CN214313861U

CN214313861U - Drive circuit, laser, and image forming apparatus

Info

Publication number: CN214313861U
Application number: CN202120422741.4U
Authority: CN
Inventors: 覃祖料; 黄超豪; 胡智敏
Original assignee: Apex Microelectronics Co Ltd; Zhuhai Pantum Electronics Co Ltd
Current assignee: Apex Microelectronics Co Ltd; Zhuhai Pantum Electronics Co Ltd
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2021-09-28
Anticipated expiration: 2031-02-25

Abstract

The embodiment of the application provides a driving circuit, a laser and an image forming device, wherein the driving circuit is a driving circuit of the laser and comprises a driving current generating circuit, a driving current detecting circuit and a driving current control circuit, the driving current generating circuit comprises a switch current generating circuit and a bias current generating circuit, the driving current control circuit comprises a sampling holding capacitor, and the sampling holding capacitor is connected with the driving current generating circuit; the driving current comprises a switching current and a bias current; the driving current detection circuit is used for generating a first control signal when judging that the driving current is larger than a first preset threshold value; the drive current control circuit is used for controlling the discharge of the sampling holding capacitor according to the first control signal so as to reduce the drive current, realize the real-time monitoring of the drive current, and when the drive current is in overcurrent, the discharge of the sampling holding capacitor enables the drive current to be reduced to a safe range, and the safe drive of the laser is realized.

Description

Drive circuit, laser, and image forming apparatus

Technical Field

The embodiment of the application relates to the technical field of laser control, in particular to a driving circuit, a laser and an image forming device.

Background

Laser printers are widely used due to their advantages of high printing speed and high resolution. The laser printer adopts a semiconductor laser to emit and receive laser, and the semiconductor laser generates driving current through a corresponding driving circuit to control the light intensity of the laser emitted by the laser emitting part. Therefore, to avoid damage to the laser due to excessive current, real-time monitoring of the drive current is required.

The drive current of a semiconductor laser consists of two parts: bias current and switching current. In a conventional driving circuit of a semiconductor laser, whether a driving current is over-current is often judged by detecting whether a switching voltage of a switching current exceeds a preset value, and when the driving current is over-current, error information is fed back.

In the detection mode, the bias current is not detected, so that the detection result has deviation; and only whether the switch current is over-current can be detected, and an effective solution to the over-current cannot be provided, so that the semiconductor laser cannot normally operate when the switch current is over-current.

SUMMERY OF THE UTILITY MODEL

In order to solve the problems of deviation in detection of the driving current of the semiconductor laser and untimely processing during overcurrent in the prior art, the embodiment of the application provides the driving circuit, the laser and the image forming device, wherein the driving circuit realizes real-time detection of the driving current, including bias current and switching current, the detection is comprehensive, and the accuracy of overcurrent detection is improved; when the driving current is over-current, the driving current is reduced through the discharge of the sampling resistor, so that the driving current is restored to a normal range, and the normal operation of the laser is ensured.

In a first aspect, an embodiment of the present application provides a driving circuit, which is suitable for a laser, such as a semiconductor laser, and includes: the driving circuit comprises a driving current generating circuit, a driving current detecting circuit and a driving current control circuit, wherein the driving current generating circuit comprises a switch current generating circuit and a bias current generating circuit, the driving current control circuit comprises a sampling holding capacitor, and the sampling holding capacitor is connected with the driving current generating circuit; the driving current generation circuit is used for generating a driving current, and the driving current comprises a switching current generated by the switching current generation circuit and a bias current generated by the bias current generation circuit; the driving current detection circuit is used for receiving the driving current and generating a first control signal when judging that the driving current is greater than a first preset threshold value; the driving current control circuit is used for receiving the first control signal and controlling the discharge of the sampling holding capacitor according to the first control signal so as to reduce the driving current.

In one possible embodiment, the driving current detection circuit includes a detection current generation module and a driving current detection module; the detection current generation module is connected with the driving current generation circuit and used for receiving the driving current and generating a detection current according to the driving current, wherein the detection current is smaller than or equal to the driving current; the driving current detection module is connected with the detection current generation module and used for receiving the detection current and judging whether the detection current is larger than a second preset threshold value, and if so, the first control signal is generated.

