JP2003264337A - Semiconductor laser driving circuit and image forming equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the high speed pulse modulation of a semiconductor laser driving current when a high power type semiconductor laser whose optical output is at least 1 W is driven. <P>SOLUTION: In this semiconductor laser driving circuit, a load adjusting circuit is installed in a generating means of a modulation level voltage. The load adjusting circuit is isolated from the generating means of the modulation level voltage by using a switch when the modulation level voltage is connected with a constant current source, and connects the generating means of the modulation level voltage with a voltage almost equivalent to a voltage after a bias level voltage is added to the modulation level voltage, when a ground voltage is connected with the constant current source. As a result, the fluctuation of the modulation level voltage in the case of pulse modulation can be restrained irrespective of the state of an on-off modulation signal, so that the laser driving current can be pulse-modulated at a high speed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser drive circuit capable of suppressing fluctuation in voltage at a modulation level which occurs when pulse-modulating a drive current of a high-power semiconductor laser, and a semiconductor laser drive circuit for the same. The present invention relates to an image forming apparatus for forming an image corresponding to an image signal on a recording material.

[0002]

2. Description of the Related Art FIG. 4 is a schematic configuration diagram of an example of a conventional semiconductor laser drive circuit. This figure is generally used as a drive circuit for a high power semiconductor laser. A semiconductor laser L on the right side of the drive circuit 52 on the left side of the drawing
D is a twisted pair cable 56 via the connector CN.
Connected by. The semiconductor laser LD has its anode connected to the ground potential and its cathode connected to the negative potential, and the drive circuit 52 is configured to extract the current supplied from the semiconductor laser LD.

The semiconductor laser drive circuit 52 of the illustrated example is composed of a voltage generator 60 and a voltage addition and constant current source 62.

First, the voltage generating section 60 includes a semiconductor laser L.
The bias level voltage Vb that determines the value of the DC bias current IB that is steadily supplied to D, and the modulation level that determines the value of the current that causes the semiconductor laser LD to oscillate by being superimposed on the bias level voltage Vb. Generates voltage Vd, and 2 sets of D / A (digital / analog)
The converters 64 and 66, the operational amplifiers 68 and 70, and the switch SW are provided.

Outputs of the D / A converters 64 and 66 are input to operational amplifiers 68 and 70, respectively. The output of the operational amplifier 68 is connected to one input terminal of the switch SW, and the other input terminal is connected to the ground potential. This switch SW is on / off (ON / OF
F) When the modulation signal is in the on state, it is connected to the output of the operational amplifier 68, and when it is in the off state, it is connected to the ground potential. The output terminal of the switch SW and the output of the operational amplifier 70 are connected via resistors R1 and R2, respectively.

In the voltage generator 60, a bias level voltage Vb is generated by the lower D / A converter 66 and operational amplifier 70 in the figure, and a modulation level voltage is generated by the upper D / A converter 64 and operational amplifier 68. Vd is generated. The modulation level voltage Vd is pulse-modulated by the switch SW according to an on / off modulation signal based on the image signal, and a pulse-modulated voltage Vd ′ of a modulation level is generated.

The voltage adding / constant current source 62 has a bias level voltage Vb generated in the voltage generator 60.
And the modulation level voltage Vd ′ after pulse modulation are added, and the laser drive current I proportional to the voltage signal of these sums is added.
It generates an LD, and includes an operational amplifier 74, transistors Tr1 and Tr2, and resistors R1 to R6. Here, the positive power supply voltage of the operational amplifier 74 is + VS, and the negative power supply voltage thereof is -VS. Also, the transistors Tr1,
Tr2 is connected in series between the positive power supply voltage + VCC and the negative power supply voltage −VCC, and has an operational amplifier 74 at its base.
Output voltage VOUT is input.

Usually, a large current of 2 A or more is required to drive a high-power semiconductor laser whose optical output exceeds 1 W. Therefore, as in the drive circuit 52 shown in FIG. 4, it is general to add the transistors Tr1 and Tr2 after the operational amplifier 74 of the voltage addition and constant current source 62 to improve the current drive capability.

