JPH01224784A - Semiconductor laser output controller - Google Patents

Abstract

PURPOSE:To prevent an abnormal driving current from flowing to a semiconductor laser by lighting the semiconductor laser at the time of stabilizing the driving output of the semiconductor laser. CONSTITUTION:Lighting of a semiconductor laser and enabling of an up/down counter 5 are simultaneously controlled based on the rise of a clock signal to control the driving current to the semiconductor laser 1 without bringing about the variance of the output in a comparator 4 at the time of stabilizing the output in the comparator 4. Consequently, since a gate signal G turns on an AND gate 21 again after the period when the output of a D/A converter 7 is stabilized, lighting is restarted when the output of the D/A converter 7 is stabilized and the current of a constant current circuit 15 is stabilized, and the light output of the semiconductor laser 1 is stabilized. Thus, abnormal signal outputs from the up/down counter 5 and the D/A converter 7 are prevented from flowing to the semiconductor laser 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser output control device used in laser printers, laser fax machines, and the like.

(Prior Art) As is well known, output control of a semiconductor laser, which is one of the elements used as a light source for a laser printer, for example, or a light source in an optical transmission device between a scanner and the above-mentioned printer, is well known. The device includes
The optical output of the semiconductor laser is detected by a photodetection circuit and compared with a predetermined reference value by a comparator. Based on this result, an up/down counter is made to count up or down, and the drive current according to the count value is digitally/
There is a method in which the analog signal is converted into an analog signal and then sent to a semiconductor laser (for example, Japanese Patent Application Laid-Open No. 171863/1983).

However, in such a semiconductor laser output control device, the output from the up/down counter is converted into an analog quantity by a digital/analog converter and then applied as a drive current to the semiconductor laser drive circuit. Because a drive current is constantly applied to the semiconductor laser drive circuit, the semiconductor laser remains lit until its output stabilizes. Moreover, the output from the digital/analog converter produces an incorrect waveform called a glitch when the data changes, and this output fluctuation causes the output to fluctuate.

The driving current of the semiconductor laser changes, and in extreme cases,
An excessive current will be passed through the semiconductor laser, which may lead to destruction or deterioration of the semiconductor laser.

(Purpose) Therefore, in view of the problems of conventional semiconductor laser output control devices, it is an object of the present invention to prevent unnecessary lighting when setting the optical output, and to control the timing when the driving output of the semiconductor laser is stabilized. An object of the present invention is to obtain a semiconductor laser output control device that can prevent an abnormal drive current from flowing to a semiconductor laser by lighting the semiconductor laser.

(Structure) In order to achieve this object, the present invention includes at least one modulation switching element connected in series to a semiconductor laser, which is turned on/off by an information signal to modulate the semiconductor laser; A constant current source is provided corresponding to the semiconductor laser and supplies a constant current to the semiconductor laser via the modulation switching element, and a current value of the constant current source is supplied to the semiconductor laser at predetermined time intervals. and a control means for controlling the light output to a predetermined value, the semiconductor laser output control means being used in the control means to control the light output of the semiconductor laser by controlling a current at a constant current source to control the light output of the semiconductor laser. a digital/analog converter for setting a value; a means for setting output data in the digital/analog converter to set the optical output of the semiconductor laser to a predetermined value; and a driver for the modulation switching element. When the input value (digital value) of the digital/analog converter changes, the semiconductor laser is disabled until the output of the digital analog converter stabilizes and the current value at the current source stabilizes. The present invention proposes to include a signal control circuit for making it differential.

According to the present invention, when setting the optical output, until the setting is completed and a drive current corresponding to the count value of the so-called up/down counter can be stably supplied from the digital/analog conversion section. It is possible to prevent the semiconductor laser from turning on during this period.

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 3.

FIG. 1 is a block diagram showing a semiconductor laser output control device according to an embodiment of the present invention.

The feature of this embodiment is that when the output is unstable in the digital/analog converter that is used to set the optical output of the semiconductor laser and converts the output from the up/down counter into an analog quantity, The point is that a signal control circuit is provided that prevents the semiconductor laser from starting by preventing the flow of drive current to the semiconductor laser.

That is, in the figure, the output control device for a semiconductor laser includes transistors 11.12 and resistors 13.14.
and a constant current circuit 15 including a transistor I6 and a resistor 17.

Note that +V and -V indicate positive and negative DC power supply voltages.

The transistor 11 in the above-mentioned differential circuit 10 constitutes a modulation switching element connected to the semiconductor laser 1, and an information signal, a so-called modulation signal S, is applied to the base. By turning on/off the constant current port 15, the current from the constant current port 15 is supplied to the semiconductor laser 1.

