JPS63211781A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To obtain a highly accurate laser driving circuit at low cost, by providing two or more D/A converters and a constant current circuit, adding the outputs of the D/A converters thereto, and inputting the result into the constant current circuit. CONSTITUTION:A microcomputer IC 1 of a semiconductor laser driving circuit incorporates A/D converter inputs PA 0 and PA 1 for driving control. A microcomputer IC 2 performs communication with a paper-transfer controlling external controller in a memory device and sends out operation timing for automatic optical-amount control for laser to an IC 1 by using the signal from an APCST. A current I is made to flow into a semiconductor laser. The current, which can output the maximum opticalamount output POMAX, is computed with the dispersion in threshold current Ith and slope efficiency alpha taken into account. The maximum current IMAX is controlled with D/As. The threshold current 0 or IthMIN-Ith is controlled with one D/A converter. The current Ith-IMAX is controlled with another D/A converter. At this time, the D/A converter, which controls 0 or IthMIN-Ith, does not control the light emitting amount. Therefore, a D/A converter, whose bit number is small, can be used. Since the D/A converter, which controls Ith-IMAX, controls the light emitting amount, a D/A converter, whose bit number is large, can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a laser recording device, and particularly to a laser drive circuit for a laser recording device having a function of automatically controlling the amount of light emitted from a semiconductor laser.

[Prior art]

Conventionally, such recording devices form an electrostatic latent image by exposing and scanning a photoreceptor using a laser beam modulated according to input information, and this is visualized with a magnetic developer called toner. 2. Description of the Related Art A so-called laser beam printer that forms an image and transfers the image onto a recording material is known.

FIG. 23 shows an example of this laser beam printer. In the figure, 1 is a photosensitive drum having a semiconductor layer of selenium or cadmium sulfide on its surface, which is rotatably supported inside the housing l, and rotates in the direction of arrow A. 2 is a semiconductor laser that emits laser light. 14 is a control circuit that controls the amount of laser light and turning on and off.The emitted laser light enters the beam expander 3 and becomes a laser light with a predetermined beam diameter.This laser light is transmitted through a plurality of mirror surfaces. Since the polyhedral mirror 4 is rotated at a predetermined speed by a constant speed rotation motor (scanner motor) 5, the laser beam emitted from the beam expander 3 is incident on the polyhedral mirror 4 that rotates at a constant speed. The light is reflected and scanned substantially horizontally, and is then imaged as a spot light by an imaging lens 6 having f/θ characteristics onto a photosensitive drum l which is charged to a predetermined polarity by a charger 13. Ru.

7 is a beam detector that detects the laser beam reflected by the reflection mirror 8. The timing of the modulation operation of the semiconductor laser 2 to obtain desired optical information on the photosensitive drum l is as follows.
It is determined by the detection signal of the beam detector 7. On the other hand, an electrostatic latent image is formed on the photosensitive drum l by a laser beam that is focused and scanned according to input information. This latent image is
After being developed with toner in the developing device 9, the cassette 10. 11.

When the image passes through the fixing device 12, the image is fixed on the recording material and delivered to a discharge section (not shown).

In such laser beam printers, the characteristics of the light amount with respect to the current of the commonly used semiconductor laser (
1-f characteristic) is as shown in FIG.

A semiconductor laser does not emit laser light until a certain threshold value (1th) is reached. Then, when the threshold value is exceeded, laser emission is performed, and in the laser emission state, the amount of light with respect to the current has a certain slope (slope efficiency: α).

In laser beam printers, the amount of light is controlled,
The laser current IT is determined so that the prescribed light fiIT is achieved. Then, by driving the laser current IT at a constant current, the light ff1I! I try to keep T constant.

However, as shown in Figure 25, the I-1 characteristic of a semiconductor laser initially has a human characteristic, and the light ff1I
! If the laser current is driven at a constant current by ITA to specify TA, the current flowing through the semiconductor laser will cause the temperature of the semiconductor laser chip to rise.
It is conceivable that the -1 characteristic changes to B or C.

If the required prescribed light m1) r8 is scanned on the photosensitive drum, it is normal, but the If characteristic changes and the laser light intensity becomes like B even though the laser current is IT. If the amount decreases, a situation may arise in which a latent image is not formed, and if the amount increases as shown in C, the laser chip may be destroyed.