In the voltage addition / constant current source 62, the relationship expressed by the following equation (1) is established between the bias level voltage Vb and the pulse-modulated modulation level voltage Vd ′ and the laser drive current ILD. ILD = (R4 / (R6 × R1)) × (Vb + Vd ′) (1) Here, R1 = R2, R4 = R5, R3 = R1 // R2
= R1 / 2. The semiconductor laser LD has the above formula (1).
It is driven according to the laser drive current ILD calculated in.

[0010]

By the way, focusing attention on the output terminal of the operational amplifier 68 which generates the voltage Vd of the modulation level, the output terminal of the operational amplifier 68 is as described above.
When the on / off modulation signal is in the on state, it is connected to the resistor R1 through the switch SW, and when the on / off modulation signal is in the off state, there is no load (open state). For this reason, the output of the operational amplifier 68 is characterized in that its load rapidly changes according to the on / off state of the on / off modulation signal.

In particular, when the on / off modulation signal changes from the off state to the on state, the load on the output terminal of the operational amplifier 68 changes abruptly, and the output voltage Vd of the operational amplifier 68 temporarily drops, as shown in FIG. Operational amplifier 6 for ON / OFF modulation signal in the lower part of the timing chart
The waveforms of the output voltage (voltage of modulation level) Vd and the laser drive current ILD of No. 8 are actually the waveforms shown in the timing charts in the central portion and the upper portion of FIG.

That is, when the state of the on / off modulation signal changes, the voltage Vd of the modulation level fluctuates greatly. As a result, in the conventional semiconductor laser drive circuit 52, the laser drive current is changed after the on / off modulation signal is turned on. IL
The time Δt required for D to stabilize at the desired value ILD1
Since d becomes relatively long and the drive current cannot be stabilized in a time shorter than Δtd, the drive current IL
There has been a problem that D cannot be pulse-modulated at high speed.

An object of the present invention is to solve the above-mentioned problems of the prior art and to drive a semiconductor laser driving current at high speed when driving a high power semiconductor laser having an optical output of 1 W or more. It is an object of the present invention to provide a laser drive circuit and an image forming apparatus that scans and exposes a recording material using the semiconductor laser drive circuit.

[0014]

To achieve the above object, the present invention provides a voltage generator for generating a voltage signal pulse-modulated according to an image signal, and a voltage signal generated by the voltage generator. And a constant current source for generating a laser drive current for driving the semiconductor laser based on the voltage level of the bias level that determines the value of the DC bias current that is constantly supplied to the semiconductor laser. Of the modulation level, the generation means of the voltage of the modulation level for determining the value of the current superposed on the voltage of the bias level to oscillate the semiconductor laser, and the generation means of the voltage of the modulation level and the constant current source. The modulation level voltage is controlled by an ON / OFF modulation signal so as to connect the modulation level voltage or the ground potential to the constant current source. And a load adjusting circuit that is connected to the modulation level voltage generating means and operates complementarily to the switch, wherein the load adjusting circuit causes the switch to change the modulation level voltage to the constant current. When connected to the source, the modulation level voltage generating means is disconnected, and when the ground potential is connected to the constant current source, the modulation level voltage generating means,
The present invention provides a semiconductor laser drive circuit, characterized in that the semiconductor laser drive circuit is connected to a voltage substantially the same as the voltage after adding the voltage of the bias level and the voltage of the modulation level after pulse modulation.

Further, the present invention is an image forming apparatus for forming an image corresponding to an image signal on a recording material, the semiconductor laser drive circuit described above, and drive control by the semiconductor laser drive circuit, A semiconductor laser that serves as an exposure light source for the recording material, an imaging optical system that controls a light beam emitted from the semiconductor laser so as to form an image near the surface of the recording material via a lens, and the semiconductor laser Based on the image signal, while moving the light beam emitted through the imaging optical system and the recording material in the main scanning direction and the sub scanning direction substantially orthogonal to the main scanning direction, the semiconductor An image forming apparatus comprising: a scanning exposure unit that scans and exposes the recording material with a light beam emitted from a laser.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A semiconductor laser drive circuit and an image forming apparatus of the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

FIG. 1 is a schematic perspective view of an embodiment of the image forming apparatus of the present invention. The image forming apparatus 10 shown in FIG.
The semiconductor laser driving circuit of the present invention drives and controls the semiconductor laser LD, which serves as an exposure light source, based on an image signal, scans and exposes the recording material A with a light beam emitted from the semiconductor laser LD, and An image corresponding to the image signal is formed, and includes a light source unit 12, a scanning exposure unit 14, and an image forming optical system 16.

