JP3332916B2 - Image forming apparatus and laser driver IC used therein - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus and used it to form an image by scanning a laser beam onto a photosensitive surface
The present invention relates to a laser driver IC used.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for forming an image by scanning a photosensitive surface with a laser beam, a laser drive circuit for driving a laser and a polygon motor drive circuit are formed on separate chips. The laser power control circuit provided in the drive circuit is A / D
The laser power is controlled by logic control by a CPU or the like using conversion and D / A conversion.

[0003]

[SUMMARY OF THE INVENTION However, the laser drive circuit is constituted by a bipolar element for logic and analog are present, if an attempt is made to form a polygon motor drive circuit and the laser drive circuit on the same chip, Logic part is composed of IIL or BiCM
It is necessary to use an OS process (a process of forming a mixture of bipolar and CMOS) to configure the logic unit with a CMOS device and the analog unit with a bipolar device. Therefore, when the IIL is used, there arises a problem that the laser power control cannot be performed at a high speed due to the frequency response of the IIL, and when the BiCMOS process is used, the manufacturing cost increases and the expensive
This causes a problem of becoming C. Therefore, high
Image forming equipment that requires precise laser power control
In, the laser driver is a discrete circuit
Configuration and does not use laser driver ICs
It is.

[0004]

An object of the present invention is to solve the above-mentioned technical problems and to control a desired laser power at a high speed.
To ensure that production costs are not
Image forming apparatus that forms an image by scanning laser light onto a photosensitive surface.
An object of the present invention is to provide a laser driver IC used for an image forming apparatus and an image forming apparatus using the same.

[0006]

[0007]

In order to achieve the above object, an image forming apparatus according to the present invention is a laser driver IC used in an image forming apparatus for forming an image by scanning a photosensitive surface with a laser beam. Image where the image signal is input
Connect the signal input terminal to the laser element connected to the laser element.
A connection terminal, a current generation circuit for generating a current, and the image signal.
A current generated by the current generating circuit based on an image signal input to the laser element connection terminal;
An on / off circuit for turning on / off the supply to the laser element via a terminal, and inputting a laser beam from the laser element;
Photodiode connection connected to active photodiode
Terminal and a signal input to the photodiode connection terminal
Based on, co for connecting a detection circuit for detecting the laser power, and the external signal input terminal for inputting an external signal for determining the laser power to target, a capacitor
Capacitor connection terminal and detected by the detection circuit.
A current control circuit having a sample and hold circuit that charges and discharges the capacitor according to laser power ,
A current control circuit for controlling a current generated by the current generating means based on the laser power detected by the detecting means and an external signal input from the input terminal. .

Preferably, the current control circuit is configured to detect
A laser power detected by the means, a comparison circuit for comparing a reference value , the sample and hold circuit,
Charging and discharging the capacitor according to the comparison result of the comparison circuit
Charge .

Preferably, the sample and hold circuit is controlled to be in a sample state only when the on / off circuit is in an on state.

[0010] Preferably, the sample and hold circuit comprises:
Having a transistor for discharging the charge of the capacitor.
Then, the laser driver IC further generates a reset signal.
A reset signal input terminal for inputting, wherein the reset
When a reset signal is input to the signal input terminal,
Using a transistor of a sample hold circuit.
Discharge the sensor charge.

Further, the image forming apparatus of the present invention has the above-described configuration.
Image forming apparatus using a laser driver IC.
You.

[0012]

[0013]

[0014]

[0015]

FIG. 1 shows a first embodiment of the present invention.

The laser diode 157 includes a laser diode chip connected to the pin 25P and a photodiode connected to the pin 26P for detecting laser power. The laser diode chip is turned on and off by transistors 108 and 107.
FF is performed. When the laser ON / OFF pin 22P becomes lower than the base reference voltage 132 of the transistor 108, the transistor 107 is turned off and the transistor 1
08 is turned ON. As a result, a current flows through the laser diode chip. This current is controlled by transistor 106. Transistor 106 forms a current mirror with transistor 105, and
4 forms a current mirror with the transistor 103.