Conventionally, the characteristics of the light amount with respect to the current of a semiconductor laser (1-f
IC that converts one digital value (characteristics) into an analog value
A control method using a D/A converter (called a D/A converter) is known, but when trying to achieve high precision,
The number of b and t' of the A converter is increased, and the cost is increased. Furthermore, depending on the input control method of the D/A converter, it may lead to destruction of the semiconductor laser.

〔the purpose〕

The present invention has been made in view of the above points, and an object of the present invention is to provide an inexpensive and highly accurate laser drive circuit.

〔Example〕

FIG. 2 is a schematic diagram of a recording device showing an embodiment of the present invention, and the recording device operates in response to an interface signal 109 with an external controller. The internal control of the recording device is
It is controlled by an internal controller called DC controller 102. Power supply to DC controller is 10
This is performed by the power supply unit shown in 4.

DC:I:/ Semiconductor laser 108 by troller 102
The photosensitive drum emits light, and the photosensitive drum 110 is irradiated by the optical scanning system 103. The photosensitive drum is housed in a cartridge 101 together with toner as a developer, and if there is no toner, each cartridge is replaced. The irradiated laser beam is developed on a photosensitive drum, transferred to paper fed from a paper cassette 105, fixed by a fixing device 111, and discharged to a paper discharge section 112. A cartridge system is used so that the photosensitive drum 110 and the developing device can be replaced as a unit. The photosensitive drum has variations in sensitivity to the semiconductor laser, and to compensate for this, a sensitivity coma 106 is attached to the cartridge. switch it to 10
Cartridges to be detected using 7 must have at least 1
Since there are two sensitivity frames, the switch 107 is a mechanism that can detect the sensitivity of the photosensitive drum and also detect the absence of a cartridge at the same time.

FIG. 3 is a diagram showing the power supply section 104 that supplies power to the DC controller in FIG. 2. power coat 201
After passing through switch 202 and breaker 203,
DC? ! A low-voltage power supply unit 204 that generates voltage and other AC supply units (
For example, the load 205n includes a fixing device and the like. )20
Branched to 6. A DC voltage to be supplied to the DC controller 102 is generated in the low voltage power supply 204 . In the low voltage power supply 204, +5V (207
) -5V (20B) +24V (209), etc. are generated and supplied to the DC controller 102.

In addition, the DC controller C1 and Asahi are connected to the above +5V.
.

In addition to -5V and +24V, a reference voltage power supply with a small current load capacity is required. In such a case, the reference voltage power source is connected to D by a circuit as shown in FIG. 4 or 5.
It is created inside the C controller 102.

FIG. 4 shows a reference voltage power supply using a voltage variable output three-terminal regulator LM317H made by NEC Corporation, which is a reprint of 301.

A +24V power supply 209 supplied from a low voltage power supply 204 to the DC controller 102 is inputted to the above-mentioned regulator 301 through a resistor 306. Output voltage■. +3.2
v307 has an external resistor 302. The relational expression determined by 303 is as shown in equation (1).

Vo# L, 25 (1+ R303/R302)
Equation (1) There is also a circuit as shown in FIG. 5 as another reference voltage power supply. From the low voltage power supply 204 to the DC controller 1
By inputting the +24 power supply 209 supplied to the 02 to the constant voltage diode 401 through the resistor 402, an output voltage 403 +8V can be obtained.

FIG. 1 is a diagram showing a semiconductor laser drive circuit of this embodiment. The ICI is a μP manufactured by NEC that has a built-in A/D converter input PAO1FAI that performs semiconductor laser drive control.
It is a one-chip microcomputer such as C7811G, and IC2 communicates with the external controller for paper conveyance control of the recording device and sends the operation timing of automatic light amount control of the semiconductor laser to ICI using the APC3T signal. Like the above-mentioned ICI, it is a one-chip microcomputer such as the μPC7811 manufactured by NEC Corporation. SW
I and SW2 are cartridge sensitivity detection and presence/absence detection switches shown in FIG. 1 to 7.

IC3 is an integrated circuit consisting of a gate array, etc., and performs signal processing of an image signal (Vin) input from an external controller.For example, when ICI detects 5WISW2 and determines that there is no cartridge, ICI informs IC3 that there is no cartridge and N0CRT. ) The N0CRT signal sent out performs operations such as gating Vin in IC3 to prevent the output signal v0 of IC3 from being sent out.

D/A converter circuit A301 and D/A shown in FIG.
The operation of converter circuit B502 will be explained.