In the illustrated example, the fiber array 24 of the light source section 12 and the image forming optical system 16 are fixed to a predetermined position on one moving support 38 to form an image forming unit 36.

In the image forming apparatus 10, first, the light source section 12 emits a multi-beam composed of a plurality of light beams arranged in a line at a predetermined interval.
A plurality of semiconductor lasers 18 and these semiconductor lasers 1
8 is provided with a plurality of optical fiber cables 20 provided in a one-to-one correspondence, and a connector array 22 and a fiber array 24 for bundling the central portion and the end portion of these optical fiber cables 20 at one place. .

Here, the plurality of semiconductor lasers 18 are arranged in a row on the heat sink 26 at a predetermined interval in the sub-scanning direction (direction of arrow c in the figure).
It is kept at a predetermined temperature by 6. A light beam for exposing the recording material A is emitted from each semiconductor laser 18. In the case of the illustrated example, one light beam is emitted from each semiconductor laser 18, and a multi-beam composed of a plurality of light beams in total is emitted.

Although not shown, each semiconductor laser 18 is driven by a semiconductor laser drive circuit of the present invention described later.

The optical fiber cable 20 is connected at its incident end face at the starting end to the corresponding emitting part of the light beam of the semiconductor laser 18. In addition, the connector array 22 bundles the central portion of the connector array 22 on the support plate 28 at a time.
The fiber array 24 allows the multi-beams emitted from the emission end face of the terminal end of the optical fiber cable 20 to be arranged on the recording material A at a predetermined interval in the sub-scanning direction so as to be arranged in a row by the support member 30. It is arranged.

The light beams emitted from the respective semiconductor lasers 18 pass through the corresponding optical fiber cables 20, and are emitted from the emission end face of the terminal end arranged in a line by the supporting member 30 of the fiber array 24.

Subsequently, in the image forming apparatus 10 shown in FIG. 1, the scanning exposure section 14 performs the scanning exposure of the recording material A by the outer drum (outer surface drum) system, and the outer drum 32 and this. The outer drum 32 is provided with a rotation driving means (not shown) and a sub-scanning means 34.

Here, the outer drum 32 has a recording material A such as a PS plate (PreSensitized plate) on the outer peripheral surface thereof.
Is mounted and is rotated at a predetermined constant speed in the main scanning direction (rotational direction of the outer drum 32) by a rotation driving means (not shown) during scanning exposure.

The sub-scanning means 34 moves the image forming unit 36 in the sub-scanning direction, and includes a moving support base 38 which is a base of the image forming unit 36 and a ball screw (driving screw).
40, a rotation driving means (not shown) for the ball screw 40, and a base 42.

Here, a V-shaped protrusion extending in the sub-scanning direction is formed in the lower portion of the movable support base 38, and a ball screw extending in the sub-scanning direction is formed in the center of the protrusion. Four
A female screw threaded with 0 is formed. Also, the base 42
Is formed with a V-shaped groove 44 that fits with the V-shaped protrusion of the movable support base 38 and extends in the sub-scanning direction. The movable support base 38 is rotationally driven (not shown). It is configured to be movable in the sub-scanning direction by the rotation of the ball screw 40 by the mechanism.

As shown in FIG. 1, the heat sink 26 of the light source section 12 and the connector array 22 are also mounted on the upper surface of the base 42.

Subsequently, in the image forming apparatus 10 shown in FIG. 1, the image forming optical system 16 forms an image of the multi-beam emitted from the light source unit 12 on the recording material A of the scanning exposure unit 14 with a predetermined spot size. The reduction optical system includes a collimator lens 46 and an imaging lens 48.