In one possible embodiment, the detection current generation module includes a first field effect transistor and a first resistor; the grid electrode of the first field effect transistor is used for receiving the driving current, the drain electrode of the first field effect transistor is used for receiving a power supply signal, the source electrode of the first field effect transistor is connected with one end of the first resistor, the other end of the first resistor is grounded, and the detection current is the current output by the source electrode of the first field effect transistor.

In one possible embodiment, the driving current control circuit further includes a second field effect transistor;

the grid electrode of the second field effect transistor is connected with the driving current detection circuit and used for receiving the first control signal; the source electrode of the second field effect transistor is grounded; the drain electrode of the second field effect transistor is connected with the first end of the sampling holding capacitor; the first end of the sampling holding capacitor is also connected with the driving current generating circuit, so that when the sampling holding capacitor discharges, the driving current is reduced along with the discharging of the sampling holding capacitor; the second terminal of the sample-and-hold capacitor is grounded.

In one possible embodiment, the first terminal of the sample-and-hold capacitor is connected to the switching current generation circuit to reduce the switching current generated by the switching current generation circuit when the sample-and-hold capacitor is discharged.

In one possible embodiment, the switching current generation circuit includes a first operational amplifier, a first switch, a third field effect transistor, and a second resistor;

one end of the first switch is connected with the output end of a laser emitting device of a laser, and the other end of the first switch is connected with the drain electrode of the third field effect transistor; the source electrode of the third field effect transistor is connected with the inverting input end of the first operational amplifier, and the grid electrode of the third field effect transistor is connected with the output end of the first operational amplifier; the positive input end of the first operational amplifier is connected with the first end of the sampling holding capacitor; one end of the second resistor is connected with the source electrode of the third field effect transistor, and the other end of the second resistor is grounded; the switch current is a current passing through the first switch when the first switch is closed.

In one possible implementation, the first terminal of the sample-and-hold capacitor is connected to the bias current generation circuit to reduce the bias current generated by the bias current generation circuit when the sample-and-hold capacitor is discharged.

In one possible embodiment, the bias current generating circuit includes a second operational amplifier, a fourth field effect transistor, and a third resistor; the drain electrode of the fourth field effect transistor is connected with the output end of a laser emitting device of the laser, the source electrode of the fourth field effect transistor is connected with the inverting input end of the second operational amplifier, and the grid electrode of the fourth field effect transistor is connected with the output end of the second operational amplifier; the positive input end of the second operational amplifier is connected with the first end of the sampling holding capacitor; one end of the third resistor is connected with the source electrode of the fourth field effect transistor, and the other end of the third resistor is grounded; the bias current is a current passing through a drain of the fourth field effect transistor.

In a second aspect, an embodiment of the present application further provides a laser, where the integrated circuit includes a laser emitting device, a laser receiving device, and a driving circuit provided in any embodiment corresponding to the first aspect of the present application.

In a third aspect, embodiments of the present application further provide an image forming apparatus including an image forming controller, a laser scanning unit, and a photosensitive drum; the laser scanning unit comprises the laser provided by the embodiment corresponding to the second aspect of the application.

The embodiment of the application provides a drive circuit, laser instrument and image forming device, this drive circuit includes drive current generation circuit, drive current detection circuit and drive current control circuit, drive current generation circuit comprises switching current generation circuit and bias current generation circuit, in order to generate drive current, drive current control circuit includes the sample hold capacitor, this sample hold capacitor is connected with drive current generation circuit, drive current detection circuit can realize real-time detection drive current, thereby when drive current detection circuit judges drive current too big, then control adopts the electric capacity to discharge, thereby reduce drive current through the mode that reduces drive voltage, realize the overcurrent protection to the laser instrument, improve the security of laser instrument operation.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

Fig. 1 is an application scenario diagram provided in an embodiment of the present application;

FIG. 2 is a schematic view of a prior art image forming apparatus;

fig. 3 is a schematic structural diagram of a driving circuit according to an embodiment of the present application;