IC31~! The gate circuit shown in 048 uses a gate using a CMO3 structure. The gate of 0MO3 is
This can be expressed by the equivalent circuit shown in FIG. input 903 )li
gh L/B/L/#VCC (7) Output stage (7) F
The ET 902 becomes ONL, the ET 901 becomes OFF, and the output 904 becomes Low level.

In addition, when the human power 903 is at a low level "v Ov", the output stage FET 901 and 0N902 are in the OFF state, and the output 904 is at the old gh level.Here, the reason why 0MO3 is used as the input of the ladder resistors RAI and RA2 is as follows. The output level of 0MO3 is High level is CM
The level is approximately the same as the OS power supply voltage Vcc level. Also, the output low level is almost the same level as the power supply GND level, and the input level is high.

Low can be seen as equivalent to a switch as shown in FIG. 1O. In case of gate by TTLIC, output) (igh L/Bevel (Vcc-1) About V, L
The ow level may rise to about 0.7V, so it cannot be regarded as a switch like the gate of 0MO3.

Therefore, the D/A converter circuit 8 of 501 becomes a circuit as shown in FIG. 11. Furthermore, as shown in Figure 11, the ladder resistor used here is composed of R (Ω) and its double, 2R (Ω). If a ladder resistor with such a configuration is used, the output of the lag resistor will be can be expressed by the following equation using each input vA0 to VA7.

Therefore, if inputs AO to A7 are all at High level, all the switches will be on the O(V) side, and V
All inputs to the ladder resistor of Ao%VA7 become 0 [V], and the output VA becomes O (V).

Also, if all the input AONA7 are at low level, all the switches will be on the V3.2 (V) side and VAO-VA7
All inputs to the ladder resistor are V3.2 (V). If all inputs to the ladder resistor are V3.2, the output voltage VA has the relationship shown in equation (3).

Therefore, it can be seen that the D/A converter circuit Aso2+' is a D/A converter that outputs voltage. That is, D/
A converter circuit circuit formula The high level of AO-A7 is expressed as "l" Low Low level, and the operational amplifier IC
5 (7) The output voltage is expressed as VA (V), AO - A7, AO is LSB, A7 is MSB and expressed in hexadecimal notation is A1, and the complement of A of 1 is expressed as 8 as shown in Figure 12. become that way. Also, as you can see in Figure 1, 503
The level shift circuit A is TTLIC's 7407 or 74.
Oven collector output type such as LSO7. Since the signal is not inverted in the gate circuit of
The inputs XAO to XΔ7 of 303 are also A as shown in FIG.
It can be handled in the same way as O to A7.

The output VA of the ladder resistor RA2 undergoes impedance conversion using a voltage floor circuit using an operational amplifier, and is made into an output VOA. IC5 is commercially available HA 17324
The input/output characteristics of the voltage floor circuit are as shown in FIG.

Under the conditions of power supply voltage Vcc, -Vcc, input VΔ
It is known that the relationship between VA and output VOA is generally VA=VOA.

However, if the input voltage VA becomes larger than the maximum output voltage VO)l, the output voltage V O = V OH, and if the input voltage VA becomes smaller than the minimum output voltage VOL, the output voltage becomes V OA=VOL.

Therefore, the relationship VA=VOA cannot be maintained unless the input voltage VA is between vOL and VOH.

In this embodiment, the power supply voltages +5V and -5V are used, and when considering the worst maximum output voltage, the input voltage VA should be approximately 3.2VMAX. When v3,2 in the figure is set to +5v, the ladder resistance output VA is input data A is OO
x), it becomes 6v. In this case, 8bi
Divide input data A by t and convert it from F F x) to 00 x)
Even if the output voltage VA is changed by F
OA increases, but after that, even if input data A is changed, the amplifier output voltage of IC5 remains at Vor-+.

Therefore, in this embodiment, the power supply voltage v3.2 of 0MO3 is set to the maximum output of the amplifier so that the amplifier output voltage VOA changes as the ladder resistance input data A changes from FFx) to 00X). The voltage VO) is made smaller than I.

Therefore, a level shift circuit A303 is configured to change the voltage without directly inputting the output of CPv to the CMO3. If the output port of the CPU is directly input to the CMOS, the input voltage will exceed the power supply voltage and the voltage will exceed 0M.
This will result in destruction of the O3IC. For this purpose, ICII to IC28 used in the level shift circuit are commercially available ICs such as 7407 and 74LSO7 having open collector outputs.

