Image forming apparatus

Abstract

To provide an image forming apparatus that, with a temperature detection circuit arranged at an interval equal to or more than a predetermined distance from a primary circuit that outputs AC voltage, can appropriately detect the temperature of a heat sink mounted in the primary circuit.SOLUTION: A heat conduction member 410 conducting heat of a heat sink 312 is arranged on a substrate 301. The heat conduction member 410 is formed from the heat sink 312 toward a thermistor 328 to a position in proximity to the thermistor 328, at an interval shorter than the interval between a primary circuit 310 and a secondary circuit 320 arranged on the substrate 301 at an interval to prevent an electrical influence caused by AC voltage and DC voltage. Since the heat conduction member 410 conducts the heat of the heat sink 312 without a large loss, a temperature detection circuit 326 can appropriately detect the temperature of the heat sink 312 by using the thermistor 328 to detect the heat of the heat conduction member 410.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine. [Background technology]

[0002] An image forming apparatus receives an AC voltage from an AC power source connected via, for example, a power cord plugged into an electrical outlet. The image forming apparatus is provided with a power supply device for supplying the AC voltage input from the AC power source and DC voltage converted from the AC voltage to a photosensitive unit, a developing unit, a fixing unit, and the like. The power supply device has a printed circuit board (conveniently referred to as a power supply board) on which electronic components, electrical components, connectors, and the like are mounted, the board having a conductive printed wiring pattern formed on its surface. The power supply board is formed with a primary circuit to which the AC voltage is input and a secondary circuit that converts the AC voltage output from the primary circuit to generate DC voltage (see Patent Document 1). The primary circuit and secondary circuit are spaced apart by a predetermined distance or more to suppress electrical influences between the AC voltage and DC voltage.

[0003] In Patent Document 1, the temperature of a heat sink mounted in a secondary circuit to dissipate heat from heat-generating circuit elements is detected using a thermistor. Then, in order to lower the temperature of the heat sink and indirectly cool the circuit elements, a cooling fan that blows air onto the heat sink is controlled according to the detected heat sink temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-177160 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the primary circuit also contains circuit elements that generate heat, and the heat from these circuit elements is dissipated by a heat sink mounted on the primary circuit. As with the secondary circuit described above, it is conceivable to control the cooling fan in such a primary circuit according to the temperature of the heat sink. However, because the thermistor detects temperature by applying a DC voltage, the temperature detection circuit including the thermistor must be placed at a certain distance from the primary circuit, just like the secondary circuit. Therefore, the thermistor could not be placed close to the heat sink mounted on the primary circuit, making it difficult to properly detect the heat sink temperature.

[0006] Therefore, the present invention aims to provide an image forming apparatus that can properly detect the temperature of a heat sink mounted on a primary circuit by using a temperature detection circuit that is arranged at a distance of at least a predetermined distance from the primary circuit that outputs AC voltage. [Means for solving the problem]

[0007] An image forming apparatus according to one embodiment of the present invention comprises a first circuit unit having a circuit element and outputting an AC voltage, a heat dissipation member that dissipates heat generated from the circuit element, a temperature detection circuit unit that detects temperature, and a heat conduction member connected to the heat dissipation member and conducting heat from the heat dissipation member, wherein a first distance from the heat conduction member to the temperature detection circuit unit is shorter than a second distance from the first circuit unit to the temperature detection circuit unit. [Effects of the Invention]

[0008] According to the present invention, a temperature detection circuit unit arranged at a distance of at least a predetermined distance from a first circuit unit that outputs an AC voltage can properly detect the temperature of the heat dissipation component via a heat conduction component connected to the heat dissipation component mounted on the first circuit unit. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a power supply unit. [Figure 3] 1A is a cross-sectional view showing a part of a power supply unit in a first embodiment, FIG. 1B is a schematic view showing a part of the back surface of the power supply unit, and FIG. 1C is an enlarged view showing the vicinity of a heat conduction member in the power supply unit. [Figure 4] 10A is a cross-sectional view showing a part of a power supply unit, FIG. 10B is a schematic view showing a part of the back surface of the power supply unit, and FIG. 10C is an enlarged view showing the vicinity of a heat conduction member in a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] <Image forming device> An embodiment of the present invention will be described below. First, an image forming apparatus according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing an image forming apparatus 201 according to this embodiment. An image forming unit 201B that forms an image on a sheet is mounted on an apparatus body 201A of the image forming apparatus 201, which may be a printer, for example, and an image reading device 202 is installed substantially horizontally above the apparatus body 201A. A discharge space S for discharging sheets is formed between the image reading device 202 and the apparatus body 201A.