The collector current flowing through the transistor 103 is determined by the operational amplifier 101, the transistor 102, and the pin 23.
It is controlled by the voltage on the non-inverting side of the operational amplifier 101 by the external resistor 161 attached to P.

Therefore, the current to the laser diode chip is controlled by the voltage on the non-inverting side of the operational amplifier 101.

When the laser ON / OFF pin 22P becomes higher than the reference voltage 132, the transistor 108
The flip-flop is turned on and the transistor 107 is turned on. As a result, a current flows through the resistor 156 attached to the pin 24P. The voltage of the laser ON / OFF pin 22P is about 1 Volt plus or minus the reference voltage 132 on the base side of the transistor 108 to turn on / off the laser.
It is off. When this voltage fluctuates greatly, ON, O
When the FF changes, the collector voltage of the transistor 106 greatly fluctuates, which adversely affects the switching characteristics of the laser.

When the laser is on, the laser power is detected by the current flowing through the photodiode. This current flows into the transistor 109 and the transistor 10
9 and the collector current of the transistor 110 serving as a current mirror. And a transistor 111,
The transistor 112 is also a current mirror, and the above-described photodiode current appears as a collector current of the transistor 112.

This current is applied to a resistor 1 externally connected to pin 1P.
58, and is converted into a voltage by this resistor.

This voltage is input to the base of the transistor 141.

The transistor 141 is a transistor 142
And the differential amplifier circuit, the transistor 14
The second reference voltage 145 on the base side is compared with the aforementioned voltage. For a voltage higher than the reference voltage 145,
The current on the transistor 142 side increases. Therefore, the current on the transistor 144 side flows more than the transistor 143. Further, the current of the transistor 147 having the current mirror configuration with the transistor 144 flows more than the current of the transistor 146 having the current mirror configuration with the transistor 143 and the transistor 149 having the current mirror configuration with the transistor 148. In other words, the capacitor 160 externally connected to the pin 8P is discharged to lower the voltage across the capacitor 160. As a result, the voltage on the non-inverting side of the operational amplifier 101 decreases, and the current of the laser diode chip decreases.

Conversely, when the voltage across resistor 158 is lower than reference voltage 145, the current in transistor 149 increases and the current in transistor 147 decreases. Therefore, the capacitor 160 is charged, and the voltage across the capacitor is increased. As a result, the voltage on the non-inverting side of the operational amplifier increases, and the current of the laser diode chip increases.

When the voltage across the external resistor 158 becomes equal to the reference voltage 145, the currents flowing through the transistors 149 and 147 become equal, and the voltage across the capacitor 160 does not fluctuate.

On the other hand, the transistor 140 is a constant current source of the differential amplifier circuit composed of the transistors 142 and 141.

The transistor 140 is a transistor 139
And a current mirror, and the transistor 138,
137, the current flowing through the transistor 139 becomes O
N, it can be turned off. When a voltage higher than the reference voltage 136 on the base side of the transistor 137 is applied to the sample and hold pin 6P, the transistor 138 is turned on, a current flows through the transistor 139, and the transistors 142 and 141 operate as described above. Then, a sample operation is performed.

On the other hand, when a voltage lower than the reference voltage 136 is applied to the sample hold pin 6P, the transistor 1
38 is turned off, and no current flows through the transistors 142 and 141, resulting in a hold operation.

Further, the transistor 135 forms a current mirror with the transistor 134, and the transistor 131 forms a current mirror with the transistor 130.

Transistor 128 and Transistor 129
, The current flowing to the transistor 130 is turned ON and OFF.

The base of the transistor 129 is connected to a reference voltage 200 slightly lower than the reference voltage 132 at the base of the transistor 108 where the laser is turned on and off. In addition, a laser ON / OFF pin 22P is connected to the base of the transistor 128.

That is, the laser on / off pin 22
When P turns on the laser, first, the transistor 108
N, followed by a sequence in which the transistor 129 is turned on. That is, the configuration is such that the sample hold circuit operates after the laser is turned on.

Also, from the above description, the transistor 133
Is determined by the current of the sample hold circuit.