As shown in Figure 14, as a D/A converter circuit, the CMOS power supply voltage is +5V, which is the CPU power supply voltage, without using a level shift circuit, and the maximum output voltage voH of the output operational amplifier is +5V or more. It is also conceivable to increase the power supply voltage of the operational amplifier to about +8V so that

Similarly, the level shift circuit B504 and the D/A converter circuit B502 are 10-bit D/A converter circuits.

505 is an addition type constant current circuit in FIG. 1, and changes the current If flowing through R6 according to the values of VO8 and VOH3-5V.

The current If for v〇8 and Von is expressed by the following formula.

However, M is R1+ R2r R”3 * R4+ RB
+ Constant determined from R6 In this example, formula (5)
Since -Vccl=-Vcc2=-5 (V) in Equation (5) is expressed by the following Equation (7).

IJ2 = NIXVOB+N2XVOA+N3 Formula (7) where Nl, N2. N3 is a constant As can be seen from the seventh equation, current 1j7 is voltage VOA or Vo
It can be seen that the current IIl can be varied by varying the input data A or B to the D/A converter circuit, which increases in proportion to s.

Here, the division of functions between the D/A converter circuit A301 and the D/A converter circuit B502 in this embodiment will be explained. The relationship between the output light iL and the current I of the semiconductor laser has the characteristics shown in FIG.

A certain threshold current! The semiconductor laser does not emit laser light until it reaches the peak, and after exceeding the threshold current rth, the semiconductor laser emits laser light.The relationship between the light ff1f and the current l at that time can be shown almost as a straight line. The slope α that has a certain slope α is called slope efficiency. Current flowing through a semiconductor laser with such characteristics■
Let us consider the case of controlling using a D/A converter.

In the IL characteristics of semiconductor lasers, the threshold value 11h varies widely. In addition, the slope efficiency α is also thick (
It has variations. The current that must be controlled by the D/A converter is calculated by considering the threshold current 11h and variations in slope efficiency α, and calculating the laser current so that it can always output the maximum output light ff1P OMAX used by the semiconductor laser. , its maximum? IX style IM 8X must be controlled with a D/A converter.

As a method to control I MAX, as shown in 31, OA ~
When controlling I MAX with one D/A converter or as shown in 33, the minimum threshold power supply 1 rh MIN
One item up to NI MAX. Considering the case where control is performed using a D/A converter, the control range of the D/A converter is large, and if an attempt is made to precisely control the amount of emitted light, the number of bits will increase, resulting in an increase in cost. There/de 32
Or, as shown in 34, control up to 0 or I th MIN-1th with one D/A converter and IIhNIMAX
Consider controlling this with another D/A converter.

Since the D/A converter that controls 0 or Ilb MIN to Ilh does not control the amount of emitted light, the amount of current variable per step may be large. That is, bi
A D/A converter with a small number of t can be used, and since the D/A converter that controls I +h-I MAX controls the amount of light emitted, the amount of current variable per step needs to be small. be. However, the current range to control is smaller than 31 or 33.
High-precision control can be achieved even if a D/A converter with the same number of bits is used.For example, if you want to achieve the same precision as 31°33, you can use a D/A converter with a smaller number of bits. can. Therefore, by using two D/A converters with different amounts of current variable per l step, inexpensive and highly accurate control can be realized.

The D/A converter circuit A in FIG. 1 controls up to Ith, and the D/A converter circuit B has the function of controlling the amount of emitted light.

Next, L1, R7, and C8 in FIG. 1 perform switching waveform shaping of the current IA, and constants are determined so that the waveform has a short rise time and no overshoot.

1 is a laser current switching circuit 506 in FIG.
, to flow to R9, or to turn off Tr3 and turn on Tr'2 to flow to laser diode LD. That is, IC7 is an AND circuit having an oven collector structure at the output stage, and has an input v.

When both LON and LON are at H” level, the output of IC7 is Vs.
If 2 becomes V s 2 H, ] ``3 is ONL
, Vs, (D voltage can be expressed by equation (8) from Tr3 (7) VBE and diode DI (7) VF.

VSIH=VS2)1-VBE-VF (8
) formula Kokonioiite Tr2 (7) VBE to V BH3
Then, Tr2 is kept in the OFF state under the condition that V SIH>-V IIE2. As a result, when the inputs vo and LON of IC7 are both "H", the current 11 is T
All current flows through r3 and no current flows to the semiconductor laser LD.

Also, if LON or vO becomes “below”, IC
7 output becomes Vs2=O, and Vsl=-VBEI-
Here, it becomes VF -V tlE2 > VS
It can be seen that if the conditions are set, Tr2 is turned on and Tr3 is turned off. That is, the input v of IC7.