[0011] At the bottom of the device main body 201A, there are arranged a plurality of sheet feeding devices 230, each having a feeding cassette 1 that stores sheets P and a feeding unit 13 that feeds sheets P from the feeding cassette 1. The sheets P used as recording materials include paper such as plain paper and cardboard, as well as special paper such as coated paper, plastic film for overhead projectors, cloth, and envelopes. Each feeding unit 13 has a pickup roller 8 that feeds sheets P from the feeding cassette 1, and a feed roller 9 and a retard roller 10 that separate and transport the sheets P fed from the pickup roller 8.

[0012] The apparatus main body 201A is also provided with a manual feed device 800, which has a manual feed tray 14 into which sheets P are manually fed, and a pickup roller 16 that feeds the sheets P stacked on the manual feed tray 14. The manual feed device 800 also has a feed roller 17 and a retard roller 18 that separate and transport the sheets P fed by the pickup roller 16.

[0013] Image forming unit 201B is a four-drum full-color electrophotographic unit. Specifically, image forming unit 201B includes a laser scanner 210 and four process cartridges PY, PM, PC, and PK that form toner images in four colors: yellow (Y), magenta (M), cyan (C), and black (K). Each of the process cartridges PY to PK includes a photosensitive drum 212, a charger 213, and a developing unit 214. Image forming unit 201B also includes an intermediate transfer unit 201C disposed above the process cartridges PY to PK, and a fixing unit 220. A toner cartridge 215 for supplying toner to the developing unit 214 is mounted above the intermediate transfer unit 201C.

[0014] The intermediate transfer unit 201C includes an intermediate transfer belt 216 wound around a drive roller 216a and a tension roller 216b. Primary transfer rollers 219 are provided inside the intermediate transfer belt 216 and contact the intermediate transfer belt 216 at positions facing each photosensitive drum 212. The intermediate transfer belt 216 is rotated counterclockwise in the drawing by the drive roller 216a, which is driven by a drive unit (not shown), and the negative polarity toner images carried on the photosensitive drums 212 are sequentially transferred in multiple layers onto the intermediate transfer belt 216 by the primary transfer rollers 219.

[0015] A secondary transfer roller 217 that transfers a toner image carried on the intermediate transfer belt 216 onto the sheet P is provided at a position facing the drive roller 216a of the intermediate transfer unit 201C. A fixing section 220 is disposed above the secondary transfer roller 217, and a first pair of discharge rollers 225a, a second pair of discharge rollers 225b, and a double-sided reversing section 201D are disposed above the fixing section 220. The double-sided reversing section 201D is provided with a pair of reversing rollers 222 that can rotate forward and backward, a re-conveying path R that conveys the sheet with an image formed on one side thereof again to the image forming section 201B, and the like.

[0016] The image forming apparatus 201 is also equipped with a control unit 100 for controlling the image forming operation, sheet feeding operation, etc. The control unit 100 controls the overall operation of the image forming apparatus 201. The control unit 100 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). Various programs and data are stored in the ROM and RAM. For example, the ROM stores programs such as image formation processing. The CPU executes the "image formation processing (program)" stored in the ROM to control the operation of the image forming apparatus 201 so as to form an image on a sheet P based on data and information received from external devices such as a personal computer, image scanner, and facsimile machine. The RAM temporarily stores the results of arithmetic processing associated with the execution of various programs.

[0017] An operation unit 730 disposed on the top of the apparatus main body 201A is connected to the control unit 100 so as to be able to input and output data. Recently, a touch panel type operation unit 730 is generally used for displaying information output from the control unit 100 and inputting information to the control unit 100. The operation unit 730 has a resistive or capacitive touch panel, and the user can perform touch operations on various screens displayed on the touch panel to set, for example, the size of the sheets P on which images are formed and the number of sheets to be output.

