JPS6310867A - Automatic output control device for laser diode - Google Patents

Abstract

PURPOSE:To hold the output of a laser diode at a regulated level automatically, by providing a duty control means, a smoothing means, a current conversion means, a comparison means, and a central control unit. CONSTITUTION:The duty control means 2 varies the pulse duty of a laser power control signal based on a control signal inputted from the central control unit 1, and outputs the signal to the smoothing means 3. The smoothing means 3 smoothes the laser power control signal to a DC analog signal, and supplies a current to the laser diode 5 through the current conversion means 4. The monitor output of the laser diode 5 to which the current is supplied, is compared with a reference voltage regulated in advance by the comparison means 6. Based on the above result, the central control unit 1 outputs the control signal to the duty control means 2, and the output of the laser diode can be held at the regulated level according to an operation set in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an automatic output control device for a laser diode that emits a laser beam based on a laser power control fl.

<Prior Art> Generally, the output of a laser diode can be increased or decreased by changing the current flowing through the laser diode, and conventionally, such output control has been performed by adjusting circuit components.

<Problems to be Solved by the Invention> Therefore, in conventional laser diode output control, the adjustment range is fixed and limited due to the adjustment of hardware circuit elements, and the drawback is that detailed control is not possible. was there.

Furthermore, adjusting the circuit elements requires the troublesome work of replacing parts as appropriate, which is very inconvenient.

The present invention was made in view of the conventional drawbacks, and it sets a reference value for the output of a laser diode, changes the output of the laser diode according to the result of comparing the reference value and the output of the laser diode, and automatically adjusts the output of the laser diode. An object of the present invention is to provide an automatic output control device for a laser diode that can keep the output constant.

<Means for Solving the Problems> The present invention provides a duty control means that can vary the pulse duty of a laser power control signal based on an input control signal, and a duty control means that is controlled by the duty control means. a smoothing means for smoothing the pulse signal smoothed by the smoothing means, a current conversion means for supplying the signal smoothed by the smoothing means to the laser diode, and comparing a monitor output of the laser diode with a predetermined reference voltage. and a central control device that outputs a control signal for instructing the pulse duty of the laser power control signal to be varied to the duty control means in response to the output from the comparison means. It is something to do.

Function> In the present invention, the duty control means varies the pulse duty of the laser power control signal based on the control signal input from the central control device, and outputs this signal to the smoothing means. This smoothing means smoothes the laser power control (ff) into a Dc analog signal and supplies current to the laser diode via the current conversion means.The monitor output of the laser diode supplied with current is determined in advance. It is compared with a reference voltage by the comparison means. Based on the result, the central controller outputs a control signal to the duty control means to automatically keep the output of the laser diode constant according to a preset operation. be able to.

<Example> Hereinafter, the automatic output control device for a laser diode of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram when an embodiment of the present invention is used in a laser printer.

In the figure, l is a central control unit, and 2 is a programmable duty control circuit that programmably controls the pulse duty of the laser power control signal (hereinafter referred to as PCON) in multiple stages based on the control signal input from the central control unit 1. control. 3 is a smoothing circuit for smoothing the duty-controlled PCON into a DC analog signal as pulse wide modulation (hereinafter referred to as PWM). Reference numeral 4 denotes a current conversion circuit for controlling the current supplied to the laser diode 5 that emits a laser beam, which biases the lowest threshold current of the laser diode 5 and constantly supplies a predetermined current to the laser diode 5. Further, the laser diode 5 is a monitor mmPIN diode 5' which is a light receiving element.
, built-in.

6 is a comparison circuit for comparing the output voltage from the PIN diode 5' with a reference voltage; the output from the comparison circuit 6 is inputted to the central control unit 1 as a reference signal LMNT; The duty control circuit 2 controls the pulse duty of the PCON based on the control signal. 7 is VIDE for image printing
This is an image signal conversion circuit that latches the O signal with a D-type flip-flop and outputs it as a print signal LDATA.

AND gate 8 and transistor 9 are connected to the LDATA or M
PCEN controls the ON and OFF of the laser diode, and APCEN becomes "High" during the auto power control period.The current flowing into the laser diode 5 increases as the "High" period of the PCON signal increases. Therefore, the laser diode 5
When a decrease in output occurs, the ON duty of the PCON signal is increased so as to increase the current flowing through the laser diode 5, thereby maintaining a constant laser output. The laser power control signal PCON is inputted from the programmable duty control circuit 2 to the smoothing circuit 3, and the pulse wide modulation signal PCON is inputted from the programmable duty control circuit 2 to the smoothing circuit 3.
It is output as WM to the current conversion circuit 4 to control the current of the laser diode 5.

This current conversion circuit 4 constantly applies a predetermined bias to the laser diode 5. This is because the optical output of the laser diode 5 is generally approximately 0 in a low current range as shown in FIG. 2, and the actual control target range is only the Y portion. Therefore, it is sufficient to apply bias only to the X portion in advance.