FIG. 4 is a schematic diagram showing the connection of the driving circuit, the imaging controller, the LD and the PD in the embodiment of FIG. 3;

FIG. 5 is a schematic diagram of a comparator according to the embodiment of FIG. 3;

FIG. 6 is a schematic diagram of a driving current detection circuit according to the embodiment of FIG. 3;

FIG. 7 is a schematic diagram of a driving current control circuit according to the embodiment of FIG. 3;

FIG. 8 is a schematic diagram of a switch current generating circuit according to the embodiment of FIG. 3;

FIG. 9 is a schematic diagram of a bias current generating circuit according to the embodiment of FIG. 3;

fig. 10 is a schematic structural diagram of a laser according to an embodiment of the present application;

fig. 11 is a schematic structural diagram of an image forming apparatus according to an embodiment of the present application.

Description of reference numerals:

100: an imaging controller;

200: a laser scanning unit;

300: a photosensitive drum;

20: a laser;

201: a laser emitting device;

202: a collimating lens;

203: a grating;

204: a cylindrical lens;

205: a polygonal mirror;

206: a motor;

207: a curved lens;

208: a diffractive optical element;

209: a light beam detector;

210: a laser driver;

211: a mirror;

220: a motor driver;

230: a drive circuit;

231: a drive current generation circuit;

2311: a switching current generating circuit;

2312: a bias current generating circuit;

232: a drive current detection circuit;

2321: a detection current generation module;

2322: a drive current detection module;

233: a drive current control circuit;

2331: an APC circuit;

20: a laser.

With the above figures, there are shown specific embodiments of the present application, which will be described in more detail below. These drawings and written description are not intended to limit the scope of the inventive concepts in any manner, but rather to illustrate the inventive concepts to those skilled in the art by reference to specific embodiments.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

The following describes the technical solutions of the present application and how to solve the above technical problems with specific embodiments. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.

The following explains an application scenario of the embodiment of the present application:

fig. 1 is a diagram of an application scenario provided in an embodiment of the present application, and as shown in fig. 1, an image forming apparatus using a semiconductor Laser, such as a Laser printer, a digital copier, and the like, generally includes an imaging controller 100, a Laser Scanning Unit (LSU) 200, and a photosensitive drum 300. The laser scanning unit 200 can scan the surface of the photosensitive drum 300 in the main scanning direction B and the sub-scanning direction a, and the image forming controller 100 is configured to control the laser beam output from the laser scanning unit 200 to perform an electrostatic latent image based on the laser beam reaching the surface of the photosensitive drum 300 to output a desired image.

Specifically, fig. 2 is a schematic configuration diagram of a related art image forming apparatus, which is composed of an image forming controller 100, a laser scanning unit 200, and a photosensitive drum 300, as shown in fig. 2. The Laser scanning unit 200 includes a Laser Diode (LD) 201, a Laser driver 210 for controlling light emission of the Laser emitting device 201, a collimator lens 202, a grating 203, a cylindrical lens 204, a polygon mirror 205, a curved lens 207, a diffractive optical element 208, a motor 206 for driving the polygon mirror 205, and a motor driver 220 for controlling the motor 206. Wherein the laser driver 210 and the motor driver 220 are both controlled by the imaging controller 100. The polygon mirror 205 includes a plurality of reflection surfaces, and a laser beam emitted by the laser emitting device 201 reaches a certain reflection surface of the polygon mirror 205 through the collimating lens 202, the grating 203, and the cylindrical lens 204 in sequence, is reflected by the reflection surface, and reaches the surface of the photosensitive drum 300 through the curved lens 207 and the diffractive optical element 208 in sequence to form an electrostatic latent image.

The laser scanning unit 200 may further include a Beam Detector (Beam Detector)209 and a mirror 211. The position where the reflecting mirror 211 is disposed corresponds to a specific position on each reflecting surface of the polygon mirror 205, and when a laser beam is incident to the specific position on any one of the reflecting surfaces of the polygon mirror 205, the beam reflected by the reflecting surface of the polygon mirror 205 will be able to be received by the reflecting mirror 211. The mirror 211 reflects the received light beam to the beam detector 209, and the beam detector 209 transmits a start scanning signal, which is generally called a line synchronization signal, to the imaging controller 100 of the image forming apparatus when detecting the light beam.

