CN209784738U

CN209784738U - Heating device and image forming apparatus

Info

Publication number: CN209784738U
Application number: CN201920661686.7U
Authority: CN
Inventors: 黄超豪; 晏丹丹
Original assignee: Zhuhai Pantum Electronics Co Ltd
Current assignee: Zhuhai Pantum Electronics Co Ltd
Priority date: 2019-05-08
Filing date: 2019-05-08
Publication date: 2019-12-13
Anticipated expiration: 2029-05-08
Also published as: WO2020224477A1

Abstract

The application discloses a heating device and an image forming apparatus, the heating device includes a heater, a power supply, a temperature detection circuit, a comparator circuit, a thyristor control circuit and a relay control circuit; the power supply is used for supplying electric energy to the heater; the temperature detection circuit is used for detecting the temperature of the heater and forming a corresponding voltage value Va according to the temperature of the heater; the comparator circuit is used for comparing the voltage value Va with a preset reference voltage value Vp and outputting a control signal according to a comparison result; and the silicon controlled control circuit and the relay control circuit are respectively used for controlling the heater to be switched on or switched off according to the control signal. According to the heating control method and the heating control device, under the condition that software control is abnormal, the control signal can be output through the comparator circuit, heating of the heater is controlled according to the control signal, and the fusing unit is prevented from being burnt out due to overhigh temperature.

Description

Heating device and image forming apparatus

Technical Field

The present disclosure relates to the field of image forming technologies, and more particularly, to a heating device and an image forming apparatus having the same.

Background

In an image forming apparatus such as a printer, a fixing unit is generally provided for fixing a toner image on a sheet after transfer. At the time of fixing, the fixing unit needs to be heated.

In the prior art, a software output control signal Fuse on/off is generally used to control a heater to be opened or closed so as to realize heating control of a fixing unit, once the software control fails, the heater can continuously heat, so that the temperature of the fixing unit is too high, and even the fixing unit can be burnt in severe cases.

SUMMERY OF THE UTILITY MODEL

In order to overcome the problems of the prior art described above, it is a primary object of the present application to provide a heating apparatus capable of preventing a temperature of a fixing unit from being excessively high.

In order to achieve the above purpose, the following technical solutions are specifically adopted in the present application:

the application provides a heating device for a fixing device, the heating device including:

A heater.

a power source for providing electrical power to the heater.

And the temperature detection circuit is used for detecting the temperature of the heater and forming a corresponding voltage value Va according to the temperature of the heater.

And the comparator circuit is connected with the temperature detection circuit and is used for comparing the voltage value Va with the reference voltage value Vp and outputting a control signal according to a comparison result.

And the silicon controlled control circuit is respectively connected with the comparator circuit and the heater and is used for controlling the heater to be turned on or off according to the control signal.

And the relay control circuit is respectively connected with the comparator circuit and the heater and is used for controlling the heater to be turned on or off according to the control signal.

Preferably, the heating device further comprises a relay protection circuit, wherein the relay protection circuit is connected with the comparator circuit and used for controlling the relay control circuit to be switched off in a time-delay manner or switched on in advance compared with the silicon controlled control circuit.

preferably, the relay protection circuit includes at least one delay circuit and at least one discharge circuit.

Preferably, the relay protection circuit comprises a first delay circuit and a first discharge circuit, wherein the first delay circuit is composed of a first capacitor and a first resistor; the first discharge circuit is composed of a first diode.

Preferably, the relay protection circuit further includes a second delay circuit and a second discharge circuit, the second delay circuit is composed of a second capacitor and a second resistor, and the second discharge circuit is composed of a second diode.

Preferably, the heating device further comprises a first MOS transistor, a gate of the first MOS transistor is connected to the comparator circuit, and a source of the first MOS transistor is grounded; and the drain electrode of the first MOS tube is connected with the controlled silicon control circuit.

Preferably, the heating device further comprises a second MOS transistor, a gate of the second MOS transistor is connected to the comparator circuit, and a source of the second MOS transistor is grounded; and the drain electrode of the second MOS tube is connected with the relay control circuit.

preferably, the comparator circuit is a hysteresis comparator circuit.