Here, the collimator lens 46 is arranged on the downstream side of the fiber array 24 in the light traveling direction,
All the multi-beam light beams emitted from the fiber array 24 are collimated light (parallel light). The imaging lens 48 includes the collimator lens 46 and the outer drum 3.
The light beam, which is arranged between the recording material A and the recording material A mounted on the outer peripheral surface of the second light beam and is emitted through the imaging lens 48, is imaged on the recording material A with a predetermined spot size.

In the image forming apparatus 10, during scanning exposure, while the outer drum 32 is rotated at a predetermined constant speed in the main scanning direction, the image forming unit 36 is moved at a predetermined constant speed in the sub scanning direction by the sub-scanning means 34. Be moved. As a result, the recording material A is two-dimensionally scanned and exposed by the multi-beam imaged on the recording material A through the semiconductor laser 18, the optical fiber cable 20, and the imaging optical system 16, and an image corresponding to the image signal is formed. It is formed on the recording material A.

The image forming apparatus of the present invention is not limited to the illustrated example, and the semiconductor laser driving circuit of the present invention described below is used to drive and control the semiconductor laser, and the semiconductor laser is connected by the scanning exposure means. The present invention can be applied to image forming apparatuses of any structure that two-dimensionally scan and expose a recording material while moving a light beam emitted through an image optical system and the recording material relatively in the main scanning direction and the sub scanning direction. is there.
The recording material is not limited to a printing plate such as a PS plate, and any conventionally known recording material can be used.

Next, the individual semiconductor lasers 18 shown in FIG.
A semiconductor laser drive circuit of the present invention for driving the laser will be described.

FIG. 2 is a schematic configuration diagram of an embodiment of the semiconductor laser drive circuit of the present invention. The semiconductor laser drive circuit 50 shown in the same figure is one in which the present invention is applied to the conventional semiconductor laser drive circuit 52 shown in FIG. 4, and the semiconductor laser LD has its anode at a ground potential and its cathode at a negative potential. It is connected to the. In addition, the voltage signal V supplied from the voltage generator 60 to the voltage addition and constant current source 62
N ′ is a positive voltage, and the drive circuit 50 is the semiconductor laser L
It is configured to draw an electric current from D.

The difference between the semiconductor laser driving circuit 50 of the present invention shown in FIG. 2 and the conventional semiconductor laser driving circuit 52 shown in FIG. 4 is that a load adjusting circuit 76 is provided. The load adjusting circuit 76 includes a resistor R7 and an N channel type FE.
A T (field effect transistor) 78 and an inverter 80 are provided. The resistor R7 and the FET 78 are connected in series between the output terminal of the operational amplifier 68 and the voltage Vss, and an ON / OFF modulation signal is input to the gate of the FET 78 via the inverter 80.

Semiconductor laser driving circuit 5 other than this
The configuration of 0 corresponds to the conventional semiconductor laser drive circuit 5 shown in FIG.
Since it is the same as No. 2, the same constituents are designated by the same reference numerals, and detailed description thereof will be omitted. The operation of the semiconductor laser drive circuit 50 shown in FIG.
6 is basically the same as the conventional semiconductor laser drive circuit 52 shown in FIG. 4 except that the fluctuation of the voltage Vd of the modulation level at the time of pulse modulation is suppressed, and therefore will be briefly described below.

That is, in the voltage generator 60, a bias level voltage Vb is generated by the D / A converter 66 and the operational amplifier 70 on the lower side in the figure, and a modulation level is generated by the D / A converter 64 and the operational amplifier 68 on the upper side. Voltage Vd
Is generated. The modulation level voltage Vd is set by the switch SW.
According to the on-off modulation signal based on the image signal, the voltage V of the modulation level pulse-modulated
d'is generated.