In order to increase the response speed of the laser emitting device 201, when the laser emitting device 201 does not emit light, a bias current is also applied to the laser emitting device 201 through the laser driver 210, and when the laser emitting device 201 needs to emit light, a switching current is superimposed on the bias current through the laser driver 210, so that a driving current is formed, and the laser emitting device 201 is driven to output a laser beam through the driving current.

When the laser driver 210 is abnormal, a driving current exceeding the specification of the laser emitting device 201 may be output, which may cause the laser beam output by the laser emitting device 201 to be undesirable, and may even cause the laser emitting device 201 to be degraded in performance, and therefore, the driving current output by the laser driver 210 needs to be detected in real time.

In the prior art, whether the driving current is over-current is often judged by detecting the switching current of the laser driver 210, and if the switching current is over-current is judged by detecting whether the switching voltage is greater than a set voltage value, the driving current is determined to be over-current, so that prompt information is generated to prevent the laser emitting device 201 from over-current operation and performance degradation.

However, the above detection method only detects whether the switching current in the driving current is excessive, and ignores the bias current, which is normally a fixed value, but the bias current is also excessive due to the influence of temperature or circuit failure. Therefore, the detection method may fail to detect the object. In addition, the above detection method can only determine whether the current is over-current, and does not disclose a technical scheme for solving the problem of over-current.

In order to solve the problems, the driving circuit provided by the application realizes real-time monitoring of the driving current of the laser through the driving current detection circuit and the driving current control circuit, and improves the accuracy and comprehensiveness of the driving current detection; and when the drive current is judged to be overcurrent, the drive current can be reduced by controlling the sampling hold capacitor of the drive current control circuit to discharge, so that the overcurrent protection of the laser is realized, and the drive current can be restored to a normal range when the drive current is overcurrent, so that the laser can normally operate.

Fig. 3 is a schematic structural diagram of a driving circuit according to an embodiment of the present application. The driving circuit is suitable for a laser, such as a semiconductor laser, and as shown in fig. 3, the driving circuit 230 provided in this embodiment includes a driving current generating circuit 231, a driving current detecting circuit 232, and a driving current control circuit 233, the driving current generating circuit 231 includes a switching current generating circuit 2311 and a bias current generating circuit 2312, and the driving current control circuit 233 includes a sample-and-hold capacitor C_shSampling hold capacitor C_sIs connected to the drive current generation circuit 231.

Wherein the driving current generating circuit 231 is used for generating the driving current I_opDriving current I_opIncluding a switching current I generated by a switching current generation circuit 2311_swAnd a bias current I generated by a bias current generating circuit 2312_bi(ii) a The driving current detection circuit 232 is used for receiving the driving current I_opAnd when judging the driving current I_opWhen the current value is greater than a first preset threshold value Th1, generating a first control signal C _ DIS; the driving current control circuit 233 is used for receiving the first control signal C _ DIS and controlling the sample-hold capacitor C according to the first control signal C _ DIS_shDischarging to reduce the drive current.

Specifically, the drive current I of the drive current generation circuit 231_opThe expression of (a) is: i is_op＝I_bi+I_swBias current I_biWhen the laser is powered on but not emitting light, it can be generated by a bias current generating circuit 2312, the bias current I_biLess than threshold current I_thThreshold current I_thTo drive the laser to emit light or outputA minimum current of the outgoing laser beam; when the laser is required to output a laser beam, the switch current generating circuit 2311 generates a switch current I by controlling the relevant switch_swThereby the switching current I_swAnd a bias current I_biAre superimposed and I_bi+I_sw＞I_thSo that the generated drive current allows the laser to output a laser beam.