On the other hand, an external resistor 15 connected to the pin 1P
8 is configured so that the collector current of the transistor 116 also flows.

The transistor 116 is a transistor 117
And constitute a current mirror.

The transistor 118 is a transistor 119
And constitute a current mirror.

When a voltage lower than the reference voltage 124 connected to the base side of the transistor 121 is applied to the pin 2P, the transistor 120 is turned on and a current flows through the transistor 119. The reference voltage 124 is applied to the pin 2P.
When a higher voltage is applied, the transistor 121 becomes O
N and the transistor 120 is turned off and the transistor 1 is turned off.
No current flows through 19.

The transistor 122 is a transistor 123
And a current mirror, and the transistor 123
The collector current of the operational amplifier 126, the reference voltage 127
, Transistor 125 and resistor 15 connected to pin 4P
9 is determined. That is, the collector current of the transistor 116 is determined by the resistor 159.

When a current flows through the transistor 116, the voltage between both ends of the resistor 158 becomes high, which is the same as when a large laser power is output, so that the laser power becomes small.

That is, the laser power can be switched by the pin 2P, and the fluctuation width of the switching power can be controlled by the resistance 1
59.

The voltage across the resistor 158 is equal to the reference voltage 1
15 and the comparator 114, and the reference voltage 1
When the voltage becomes larger than 15, the transistor 113
Is turned on to discharge the capacitor connected to the pin 8P through the resistor 202. This turns off the laser when the laser power exceeds a predetermined value.
The laser is not broken.

A reset pin 7P is provided so that when the voltage of the pin 7P becomes higher than the reference voltage 154, the transistor 152 is turned on and the transistor 151 is turned off. Accordingly, no current flows through the transistor 201, and no current flows through the transistor 133 that forms a current mirror with the transistor 201. That is, as described above, current does not flow through the sample and hold circuit, and the sample and hold circuit does not operate.

The transistor 153 has a current source 15
A current of 0 flows, and the same current flows through the transistor 153 and the transistor 155 which is a current mirror.

As a result, the non-inverting terminal of the operational amplifier 101 becomes the GND level, and the laser power is not output.

On the same chip, a hall motor controller 162 and driver transistors 163, 16
4, 165, 166, 167, 168 are constituted by bipolar elements. The resistors 169 and 173 are the Hall elements 17
0, 171, and 172 are determined. The Hall elements 170, 171 and 172 detect the rotor position of the motor, and input the voltage to the pins 17P, 18P, 19P, 20P and 21P.

The Hall motor controller 162 determines an appropriate drive transistor from the rotor position information from the Hall elements 170, 171 and 172, and
Stator coil 1 to which P, 10P and 11P are connected
Current flows through 74, 175 and 176.

The rotation speed of the rotor is detected by the tachogenerator 177 and is input to the pins 13P and 14P. The speed information of the tacho generator 177 is
It is compared with the basic clock CLK input to P, controls the current flowing to the motor, and is controlled to the rotation speed based on the basic clock of the pin 15P. Resistor 178 is pin 1
2P, for detecting the above-mentioned current of the stator coil.

As shown in FIG. 2, the above-described monolithic driver IC 253 includes a laser 254 and a connector 256 on an iron substrate 251 constituting a polygon motor.
Implemented with 252 is a polygon mirror.

The pin 3P is a power supply voltage for laser control, the pin 5P is a GND, and the pin 27P is a power supply pin for a polygon motor.

[Other Embodiments] FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

Parts that are the same as in the first embodiment are given the same reference numerals, and description thereof is omitted here. The difference from the first embodiment lies in a reset circuit and a laser power abnormality detection circuit.

In the first embodiment, the transistor of the reset circuit and the transistor for abnormality detection are connected to the pin 8P of the capacitor for sample and hold. In this case, if the hold time is extremely long, the influence of the leakage current of the collector and the base of the transistor may increase. The second embodiment is a circuit which makes it possible to make the hold time longer, and makes it possible to reduce the influence of the leakage current of the collector and the base of the transistor.

