JPH03109586A - Semiconductor laser driving method - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a semiconductor laser by maximizing the output value of an up-down counter, controlling a driving circuit by means of a control circuit, and minimizing a driving current, when a power source is turned on. CONSTITUTION:The output value of the up-down counter 7 is maximized, the driving circuit 2 is controlled by the control circuit 10, and the driving current Iop is minimized, when the power source is turned on. Desirably, the output value of the up-down counter 7 is discriminated. When this output value is maximum or minimum, display means 23 and 25 display the fact that the semiconductor laser 1 is abnormal, and when the output value is maximum, a counting action is stopped. Thus, the semiconductor laser 1 is prevented from being deteriorated caused by an over-current and is controlled so as to obtain a desired light output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser driving method in an optical writing system that uses a semiconductor laser as a light source, such as a laser printer or a laser plotter.

BACKGROUND OF THE INVENTION In recent years, semiconductor lasers have been used as light sources for this type of optical writing system because they can be directly modulated and the amount of light can be easily controlled. Here, if a failure occurs in the drive circuit control system of the semiconductor laser and an overcurrent flows, the semiconductor laser will be destroyed, so protection is important and countermeasures are desired.

In this regard, for example, according to Japanese Patent Application Laid-Open No. 58-159251, if the scanning synchronization signal of the semiconductor laser cannot be detected within a predetermined time (the motor for rotating the polygon mirror is (due to rotational abnormality), the drive of the semiconductor laser is stopped to protect it.

Problems to be Solved by the Invention However, such countermeasures are taken during operation, and when the power is turned on, the semiconductor laser is rapidly started up due to an excessive drive current, so it is likely to deteriorate.

Further, even if the semiconductor laser has deteriorated, such an abnormality cannot be detected during actual operation, and the deterioration abnormality may progress further.

Means for Solving the Problems A drive circuit that supplies a drive current to a semiconductor laser, and a base 4! that corresponds to a predetermined optical output. ! A comparator that compares the magnitude of the voltage and a detected voltage photoelectrically converted corresponding to the optical output of the semiconductor laser, an up/down counter that determines an up or down operation mode depending on the magnitude result, and an up/down counter comprising a D/A converter that converts an output value of a counter into a current value, and a control circuit that controls the drive circuit and controls the drive current according to the current value output from the D/A converter, In the semiconductor laser driving method for causing the semiconductor laser to emit light with the predetermined optical output, in the invention according to claim 1, the output value of the up/down counter is maximized when power is turned on, and the driving circuit is controlled by a control circuit. Drive current was minimized.

In the invention according to claim 2, the output value of the up-down counter is determined, and when the output value is the maximum or minimum, the display means displays that the semiconductor laser is abnormal, and
When the output value is maximum, the up/down counter is loaded and the counting operation is stopped.

According to the invention described in claim 1, when the power is turned on, oscillation is started with the driving current to the semiconductor laser being at its minimum, so that the semiconductor laser can achieve the desired optical output without being degraded by excessive current. will be controlled by.

Furthermore, the fact that the output value of the up/down counter continues to be at the maximum or minimum and the drive current is at the minimum or maximum is due to an abnormality such as deterioration of the semiconductor laser. According to the invention as claimed in claim 2, the situation in which the output value of the up-down counter becomes the maximum or minimum is determined, and when such a situation occurs, the display means displays the fact, so that the semiconductor laser It is possible to detect abnormalities such as deterioration.

At this time, when the output value of the up-down counter is at its maximum, if it continues to operate, the drive current may change rapidly from the minimum value to the maximum value, further deteriorating the semiconductor laser. There is no problem since it will be stopped.

Example An embodiment of the present invention will be described with reference to the drawings.

First, a drive circuit 2 is connected to the semiconductor laser l. This drive circuit 2 consists of an analog power supply V, a resistor R, and a transistor Tr, and a drive current Io to the semiconductor laser 1.
p flows. Here, the semiconductor laser l is
A write image signal Video is inputted to the drive circuit 2 via an inverter 3 in order to perform modulation drive according to the q write image signal Video. The optical output of such a semiconductor laser 1 is received by a built-in photodiode 4, and a photovoltaic current proportional to the optical output is converted into a voltage by a current-voltage converter 5 to obtain a detection voltage Vm. This detection voltage Vm is determined in the comparator 6 by a base r corresponding to a predetermined target optical output.
11 voltage Vr in magnitude.

Up-down (U/
D) A counter 7 is provided.

The U/D counter 7 counts up or down the system clocks C1, , K according to the output of the comparator 6 during APC (Auto Power Control) operation. The count output value of this U/D counter 7 is converted into a current value 1c by a D/A converter 8. This current value Ic is converted into a control voltage by a control circuit 1.0 comprising an amplifier 9 connected to the base of the transistor Tr of the drive circuit 2. Therefore, the drive current lop for the semiconductor laser l is increased or decreased by the pull-in current Ic, and is based on the detection voltage Vm? The drive current Iop is controlled so as to provide a predetermined optical output in accordance with the voltage Vr. In this embodiment, as shown in FIG. 2, when the detected voltage Vm crosses the base voltage Vr a predetermined number of times, in this case four times, the APC operation is ended and the counting operation of the U/D counter 7 is started. The output value (ie, Iop) is maintained until writing for one line is completed.

In addition to such basic operation control, the present embodiment performs operation control as follows. When the power is turned on, the system clock CLK is generated, and the signal T indicating the A I) C period is generated.
. becomes H level, and the write image signal Video becomes L level. Here, both analog power supplies V and v slowly rise via the slow starter. In addition, the signal S to the AND gate 11 connected to the load terminal D of the U/D counter 7 is emitted after it is confirmed that all the power supplies have reached a predetermined value, so when the power is turned on, the signal S to the AND gate 11 connected to the load terminal D is emitted.
One counter 7 loads all input data at H level and maximizes its output. That is, the D/A converter 8
The output values for [, SB to MSB are all 1 level. Therefore, the current 1 drawn by the control circuit IO
c becomes the maximum, and the semiconductor laser l has the minimum drive current 1
Oscillation starts at op (min).

In this state, since Vm)Vr (<O), the output of the comparator 6 is at H level, and the U/D counter 7 is operated in the down mode. Therefore, the pull-in current 1c decreases from the value at power-on, the base potential of the transistor Tr decreases, the drive current lop increases, and the optical output of the semiconductor laser 1 increases. As a result of this operation, when Vm (Vr) is reached, the output of the comparator 6 becomes L level, the U/D counter 7 is switched to the up mode, the draw current Ic increases again, and the drive current Iop is decreased to The light intensity of the laser l is weakened. In this way, the detection voltage Vm (laser light output) repeats increases and decreases around the reference voltage Vr, but as shown in Figure 2, the state of Vm (Vr) occurs four times. , the output Q3 of the counter ICl3 changes to the L level via the flip-flop 12.This output Q3 changes to the A
It is input to the D gate 14 and controls the EP terminal of the U/D counter 7, and when the output Q becomes L level, the U
/D counter 7 becomes disabled state, and at that time (
The output value of the fourth time is held until the next APC period.