Preferably, the hysteresis comparison circuit includes a sixteenth resistor and a comparator, and two ends of the sixteenth resistor are respectively connected to the input end of the comparator and the output end of the comparator.

Accordingly, the present application also provides an image forming apparatus including the heating device described above.

Compared with the prior art, the fixing device has the advantages that the hardware control circuit is arranged, under the condition that software control is abnormal, the control signal can be output through the comparator circuit, heating of the heater is controlled according to the control signal, and burning-out of the fixing unit due to overhigh temperature is avoided.

Drawings

Fig. 1 is a schematic circuit diagram of a heating device according to an embodiment of the present application.

Fig. 2 is an overall timing diagram of the over-temperature protection according to the embodiment of the present application.

Fig. 3 is a schematic circuit diagram of a heating device according to another embodiment of the present application.

Fig. 4 is an overall timing diagram of the hysteresis over-temperature protection according to the embodiment of the present application.

Fig. 5 is a schematic configuration diagram of the image forming apparatus.

The attached drawings are as follows:

1-a temperature detection circuit;

2-a comparator circuit;

3-a silicon controlled control circuit;

4-a relay control circuit;

5-a relay protection circuit;

100-a carton;

101-a paper feed roller;

102-a first transport roller;

103-a second conveying roller;

104-a process cartridge;

105-a laser;

106-a transfer roller;

107-a fixing unit;

108-a third transport roller;

109-a fourth conveying roller;

110-a fifth carrying roller;

111-discharge carton;

112-a photosensitive drum;

113-a charging roller;

114-a developer roller;

115-paper.

Detailed Description

in order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

in the description of the present application, unless explicitly stated or limited otherwise, the terms "first", "second", and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means two or more unless specified or indicated otherwise; the terms "connected," "fixed," and the like are to be construed broadly and may, for example, be fixedly connected, detachably connected, integrally connected, or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Embodiments of the present application disclose a heating device for an image forming apparatus including a fixing unit, the heating device for heating the fixing unit in the image forming apparatus.

As shown in fig. 1, the heating apparatus includes a heater LD1, a power source CN1, a temperature detection circuit 1, a comparator circuit 2, a thyristor control circuit 3, and a relay control circuit 4. The heater LD1 is used to heat the fixing unit, and the power source CN1 is used to supply power to the heater LD 1. The temperature detection circuit 1 is used for detecting the temperature of the heater LD1 and forming a corresponding voltage value Va according to the temperature. The input end of the comparator circuit 2 is connected to the temperature detection circuit 1, and is configured to compare the voltage value Va with a preset reference voltage value Vp, and output a control signal according to a comparison result. The thyristor control circuit 3 is connected to the comparator circuit 2 and the heater LD1 respectively, and is configured to control the heater LD1 to turn on or off according to a control signal output by the comparator circuit 2. The relay control circuit 4 is connected to the comparator circuit 2 and the heater LD1, respectively, and is configured to control the heater 1 to be turned on or off according to a control signal output by the comparator circuit 2.

In the concrete control process, when the heating temperature of the heater LD1 is within the preset normal range,

Va > Vp, the comparator circuit 2 outputs low level, the thyristor control circuit 3 and the relay control circuit 4 are respectively closed, the current reflux of the heater LD1 is conducted, and the heater LD1 is normally heated. If the software input signal Fuse _ on/off is invalid, the heater LD1 is continuously heated, when the heating temperature of the heater LD1 exceeds a preset normal range, such as 220 ℃, Va < Vp, the output of the comparator circuit 2 jumps from low level to high level, the thyristor control circuit 3 and the relay control circuit 4 are respectively disconnected, the current backflow of the heater LD1 is disconnected, and the heater LD1 stops heating.

By arranging the comparator circuit 2, under the condition that software output control is abnormal, the heating of the heater can be controlled by the comparator circuit 2 to output a control signal, namely, the heating of the heater is controlled by a hardware circuit, and the fusing unit is prevented from being burnt out due to overhigh temperature. Meanwhile, the present application is provided with a thyristor control circuit 3 and a relay control circuit 4 for controlling the heating of the heater LD1 together. When external factors (such as entry of insects and thunder) cause short circuit of the thyristor control circuit 3, so that the thyristor control circuit 3 fails to control the heater LD1, the relay control circuit 4 can control the heater LD1 to be turned off, and the heater LD1 is prevented from continuously heating to cause overhigh temperature of the fixing unit.

