JP3703270B2 - Laser drive device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser driving device in an image forming apparatus.
[0002]
[Prior art]
In the laser driving device in the image forming apparatus, in order to set the laser light quantity to a predetermined value, the fluctuation amount of the light quantity monitor current output from the photo diode that monitors the light quantity of the laser diode is detected, and the current for correcting the fluctuation quantity Is the laser diode drive current.
[0003]
By the way, there is an upper limit to the current supplied to the laser diode, and if it exceeds this, the laser diode will be destroyed. In order to prevent this, conventionally, an upper limit value is set for the current to be supplied, and no more current is supplied to the laser diode by the current limiter.
[0004]
[Problems to be solved by the invention]
However, in the conventional example described above, the set value of the current limiter is a fixed value in the laser diodes of different types, although the upper limit values thereof are different. Laser diodes that are near the end of their life require more current to obtain the same amount of light compared to new laser diodes. Therefore, depending on the set value of the current limiter, a sufficient amount of light cannot be obtained from the laser diode that is near the lifetime.
[0005]
Therefore, the present invention provides a laser drive device in which the drive current limit value of a laser diode can be set for each individual laser diode in consideration of aging, and the drive current limit value of the laser diode does not suddenly increase. The purpose is to do.
[0006]
In addition, the present invention monitors the laser diode drive current and varies the set value of the current limiter sequentially from that value, so that the current to the laser diode is applied only when a sharp rise in the laser diode drive current occurs. An object of the present invention is to provide a laser driving device that cuts off the supply of the laser beam.
[0007]
Furthermore, the present invention monitors the laser diode drive current and varies the set value of the current limiter sequentially from that value to supply the laser diode to the laser diode only when a sharp rise in the laser diode drive current occurs. It is an object of the present invention to provide a laser driving device that suppresses a value to be equal to or less than a set value of a current limiter.
[0008]
Furthermore, the present invention monitors the laser diode drive current and varies the set value of the current limiter sequentially from that value, so that the laser diode emits light only when a sharp rise in the laser diode drive current occurs. It is an object of the present invention to provide a laser drive control method that forcibly stops.
[0009]
Furthermore, the present invention monitors the laser diode drive current and varies the set value of the current limiter sequentially from that value, so that only when the laser diode drive current rises sharply, the laser diode drive current An object of the present invention is to provide a laser drive control method that removes high frequency noise components.
[0010]
[Means for Solving the Problems]
A laser drive device according to the present invention includes a laser device including a laser diode and a photodiode that monitors a light amount of the laser diode and outputs the light amount as a light amount monitor current, and current-voltage conversion that converts the light amount monitor current into a voltage signal Means, a reference voltage generating means for generating an arbitrary voltage as a comparison reference, a comparing means for comparing output signals of the current-voltage converting means and the reference voltage generating means, and an output of the comparing means being sampled First signal holding means for sampling and holding based on the hold control signal to output a sample signal, current generating means for generating a current corresponding to the voltage level of the sample signal, and output current of the current generating means Modulation means for modulating a modulated current based on an external video signal and outputting a modulated current, and the laser die by the modulated current In a laser driving device for driving a mode, when the output current exceeds a limit value, a control means for controlling the modulation current, and an update means for updating the limit value according to the level of the new sample signal with the door, when the output current is determined to exceed the limit value immediately before the update by said control means, it means ceases the updating operation of the limit value by the updating means.
[0011]
In the laser driving apparatus according to the present invention, the control means is means for cutting off supply of the output current to the modulation means.
[0012]
Alternatively, in the laser driving apparatus according to the present invention, the control means is means for absorbing an excess of the output current with respect to the limit value .
[0013]
Alternatively, the laser driving apparatus according to the present invention is characterized in that the control means is means for cutting off supply of the external video signal to the modulation means.
[0014]
Alternatively, in the laser driving apparatus according to the present invention, the control means is means for reducing a high-frequency component of the output current supplied to the modulation means.