The pulse-modulated voltage Vd 'of the modulation level and the voltage Vb of the bias level generated by the voltage generator 60 are supplied to the operational amplifier 74 of the voltage addition and constant current source 62 via the resistors R1 and R2, respectively. It In the voltage addition and constant current source 62, the operational amplifier 74
The laser drive current ILD proportional to the sum of the voltage signals of the voltage signals Vb and Vd ′ supplied from the voltage generator 60 by the transistor Tr2 and the resistors R1 to R6.
Is generated, and the semiconductor laser LD is driven according to the voltage addition and the laser drive current ILD generated by the constant current source 62.

If the on / off modulation signal is in the on state (high level in this embodiment), the switch SW
Thus, the output terminal of the operational amplifier 68 and the resistor R1 are electrically connected. The load adjustment circuit 76 operates complementarily to the switch SW. That is, in this case, the high level of the on / off modulation signal is inverted by the inverter 80 to a low level, and therefore the FET 78 is turned off, so that it is electrically disconnected from the output terminal of the operational amplifier 68.

On the other hand, when the on / off modulation signal is in the off state (low level in this embodiment), the switch SW electrically connects the ground potential and the resistor R1,
The output terminal of the operational amplifier 68 is opened. At this time, in the load adjusting circuit 76, the low level of the on / off modulation signal is inverted by the inverter 80 to become a high level, and therefore the FET 78 is turned on, so that the output terminal of the operational amplifier 68 is connected to the voltage Vss via the resistor R7 and the FET 78. To be done.

Therefore, the resistors R7 and R1 have substantially the same resistance value, and the voltage Vss and the voltage VN 'of the inverting input terminal of the operational amplifier 74 are substantially the same voltage, so that the on / off modulation signal is turned on / off. Regardless, the load on the output terminal of the operational amplifier 68 can be made constant at all times, so that the voltage V
It is possible to prevent the variation of d.

Vss = VN '= (R3 / (R3 +
R5)) * VM = (R3 / (R3 + R5)) * VLD. Here, VM is the output voltage of the semiconductor laser drive circuit 50, and VLD is the forward voltage of the semiconductor laser LD.

That is, in the semiconductor laser drive circuit 50 of the present invention, when the laser drive current ILD is pulse-modulated, as shown in the timing chart of FIG. 3, the fluctuation of the modulation level voltage Vd when the on / off modulation signal changes. Since it is extremely small, the laser drive current ILD can be stabilized in a short time. Therefore, the laser drive current IL
D can be pulse-modulated at high speed, and the image forming apparatus 10 using the semiconductor laser drive circuit 50 of the present invention can form a high-quality image on the recording material at high speed.

The semiconductor laser driving circuit of the present invention is
Regardless of the state of the on-off modulation signal, the purpose is to provide a load adjustment circuit at the output terminal of the means for generating the modulation level voltage Vd in order to suppress fluctuations in the modulation level voltage Vd during pulse modulation. However, the specific circuit configuration other than this is not limited at all. Similarly, the specific circuit configuration of the load adjusting circuit is not limited at all, and another circuit that realizes a similar function may be used.

The image forming apparatus of the present invention drives and controls the semiconductor laser LD using the semiconductor laser drive circuit of the present invention to form an image corresponding to an image signal on a recording material. The specific configuration of is not limited at all. Further, in the example shown in FIG. 2, the anode of the semiconductor laser LD is connected to the ground potential and the cathode is connected to the negative potential, but this is not a limitation, and the cathode is connected to the ground potential and the anode is connected to the positive potential. The polarity of the signal of each part of the semiconductor laser drive circuit may be changed accordingly.

The semiconductor laser drive circuit and the image forming apparatus of the present invention are basically as described above. that's all,
Although the semiconductor laser drive circuit and the image forming apparatus of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various improvements and changes may be made without departing from the spirit of the present invention. Of course.