Because when through same signal control silicon controlled rectifier and relay, can have the problem that the relay electrified switch was opened with the electrification, and if the relay electrified switch or electrified switch, can cause the contact adhesion of relay, damage relay produces the heating trouble.

In order to prevent the relay from working with electricity, the heating device further comprises a relay protection circuit 5, wherein the relay protection circuit 5 is respectively connected with the comparator circuit 2, the silicon controlled control circuit 3 and the relay control circuit 4 and used for enabling the relay control circuit 4 to be switched off in a time delay manner or closed in advance compared with the silicon controlled control circuit 3, and the relay is prevented from being bonded with a contact of the relay due to the fact that the relay is electrified or switched on, damaging the relay and generating heating faults.

in this embodiment, the relay protection circuit 5 includes a first delay circuit, a first discharge circuit, a second delay circuit, and a second discharge circuit, and the relay control circuit 4 is turned off in a delayed manner by the first delay circuit and the second discharge circuit as compared with the thyristor control circuit 3, and the relay control circuit 4 is turned on in advance by the second delay circuit and the first discharge circuit as compared with the thyristor control circuit 3.

Specifically, the first delay circuit includes a first resistor R1 and a first capacitor C1, the first discharge circuit includes a first diode D1, the second delay circuit includes a second resistor R2 and a second capacitor C2, and the second discharge circuit includes a second diode D2.

It is understood that in other embodiments, the relay protection circuit 5 may only include the first delay circuit and the first discharging circuit, and the relay control circuit 4 is turned off in a delayed manner by the first delay circuit compared with the thyristor control circuit 3. The first capacitor C1 is discharged through the first discharging circuit, so that the relay control circuit 4 is closed in advance compared with the silicon controlled control circuit 3, and the silicon controlled rectifier is closed only when an Alternating Current (AC) zero crossing point is detected (the AC zero crossing detection circuit is not shown), namely, the possibility that the silicon controlled rectifier is closed after the relay is higher, so that the relay control circuit 4 can be closed in advance compared with the silicon controlled control circuit 3 only through the first discharging circuit and the AC zero crossing detection circuit. However, in a manner that the relay control circuit 4 is delayed and disconnected compared with the thyristor control circuit 3 through the first delay circuit and the second discharge circuit and the relay control circuit 4 is closed in advance compared with the thyristor control circuit 3 through the second delay circuit and the first discharge circuit, when the zero-crossing point and the fixation heating opening signal (the software outputs the control signal Fuse on and the comparator circuit 2 outputs the low-level control signal) arrive at the same time, the relay control circuit 4 can still be ensured to be delayed and disconnected compared with the thyristor control circuit 3.

The temperature detection circuit 1 includes a third resistor R3 and a thermistor RT 1. The comparator circuit 2 includes a comparator U1, a fifth resistor R5, and a sixth resistor R6.

The third resistor R3 is a voltage dividing resistor, one end of which is connected to the input voltage VREF, the other end of which is connected to one end of the thermistor RT1, and the other end of the thermistor RT1 is grounded to DCND. One end of the fifth resistor R5 is connected to the input voltage VREF, the other end of the fifth resistor R5 is connected to the non-inverting input terminal of the comparator U1 and one end of the sixth resistor R6, the other end of the sixth resistor R6 is grounded DGND, and the voltage VREF, the fifth resistor R5 and the sixth resistor R6 are used for generating the reference voltage value Vp; the inverting input terminal of the comparator U1 is connected with one end of the third resistor R3 connected with the thermistor RT 1.

An output Vo of the comparator U1 is connected to one end of the fourth resistor R4, one end of the first resistor R1, a cathode of the first diode D1, one end of the second resistor R2, and an anode of the second diode D2. The fourth resistor R4 is a pull-up resistor, and the other end of the fourth resistor R4 is connected with 3.3V voltage. The other end of the second resistor R2 and the cathode of the second diode D2 are connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is grounded DGND. The other end of the first resistor R1 and the positive electrode of the first diode D1 are connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is grounded DGND.