[0015]
Furthermore, in the laser driving apparatus according to the present invention, the updating means further includes a second signal holding means for further sampling and holding the new sample signal, and amplifying the output of the second signal holding means to output the output. And amplifying means for setting a limit value.
[0016]
Further, in the laser driving apparatus according to the present invention, the updating means further includes an output current limit setting means for setting a limit value of the output current, and a weighting between the output of the output current limit setting means and the output of the amplification means. Weighted average calculating means for setting the average to the predetermined value .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 is a block diagram for explaining a laser driving apparatus according to Embodiment 1 of the present invention.
[0018]
A semiconductor laser 1 includes a laser diode that emits laser light and a photo diode that monitors the light emission level. The photo diode outputs a current corresponding to the light emission amount of the laser diode, and the current is converted into a voltage in the IV conversion circuit 2. The voltage-converted signal is compared with the output voltage value of the reference voltage generation circuit 3 by the comparator 4.
[0019]
Reference numeral 6 denotes a sample & hold circuit which repeats the sample mode and the hold mode with an arbitrary period. In the sample mode, the capacitance of the hold capacitor 7 is charged when the output voltage value of the IV conversion circuit 2 is smaller than the output voltage value of the reference voltage generation circuit 3, and is discharged when the output voltage value is larger. Thus, the amount of light emitted from the semiconductor laser 1 is kept constant by controlling the laser drive current 9 supplied from the constant current circuit 8 to the semiconductor laser 1.
[0020]
The modulation control circuit 10 performs ON / OFF control of the semiconductor laser 1 by switching according to the video (/ VDO) signal 11 while maintaining an arbitrarily set laser diode drive current value in the hold mode.
[0021]
The variable threshold current limiter 11 is inserted between the constant current circuit 8 and the modulation control circuit 10 to detect a constant current output signal 21 that is a voltage proportional to the laser drive current 9, and to set a limit setting reference signal that is a timing reference. 22, the laser drive current 9 is cut off when an overcurrent occurs.
[0022]
FIG. 2 is a timing chart showing the operating principle of the variable threshold current limiter 20.
[0023]
The drive current limit value is the maximum current value that can be passed to the laser, and if this value is exceeded, the laser will be destroyed. The laser drive current 9 represented by the constant current output signal 21 is a drive current of the semiconductor laser 1 and fluctuates at the timing of the sample & hold control signal 5.
[0024]
On the other hand, the variable current limit signal 30 varies the limit value corresponding to the laser drive current 9, and the variable timing is, for example, the limit value setting signal 25 output immediately after the sample mode of the sample & hold control signal 5. Determined by.
[0025]
The overcurrent generation flag 33 is output when the laser drive current 9 exceeds the variable current limit signal 30. In FIG. 2, when an overcurrent that exceeds the variable current limit signal 30 is generated in the laser drive current 9 as indicated by a broken line, an overcurrent generation flag 33 is output to cut off the laser drive current 9. Further, when the overcurrent generation flag 33 is output, the output of the limit value setting signal 25 is stopped and the variable current limit signal 30 is not updated.
[0026]
FIG. 3 is a block diagram showing details of the threshold variable current limiter 20.
[0027]
The constant current output signal 21 output from the constant current circuit 8 is input to the limit value sample & hold circuit 23. The limit value control circuit 24 generates a limit value setting signal 25 based on the limit setting reference signal 22. In the constant current output signal 21, the voltage of the limit value hold capacitor 26 charged by the limit value setting signal 25 is amplified to an arbitrary value by the mitt value amplifier 27. A variable limit signal 30 is generated by a variable current limit signal setting circuit 29 inserted between the output of the limit value amplifier 27 and the current limit value setting circuit 28. The variable limit signal 30 is obtained, for example, by the variable limit setting circuit 29 configured by resistance division at the voltage dividing ratio between the output value of the current limit value setting circuit 28 and the output of the limit value amplifier 27. As a result, the constant current output signal 21 The corresponding variable current limit signal 30 is obtained.