In the reset circuit, the transistor 15
The operations up to 5 are the same as in the first embodiment.

That is, when a collector current flows through the transistor 155, a collector current flows through the transistor 301 and a current flows through the collector of the transistor 302 which is a current mirror with the transistor 301. As a result, as described in the first embodiment, the transistor 140 is in the OFF state, so that a current flows through the transistor 144, further flows a current through the transistor 147, discharges the capacitor, and resets as in the first embodiment. State. In the laser power abnormality detection circuit, the voltage between both ends of the resistor 158 is compared with the reference voltage 303 by the transistors 304, 305, 307, and 308. If the voltage becomes larger than the reference voltage, the current of the current source 306 flows through the transistor 310. Flows through the transistor 309 serving as a current mirror, and flows a current through the transistor 301. The rest is the same as the operation of the reset circuit.

The monolithic driver IC according to the second embodiment is also mounted as shown in FIG.

[0056]

As described above, according to the present invention,
To perform the control to the desired laser power at high speed
Lasers that can be manufactured and do not increase production costs
An image forming device that scans light on a photosensitive surface to form an image
Laser driver IC used and image using the same
A forming device can be provided .

[0057]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a monolithic driver IC according to a first embodiment of the present invention.

FIG. 2 is a mounting diagram of a monolithic driver IC of the present invention.

FIG. 3 is a circuit diagram of a monolithic driver IC according to a second embodiment of the present invention.

[Explanation of symbols]

101, 126 Operational amplifier 102, 113, 116, 123, 125, 128, 1
31, 133, 135, 137, 144, 146, 14
9, 151, 153, 155, 163, 168, 201
Transistor 114 Comparator 115, 124, 127, 132, 136, 145, 1
54, 200 Reference voltage 150 Current source 156, 158, 159, 161, 169, 173, 1
78, 202 Resistance 157 Laser 160 Capacitor 162 Hall motor control circuit 170, 172 Hall element 174, 176 Stator coil 251 Metal substrate 254 Laser unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-287163 (JP, A) JP-A-1-234867 (JP, A) JP-A-62-8864 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) B41J 2/44 G03B 27/32 G03B 27/72 G03F 7/20 505

Claims (5)

(57) [Claims] 1. A laser driver IC used in an image forming apparatus for forming an image by scanning a photosensitive surface with a laser beam, wherein the laser driver IC is connected to an image signal input terminal for inputting an image signal and a laser element. A laser element connection terminal, a current generation circuit for generating a current, and a video signal input terminal.
Te, the current generated by said current generating circuit, the Le
An on / off circuit for turning on / off the supply to the laser element via a laser element connection terminal, and a photo diode for inputting laser light from the laser element
A photodiode connection terminal connected to the photodiode and a signal input to the photodiode connection terminal.
Te, a detection circuit for detecting the laser power, and the external signal input terminal for inputting an external signal for determining the laser power to the target, and the capacitor connecting terminals for connecting the capacitor, detected by the detecting circuit According to laser power
A current control circuit having a sample-and-hold circuit for charging and discharging the capacitor , wherein the current generation means based on the laser power detected by the detection means and an external signal input from the input terminal. A laser driver IC used in an image forming apparatus, comprising: a current control circuit for controlling a generated current. 2. The current control circuit according to claim 1, wherein:
With a laser power detected I, a comparison circuit for comparing the reference value, the sample-and-hold circuit, the comparison
The laser driver IC used in the image forming apparatus according to claim 1, wherein the capacitor is charged and discharged according to a comparison result of a circuit . 3. The laser used in the image forming apparatus according to claim 1, wherein the sample / hold circuit is controlled to be in a sample state only when the on / off circuit is in an on state. Driver IC. (4) The sample and hold circuit is
Discharge the charge of the capacitor The transistor
The reset signal is further input to the user driver IC.
A reset signal input terminal;
When a reset signal is input to the
Charge of the capacitor using the transistor of the
4. Any of claims 1 to 3, wherein
Driver I used in the image forming apparatus described in 1 above
C. 5. An image forming apparatus using the laser driver IC according to claim 1.