The heating device further comprises a first MOS transistor Q1, a second MOS transistor Q2, a seventh resistor R7 and an eighth resistor R8. The thyristor control circuit 3 comprises a ninth resistor R9, a first triode Q3, an optocoupler OP1 and a thyristor SCR 1. The relay control circuit 4 includes a thirteenth resistor R13, a second transistor Q4, and a relay RL 1.

One end of a seventh resistor R7 is connected with the cathode of the second diode D2, the other end of the seventh resistor R7 is connected with the gate of the first MOS tube Q1, the source of the first MOS tube Q1 is grounded DGND, the drain of the first MOS tube Q1 is connected with one end of a ninth resistor R9 and the base of the first triode Q3, and the other end of the ninth resistor R9 and the emitter of the first triode Q3 are grounded DGND; the collector of the first transistor Q3 is connected to a thyristor SCR1 via an optocoupler OP1, and the thyristor SCR1 is disposed on the current loop of the heater LD 1.

one end of the eighth resistor R8 is connected to the anode of the first diode D1, the other end of the eighth resistor R8 is connected to the gate of the second MOS transistor Q2, and the source of the second MOS transistor Q2 is grounded DGND; the drain of the second MOS transistor Q2 is connected to one end of the thirteenth resistor R13 and the base of the second transistor Q4, and the other end of the thirteenth resistor R13 and the emitter of the second transistor Q4 are grounded DGND; the collector of the second triode Q4 is connected with a relay RL1, and a relay RL1 is arranged on a current circuit of the heater LD 1.

In the present embodiment, the heater is a halogen lamp, and it is understood that in other embodiments, the heater may also be a ceramic heater.

According to the circuit, the output signal of one comparator U1 is used for simultaneously controlling the on-off of the SCR1 and the relay RL1, so that the circuit structure is simple.

as shown in fig. 2, in the over-temperature protection of the heater, when the temperature of the heater LD1 is normal, the voltage Va > Vp of the thermistor RT1, the output Vo of the comparator U1 is at a low level, the first MOS transistor Q1 and the second MOS transistor Q2 are turned off, the first transistor Q3 and the second transistor Q4 are turned on, the thyristor SCR1 and the relay RL1 are closed, and the heater LD1 operates normally.

when software control is out of control, the heater LD1 continuously heats to make the temperature exceed the set temperature T1 (for example, 225 ℃), the voltage Va at two ends of the thermistor RT1 decreases to cause Va < Vp, at this time, the output Vo of the comparator U1 jumps from low level to high level, the first MOS transistor Q1 is turned on, the second MOS transistor Q2 is continuously turned off, the first triode Q3 is turned off, the second triode Q4 is continuously turned on, the silicon controlled rectifier SCR1 is turned off, the relay RL1 is continuously turned on, the current backflow of the heater LD1 is cut off, and the heater LD1 does not heat any more. After the time delay t1 of the first time delay circuit, the second MOS tube Q2 is conducted, the second triode Q4 is cut off, and the relay RL1 is disconnected. At this time, after the thyristor SCR1 and the relay RL1 are turned off, the temperature of the thermistor RT1 is slowly decreased, and when the temperature thereof is decreased to be below a set value T1 (for example, 225 ℃), namely Va > Vp, the output Vo of the comparator U1 jumps from a high level to a low level, the first MOS transistor Q1 is continuously turned on, the second MOS transistor Q2 is turned off, the first transistor Q3 is continuously turned off, the second transistor Q4 is turned on, the thyristor SCR1 is continuously turned off, the relay RL1 is turned on, the current backflow of the heater LD1 is continuously cut off, and the heater LD1 is heated in a delayed manner. After the time delay t2 of the second delay circuit, the first MOS transistor Q1 is cut off, the first triode Q3 is turned on, and the silicon controlled rectifier SCR1 is turned on. The thyristor SCR1 and the relay RL1 are closed again, and the heater LD1 heats the fixing unit again.