[0028]
The limit comparator 31 compares the constant current output signal 21 and the variable current limit signal 30. When the constant current output signal 21 exceeds the variable current limit signal 30 due to overcurrent, an overcurrent generation flag 33 is output. . At this time, the cut-off transistor 32 is inserted between the modulation control circuit 10 and the constant current circuit 8, and when the overcurrent generation flag 33 is output, the cut-off transistor 32 is turned off and the laser diode drive current is cut off. At the same time, the overcurrent generation flag 33 stops the output of the limit value setting signal 25 in the limit value control circuit 24 and stops updating the variable current limit signal 30.
[0029]
[Embodiment 2]
FIG. 4 is a block diagram for explaining a laser driving apparatus according to the second embodiment of the present invention. The limit value variable type current clipper 35 detects the constant current output signal 21 and, based on the limit setting reference signal 22, cuts off the laser drive current 9 and absorbs the overcurrent.
[0030]
FIG. 5 is a timing chart showing the operating principle of the limit value variable current clipper 35.
[0031]
The drive current limit value is the maximum current value that can be passed to the laser, and if this is exceeded, the laser will be destroyed. The laser drive current 9 represented by the constant current output signal 21 is a drive current of the semiconductor laser 1 and fluctuates at the timing of the sample & hold control signal 5.
[0032]
On the other hand, the variable current limit signal 30 varies the limit value corresponding to the laser drive current 9, and the variable timing is, for example, the limit value setting signal 25 output immediately after the sample mode of the sample & hold control signal 5. Determined by.
[0033]
The overcurrent generation flag 33 is output when the laser drive current 9 exceeds the variable current limit signal 30. In FIG. 3, when an overcurrent that exceeds the variable current limit signal 30 occurs as shown by a broken line in the laser drive current 9, only the overcurrent is absorbed from the laser drive current 9, and the semiconductor laser 1 is Is controlled so that the laser drive current 9 greater than or equal to the variable current limit signal 30 is not supplied. Further, when an overcurrent occurs, the overcurrent generation flag 33 is output, the output of the limit value setting signal 25 is stopped, and the variable current limit signal 30 is not updated.
[0034]
FIG. 6 is a block diagram showing details of the limit value variable current clipper 35.
[0035]
The constant current output signal 21 output from the constant current circuit 8 is input to the limit value sample & hold circuit 23. The limit value control circuit 24 generates a limit value setting signal 25 based on the limit setting reference signal 22 that is a timing reference. In the constant current output signal 21, the voltage of the limit value hold capacitor 26 charged by the limit value setting signal 25 is amplified to an arbitrary value by the mitt value amplifier 27. A variable current limit signal 30 is generated by a variable current limit signal setting circuit 29 inserted between the output of the limit value amplifier 27 and the current limit value setting circuit 28. The variable limit signal 30 is obtained, for example, by a variable current limit signal setting circuit 29 configured by resistance division at a voltage dividing ratio between the output value of the current limit value setting circuit 28 and the output of the limit value amplifier 27. As a result, the constant current output signal The variable current limit signal 30 corresponding to 21 is obtained.
[0036]
The limit comparator 31 compares the constant current output signal 21 and the variable current limit signal 30. When the constant current output signal 21 exceeds the variable current limit signal 30 due to overcurrent, an overcurrent generation flag 33 is output. . Reference numeral 36 denotes a clip circuit, which is composed of, for example, a transistor, a diode, and a buffer amplifier. When the overcurrent generation flag 33 is output, the clip circuit 36 is operated to cut off the laser drive current 9 and simultaneously absorb the amount up to the variable current limit signal 30.
[0037]
When the overcurrent generation flag 33 is output, the limit value control circuit 24 stops outputting the limit value setting signal 25 and stops updating the variable current limit signal 30.