Or, when LON is at "L" level, Tr3 is in the OFF state, Tr2 is in the ON state, and the current If is Tr2
The current flows through the semiconductor laser LD.

C6, C7, R13, R14, R15 flow to the semiconductor laser Ii! B2 is a diode that prevents reverse voltage from being applied to the semiconductor laser LD.

LDI is a semiconductor laser with a built-in photodetector PD for the motor.

507 is a photodetector output adjustment circuit.

As shown in FIG. 15, the output beam from the semiconductor laser LDI is radially output. A lens called a collimating lens 21 is used to convert the light into parallel light. If the power at that time is Pl, the power will be P2 by the time the laser beam reaches the photosensitive drum 110. This is because the light from P is reflected by the optical means 22 such as a rotating polygon mirror and then communicated to the drum. However, P
When 2/PI=B+, Bl becomes a constant in the specified device as the efficiency of the optical system. However, the semiconductor laser output light amount P0 and the light after the collimator lens ffi p +
Alternatively, the relationship of the light mP2 on the drum changes greatly as shown in FIG. 16 due to variations in LDI.

If approximately pH/po=B2, then B2=70
It varies up to about 25%. Furthermore, the relationship between the current 1po flowing through the photodetector for monitoring the amount of semiconductor laser light and the output light ff1po also varies widely, as shown in FIG. 17. IPP at approximately P(,=5mW
=0.4mA to about 3.0mA.

Therefore, I put a resistor in series with the photodetector Po.
Let us consider adjusting the series resistance value RPD of the monitor photodetector Vpo and the collimator lens output light fiP or the light mP2 on the drum surface as shown in FIG. 18, assuming that po x Rpo = V PD.

Collimator efficiency 70%~25%, monitor current 1 po
.

Since the variation is large from 0.4 mA to 3 mA, the resistance value adjustment range of the series resistor RPP is wide (and the optical ffi p I
51 requires highly accurate adjustment because the adjustment accuracy of the relationship between B2 and monitor photodetector voltage VI'D becomes the accuracy of laser light amount adjustment. For example 100Ω~50
Considering the case of adjusting 00Ω, it would be better to use one variable resistor of 5Ω per rotation in terms of cost, but it would be difficult to make high-precision adjustment. Further, if a multi-rotation variable resistor of Ω is used for 5, highly accurate adjustment is possible, but the cost becomes high. Therefore, in the 507 photodetector output adjustment circuit shown in Fig. 1, a variable resistor VR2 of Ω is connected to 2, and a fixed resistor is connected to R16: IKΩ, and R17: Ω to 2.
R30: A configuration such as 100Ω is used. Also R16.
R17 has a jumper pattern with cut points CPI, CP2. CP3 and series resistor RPC
is 1100~310 without doing anything until 100~2100Ω
The configuration is such that CPI is cut down to 0Ω, CB2 is cut L/ from 2100 to 4100Ω, and CB3 is cut from 3100 to 5100Ω.This improves the accuracy of adjustment and uses an inexpensive one-turn volume and fixed resistor. It is structured as follows.

508 in FIG. 1 is a photodetector voltage amplification circuit, and the relationship between the input VPP and the output VM is expressed by the formula (9)% VM = 7XVPD (9) Formula IC8 is an operational amplifier with characteristics similar to the commercially available HA 17324. It is. The output of IC8 is connected to the input of the A/D converter of the microcomputer, and has the ability to decompose Vcc into 8 bits. If +5V is input to Vcc of lc8, the output will only rise to the maximum output voltage V01-1. Naturally, due to the characteristics of the operational amplifier (OP amplifier), the VOH is 3.
The voltage will be about 2v. Therefore, in order to fully use the 8-bit +5V A/D converter of the microcomputer, it is necessary to ensure a maximum output voltage VOH of about +5V.

Therefore, the power supply voltage of IC8 is set to +8v, and the maximum output voltage VOH is set to +5v or more. In that case, the output V of IC8
Since there is a possibility that M may exceed +5V, a constant voltage diode ZDI is used to set the condition that VM≦Vcc.

509 in Fig. 1 is a laser light amount setting circuit, and normally JPI and JP2 are shorted, and R22 and R
23, v7, which determines the light amount setting voltage VT, can be expressed by equation (10).

Also, by turning JPI and JP2 into ovens, VRI
This makes it possible to vary the VT.