In some embodiments, the switch current generating circuit 2311 comprises a first switch SW1, which may be any one of a button switch, a key switch, a toggle switch, a membrane switch, a dot switch, etc., and when the first switch SW1 is turned on, the switch current generating circuit 2311 generates the switch current I_sw。

In some embodiments, the driving current detection circuit 232 may include a comparator for determining the driving current I collected_opWhether or not it is greater than the first preset threshold Th1, and when so, generates the first control signal C _ DIS to control the sample-and-hold capacitor C of the driving current control circuit 233_shDischarging is performed to reduce the driving current I_opUp to the drive current I_op≤Th1。

Specifically, the comparator may be any one of current comparators for comparing the preset first preset threshold Th1 with the driving current I_opThe size of (2).

In some embodiments, the driver circuit 230 may also be referred to as a driver, a laser driver.

In this embodiment, the driving circuit includes a driving current generating circuit, a driving current detecting circuit and a driving current control circuit, the driving current generating circuit is composed of a switching current generating circuit and a bias current generating circuit to generate a driving current, the driving current control circuit includes a sample-and-hold capacitor, the sample-and-hold capacitor is connected with the driving current generating circuit, the driving current detecting circuit can detect the driving current in real time, and when the driving current detecting circuit judges that the driving current is too large, the capacitor is controlled to discharge, so that the driving current is reduced by reducing the driving voltage, the overcurrent protection of the laser is realized, and the safety of the laser operation is improved.

Fig. 4 is a schematic connection diagram of a driving circuit, an imaging controller, an LD, and a PD in the embodiment shown in fig. 3 of the present application, as shown in fig. 4, the imaging controller 100 is connected to the driving circuit 230 through a Low Voltage Differential Signal (LVDS) transmission line, the driving circuit 230 is respectively connected to an output terminal of the laser emitting device LD and an input terminal of the laser receiving device PD, the input terminal of the LD and the output terminal of the PD are both connected to a power Signal VCC, the input terminal of the PD is further connected to one end of an adjustable resistor Rpd, the other end of the adjustable resistor Rpd is grounded, and the adjustable resistor Rpd is used for converting an induced current of the PD into an excitation Voltage Vm.

Fig. 5 is a schematic structural diagram of the comparator in the embodiment shown in fig. 3, as shown in fig. 5, the comparator includes a third operational amplifier AM3, a first voltage-dividing resistor R11 and a second voltage-dividing resistor R12, the second voltage-dividing resistor R12 is connected in series with the first voltage-dividing resistor R11, a non-inverting input terminal "+" of the third operational amplifier AM3 is used for receiving the driving current I_opThe inverting input terminal "-" is connected to one end of the first voltage-dividing resistor R11, the output terminal of the third operational amplifier AM3 is configured to output the first control signal C _ DIS, the other end of the first voltage-dividing resistor R11 is connected to the power signal VCC, one end of the second voltage-dividing resistor R12 is grounded, the other end of the second voltage-dividing resistor R12 is connected to the first voltage-dividing resistor R11, the first preset threshold Th1 is a current flowing through the first voltage-dividing resistor R11, and the expression is:

thus, when the input value at the non-inverting input terminal of the third operational amplifier AM3 is larger than the input value at the inverting input terminal, the current I is driven_opWhen the first threshold value Th1 is greater than the first preset threshold value, the output terminal outputs the first control signal C _ DIS. An output terminal of the third operational amplifier AM3 is connected to the driving current control circuit 233 to transmit the first control signal C _ DIS to the driving current control circuit 233 to control the sample-and-hold capacitor C_shAnd discharging is performed.

In some embodiments, the drive current detection circuit232 may also include a current mirror module to generate the drive current I_opThe mirror current of (2) is subsequently detected and determined instead of the driving current, that is, it is determined whether the mirror current is greater than a first preset threshold Th 1.

Fig. 6 is a schematic structural diagram of the driving current detection circuit in the embodiment shown in fig. 3 of the present application, and as shown in fig. 6, the driving current detection circuit 232 includes a detection current generation module 2321 and a driving current detection module 2322.