[0038]
[Embodiment 3]
FIG. 7 is a block diagram for explaining a laser driving apparatus according to Embodiment 3 of the present invention. The limit value variable modulation data control circuit 40 detects the constant current output signal 21 indicating the current amount of the laser drive current 9, and / VDO when an overcurrent occurs based on the limit setting reference signal 22 that is a timing reference. The signal 11 is controlled to forcibly turn off the semiconductor laser 1.
[0039]
FIG. 8 is a timing chart showing the operating principle of the limit value variable modulation data control circuit 40.
[0040]
The drive current limit value is the maximum current value that can be passed to the laser, and if this is exceeded, the laser will be destroyed. The laser drive current 9 represented by the constant current output signal 21 is a drive current of the semiconductor laser 1 and fluctuates at the timing of the sample & hold control signal 5.
[0041]
On the other hand, the variable current limit signal 30 varies the limit value corresponding to the laser drive current 9, and the variable timing is, for example, the limit value setting signal 25 output immediately after the sample mode of the sample & hold control signal 5. Determined by.
[0042]
The overcurrent generation flag 33 is output when the laser drive current 9 exceeds the variable current limit signal 30. In FIG. 3, when an overcurrent that exceeds the variable current limit signal 30 is generated in the laser drive current 9 as indicated by a broken line, an overcurrent generation flag 33 is output. The / VDO control signal 41 is a data signal that forcibly turns off the semiconductor laser 1 when the overcurrent generation flag 33 is output based on the / VDO signal 11. Further, when the overcurrent generation flag 33 is output, the output of the limit value setting signal 25 is stopped and the variable current limit signal 30 is not updated.
[0043]
FIG. 9 is a block diagram showing details of the limit value variable modulation data control circuit 40.
[0044]
The constant current output signal 21 output from the constant current circuit 8 is input to the limit value sample & hold circuit 23. The limit value control circuit 24 generates a limit value setting signal 25 based on the limit setting reference signal 22 that is a timing reference. In the constant current output signal 21, the voltage of the limit value hold capacitor 26 charged by the limit value setting signal 25 is amplified to an arbitrary value by the mitt value amplifier 27. A variable current limit signal 30 is generated by a variable current limit signal setting circuit 29 inserted between the output of the limit value amplifier 27 and the current limit value setting circuit 28. The variable current limit signal setting circuit 29 is configured such that the variable current limit signal 30 is a variable current limit signal setting circuit 29 configured by, for example, resistance division, and a voltage dividing ratio between the output value of the current limit value setting circuit 28 and the output of the limit value amplifier 27. As a result, a variable current limit signal 30 corresponding to the constant current output signal 21 is obtained.
[0045]
In the limit comparator 31, the constant current output signal 21 and the variable current limit signal 30 are compared, and when the variable current limit signal 30 is exceeded due to an overcurrent, an overcurrent generation flag 33 is output. A modulation data control circuit 42 generates a / VDO control signal 41 that forcibly turns off the / VDO signal 11 when the overcurrent generation flag 33 is output.
[0046]
When the overcurrent generation flag 33 is output, the limit value control circuit 24 stops outputting the limit value setting signal 25 and stops updating the variable current limit signal 30.
[0047]
[Embodiment 4]
FIG. 10 is a block diagram for explaining a laser driving apparatus according to Embodiment 4 of the present invention. The variable snubber control circuit 50 detects a constant current output signal 21 representing the amount of laser drive current 9 and suppresses a high frequency response when an overcurrent occurs based on a limit setting reference signal 22 that is a timing reference. As a result, supply of a sharp overcurrent to the semiconductor laser 1 is prevented.
[0048]
FIG. 11 is a timing chart showing the operation principle of the variable snubber control circuit 50.
[0049]
The drive current limit value is the maximum current value that can be passed to the laser, and if this is exceeded, the laser will be destroyed. The laser drive current 9 represented by the constant current output signal 21 is a drive current of the semiconductor laser 1 and fluctuates at the timing of the sample & hold control signal 5.