The present invention will be described in detail with reference to the circuit shown in FIG. 1 and the flowcharts shown in FIGS. 6, 7, and 8. The microcomputer IC2 that controls the automatic adjustment of the light m of the semiconductor laser, the microcomputer ICI that controls the operation of the recording device, determines whether the timing when the automatic semiconductor laser light amount adjustment start (APCS'r) signal becomes TRUE or not. The semiconductor laser light intensity automatic adjustment operation (AP
C). This operation will be explained according to a flowchart. Figure 6 shows the microcomputer IC from microcomputer IC2.
The case where APC3T is sent to I is shown. .

Power is turned on to the recording device (step 601), and +5V 207 is supplied from the low voltage power supply 204 to the 1 internal controller 102.
etc. power is supplied. Then, ICI, IC2,
Other electronic devices start operating. In particular, the ICI performs internal control of the recording device and at the same time
Interface signals such as those shown at 12 are used to communicate with external control devices.

Among the interface signals, there is a signal called PRINT510 that instructs the recording device to enter a printing state. In step 602, the ICI judges this PRINT signal. When the PRINT signal becomes TRUE, the ICI detects the status of the recording device, judges whether it is in a printable state such as no paper or cartridge, and returns to step 602. If printing is not possible as shown at 603, a step 604 of displaying an abnormal state externally or notifying the user using an interface signal is performed.If the printing is possible, a printing operation is performed according to step 605. Start. Specifically, it feeds paper from the paper feed set 109, sets the potential on the photosensitive drum, starts rotating the scanner motor, and so on. Thereafter, in step 606, the semiconductor laser beam m automatic adjustment start signal APCST signal is selected for IC2 from the ICI. Upon receiving this, the IC 2 goes to the flowchart of FIG. 8, which will be explained later, and performs the AI'C operation in step 607. Thereafter, in step 608, a printing operation is performed according to a known electrophotographic process, and in step 609, when the printing operation is completed, the light n of the semiconductor laser is controlled to be minimized.

Figure 7 shows the semiconductor laser beam m forced from outside the recording device.
This is a flowchart 1 showing a case where adjustment is performed. In step 701, the power is turned on to the recording device, and the ICI and
Electronic elements such as IC2 start operating. Among them, ICI
In step 702, monitors whether the forced semiconductor laser light amount adjustment signal MLON signal from the outside is TRUE. When the MLON signal becomes 1" RU E, the PC operation is performed to 703. This step 7
The 03 APC operation will be explained in detail using the flowchart in FIG. 8. As shown in step 704,
Detection is performed by SWI and SW2 after the APC operation is completed or during the AI'C operation. If the cartridge runs out, the process moves to step 705, where the APC state is canceled, that is, the amount of semiconductor laser light is controlled to be minimized.

Also, when there is a cartridge, M L ON
continues to maintain the APC state during 1' RU E, and M
Step 7 with LON set to FALSE
05 APC is released, and the amount of semiconductor laser light is controlled to be minimum.

FIG. 8 is a flowchart showing in detail the APC operation shown in step 607 of FIG. 6 or step 703 of FIG.

Step 801 indicates when the APC3T from the IC2 or the forced laser ON signal MLON from the outside becomes TRUE. At this time, the current flowing through the semiconductor laser before the start of APC operation is minimized to minimize the laser beam (2). Specifically, ICI output xAONxA7 and XBO
-D/A by setting all XB9 to “I(” level)
Step 802: Minimize l by minimizing converter outputs VOA and VOB; then step 8
In step 03, whether or not there is a cartridge containing a photosensitive drum is detected by SW1 and SW2 of 107, and if it is determined that there is no cartridge, in step 804,
The target value of the amount of laser light in the APC operation is set to the minimum, and in step 805, as in step 802, the If that should flow to the laser is controlled to be the minimum, and the APC operation is terminated in step 806.If there is a cartridge in step 803, If determined, step 80
In step 7, a target value for controlling the amount of laser light in the APC operation is determined.

