduced.

A timing chart of this operation is shown in FIG.

Incidentally, in a semiconductor laser having a plurality of light emitting parts in one package, there is mutual thermal interference due to the influence of self-heating by each light emitting element, and the effect of bias current becomes even more severe. Further, even in such a semiconductor laser having a plurality of light emitting parts, there is often only one photodetector 9 for detecting its optical output. In this case, for example, in a semiconductor laser having four light emitting parts, as shown in the timing chart of FIG. It is necessary to time-divisionally control the drive current of each light emitting section, and the period allowed for drive current control of each light emitting section becomes shorter. 1 is fixed at a predetermined level and only the drive current II is set for each scan.

According to the embodiment described above, the bias current is set to a safe value that does not exceed the threshold current, taking into account the variations in the luminous efficiency of the semiconductor laser and therefore the variations in the threshold current level. Compared to conventional devices, the bias current can be brought closer to the threshold current, increasing the bias current and making such devices even more effective.

(Effects) As described above, according to the present invention recited in each of the claims, in a device that scans a semiconductor laser beam to form an image, fluctuations in light amount due to self-heating when the semiconductor laser is turned on can be avoided. By automatically and efficiently controlling the bias current value to a value closer to the threshold current value, the latent image potential on the photoreceptor due to light output fluctuations can be reduced. It is possible to provide a laser output control device that can reduce changes in .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the laser output side 'a device according to the present invention, FIG. 2 is a circuit diagram showing details of the device in FIG. 1, and FIG. 3 is a laser output control according to the present invention. A circuit diagram similar to FIG. 2 showing a modified embodiment of the device, FIG. 4 a block diagram showing a laser scanning device used in the laser output control device according to the present invention, FIGS. 5, 6, and 7. is a timing chart showing the operation of the laser output control device according to the present invention, FIG. 8 is a block diagram showing the conventional semiconductor laser output control device, and FIG. 9 is a timing chart showing the operation of the conventional semiconductor laser output control device of FIG. FIG. 10 is a block diagram showing the control circuit, FIG. 10 is a characteristic diagram showing the amount of variation in optical output, and FIG. 11 is a block diagram showing another example of conventional WnK. 1... Semiconductor laser, 3... Rotating polygon mirror, 5...
Photosensitive drum, 7... Signal processing circuit, 8... Laser drive circuit, 9... Photodetector, 20... Application circuit, 2
1... Detection circuit, 22... Bias current control means,
23... Drive circuit, 24... Detection circuit, 25...
Drive current; νIiB means. Figure 4 Figure 7 P, SEr, 4

Claims (7)

[Claims] (1) In a laser output control device that has a photodetection means for detecting the optical output of a semiconductor laser and controls a driving current of the semiconductor laser according to the output of the photodetection means, the output of the photodetection means is monitored. bias current control means for detecting a threshold current value of the semiconductor laser and applying a current smaller than the threshold current to the semiconductor laser; and a bias current control means for monitoring the output of the photodetection means to 1. A laser output control device comprising: drive current control means for controlling a drive current so that the optical output of the laser becomes a predetermined value. (2) The device according to claim 1, comprising a scanning means for scanning the light of the semiconductor laser, and a scanning light detection means for detecting the scanning light by the scanning means. Laser output control device. (3) In a laser output control device that includes a photodetection means for detecting the optical output of a semiconductor laser and controls a drive current of the semiconductor laser according to the output of the photodetection means, the output of the photodetection means is monitored. to detect the value of the threshold current of the semiconductor laser, and to supply a current to the semiconductor laser at a constant rate with respect to the threshold current, which does not exceed the threshold current even when the power supply and temperature change. and drive current control means that monitors the output of the photodetector and controls the drive current so that the optical output of the semiconductor laser becomes a predetermined value. Laser output control device. (4) The laser according to claim 3, characterized in that the laser comprises a scanning means for scanning the light of the semiconductor laser, and a scanning light detection means for detecting the scanning light by the scanning means. Output control device. (5) A laser driving device that includes a photodetection means for detecting the light output of a semiconductor laser and controls a driving current of the semiconductor laser according to the output of the photodetection means, and a scanning device that scans the light of the semiconductor laser. and a laser scanning device having a scanning light detecting means for detecting the scanning light by the scanning means, wherein the laser driving device monitors the output of the light detecting means and controls the output of the semiconductor laser. bias current control means for detecting the value of a threshold current and applying a current smaller than the threshold current to the semiconductor laser; and monitoring the output of the photodetection means to adjust the optical output of the semiconductor laser to a predetermined level. During standby, only the bias current is set based on the detection signal of the scanning light detection means by optical scanning, and the optical scanning for image formation is performed. A laser output control device characterized in that during the period, only the drive current is set based on the detection signal of the scanning light detection means. (6) A laser drive device that includes a photodetector that detects the light output of a semiconductor laser and controls a drive current of the semiconductor laser according to the output of the photodetector, and a scanning device that scans the light of the semiconductor laser. and a laser scanning device having a scanning light detection means for detecting the scanning light by the scanning means, wherein the laser driving device starts a control operation based on an input signal, and the laser driving device starts a control operation based on an input signal, and bias current control means that monitors the output of the means to detect a threshold current value of the semiconductor laser, applies a current smaller than the threshold current to the semiconductor laser, and outputs a bias set completion signal; means for applying a current to the semiconductor laser such that the scanning light of the scanning means has a first predetermined value of light output detectable by the scanning light detection means based on the bias set completion signal; drive current control means for monitoring the output of the light detection means based on the scanning light detection signal from the light detection means and controlling the applied current so that the optical output of the semiconductor laser becomes a predetermined value; Characteristic laser output control device. (7) In a laser output control device that has a photodetection means for detecting the light output of a semiconductor laser and controls a driving current of the semiconductor laser according to the output of the photodetection means, the laser drive device bias current control means for monitoring the output of the light detection means to detect the level of a threshold current of the semiconductor laser and applying a current smaller than the threshold current to the semiconductor laser; A laser comprising a driving current control means for controlling an applied current so that the optical output is at a predetermined level, and sequentially setting a bias current and a driving current based on a detection signal of the scanning light detecting means. Output control device.