Further, the VIDEO signal is latched by the D-type flip-flop of the process control unit 7 and output to the LD.
Output as ATA. Here, in the AND gate 8, when the LDATA is @)iii'', the current of the laser diode 5 is bypassed to the transistor 9, the laser is turned off, and a non-exposed area is formed on the photoreceptor.The laser diode 5 is connected as described above. It has a built-in PIN diode 5/ for monitoring, and its output current is used to adjust the optical output and prevent damage due to excessive light emission.The output current of the PIk diode is converted into a voltage, and then compared with the reference voltage by a comparator circuit 6 and automatically A reference signal LMNT for power control p is generated.

FIG. 3 is a flowchart showing the operation of the automatic power controller, and FIG. 4 is a time chart during this operation.

First, the central controller l sets the enable signal APCEN for auto power control to @Low'' state (nl) and outputs a control start signal to the programmable duty control circuit 2. At this time, the programmable duty control circuit 2 outputs a control start signal. The circuit 2 outputs a count value N (for example, 128) corresponding to a preset duty to a counter A.

Set in counter B (n2.n3).

Next, when the counter A is set to N (n4), the duty PCON based on the count value N is issued by the programmable duty control circuit 2 (Fig. 4, PCON).
1) of CON. Further, the counter B is a control value for power control (t-), and the control value B is obtained by dividing N by half (n5), and this value is added to or subtracted from the value of the counter A as described later.

By repeating the loop from n4 to n9, the value of the counter A can be gradually brought closer to the target value.

PCON generated from the programmable duty control circuit 2 is smoothed into a DC analog signal by a smoothing circuit 3, and a current exchange circuit 4 controls the current supplied to the laser diode 5.

The output from the laser diode 5, that is, the output from the PIN diode 5', and the reference voltage are compared in the comparison circuit 6 (n6), and as a result, the gate signal LMNT becomes "High".
In the case of ', the counter A of the programmable duty control circuit 2 is set to count based on the control signal input from the central control unit 1 (n7). Also, the reference signal L
This calculation operation of MNT is repeated until the value of counter B reaches the minimum value of 1. When the value of counter B reaches l (n9), a signal of B=1 is input from programmable duty control circuit 2 to central controller l, and APCEN
becomes 'High' (nlO), and the laser diode 5 is turned on and off by the LDATA signal of the process control unit 7.

This automatic power control operation is illustrated in FIG. 5, where the vertical axis represents the value of counter A and the horizontal axis represents the number n of automatic power control operations. As shown in the figure, if the output voltage of the laser diode 5 that corresponds to the value of counter A is smaller than the reference value, LMNT
becomes @Low”, and if the output voltage of laser diode 5 based on the value of counter A is large, LMNT becomes Hi.
gh”.

becomes. As shown in the figure, as the auto power control operation is repeated, A gradually approaches the target value.

As described above, the present invention compares the output of the monitor mmPIN diode built into the laser diode 5 with a reference voltage and makes the output of the laser diode constant according to a preset operation based on that value. be.

In this embodiment, only the preprocessing up to the start of printing is explained, but the comparator circuit 6 always compares the reference voltage and the output voltage of the laser diode 5, and when no image is being formed, that is, when LDATA is When it is "High", APCEN can be set to "Low" and automatic power control operation can be performed.

Effects> The present invention provides a duty control means that can vary the pulse duty of a laser power control signal based on an input control signal, and a system for smoothing the duty-controlled pulse signal by the duty control means. current converting means for supplying the signal smoothed by the smoothing means to the laser diode, and comparison means for comparing the monitor output of the laser diode with a predetermined reference voltage; and a central control device that outputs to the duty control means a control signal instructing a pulse duty angle change of the laser power control signal in response to the output from the comparison means, so that the output of the laser diode is set to a reference voltage. Based on the results, the output of the laser diode can be automatically maintained constant according to preset operations.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the automatic small current value and optical output of the laser diode of the present invention, Fig. 3 is a flowchart showing the operation of the auto power control of the same device, and Fig. 4 is a diagram showing the auto power control + of the same device. ) Time chart during V operation, FIG. 5 is a diagram showing the state of counter A during auto power control operation. l: central control unit, 2: programmable duty control circuit, 3: smoothing circuit, 4: current conversion circuit, 6: comparison circuit. Agent Patent Attorney Takeshi Sugiyama (and 1 other person) ltA a2 Diagram

Claims (1)

[Claims] 1. a duty control means capable of varying the duty of the pulse of the laser power control signal based on an input control signal; a smoothing means for smoothing the laser power control signal duty-controlled by the duty control means; current conversion means for supplying the signal smoothed by the smoothing means to the laser diode; comparison means for comparing the monitor output of the laser diode with a predetermined reference voltage; and an output from the comparison means. an automatic output control device for a laser diode, comprising: a central control device that outputs a control signal for variably instructing the pulse duty of a laser power control signal to the duty control means in response to the pulse duty of the laser power control signal.