In the protective relay, when the comparator U1 outputs a high level, the second diode D2 is turned on, and the second MOS transistor Q2 is turned on with a delay time from the first MOS transistor Q1. When the comparator U1 outputs a low level, the first diode D1 is turned on, the second diode D2 is turned off in the reverse direction, and the second MOS transistor Q2 is turned off earlier than the first MOS transistor Q1. Namely, when the comparator U1 outputs high level, the relay RL1 is disconnected with the time delay T1 of the SCR, and T1 is more than or equal to 10 ms. When the comparator U1 outputs a low level, the relay RL1 is closed earlier than the thyristor SCR by time t2, and during the time period t2, the heater does not start heating yet because the thyristor is closed with a delay, and thus the temperature continues to drop.

the present application also discloses another embodiment mode, in this embodiment, the circuit structure of the heating device is basically the same as that of the heating device described above, and the difference is only that the comparator circuit 2 of this embodiment is a hysteresis comparator circuit.

According to the application, through the arrangement of the hysteresis comparator circuit, under the condition that software control is out of control, frequent switching of the silicon controlled rectifier and the relay is reduced, and the service life of a device is prolonged while energy consumption is reduced.

as shown in fig. 3, the hysteresis comparator circuit includes a fifth resistor R5, a sixth resistor R6, a sixteenth resistor R16 and a comparator U1, one end of the fifth resistor R5 is connected to the input voltage VREF, the other end of the fifth resistor R5 is connected to the non-inverting input terminal of the comparator U1 and one end of the sixth resistor R6, and the other end of the sixth resistor R6 is grounded DGND; two ends of the sixteenth resistor R16 are connected to the non-inverting input terminal of the comparator U1 and the output terminal of the comparator U1, respectively.

As shown in fig. 4, in the over-temperature protection of the heater, when the temperature of the heater LD1 is normal, the voltage Va > Vp of the thermistor RT1, the output Vo of the comparator U1 is low, the first MOS transistor Q1 and the second MOS transistor Q2 are turned off, the first transistor Q3 and the second transistor Q4 are turned on, the thyristor SCR1 and the relay RL1 are closed, and the heater LD1 is normally heated.

Under the condition that software control is out of control, the heater LD1 is continuously heated, the temperature of the heater LD1 exceeds the set temperature T1 (for example, 225 ℃), the voltage Va at the two ends of the thermistor RT1 is reduced, and Va < Vp is caused, namely, the output Vo of the comparator U1 jumps from low level to high level, the first MOS tube Q1 is conducted, the second MOS tube Q2 is continuously cut off, the first triode Q3 is cut off, the second triode Q4 is continuously conducted, the silicon controlled rectifier SCR1 is disconnected, the relay RL1 is continuously conducted, the current backflow of the heater LD1 is cut off, the heater LD1 is not heated any more, and an over-temperature prompt is sent to a user. After the time delay t1 of the first time delay circuit, the second MOS tube Q2 is conducted, the second triode Q4 is cut off, and the relay RL1 is disconnected. At this time, after the thyristor SCR1 and the relay RL1 are turned off, the temperature of the thermistor RT1 is slowly decreased, and when the temperature thereof falls below a set value T2(T2< T1, for example, equal to or lower than the normal fixing temperature), that is, Va > Vp, the output Vo of the comparator U1 is at a low level, the first MOS transistor Q1 is continuously turned on, the second MOS transistor Q2 is turned off, the first transistor Q3 is continuously turned off, the second transistor Q4 is turned on, the thyristor SCR1 is continuously turned off, the relay RL1 is turned on, the current reflux of the heater LD1 is continuously interrupted, and the heater LD1 is heated with a delay. After the time delay t2 of the second delay circuit, the first MOS transistor Q1 is cut off, the first triode Q3 is turned on, and the silicon controlled rectifier SCR1 is turned on. The thyristor SCR1 and relay RL1 close again and heater LD1 heats up again.

in the protective relay, when the comparator U1 outputs a high level, the second diode D2 is turned on, and the second MOS transistor Q2 is turned on with a delay time from the first MOS transistor Q1. When the comparator U1 outputs a low level, the first diode D1 is turned on, the second diode D2 is turned off in the reverse direction, and the second MOS transistor Q2 is turned off earlier than the first MOS transistor Q1. Namely, when the comparator U1 outputs high level, the relay RL1 is disconnected with the time delay t1 of the SCR, and t1 is more than or equal to 10 ms; when the comparator U1 outputs a low level, the relay RL1 closes earlier than the silicon controlled SCR by time t 2.