The detection current generating module 2321 is connected to the driving current generating circuit 231, and is configured to receive the driving current I_opAnd according to the driving current I_opGenerating a detection current I_miWherein the current I is detected_miLess than or equal to the drive current I_op(ii) a The driving current detection module 2322 is connected to the detection current generation module 2321, and is configured to receive the detection current I_miAnd determining the detection current I_miIf the current value is greater than the second preset threshold Th2, if so, the first control signal C _ DIS is generated.

Specifically, the detection current I is generated by the detection current generation module 2321_miBased on the detected current I_miSubsequent over-current detection is carried out, so that the driving current I in the subsequent over-current detection step is avoided_opAn influence is produced. The over-current detection refers to a process corresponding to the driving current detection module 2322 and the driving current control circuit.

In some embodiments, the detection current generation module 2321 includes a first field effect transistor M1 and a first resistor R1; wherein, the grid of the first field effect transistor M1 is used for receiving the driving current I_opThe drain of the first fet M1 is used for receiving the power supply signal VCC, the source of the first fet M1 is connected to one end of the first resistor R1, the other end of the first resistor R1 is grounded, and the detection current I is detected_miThe current output for the source of the first fet M1.

In some embodiments, the first fet M1 is an NMOS (N Metal Oxide Semiconductor) transistor.

The detection current composed of the first field effect transistor M1 and the first resistor R1 generates a current 2321Current pair of driving currents I_opThe mirror image of (1) avoids the influence I of the subsequent detection process on the drive current_opAnd the structure is simple and easy to realize.

In some embodiments, the driving current Control circuit 233 may include an APC (Automatic Power Control) circuit to stabilize the optical Power of the laser emitting device.

In some embodiments, the driving current control circuit 233 further includes a second field effect transistor M2; the gate of the second field effect transistor M2 is connected to the driving current detection circuit 232, and is configured to receive the first control signal C _ DIS; the source electrode of the second field effect transistor M2 is grounded; drain of the second field effect transistor M2 and the sample-and-hold capacitor C_shIs connected with the first end of the first connecting pipe; sample-and-hold capacitor C_shIs further connected to a drive current generation circuit 231 for sampling and holding the capacitor C_shDuring discharge, drive current I_opThen the speed is reduced; sample-and-hold capacitor C_shThe second terminal of (a) is grounded.

In some embodiments, the second fet M2 is an NMOS transistor.

FIG. 7 is a schematic structural diagram of the driving current control circuit according to the embodiment shown in FIG. 3, as shown in FIG. 7, the driving current control circuit 233 includes a second FET M2 and an APC circuit 2331, wherein the APC circuit 2331 includes a sample-and-hold capacitor C_shFig. 7 shows a specific connection relationship among the fourth operational amplifier AM4, and the second switch SW 2.

Wherein, the sampling hold capacitor C_shIs connected to the drain of the second fet M2 and one end of a second switch SW2, and a sample-and-hold capacitor C_shThe second terminal P2 is grounded; the source electrode of the second field effect transistor M2 is grounded, and the grid electrode is used for receiving a first control signal C _ DIS; the other end of the second switch SW2 is connected to the output end of a fourth operational amplifier M4, the positive input end of the fourth operational amplifier M4 is used for receiving a reference voltage Vref, the negative input end is used for receiving an excitation voltage Vm of a laser receiving part (Photo Diode, PD), and a sample-hold capacitor C_shSample and hold the error signal output from the fourth operational amplifier AM4, thereby enabling the APC circuit 2331A switching current I capable of generating circuit 2311_swOr bias current I of bias current generating circuit 2312_biIs adjusted so that LD is at the driving current I_opThe lower light emission intensity coincides with the light intensity of the LD corresponding to the reference voltage Vref.

In some embodiments, the sample-and-hold capacitor C_shIs connected to the switch current generating circuit 2311 as the sample-and-hold capacitor C_shDuring discharging, the switching current I generated by the switching current generation circuit 2311 is reduced_sw。

In particular, when the capacitor C is sampled and held_shDuring discharging, the switching voltage Vsw corresponding to the switching current generation circuit 2311 is decreased, thereby decreasing the switching current I_sw。

Fig. 8 is a schematic structural diagram of the switching current generating circuit in the embodiment shown in fig. 3 of the present application, and as shown in fig. 8, the switching current generating circuit 2311 includes a first operational amplifier AM1, a first switch SW1, a third fet M3, and a second resistor R2.