[0050]
On the other hand, the variable current limit signal 30 varies the limit value corresponding to the laser drive current 9, and the variable timing is, for example, the limit value setting signal 25 output immediately after the sample mode of the sample & hold control signal 5. Determined by.
[0051]
The snubber control signal 53 is turned on when the laser drive current 9 exceeds the variable current limit signal 30. In FIG. 11, when an overcurrent that exceeds the variable current limit signal 30 occurs as shown by a broken line in the laser drive current 9, the snubber control signal 53 is turned on. When the snubber control signal 53 is turned on, the connected snubber circuit 51 (FIG. 12) acts to suppress the frequency response of the laser drive current 9, thereby preventing an overcurrent from flowing through the semiconductor laser 1. Further, when the overcurrent generation flag generated based on the snubber control signal 53 is output, the output of the limit value setting signal 25 is stopped and the variable current limit signal 30 is not updated.
[0052]
FIG. 12 is a block diagram showing details of the variable snubber control circuit 50.
[0053]
The constant current output signal 21 output from the constant current circuit 8 is input to the limit value sample & hold circuit 23. The limit value control circuit 24 generates a limit value setting signal 25 based on the limit setting reference signal 22. In the constant current output signal 21, the voltage of the limit value hold capacitor 26 charged by the limit value setting signal 25 is amplified to an arbitrary value by the mitt value amplifier 27. A variable current limit signal 30 is generated by a variable current limit signal setting circuit 29 inserted between the output of the limit value amplifier 27 and the current limit value setting circuit 28. The variable current limit signal 30 is obtained, for example, by a variable current limit signal setting circuit 29 configured by resistance division by the voltage dividing ratio of the output value of the current limit value setting circuit 28 and the output of the limit value amplifier 27, and as a result, a constant current output. A variable current limit signal 30 corresponding to the signal 21 is obtained.
[0054]
The limit comparator 31 compares the constant current output signal 21 with the variable current limit signal 30, and outputs a snubber control signal 53 when the variable current limit signal 30 is exceeded due to overcurrent. Reference numeral 51 denotes a snubber circuit that adopts a configuration that suppresses the high frequency response of the laser drive current 9 when the snubber control signal 53 is turned on.
[0055]
Further, when the overcurrent generation flag 33 is generated from the signal obtained by reversing the polarity of the snubber control signal 53 by the inverter 54 and outputted, the limit value control circuit 24 stops the output of the limit value setting signal 25, The update of the variable current limit signal 30 is stopped.
[0056]
【The invention's effect】
As described above, according to the first embodiment, the threshold value of the current limiter is generated from the laser drive current and is sequentially updated so that only the sudden overcurrent generated in the current source is applied to the laser diode. By cutting off the current supply, it is possible to make the most effective use within the lifetime range regardless of the type of laser diode and to achieve the effect of preventing overcurrent.
[0057]
Further, according to the second embodiment, the current limiter threshold is generated from the laser drive current and is sequentially updated, and an effective current supply bypass is provided only for a sudden overcurrent generated in the current source. Thus, there is an effect that it is possible to make the most effective use within the lifetime range regardless of the type of the laser diode and to prevent overcurrent without interrupting the current.
[0058]
Further, according to the third embodiment, the threshold of the current limiter is generated from the laser drive current, and is sequentially updated, and the laser diode is forcibly turned off only for a sudden overcurrent generated in the current source. Thus, there is an effect that the use in the life range can be effectively utilized to the maximum regardless of the type of the laser diode, and the overcurrent prevention is realized by the labor saving of the circuit configuration.
[0059]
According to the fourth embodiment, the threshold value of the current limiter is generated from the laser drive current and is sequentially updated, and the high frequency noise component of the laser drive current is only applied to the sudden overcurrent generated in the current source. By removing the, the over-current prevention can be realized by saving the circuit configuration without interrupting the current, and can be used to the maximum extent possible regardless of the type of laser diode. Play.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a laser driving device according to a first embodiment of the present invention.