In determining the amount of laser light, it is necessary to determine the light ff1P2 on the photosensitive drum surface, as shown in FIG. In this embodiment, the photodetector output adjustment circuit 507 and PD? l! The light ffi on the photosensitive drum surface is
The relationship between P2 and the monitor voltage XM is as shown in FIG. Therefore, the current 11 flowing through the laser is converted into ICI output boat data XAO~xA7,
By changing the use of BO to xB9, monitoring the amount of light from the semiconductor laser emitted according to the current using the monitor voltage VM, and adjusting the monitor voltage to a certain voltage, the light ffi P2 on the photosensitive drum surface can be changed. It is easy to understand that the amount of light can be adjusted to a certain level. Therefore, in step 807, the target value of the amount of laser light is determined by determining the target value of the monitor voltage VM. The target value of the monitor voltage VMC is the output V of the laser light amount setting circuit 509.
T, the cartridge detection switch SW
It is adjusted and determined by the data of I and SW2.

The photosensitive drum 110 has variations in sensitivity to the amount of light from the semiconductor laser, and is divided into three levels, and the sensitivity frame 106 of the cartridge is changed depending on the difference in sensitivity. This is detected by the detection switches 107, SWI and SW2. In this example, if only SWI is pressed, the sensitivity standard... Kai Kaimon aS
If only W2 is pressed, it is detected that the sensitivity is good...song...open/open bIf both SWI and SW2 are pressed, it is detected that the sensitivity is poor and the song c is detected. Therefore, the target values of the monitor voltage under conditions a, b, and c are as follows in this embodiment.

Target value VTOa: VTO=VTX0.9b:VT
O=VTX0.8 C:VTO:VT In this way, by determining the target value of the monitor voltage based on the sensitivity information of the photosensitive drum and the output VT of the laser light amount setting circuit, the target value of the laser light m is set in step 807. .

Next, in step 808, IC1 sets LON to "L".
level, the Tr of the laser current switching circuit 506
2 as ONL, control is performed so that a current 1j7 determined by an additive constant current circuit 505 flows through the semiconductor laser LP.

In step 809, the laser light amount monitor voltage VM is checked, and in step 810, the monitor voltage VM is checked.
It is determined whether the threshold current is above or below the threshold current specified voltage VMTA. If the monitor voltage VM is smaller than VMT8, the input of the D/Δ converter is changed in step 811. When changing the input of D/A converter A, it is normal to change the input one step at a time, but in this embodiment, as shown in FIG. Voltage V MTA 50
% value: From VMTAβ, change the input in 3 steps, 7M・75% value to VMT after 8β: VMT 8α, change the input in 2 steps, and after VMTAα, up to the threshold current specified voltage VMTΔ By changing the value one step at a time, it has the same accuracy as the method of changing the entire area one step at a time, and control can be performed in a shortened time required for adjustment.

Furthermore, when the input to the D/A converter circuit is output from the output port of the ICI, the ICI is an 8-bit microcomputer and can only change the output of 8 bits at a time. Like the input of level shift circuit A in Figure 1, 8
Port PDO- bit can be changed at once
Since it is controlled by PD7, the output value can be changed at once, but due to the circuit design, the upper B I
'I' If only XA7 is output from a different port group PFO, lower BIT PDO-PD6
It is necessary to change the upper BITPFO after changing . In other words, when transitioning from state 41 to state 42 in FIG. 22, XA (hexadecimal value representation) is
ox)-+EFX), but in some cases, in the case of a transition from state 43 to state 44, if port F is specified first, then XA is 80x) + 0
0X) →7FX). Here, when the output value of XA is 00x), the input of the D/A converter is the maximum, the current 147 is the maximum, and there is a possibility that the semiconductor laser will be destroyed.

Therefore, if the input data of the D/A converter spans two or more port groups, it is necessary to specify the lower port group first.If this is done, the transition from state 43 to state 44 described above will occur. is specified before port D, and then port F, so XA is 80x)
4 FFx) -7Fx), and the output value of XA is FFx), but the input of the D/8 converter called FFx) is the input that controls the current 1/ to the minimum. Yes, the laser has a minimum amount of light m and will never lead to destruction. Therefore, when input data to a D/A converter is determined using a microcomputer, it is necessary to define the lower port group (BIT) first.

Step 809. 810. Using the loop 811, the monitor voltage VM is controlled to become the threshold current regulation voltage VMTA.

In step 812, when the monitor voltage VM is equal to the threshold current specified voltage VMTA, the laser is emitting laser light and emits a sufficient amount of light to form a latent image on the photosensitive drum. Therefore, the laser current is set to a value obtained by multiplying the threshold specified current ITA by a certain percentage (for example, 80%, etc.), and the laser current at that time is set as the set threshold current IΔT. The monitor voltage VM is checked in step 813 while the set threshold current IAT is flowing through the semiconductor laser. If the monitor voltage VM exceeds the threshold current specified voltage V MTA in step 814, step 81
In step 5, the input to the D/A converter is controlled to minimize the laser current, the amount of laser light is minimized, and the threshold current control is performed again. If the threshold current to the D/A converter circuit 8 is normally controlled, the light emission current control from step 816 onwards is performed.