One end of the first switch SW1 is connected with an output end of a Laser Diode (LD) of the Laser, and the other end of the first switch SW1 is connected with a drain of the third field-effect transistor M3; the source electrode of the third field-effect transistor M3 is connected with the inverting input end of the first operational amplifier AM1, and the gate electrode of the third field-effect transistor M3 is connected with the output end of the first operational amplifier AM 1; the positive input end of the first operational amplifier AM1 and the sample-and-hold capacitor C_shThe first terminal P1, the voltage corresponding to the positive input terminal of the first operational amplifier AM1 is the switching voltage Vsw; one end of the second resistor R2 is connected with the source electrode of the third field effect transistor M3, and the other end of the second resistor R2 is grounded; switching current I_swIs the current through the first switch SW1 when the first switch SW1 is closed.

In particular, when the capacitor C is sampled and held_shUpon discharge, the potential at its first terminal P1 increases, resulting in a decrease of the potential at the positive input terminal of the first operational amplifier AM1, i.e. the voltage corresponding to the positive input terminal, the switching voltage Vsw decreases, and the switching current I thereby decreases_swAlso reduces the current, realizes the overcurrent protection。

In some embodiments, the third fet M3 is an NMOS transistor.

In some embodiments, the sample-and-hold capacitor C_shIs connected to the bias current generating circuit 2312 to sample and hold the capacitor C_shIn discharging, the bias current I generated by the bias current generation circuit 2312 is reduced_bi。

Fig. 9 is a schematic structural diagram of the bias current generating circuit in the embodiment shown in fig. 3 of the present application, and as shown in fig. 9, the bias current generating circuit 2312 includes a second operational amplifier AM2, a fourth field effect transistor M4, and a third resistor R3.

The drain of the fourth field-effect transistor M4 is connected with the output end of the laser emitting device LD of the laser, the source of the fourth field-effect transistor M4 is connected with the inverting input end of the second operational amplifier AM2, and the gate of the fourth field-effect transistor M4 is connected with the output end of the second operational amplifier AM 2; the positive input end of the second operational amplifier AM2 and the sample-and-hold capacitor C_shThe first terminal P1 of the second operational amplifier AM2 is connected, and the voltage of the positive input terminal of the second operational amplifier AM2 is the bias voltage Vbi; one end of the third resistor R3 is connected with the source electrode of the fourth field effect transistor M4, and the other end of the third resistor R3 is grounded; bias current I_biIs the current through the drain of the fourth fet M4.

In particular, when the capacitor C is sampled and held_shUpon discharge, the potential at its first terminal P1 increases, resulting in a decrease of the potential at the forward input terminal of the first operational amplifier AM1, i.e. the voltage corresponding to the forward input terminal, the bias voltage Vbi decreases, and the bias current I thereby decreases_biAnd the current is reduced, and overcurrent protection is realized.

In some embodiments, the fourth fet M4 is an NMOS transistor.

In some embodiments, the sample-and-hold capacitor C_shMay be provided to be connected to both the switching current generation circuit 2311 and the bias current generation circuit 2312 when the current I is driven_opDuring overcurrent, the sampling hold capacitor C_shDischarging, switching the current I_swAnd a bias current I_biIs lowered along with the above-mentioned movement, thereby realizing loweringLow drive current I_opAnd overcurrent protection is realized.

The embodiment of the application does not limit the parameters and types of the components and can be designed according to specific requirements.

Fig. 10 is a schematic structural diagram of a laser device according to an embodiment of the present application, and as shown in fig. 10, the laser device 20 includes a laser emitting device LD, a laser receiving device PD, and a driving circuit 230.

The driving circuit 230 may be a driving circuit provided in any one of the embodiments shown in fig. 3 to 9 of the present application.

Specifically, the laser may be provided in a laser scanning unit of the image forming apparatus.

