JPS6327161A - Beam quantity controller for semiconductor laser - Google Patents

Abstract

PURPOSE:To maintain the intensity of semiconductor laser output constant by providing a counter and a comparator, etc., and continuously controlling the emission quantity of semiconductor laser beam to be close to a reference value as long as a beam quantity adjusting signal and a video signal are inputted. CONSTITUTION:If the T-signal for beam quantity adjusting is inputted to an OR circuit 10, a switchi circuit 9 is made turn ON by the output of the circuit 10, and the counter 5 also is made in an enable-state. As the counter 5 continues counting up, a current flowing through the semiconductor laser 1 comes increasingly large, the quantity of light is converted to an electrical quantity by a photodetector circuit 2, and is compared with the reference signal from a reference level setting circuit 3 by the comparator 4. Accordingly, if the detection signal from the circuit 2 comes larger than the reference signal, the counter 5 truns to down mode, but if the said signal comes larger than the reference signal, the counter 5 turns to up mode so that the level is controlled to approach the reference signal. Furthermore, the counting value is adjsuted and held by using the T-signal from the counter 5, a current in proportion to which is supplied to the laser 1. Thus, the photoelectrical intensity of the laser 1 is maintained constant.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser light amount control device used in a laser printer or the like.

(Prior Art) The optical output of a semiconductor laser is extremely unstable with respect to temperature, and in an environment where the ambient temperature changes, it is necessary to stabilize the optical output by using some means.

Conventional semiconductor laser light amount control devices use a feedback method in which the amount of light emitted by the semiconductor laser is sampled at regular intervals and the amount of light emitted from the semiconductor laser is controlled to a constant value based on the sampling data. However, with this feedback control method, the light output intensity of the semiconductor laser decreases even if the driving current is kept constant, so even if the amount of light emitted by the semiconductor laser is sampled at a certain time interval and controlled to a constant value, between each sampling It cannot be held at a constant value.

Furthermore, Japanese Patent Laid-Open No. 59-147568 discloses a method in which the sight of a semiconductor laser is adjusted only when a timing signal is intermittently output or immediately after a switch is operated in a laser printer, and the driving current of the semiconductor laser is kept constant at other times. It is being However, in this method, the driving current of the semiconductor laser is kept constant during the period when the semiconductor laser is modulated with a video signal to record an image, so the optical output intensity of the semiconductor laser decreases.

(Objective) It is an object of the present invention to provide a semiconductor laser light amount control device that can improve the above-mentioned drawbacks and keep the optical output intensity of a semiconductor laser constant.

(Structure) The present invention includes a detection means for detecting the optical output of a semiconductor laser;
A comparison circuit that compares the output signal of this detection means with a reference signal, a counter that is controlled by the output signal of this comparison circuit, a digital/analog conversion circuit that converts the output signal of this counter into an analog quantity, and this digital/analog conversion circuit that converts the output signal of this counter into an analog quantity. It has a current amplification circuit that causes a current proportional to the output signal of the analog conversion circuit to flow through the semiconductor laser, and a control means, and the control means enables the counter while the light amount adjustment signal and the video signal are being output. The amount of light emitted from the semiconductor laser is continuously controlled to be near the reference value.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the invention.

The semiconductor laser 1 is used as a light source in a laser printer, and the photodetector circuit 2 receives a back beam emitted backward from the semiconductor laser 1 and outputs a detection signal according to the beam intensity. The reference level setting circuit 3 generates a constant potential reference signal corresponding to the standard of the amount of light emitted from the semiconductor laser 1, and the ratio j calibration circuit 4 generates a detection signal from the optical detection circuit 2 and a reference signal from the reference level setting circuit 3. Compare with. The up/down counter 5 enters the down mode if the output signal of the comparator circuit 4 is input to the up/down terminal and the detection signal is greater than the reference signal, and enters the down mode if the detection signal is smaller than the reference signal. The up/down counter 5 counts the oscillation signal of the oscillation circuit 6 when the enable signal is input from the OR circuit 10, and holds the count value at that point in time when the enable signal from the OR circuit 10 is turned off. The count value of the up/down counter 5 is converted into an analog quantity by a digital/analog conversion circuit 7 and amplified by a current amplification circuit 8. The switch circuit 9 receives the T signal and the video signal via an OR circuit 10, and operates in response to a high level input from the OR circuit 10. When the switch circuit 9 is turned on, it supplies the current from the current amplifier circuit 8 to the semiconductor laser 1, and when it is turned off, no current flows through the semiconductor laser 1. As is well known, the beam emitted forward from the semiconductor laser 1 is deflected by a deflector and scanned on a photoreceptor to form an electrostatic latent image, and this latent image is developed by a developer and transferred to transfer paper. be done. The above T signal is applied to the semiconductor laser 1 outside the printing period from the end of one line scanning to the start of the next line scanning.
This is a signal for lighting up the semiconductor laser 1, a signal for adjusting the light amount of the semiconductor laser 1, and a signal for shortening the standby mode of the semiconductor laser 1.

When the T signal is now input to the OR circuit 10, the switch circuit 9 is turned on by the T signal from the OR circuit 10, and the counter 5 is reenabled by the T signal from the OR circuit 10. Therefore, as the counter 5 counts up, the current flowing through the semiconductor laser 1 increases. The amount of light from the semiconductor laser 1 is converted into an electrical amount by a photodetector circuit 2, and compared with a reference signal from a reference level setting circuit 3 by a comparison circuit 4 to determine whether or not to set the mode of the counter 5 to a down mode. When the detection signal of the photodetector circuit 2 becomes larger than the reference signal, the counter 5 enters the down mode. When the detection signal of the photodetector circuit 2 becomes smaller than the reference signal, the counter 5 enters the up mode. In this way, when the output signal of the OR circuit IO is at a high level, the counter 5 repeats counting up and counting down with the value corresponding to the reference signal as the boundary (see FIG. 2). When the T signal goes low, the output signal of the OR circuit 10 goes low, and the counter 5 becomes disabled and holds the count value until the next time the output signal of the OR circuit 10 goes high.

Then, when the video signal is input to the OR circuit 10.

The output signal of the OR circuit 10 becomes high level, the switch circuit 9 is turned on, and a current proportional to the count value adjusted and held by the T signal of the counter 5 is supplied to the semiconductor laser 1. At the same time, the counter 5 is enabled by the output signal of the OR circuit 10 and counts up or down by the output signal of the comparison circuit 4, and the drive current of the semiconductor laser 1 changes constantly, causing the amount of light emitted by the semiconductor laser 1 to change. Stabilized to reference value.

(Effects) As described above, according to the present invention, the light emission amount of the semiconductor laser is continuously controlled to be near the reference value while the light amount adjustment signal and the video signal are input, so that the light output intensity of the semiconductor laser is can be kept constant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a timing chart of the same embodiment. 1... Semiconductor laser, 2... Detection means, 4...
...Comparison circuit, 5...Counter, 7...Digital/analog conversion circuit, 8...Current amplification circuit, 10
...OR circuit.

Claims (1)

[Claims] A detection means for detecting the optical output of the semiconductor laser, a comparison circuit for comparing the output signal of the detection means with a reference signal, a counter controlled by the output signal of the comparison circuit, and an analog quantity for the output signal of the counter. Digital to convert/
An analog conversion circuit, a current amplification circuit that flows a current proportional to the output signal of the digital/analog conversion circuit to the semiconductor laser, and the counter is enabled while the light amount adjustment signal and video signal are being output. A semiconductor laser light amount control device comprising: control means for continuously controlling the light emission amount of the semiconductor laser to be near a reference value.