[0047]

As described in detail above, in the semiconductor laser drive circuit of the present invention, the load level adjusting circuit is provided in the modulation level voltage generating means, and the modulation level voltage is connected to the constant current source by the switch. In this case, disconnect the load adjustment circuit from the modulation level voltage generation means, and if the ground potential is connected to the constant current source, change the modulation level voltage generation means to the bias level voltage and after pulse modulation. The voltage of the modulation level is added, and the voltage is connected to substantially the same voltage. Further, the image forming apparatus of the present invention uses the semiconductor laser driving circuit of the present invention to drive and control the semiconductor laser and form an image corresponding to the image signal on the recording material. This allows
According to the semiconductor laser drive circuit of the present invention, the fluctuation of the voltage of the modulation level at the time of pulse modulation can be suppressed very slightly regardless of the state of the on / off modulation signal, and the laser drive current can be pulse-modulated at high speed. it can. Further, according to the image forming apparatus of the present invention, there is an effect that a high quality image can be formed on a recording material at high speed.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of a semiconductor laser drive circuit of the present invention.

FIG. 3 is a timing chart of an example showing a relationship between an on / off modulation signal, a modulation level voltage, and a laser drive current in the semiconductor laser drive circuit of the present invention shown in FIG.

FIG. 4 is a schematic configuration diagram of an example of a conventional semiconductor laser drive circuit.

5 is a timing chart showing an example of a relationship between an on / off modulation signal, a modulation level voltage, and a laser drive current in the conventional semiconductor laser drive circuit shown in FIG.

[Explanation of symbols]

10 image forming apparatus 12 Light source 14 Scanning exposure unit 16 Imaging optical system 18 Semiconductor laser 20 optical fiber cable 22 connector array 24 fiber array 26 heat sink 28 Support plate 30 Support member 32 outer drum 34 Sub-scanning means 36 Imaging unit 38 Moving support 40 ball screw (drive screw) 42 base 44 groove 46 Collimator lens 48 Imaging lens 50,52 Semiconductor laser drive circuit 56 twisted pair cable 60 voltage generator 62 Voltage addition and constant current source 64,66 D / A converter 68, 70, 74 operational amplifier 76 Load adjustment circuit 78 FET CN connector LD semiconductor laser R1 to R7 resistance SW switch Tr1, Tr2 transistor

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C162 AE23 AE28 AE48 AF14 AF72                       AH75 FA04 FA18 FA48                 2C362 AA07 AA55 AA61 CB71                 5F073 BA07 EA14 GA02 GA24 GA25

Claims (2)

[Claims] 1. A voltage generator for generating a voltage signal pulse-modulated according to an image signal, and a laser drive current for driving a semiconductor laser based on the voltage signal generated by the voltage generator. A constant current source, wherein the voltage generation unit is a bias level voltage generation unit that determines the value of a DC bias current that is constantly supplied to the semiconductor laser; and the semiconductor device that is superimposed on the bias level voltage. A modulation level voltage generating means for determining the value of the current for oscillating the laser, and a modulation level voltage generating means arranged between the modulation level voltage generating means and the constant current source, and the modulation level voltage or ground depending on an on / off modulation signal. A switch, which is controlled to connect an electric potential to the constant current source, pulse-modulates the voltage of the modulation level and a means for generating the voltage of the modulation level are connected. And a load adjusting circuit that operates in a complementary manner with the switch, wherein the load adjusting circuit, when the voltage of the modulation level is connected to the constant current source by the switch, the voltage of the modulation level. When the ground potential is connected to the constant current source, the voltage generator of the modulation level is added with the voltage of the bias level and the voltage of the modulation level after pulse modulation. A semiconductor laser drive circuit characterized in that it is connected to a voltage substantially the same as a subsequent voltage. 2. An image forming apparatus for forming an image corresponding to an image signal on a recording material, the semiconductor laser driving circuit according to claim 1, and the semiconductor laser driving circuit drivingly controlling the recording material. Of the semiconductor laser as an exposure light source, an imaging optical system for controlling a light beam emitted from the semiconductor laser so as to form an image near the surface of the recording material through a lens, and the semiconductor laser to form the connection. Based on the image signal, the semiconductor laser is moved from the semiconductor laser while relatively moving the light beam emitted through the image optical system and the recording material in the main scanning direction and the sub scanning direction substantially orthogonal to the main scanning direction. An image forming apparatus comprising: a scanning exposure unit that scans and exposes the recording material with an emitted light beam.