Fig. 11 is a schematic structural diagram of an image forming apparatus according to an embodiment of the present application, and as shown in fig. 11, the image forming apparatus includes an image forming controller 100, a laser scanning unit 200, and a photosensitive drum 300.

The laser scanning unit 200 includes the laser 20 provided in the embodiment shown in fig. 10.

Specifically, the image forming apparatus may further include a housing, a consumable cartridge, and the like.

Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

It will be understood that the present application is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims

1. A driving circuit applied to a laser, comprising: the driving circuit comprises a driving current generating circuit, a driving current detecting circuit and a driving current control circuit, wherein the driving current generating circuit comprises a switch current generating circuit and a bias current generating circuit, the driving current control circuit comprises a sampling holding capacitor, and the sampling holding capacitor is connected with the driving current generating circuit;

the driving current generation circuit is used for generating a driving current, and the driving current comprises a switching current generated by the switching current generation circuit and a bias current generated by the bias current generation circuit;

the driving current detection circuit is used for receiving the driving current and generating a first control signal when judging that the driving current is greater than a first preset threshold value;

the driving current control circuit is used for receiving the first control signal and controlling the discharge of the sampling holding capacitor according to the first control signal so as to reduce the driving current.

2. The circuit of claim 1, wherein the driving current detection circuit comprises a detection current generation module and a driving current detection module;

the detection current generation module is connected with the driving current generation circuit and used for receiving the driving current and generating a detection current according to the driving current, wherein the detection current is smaller than or equal to the driving current;

the driving current detection module is connected with the detection current generation module and used for receiving the detection current and judging whether the detection current is larger than a second preset threshold value, and if so, the first control signal is generated.

3. The circuit of claim 2, wherein the sense current generation module comprises a first field effect transistor and a first resistor;

the grid electrode of the first field effect transistor is used for receiving the driving current, the drain electrode of the first field effect transistor is used for receiving a power supply signal, the source electrode of the first field effect transistor is connected with one end of the first resistor, the other end of the first resistor is grounded, and the detection current is the current output by the source electrode of the first field effect transistor.

4. The circuit of claim 1, wherein the drive current control circuit further comprises a second field effect transistor;

the grid electrode of the second field effect transistor is connected with the driving current detection circuit and used for receiving the first control signal; the source electrode of the second field effect transistor is grounded; the drain electrode of the second field effect transistor is connected with the first end of the sampling holding capacitor;

the first end of the sampling holding capacitor is also connected with the driving current generating circuit, so that when the sampling holding capacitor discharges, the driving current is reduced along with the discharging of the sampling holding capacitor; the second terminal of the sample-and-hold capacitor is grounded.

5. The circuit of any of claims 1-4, wherein the first terminal of the sample-and-hold capacitor is coupled to the switching current generation circuit to reduce the switching current generated by the switching current generation circuit when the sample-and-hold capacitor is discharged.

6. The circuit of claim 5, wherein the switching current generation circuit comprises a first operational amplifier, a first switch, a third field effect transistor, and a second resistor;

7. The circuit of any of claims 1-4, wherein the first terminal of the sample-and-hold capacitor is coupled to the bias current generation circuit to reduce the bias current generated by the bias current generation circuit when the sample-and-hold capacitor is discharged.

8. The circuit of claim 7, wherein the bias current generating circuit comprises a second operational amplifier, a fourth field effect transistor, and a third resistor;

the drain electrode of the fourth field effect transistor is connected with the output end of a laser emitting device of the laser, the source electrode of the fourth field effect transistor is connected with the inverting input end of the second operational amplifier, and the grid electrode of the fourth field effect transistor is connected with the output end of the second operational amplifier; the positive input end of the second operational amplifier is connected with the first end of the sampling holding capacitor; one end of the third resistor is connected with the source electrode of the fourth field effect transistor, and the other end of the third resistor is grounded; the bias current is a current passing through a drain of the fourth field effect transistor.

9. A laser comprising laser emitting means, laser receiving means and a drive circuit as claimed in any one of claims 1 to 8.

10. An image forming apparatus includes an image forming controller, a laser scanning unit, and a photosensitive drum;

wherein the laser scanning unit comprises the laser of claim 9.