FIG. 2 is a timing chart showing the operation principle of the laser driving device according to the first embodiment of the present invention.
FIG. 3 is a main block diagram of a laser driving circuit according to the first embodiment of the present invention.
FIG. 4 is a schematic diagram of a laser driving device according to Embodiment 2 of the present invention.
FIG. 5 is a timing chart showing the operation principle of the laser driving device according to the second embodiment of the present invention.
FIG. 6 is a main block diagram of a laser driving circuit in Embodiment 2 of the present invention.
FIG. 7 is a schematic diagram of a laser driving device according to Embodiment 3 of the present invention.
FIG. 8 is a timing chart showing an operation principle of a laser driving device according to Embodiment 3 of the present invention.
FIG. 9 is a main block diagram of a laser driving circuit according to a third embodiment of the present invention.
FIG. 10 is a schematic diagram of a laser driving device according to Embodiment 4 of the present invention.
FIG. 11 is a timing chart showing an operation principle of a laser driving device according to Embodiment 4 of the present invention.
FIG. 12 is a main block diagram of a laser drive circuit in Embodiment 4 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Current-voltage (IV) conversion circuit 3 Reference voltage generation circuit 4 Comparator 5 Sample & hold control signal 6 Sample & hold circuit 7 Hold capacitor 8 Constant current circuit 9 Laser drive current 10 Modulation control circuit 11 Video (/ VDO) signal 20 Threshold variable type current limiter 21 Constant current output signal 22 Limit setting reference signal 23 Limit value sample & hold circuit 24 Limit value control circuit 25 Limit value setting signal 26 Limit value hold capacitor 27 Limit value amplifier 28 Current Limit value setting circuit 29 Variable current limit signal setting circuit 30 Variable current limit signal 31 Limit comparator 32 Cutoff transistor 33 Overcurrent generation flag 35 Limit value variable type current clipper 36 Clip circuit 40 Limit value variable type modulation data control circuit 41 Video / VDO) control signal 42 modulation data control circuit 50 variable snubber control circuit 51 snubber circuit 52 Snubber signal 53 snubber control signal 54 inverter

Claims (7)

A laser device composed of a laser diode and a photodiode that monitors the light amount of the laser diode and outputs the light amount as a light amount monitor current;
Current-voltage conversion means for converting the light intensity monitor current into a voltage signal;
A reference voltage generating means for generating an arbitrary voltage as a comparison reference;
Comparing means for comparing output signals of the current-voltage converting means and the reference voltage generating means;
First signal holding means for sample-holding the output of the comparison means based on a sample-hold control signal and outputting a sample signal;
Current generating means for generating a current that varies according to the voltage level of the sample signal;
Modulation means for modulating the output current of the current generating means based on an external video signal and outputting a modulated current;
In a laser driving device for driving the laser diode by the modulation current,
Control means for controlling the modulation current when the output current exceeds a limit value;
Updating means for updating the limit value according to the level of the new sample signal ,
When the output current is determined to exceed the limit value immediately before the update by said control means, a laser driving device which is characterized that you cancel the update operation of the limit value by the updating means.   2. The laser driving apparatus according to claim 1, wherein the control means is means for cutting off supply of the output current to the modulation means.   2. The laser driving apparatus according to claim 1, wherein the control means is means for absorbing an excess of the output current with respect to the limit value.   2. The laser driving apparatus according to claim 1, wherein the control means is means for cutting off supply of the external video signal to the modulation means.   2. The laser driving apparatus according to claim 1, wherein the control means is means for reducing a high frequency component of the output current supplied to the modulation means. The update means includes second signal holding means for further sample-holding the new sample signal, and amplification means for amplifying the output of the second signal holding means and using the output as the limit value. The laser driving device according to claim 1, wherein:   The updating means further includes an output current limit setting means for setting a limit value of the output current, and a weighted average calculation using a weighted average of the output of the output current limit setting means and the output of the amplifying means as the predetermined value. The laser driving device according to claim 6, further comprising: means.

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