Further, in the constant current circuit 15 described above, digital/
An output voltage from an amplifier 18 that amplifies the output of the analog converter 7 is applied to the base of the transistor 16, and the current is controlled according to this voltage.

That is, the drive current control unit that controls the current in the constant current source 15 described above includes a photodetection circuit 2 that includes a photodiode or the like that detects the light intensity (light output) of the semiconductor laser 1.
The optical output of the semiconductor laser 1 detected by the photodetector circuit 2 is amplified by the amplifier 3 to a voltage proportional to the optical intensity, and the comparator 4 sets the reference voltage V ref to obtain a predetermined optical output. They are compared and binarized. Then, the output signal of the comparator 4 is applied to the up/down terminal U/D of the up/down counter 5 to control the counting mode of the up/down terminal 5, and when the optical output of the semiconductor laser 1 is greater than a predetermined value, When the output voltage of the amplifier 3 is higher than the reference voltage Vref, the up/down counter 5 acts as a down counter and counts down the clock signal from the oscillator 6, and the optical output from the semiconductor laser 1 is smaller than a predetermined value. When the output voltage of the amplifier 3 is smaller than the reference voltage V ref, the up/down counter 5 acts as an up counter and counts up the clock signal from the oscillator 6 by one power count.

The output signal from the up/down counter 5 is converted into an analog signal by the digital/analog converter 7, amplified by the amplifier 18, and applied to the base of the transistor 16. Therefore, in the drive current control section, the current of the constant current circuit 15 changes in proportion to the output of the digital/analog converter 7, thereby changing the optical output of the semiconductor laser 1 by one power count. By repeating this process, the optical output of the semiconductor laser 1 approaches the predetermined value one power count at a time while the optical power control signal is being input.

When the optical output of the semiconductor laser 1 reaches a predetermined value, the comparator 4
When the output signal of the comparator 4 is inverted, the edge detection circuit 8 detects the rising edge of the output signal of the comparator 4 and disables the up/down counter 5. Therefore, the count value of the up/down counter 5 is held as is, and the optical output of the semiconductor laser 1 is controlled so that the output signal of the amplifier 3 becomes equal to the reference voltage V ref. Note that the edge detection circuit 8 may detect only a rising edge or a falling edge of the output signal of the comparator 4, and may disable the up/down counter 5.

On the other hand, the above-mentioned edge detection circuit 8 receives the clock signal from the oscillator 6 as well as the power control signal P applied when setting the drive current in the drive current control section. When the above-mentioned power control signal P is input, the edge detection circuit 8 detects the rising edge of the clock signal from the oscillator 6 and outputs the up/down counter 5.
It outputs a hay enable signal and also outputs a gate signal to an AND gate 21 in a signal control circuit 19, which will be described later.

That is, the signal control circuit 19 is a modulation signal switching circuit that controls the lighting timing of the semiconductor laser 1 according to the input of the modulation signal S and the power control signal P.
Alternatively, the OR gate 2 to which the power control signal P is input
0, the output signal from this OR gate 2°, and an AND gate 21 which receives the gate signal G from the edge detection circuit 8 described above. is applied to the base of

For example, when the semiconductor laser 1 is used as a light source of a laser printer, the power control signal P described above is generated when the semiconductor laser 1 is not recording an image on the photoreceptor, and when the semiconductor laser 1 scans the photoreceptor, the image is recorded. This is a signal that disappears when recording is performed.

Although the present embodiment has the above-described configuration, the modulation signal S is input and one of the input terminals of the OR gate 20 is on, and the power control signal P is not input and the other input terminal of the OR gate 20 is off. If so, the edge detection circuit 8 stops operating and sets the up/down counter 5 to a disabled state.

Therefore, while the up/down counter 5 holds its count value, it outputs a gate signal G based on the power control signal P to the AND gate 21 in the signal control circuit 19, and turns on the output of the AND gate 21 in the signal control circuit 19. The modulation signal S causes the semiconductor laser 1 to be turned on. At this time, since the count value of the up/down counter 5 is held, the output from the digital/analog converter 7 corresponds to the count value of the up/down counter 5, and is passed through the amplifier 18 to the constant current circuit 15. is added to the base of the transistor 16 to keep the optical output of the semiconductor laser 1 constant.

On the other hand, when setting the drive current of the semiconductor laser 1, the power control signal P is turned on, and the edge detection circuit 8 releases the up/down counter 5 from the disabled state. Therefore, in the up/down counter 5, the optical detection circuit 2 detects the optical output from the semiconductor laser 1, and the comparator 4 compares the signal voltage from the amplifier 3 with respect to the reference voltage Vref. is controlled, so the count value changes corresponding to one force count. On the other hand, when the power control signal P is turned on when the count value changes as described above, the edge detection circuit 8 sets the up/down counter 5 to the enabled state based on the rising edge of the clock signal from the oscillator 6, as shown in FIG. At the same time, the gate signal G is no longer input to the AND gate 21 in the signal control circuit 19, and the modulation switching element 11 is made inactive.

This is a digital /
This is to prevent the output of the analog converter 7 from becoming unstable due to glitches or the like, and to prevent excessive current from flowing to the semiconductor laser 1 due to this output fluctuation. When the up/down counter 5 operates at the rising edge of a signal, the enable state is controlled at the falling edge of the clock signal. Therefore, the up/down counter 5 is enabled when the output from the drive current control section including the semiconductor laser 1 and the amplifier etc. is stabilized, and the count is controlled at the next rising edge of the clock signal, and the constant current circuit 15 The output can be changed gradually.

Further, as described above, at the time when the power control signal P is generated, the AND gate 21 in the signal control circuit 19 is turned off, so that the modulation operation by the modulation signal S is turned off, and thereby, When the up/down counter 5 is counting, excessive current is prevented from flowing to the semiconductor laser 1 due to the occurrence of glitches due to changes in the count value.

In this way, by performing both the lighting control of the semiconductor laser 1 and the enable control of the up/down counter 5 at the same time using the rising edge of the clock signal as a reference, fluctuations in the output of the comparator 4 can be avoided. , the drive current to the semiconductor laser 1 can be controlled when the output from the comparator 4 becomes stable.

Therefore, as shown in the second diagram, the gate signal G turns on the AND gate 21 again after the period in which the output from the digital/analog converter 7 is stabilized, so that the semiconductor laser 1 converts the digital/analog. When the output of the amplifier 7 becomes stable and the current of the power outage flow path 15 becomes stable, the lighting is restarted, the optical output of the semiconductor laser 1 becomes stable, and then the output of the amplifier 3 becomes stable. The output from the device 4 becomes stable, and at this point the up/down counter 5 is set to an enabled state. Thereafter, the optical output of the semiconductor laser 1 is controlled in the state described above, but if the output of the comparator 4 is in a state opposite to the previous signal, the edge detection circuit 8 detects the rising edge of the edge. Detect and control up/down counter enable moto.

The above-described semiconductor output control device is not only applicable to those having a single drive current control section as shown in FIG. 1, but also can be applied to multi-level modulation as shown in FIG. It is also possible to apply the present invention to a semiconductor laser output control device.

That is, the semiconductor laser output control device shown in FIG. 3 is one in which three of the control devices shown in FIG.
0-2.20-3 and AND gate 21-1.21-
2.21-3 signal control circuit 19-1.19-2
．． 19-3 are connected to each other.

(Effects) According to the present invention, when setting the optical output of the semiconductor laser, the output of the semiconductor laser becomes unstable while the output of the digital/analog converter becomes unstable according to the change in the output of the up/down counter. Based on the setting command signal for setting the optical output, it is possible to prevent abnormal signal output from the up/down counter and digital/analog converter from flowing to the semiconductor laser. This makes it possible to prevent destruction and deterioration of the laser.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a semiconductor laser output control device according to an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the main parts in the block diagram shown in FIG. 1, and FIG. 3 is the same as that shown in FIG. 1. FIG. 2 is a block diagram corresponding to FIG. 1 showing a modification of the semiconductor laser output control device shown in FIG. 1... Semiconductor laser, 10.50.60.70...
- Differential circuit, 11.51, 61.71... Modulation switching element, 15.55.65.75... Constant current circuit, 4... Comparator constituting control means, 5... - Up/down counter constituting control means, 7... Digital/analog converter, 8... Edge detection circuit, 19
...Modulation signal control circuit constituting the signal control circuit, 20
. . . OR gate constituting the modulation signal control circuit, 21.
...AND gate that constitutes the modulation signal control circuit.

Claims (1)

[Claims] Turn on/off by an information signal connected in series to a semiconductor laser.
at least one modulation switching element provided to modulate the semiconductor laser when turned off; and a modulation switching element provided corresponding to the semiconductor laser to supply a constant current to the semiconductor laser via the modulation switching element. Semiconductor laser output control means comprising a constant current source for supplying a constant current source, and a control means for controlling the current value of the constant current source so that the optical output of the semiconductor laser becomes a predetermined value at predetermined time intervals, the control means It is used in a digital/analog converter that sets the current value in a constant current source to control the optical output of the semiconductor laser, and a digital/analog converter that monitors the optical output of the semiconductor laser and converts the monitoring results into an optical signal. - a photodetector for electrical conversion; a means for setting output data in the digital/analog converter to set the optical output of the semiconductor laser to a predetermined value; and a drive unit for the modulation switching element; . A semiconductor laser output control device comprising: a signal control circuit for inactivating the semiconductor laser until the output from the digital/analog converter becomes stable.