In step 816, the laser light amount monitor voltage VM is checked, and in step 817, it is determined whether the monitor voltage VM is larger or smaller than the light emission amount setting voltage VTO. If the monitor voltage VM is smaller than VTO, the input to the D/A converter circuit B is changed in step 818. When changing the input of the D/A converter circuit B in step 818, it is normal to change the input one step at a time, but as shown in FIG. Until the monitor voltage VM reaches the 50% value of the light emission setting voltage vTo: vTβ, the input is changed by 3 steps, and after VTβ, the input is changed to 75% of vTo.
% value: The input is changed in 2 steps up to vTα, and V
From Tα to VTO, the monitor voltage VM is controlled to become the light emission amount setting voltage vTo by changing it in steps of l. Then, the monitor voltage Vμ is controlled to the light emission amount setting voltage vTo. In other words, the AI'C operation ends at step 819 when controlling the laser light m to the specified light intensity ends. [Effect] As explained above, two or more D/A used in the semiconductor laser drive circuit of the recording apparatus By adding the outputs of the converters and using the result as input to the constant current circuit, there is an effect that highly accurate control can be performed without increasing costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a semiconductor laser drive circuit in this embodiment, FIG. 2 is a schematic diagram of a recording apparatus to which the present invention can be applied, FIG. 3 is a diagram for explaining the power supply unit 104, FIG. Figure 5 is a diagram showing the reference voltage power supply, Figures 6, 7, and 8 are flowcharts for controlling the light amount of this embodiment, Figure 9 is a diagram showing the equivalent circuit of the gate circuit, and Figure 1O. is a diagram for explaining the operation of the gate circuit, and FIG. 11 is a diagram for explaining the operation of the gate circuit.
Figure 12 is a diagram showing the equivalent circuit of the converter, Figure 12 is a diagram to explain the operation of the D/A converter, Figure 13 is a diagram showing the input/output characteristics of the voltage floor circuit, and Figure 14 is a diagram showing the D/A converter and other circuits. Figure 15 is a diagram showing an example of the configuration of the semiconductor laser LDI.
Figure 6 shows the relationship between the output light amount of the semiconductor laser and the light amount after the collimator lens, Figure 17 shows the relationship between the current flowing through the photodetector for monitoring the laser light amount and the output light amount, and Figure 18 shows the relationship between the output of the photodetector for monitoring and the amount of light output. Figure 191J is a diagram showing the relationship between the output light quantity of the collimator lens, Figure 191J is a diagram showing the current-light quantity characteristic of a semiconductor laser, Figure 20 is a diagram explaining the relationship between monitor voltage and laser current, Figure 21 is the same as Figure 1. Figure 22 is a diagram showing a modification example of the level shift circuit; Figure 22 is a diagram showing an example of input to the level shift circuit;
24 is a diagram showing the current-light amount characteristics of a semiconductor laser, and FIG. 25 is a diagram showing the current-light amount characteristics of a semiconductor laser. Here, ICI and IC2 are one-chip microcomputers, 501. 502 is a D/A converter circuit, 5
03.504 is a level shift circuit, 505 is an addition type constant current circuit, 506 is a laser current switching circuit, 507
508 is a photodetector voltage amplification circuit, and 509 is a laser light amount setting circuit. Patent applicant Canon Co., Ltd., y-'l/ Figure 4 Moe 5 Figure Otsu and No. HL Enclosure A7 AA A5 A4 A3 A2 A/ AD
VA A λ1 1 1 1 1 1
1 1 0 FF, I 00. )1 1
1/f l I OTTXkCFE-+
01g+10000000 zVtc 8Qg
1 77.10 0 0 0 0 0 0 0 ””
” QQ-+ FF. XA'7 XA6 XA5 XA4 XA3 XA2
XA/ XAoXA XA hug/?彉 力 Vo＾ Figure 77 79th edition
Shi+Bo-)7Fm+7E Riho? ? Figure 25

Claims (1)

[Claims] A semiconductor laser drive circuit of a recording device includes at least two D/A converters and a constant current circuit, and the outputs of the at least two D/A converters are added and used as input to the constant current circuit. A semiconductor laser drive circuit characterized by: