JPH1044505A - Optical output control circuit for semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical output control circuit for a semiconductor laser device capable of controlling an optical output of the semiconductor laser device in a condition near the actual image-forming condition by a method wherein the semiconductor device is set in a pulse emission condition and a feedback optical quantity control is applied thereto. SOLUTION: A semiconductor laser device 1 is activated in a pulse emission condition by a predetermined duty ratio in an APC (automatic power control) interval and an average optical quantity is monitored and a feedback control is applied thereto. As a result, since the semiconductor laser device is activated also in the APC internal in a state similar to that in an image forming interval, it is possible to prevent the output power of the laser device in the image forming interval from exceeding a predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light output control circuit for a semiconductor laser.

More specifically, the present invention performs laser pulse driving in a laser beam printer or the like, and intermittently performs APC (Auto Power Control).
1) The present invention relates to a light output control circuit of a semiconductor laser, which is preferably applied to a device that performs an operation.

[0003]

2. Description of the Related Art FIG. 2 shows general current-light output characteristics of a semiconductor laser. As can be seen from the figure, since the light output characteristics of the semiconductor laser are sensitive to temperature changes, even when driven at a constant current, the light output greatly fluctuates due to changes in ambient temperature or self-heating.

In order to cope with the temperature dependence of the light output,
A photodiode generally called a monitor diode is incorporated in the package of the semiconductor laser. By monitoring the optical output of the semiconductor laser and controlling the drive current, the optical output can be kept constant.

[0005] A driving circuit of a semiconductor laser having the above-described feedback mechanism is called an APC circuit.

In a drive circuit such as a laser beam printer which turns on / off a semiconductor laser by an image signal, the laser lighting time is irregular.
APC by continuously turning on the laser for a certain time outside the image area
It is common to operate a circuit.

FIG. 3 shows an example of such an intermittent APC circuit.

In FIG. 3, 1 is a semiconductor laser, 2 is a monitor diode, 3 is a current switching circuit for turning on / off a drive current of the semiconductor laser, 4 is a current source for supplying a drive current of the semiconductor laser, and 5 is a monitor diode. 2, a resistor for converting the current output into a monitor voltage, 7 a reference voltage source, 8 a comparator for comparing the monitor voltage with the reference voltage, 9 an up / down counter, 10 an oscillation circuit for generating a clock for the counter 9, 11 Is an AND gate for supplying a clock to the counter 9 only within the APC section, and 12 is a D for converting the count output of the counter 9 into a control signal of the drive current source 4.
An / A converter 31 is an OR gate for synthesizing the image signal and the APC section signal to generate a laser on / off signal.

Next, the operation of the APC circuit shown in FIG. 3 will be described.

First, in the APC section, the APC section signal becomes high, the laser 1 is turned on, and a clock is supplied to the counter 9.

The output of the monitor diode 2 is converted into a voltage by a resistor 5 and compared with a reference voltage 7 by a comparator 8.

The result of the comparison becomes an up / down signal of the counter 9. The counter 9 counts up when the monitor voltage is lower than the reference voltage, and counts down when the monitor voltage is higher than the reference voltage.

The count output of the counter 9 is converted into an analog voltage by the D / A converter 12 and is applied to the drive current source 4.
Control signal.

Since the magnitude of the drive current is determined in proportion to the magnitude of the count output, feedback control is performed, and as a result, the magnitude of the laser drive current is determined so that the monitor voltage becomes equal to the reference voltage.

Next, outside the APC section, the APC section signal becomes low, and the supply of the clock to the counter 9 stops, so that the count output keeps a constant value and the analog output of the D / A converter 12 also becomes constant. Therefore, the driving current source 4
Is also fixed.

As a result, in the image forming section, the semiconductor laser 1 is turned on / off in accordance with the image signal with the current value determined in the previous APC section. In a laser beam printer or the like using a semiconductor laser, such an APC section is periodically provided to control the laser light output to be constant.

[0017]

However, in the conventional example described above, the semiconductor laser is often driven differently between the APC section and the image forming section.

The reason is that the semiconductor laser is continuously lit during the APC section, and the pulse is often turned on and off during the image forming section.

As described above, the power of the semiconductor laser greatly varies depending on the temperature. In addition, since the semiconductor laser generally has poor luminous efficiency, the self-temperature rise by lighting is large.

For this reason, the temperature of the semiconductor laser is generally higher in the APC section during the continuous lighting than in the image forming section during the pulse lighting, and if the laser driving current is determined in that state, the temperature in the image forming section is Since the temperature of the semiconductor laser is lowered, an optical output exceeding a predetermined value may be output.

There is not much problem when the semiconductor laser is used at an optical output sufficiently lower than the rated output. However, when the semiconductor laser is used near the rated output, the laser power is instantaneously increased to the rated output. May be exceeded, which may adversely affect the life of the laser.

Therefore, an object of the present invention is to provide
An object of the present invention is to provide a light output control circuit of a semiconductor laser capable of controlling the light output of the semiconductor laser in a state close to the time of actual image formation by applying a feedback light amount control in a pulse lighting state of the semiconductor laser.

[0023]

In order to achieve the above object, the present invention provides a light output control circuit for controlling the light output of a semiconductor laser to be constant by performing feedback control only in a specific section. A monitor diode for monitoring the output of the monitor diode, an averaging means for integrating the output of the monitor diode over time, and averaging the output of the monitor diode, and a comparing means for comparing the averaged output of the monitor diode with a predetermined reference value. Control means for controlling the drive current value of the semiconductor laser based on the output of the comparison means; holding means for holding the drive current value of the semiconductor laser except in the specific section; and turning on the drive current of the semiconductor laser. Switching means for turning on / off the semiconductor laser by turning on / off the semiconductor laser. Performs feedback control to Heather is pulse lit, is to stabilize the light output.

[0024] In addition, there is provided PWM means for converting digital data of a plurality of bits inputted from the outside into an on / off signal of the semiconductor laser by pulse width modulation (PWM). The output can be fixed to a pulse train having a predetermined duty ratio, and the semiconductor laser can be turned on / off using only the pulse train.

Alternatively, in addition to the above, fixed duty pulse generating means for generating a pulse having a predetermined duty ratio is provided, and in the specific section, the laser is turned on / off only by the output of the fixed duty pulse generating circuit. Is also possible.

The means for controlling the drive current value of the semiconductor laser comprises an up / down counter and a D / A converter, and the means for holding the drive current value stops the clock of the up / down counter. A configuration in which the drive current value is held can be employed.

Thus, the present invention can be applied to both a halftone printer and a binary printer.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser APC circuit to which the present invention is applied turns on a semiconductor laser at a predetermined duty ratio in an APC section, monitors the average light quantity, and performs feedback control. This allows
Also in the APC section, the semiconductor laser is turned on in substantially the same state as in the image forming section, so that the laser light output can be prevented from exceeding a predetermined value in the image forming section.

FIG. 1 shows a first example of the semiconductor laser APC circuit.
An embodiment will be described. In the figure, 1 is a semiconductor laser, 2 is a monitor diode incorporated in the same package as the semiconductor laser 1, 3 is a current switching circuit for turning on / off the drive current of the semiconductor laser 1, and 4 is a drive current of the semiconductor laser 1. 5 is a resistor for converting the current output of the monitor diode 2 to a monitor voltage, 6 is an integrating circuit (low-pass filter) for averaging the monitor voltage, 7 is a reference voltage source, and 8 is averaged. A comparator for comparing the monitor voltage with the voltage of the reference voltage source 7, an up / down counter 9, an oscillation circuit 10 for generating a clock for the counter 9, and a clock 11 for supplying the clock to the counter 9 only within the APC section. An AND gate 12 converts the count output of the counter 9 into a control signal of the drive current source 4. A D / A converter. A PWM circuit 13 converts a digital image data signal into a laser on / off signal by pulse width modulation (PWM), and outputs a signal having a predetermined pulse width continuously when the APC section signal is high. ing.

Here, the PWM circuit 13 converts a digital image data signal into an analog voltage by a D / A converter and compares it with a triangular wave by a comparator to generate a pulse width signal. There are various types such as a type using a ramp waveform instead of a triangular wave, and a type digitally controlling the start / end position of a pulse.

The timing chart shown in FIG. 4 shows the operation of the APC circuit according to the present embodiment. As shown in the figure, the image data signal (8b in this embodiment)
It digital data) is a value corresponding to the density of the image to be formed in the image forming section, and otherwise is all zero (00H in hexadecimal notation).

The present embodiment is based on the premise that a portion where the laser light is emitted is developed with toner to form an image.

Therefore, in the image data 00H, the laser is hardly turned on, and no image is formed.

Of course, the semiconductor laser APC circuit of the present invention is also effective in the opposite case (that is, a system in which a portion where the laser does not emit light is developed).

In the image forming section, the PWM circuit outputs a pulse having a width corresponding to the input image data, and the pulse turns on / off the laser.

On the other hand, in the APC section, as shown in FIG. 4, the PWM circuit continuously outputs pulses of a constant width,
Turn on the laser at a constant duty ratio.

In the APC section, the value obtained by averaging the monitor voltage by the integrating circuit becomes substantially constant, and the feedback control is performed so that the value becomes equal to the reference voltage.

As described above, in the pulse lighting state, the APC
, The light output of the semiconductor laser can be controlled in a state close to the time of image formation, and a more accurate and safe APC circuit can be realized.

In determining the pulse width in the APC section, a method of preparing a standard image and measuring the ratio of the laser light emission to obtain the standard image may be considered.

In most originals handled by copiers, printers and the like, since there are many white base portions, the laser lighting time is short and the temperature rise of the laser is small.

Utilizing this property, when the semiconductor laser is continuously pulsed, a duty ratio such that the package temperature does not rise more than the ambient temperature is experimentally found, and the laser is lit with the pulse width. You may.

Other Embodiments In the above-described embodiment, the case of a halftone printer in which the density of an image is represented by 8-bit data is described.
The case of a printer represented by a value will be described.

Semiconductor laser APC according to the present embodiment
FIG. 5 shows a block diagram of the circuit. In the figure, since an image is represented by a binary value of laser on or off for each dot, the image signal is represented by one line.

Semiconductor laser APC according to the present embodiment
The circuit is almost the same as that of the above-described embodiment, however, unlike the halftone printer as in the above-described embodiment, since it does not have a PWM circuit, a circuit for generating a pulse with a constant duty in the APC section. Is required.

This is the fixed duty pulse generation circuit 51 shown in FIG. This fixed duty pulse generation circuit can be easily configured by a combination of a circulation counter and a gate, for example.

In FIG. 5, reference numeral 52 denotes an OR gate for synthesizing the output of the fixed duty pulse generation circuit 51 and the image signal, and 53 and 54 denote gates for invalidating the image signal in the APC period.

The timing chart shown in FIG. 6 shows the operation of the APC circuit according to the present embodiment.

The operation of the APC circuit according to this embodiment is almost the same as that of the previous embodiment. That is, the image signal becomes high when dots are formed in the image forming section, and the laser is turned on.

Outside the image forming section, the image signal remains low and the laser is not turned on.

On the other hand, in the APC section, the fixed duty pulse generation circuit operates to output a pulse train having a constant period to turn on the laser.

In this APC section, the value obtained by averaging the monitor voltage by the integrating circuit becomes a substantially constant value, and the feedback control is performed so that the value becomes equal to the reference voltage.

In the binary printer as in the present embodiment, the speed of the current switching circuit for turning on / off the semiconductor laser is lower than in the halftone printer as in the first embodiment. Also, since there is no fast clock in the system, the frequency of the pulse output of the fixed duty pulse generating circuit must be lowered.

Accordingly, the time constant of the monitor output integration circuit must be increased, so that the time required for the APC section is longer than in the above-described embodiment.

As described above, in the pulse lighting state, the APC
, The light output of the semiconductor laser can be controlled in a state close to the time of image formation, and a more accurate and safe APC circuit can be realized.

[0055]

As described above, according to the present invention, the light output of the semiconductor laser can be controlled in a state close to the time of actual image formation by performing feedback light quantity control with the semiconductor laser in a pulse lighting state. An accurate and safe light output control circuit can be realized.

The present invention is applicable not only to a halftone printer but also to a binary printer.

[Brief description of the drawings]

FIG. 1 shows a semiconductor laser AP according to a first embodiment.
It is a block diagram which shows C circuit.

FIG. 2 is a diagram showing general current-light output characteristics of a semiconductor laser.

FIG. 3 is a block diagram illustrating a conventionally known semiconductor laser APC circuit.

FIG. 4 shows a semiconductor laser AP according to the first embodiment.
FIG. 4 is a timing chart showing the operation of the C circuit.

FIG. 5 shows a semiconductor laser AP according to a second embodiment.
It is a block diagram which shows C circuit.

FIG. 6 shows a semiconductor laser AP according to a second embodiment.
FIG. 4 is a timing chart showing the operation of the C circuit.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 monitor diode 3 current switching circuit 4 drive current source 5 resistor 6 integration circuit (LPF) 7 reference voltage source 8 comparator 9 up / down counter 10 oscillation circuit 11 AND gate 12 D / A converter 13 PWM circuit

Claims (9)

[Claims] 1. An optical output control circuit that performs feedback control only in a specific section to control the optical output of a semiconductor laser to be constant, comprising: a monitor diode for monitoring the output of the semiconductor laser; and an output of the monitor diode. Averaging means for performing time integration and averaging; comparing means for comparing the averaged output of the monitor diode with a predetermined reference value; and controlling the drive current value of the semiconductor laser based on the output of the comparing means. Control means for controlling the driving current value of the semiconductor laser except for the specific section; and switching means for turning on / off the driving current of the semiconductor laser to turn on / off the semiconductor laser. In the specific section, feedback control is performed by pulse-lighting the semiconductor laser. A semiconductor laser optical output control circuit, characterized in that to stabilize the light output. 2. The optical output control circuit of a semiconductor laser according to claim 1, further comprising: a plurality of bits of digital data input from the outside being converted into an on / off signal of the semiconductor laser by pulse width modulation (PWM). A light source of the semiconductor laser, comprising a PWM means for converting, and in the specific section, an output of the PWM means is fixed to a pulse train having a predetermined duty ratio, and the semiconductor laser is turned on / off only by the pulse train. Output control circuit. 3. The semiconductor laser light output control circuit according to claim 1, further comprising a fixed duty pulse generating means for generating a pulse having a predetermined duty ratio, wherein said fixed duty pulse is generated in said specific section. An optical output control circuit for a semiconductor laser, wherein the laser is turned on / off only by the output of a pulse generation circuit. 4. The optical output control circuit for a semiconductor laser according to claim 1, wherein the means for controlling a drive current value of the semiconductor laser comprises an up / down counter and a D / A converter. A light output control circuit for a semiconductor laser, wherein the holding means holds the drive current value by stopping the clock of the up / down counter. 5. The light output control circuit for a semiconductor laser according to claim 1, wherein the light output control circuit is applied to a halftone printer that represents the density of an image by N-bit data. 6. The light output control circuit of a semiconductor laser according to claim 1, wherein the light output control circuit is applied to a binary printer that expresses an image by binary data. 7. The light output control circuit of a semiconductor laser according to claim 1, wherein a low-pass filter is used as said averaging means. 8. The light output control circuit of a semiconductor laser according to claim 2, wherein the PWM means converts the digital image data into an analog voltage by a D / A converter, and compares the analog voltage with a triangular wave by a comparator. An optical output control circuit for a semiconductor laser, which forms a pulse width signal. 9. The light output control circuit of a semiconductor laser according to claim 3, wherein said fixed duty pulse generating means is constituted by a circulation counter and a gate.