accordingly, an embodiment of the present application also discloses an image forming apparatus, as shown in fig. 5, including a paper cassette 100, a paper feed roller 101, a first conveying roller 102, a second conveying roller 103, a process cartridge 104, a laser 105, a transfer roller 106, a fixing unit 107, a third conveying roller 108, a fourth conveying roller 109, a fifth conveying roller 110, a discharge paper cassette 111, a photosensitive drum 112, a charging roller 113, a developing roller 114, and the above-described heating device. The photosensitive drum 112, the charging roller 113, and the developing roller 114 are provided in the process cartridge 104, the first conveying roller 102 and the second conveying roller 103 are provided in a paper feeding path of the image forming apparatus, respectively, and the third conveying roller 108, the fourth conveying roller 109, and the fifth conveying roller 110 are provided in a paper discharging path of the image forming apparatus, respectively.

The paper cassette 100 stores paper 115, the paper feed roller 101 conveys the paper 115 stored in the paper cassette 100 to a paper feed path, and the first conveying roller 102 and the second conveying roller 103 convey the paper 115 to a nip of the photosensitive drum 112 and the transfer roller 106. The charging roller 113 is used for charging the surface of the photosensitive drum 112, the laser 105 is used for emitting laser beams to form an electrostatic latent image on the surface of the photosensitive drum 112, and the developing roller 114 is used for developing and forming a carbon powder image on the surface of the photosensitive drum 112. The heating device is used to heat the fixing unit 107. When the paper 115 passes through the nip between the photosensitive drum 112 and the transfer roller 106, the photosensitive drum 112 transfers the toner image formed on the surface thereof to the paper by the transfer roller 106 or the like. The fixing unit 107 is configured to convey the sheet 115, on which the toner image is fixed on the sheet 115, to the discharge paper cassette 111 via the third conveying roller 108, the fourth conveying roller 109, and the fifth conveying roller 110.

the above description is only for the preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A heating device for heating a fixing unit in an image forming apparatus, characterized by comprising:

a heater;

A power supply for providing electrical power to the heater;

the temperature detection circuit is used for detecting the temperature of the heater and forming a corresponding voltage value Va according to the temperature of the heater;

The comparator circuit is connected with the temperature detection circuit and is used for comparing the voltage value Va with a preset reference voltage value Vp and outputting a control signal according to a comparison result;

the silicon controlled control circuit is respectively connected with the comparator circuit and the heater and is used for controlling the heater to be turned on or off according to the control signal;

2. the heating device of claim 1, further comprising a relay protection circuit coupled to the comparator circuit for controlling the relay control circuit to open at a time delay or close at an earlier time than the thyristor control circuit.

3. The heating device of claim 2, wherein the relay protection circuit comprises at least one time delay circuit and at least one discharge circuit.

4. The heating device of claim 3, wherein the relay protection circuit comprises a first delay circuit and a first discharge circuit, the first delay circuit being comprised of a first capacitor and a first resistor; the first discharge circuit is composed of a first diode.

5. the heating device of claim 4, wherein the relay protection circuit further comprises a second delay circuit and a second discharge circuit, the second delay circuit being comprised of a second capacitor and a second resistor, the second discharge circuit being comprised of a second diode.

6. The heating device according to claim 1, further comprising a first MOS transistor, wherein a gate of the first MOS transistor is connected to the comparator circuit, and a source of the first MOS transistor is grounded; and the drain electrode of the first MOS tube is connected with the controlled silicon control circuit.

7. The heating device according to claim 1, further comprising a second MOS transistor, wherein a gate of the second MOS transistor is connected to the comparator circuit, and a source of the second MOS transistor is grounded; and the drain electrode of the second MOS tube is connected with the relay control circuit.

8. the heating device of claim 1, wherein the comparator circuit is a hysteresis comparator circuit.

9. the heating device as claimed in claim 8, wherein the hysteresis comparator circuit comprises a sixteenth resistor and a comparator, and two ends of the sixteenth resistor are respectively connected to the input end of the comparator and the output end of the comparator.

10. an image forming apparatus characterized by comprising the heating device according to any one of claims 1 to 9.