Here, the amount of current 1c drawn is set so that the emission power at re(max) <the emission power at a predetermined emission power (I c (min) = 0).However, in the unlikely event that the semiconductor laser During the APC period, the optical output may drop to the reference voltage V due to
If the value does not increase or decrease by an amount corresponding to r, the U/D counter 7 continues to be in up mode or down mode, and finally the output value of the U/D counter 7 reaches the maximum Dmax or the minimum Dmin. In order to detect such a state, in this embodiment, Dmax-Dmi is set for the U/D counter 7.
A discriminating circuit film 5 is formed for n discriminating times. This Dmax −D
The min discrimination circuit 15 detects the most significant MSB of the U/D counter 7.
and the gate circuit connected to the PC terminal 16.17°18
and four flip-flops of IC configuration 19°20.2
1.22. When the above state (maximum or minimum) is reached, the MSB and RC of the U/D counter 7 are output,
The output of either flip-flop 21 or 22 is inverted. When the output of the flip-flop 21 is inverted by Dmin detection, the LED 23 serving as a display means is lit via the driver 24 to display an abnormality in the semiconductor laser indicating that the drive current is Iop(max). On the other hand, D max
When the output of the flip-flop 22 is inverted as a result of the detection, an LED 25 serving as a display means is turned on via a driver 26 to indicate an abnormality in the semiconductor laser indicating that the drive current is I op (min). At the same time, the inverted output of the flip-flop 22 causes the J/D counter 7 to be loaded via the AND gate 11, and the counting operation is stopped. This prevents damage to the semiconductor laser I caused by the pull-in current Ic = 0 and an excessive drive current Iop flowing through the semiconductor laser I.

In addition, FIG. 3 shows AP among various signals involved in image writing.
A signal T indicating the C period. and ■Line write width signal L G
5 is a timing chart showing the relationship between ATE, signal T1, and write image signal V1deo.

If the detected voltage Vm does not cross the reference voltage Vr four times during the APC period, the signal T. The APC operation is forcibly terminated.

Effects of the Invention Since the present invention is configured as described above, according to the first aspect of the invention, when the power is turned on, the output value of the up/down counter is set to the maximum and the drive circuit is controlled by the control circuit, so that the semiconductor laser starts oscillation in a state where the drive current is minimum, resulting in a start that does not cause deterioration.According to the invention as claimed in claim 2, the output value of the up/down counter is determined, and this output value is the maximum. Or, when the output value is the minimum, the display means indicates that there is an abnormality in the semiconductor laser, and when the output value is the maximum, the up-down counter is loaded and the counting operation is stopped. When it is possible to identify an abnormality in which the output value of the down counter reaches the maximum or minimum, and when the output value of the up/down counter is at the maximum, the counting operation of the up/down counter is stopped, so the drive current when the up/down counter continues to operate is It is possible to protect the semiconductor laser from deterioration caused by a sudden change in the value from the minimum value to the maximum value.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a block diagram, FIG. 2 is a waveform diagram showing the timing at which APC operation ends, and FIG. 3 is a timing chart of various signals.

Claims (1)

[Claims] 1. A drive circuit that supplies a drive current to a semiconductor laser, a reference voltage corresponding to a predetermined optical output, and a detection voltage photoelectrically converted corresponding to the optical output of the semiconductor laser are compared in magnitude. A comparator, an up/down counter whose up or down operation mode is determined depending on the magnitude result, a D/A converter that converts the output value of the up/down counter into a current value, and a D/A converter. and a control circuit that controls the drive current by controlling the drive circuit according to an output current value, the semiconductor laser drive method causing the semiconductor laser to emit light with the predetermined optical output, the method comprising: turning on the power; 1. A method for driving a semiconductor laser, wherein the output value of the up/down counter is set to a maximum value, and the drive circuit is controlled by the control circuit to minimize the drive current. 2. A drive circuit that sends a drive current to the semiconductor laser, a comparator that compares the magnitude of a reference voltage corresponding to a predetermined optical output and a detection voltage photoelectrically converted corresponding to the optical output of the semiconductor laser, and the comparator that An up/down counter whose up or down operation mode is determined according to the result, a D/A converter that converts the output value of the up/down counter into a current value, and a D/A converter that converts the output value of the up/down counter into a current value. and a control circuit that controls the drive current by controlling the drive circuit accordingly, and causes the semiconductor laser to emit light with the predetermined optical output, wherein the output value of the up-down counter is and when the output value is the maximum or minimum, the display means displays a message indicating that the semiconductor laser is abnormal, and when the output value is the maximum, the up/down counter is loaded and the counting operation is stopped. A method for driving a semiconductor laser.