[0018] Next, the image forming operation of the image forming apparatus 201 will be described. An image of an original document read by the image reading device 202 is subjected to image processing by the control unit 100, converted into an electrical signal, and transmitted to a laser scanner 210 of the image forming unit 201B. In the image forming unit 201B, a photosensitive drum 212, the surface of which has been uniformly charged to a predetermined polarity and potential by a charger 213, is irradiated with laser light from the laser scanner 210, and the drum surface is exposed as the photosensitive drum 212 rotates. As a result, electrostatic latent images corresponding to yellow, magenta, cyan, and black are formed on the surface of the photosensitive drum 212 of each process cartridge PY to PK. These electrostatic latent images are developed and visualized with toner of each color supplied from a developer 214, and then are primarily transferred from the photosensitive drum 212 to the intermediate transfer belt 216, superimposed on each other, by a primary transfer bias applied to a primary transfer roller 219.

[0019] In parallel with this toner image forming operation, sheets P are fed one by one from either the sheet feeding device 230 or the manual feeding device 250 toward the registration roller pair 240. The registration roller pair 240 corrects any skew of the sheet P, and then sends the sheet P toward the secondary transfer roller 217 in accordance with the progress of toner image formation by the image forming unit 201B. In a transfer unit formed between the secondary transfer roller 217 and the intermediate transfer belt 216, a full-color toner image is secondarily transferred all at once onto the sheet P by a secondary transfer bias applied to the secondary transfer roller 217. The sheet P onto which the toner image has been transferred is transported to the fixing unit 220, where the toner is melted by heat and pressure applied thereto, thereby fixing the toner image to the sheet P. The fixing unit 220 is heated by a heater (not shown).

[0020] Thereafter, the sheet P on which the toner image has been fixed is discharged into the discharge space S by the first discharge roller pair 225a or the second discharge roller pair 225b provided downstream of the fixing unit 220, and is stacked on the stacking unit 223 arranged at the bottom of the discharge space S. When forming images on both sides of the sheet P, the sheet P on which the image has been formed on the first side is conveyed to the re-conveyance path R in a reversed state by the reversing roller pair 222, and is conveyed again to the image forming unit 201B. Then, the sheet P on which the image has been formed on the second side by the image forming unit 201B is discharged to the stacking unit 223 by the first discharge roller pair 225a or the second discharge roller pair 225b.

[0021] Note that the above image forming unit 201B is just one example, and a direct transfer type image forming unit that directly transfers a toner image formed on the photosensitive drum 212 to the sheet P may be used, or an inkjet type or offset printing type image forming unit may be used.

[0022] The image forming apparatus 201 receives power required to drive the image forming apparatus 201 from an external AC power supply 710. The image forming apparatus 201 includes a power supply unit 300 connected to the AC power supply 710 via a power cord 700, and the power supply unit 300 supplies AC voltage input from the AC power supply 710 and DC voltage converted from the AC voltage to each unit of the apparatus.

[0023] <Power supply section> Next, the power supply unit 300 will be outlined in detail with reference to Fig. 2. However, for convenience of illustration, the thermal conductive member 410 (see Figs. 3(a) and 3(b)), which will be described later, is omitted from Fig. 2. Note that the primary circuit 310 and the secondary circuit 320 may have circuit elements other than those shown mounted on the printed wiring patterns, but these are not shown here.

[0024] 2, the power supply unit 300 has a primary circuit 310 as a first circuit unit, a secondary circuit 320 as a second circuit unit, and a temperature detection circuit 326, which are arranged on a substrate 301. A conductive printed wiring pattern is formed on the surface of the substrate 301, and the primary circuit 310, the secondary circuit 320, and the temperature detection circuit 326 are electronic circuits formed by mounting circuit elements such as electronic and electrical components on the printed wiring pattern on the substrate 301. In this embodiment, a substrate 301 having a printed wiring pattern formed on one side thereof is used (see FIG. 3(a) described later).

[0025] The primary circuit 310 includes a filter circuit (not shown) that removes noise from the AC voltage input from the AC power supply 710 and distributes the voltage to each load, and a triac 311 that supplies the AC voltage from which the noise has been removed by the filter circuit to the fixing unit 220. The secondary circuit 320 includes an FET 321, a transformer 322, a rectifier diode 323, and a smoothing capacitor 324, and is an AC / DC conversion circuit that converts the AC voltage from which the noise has been removed, output from the primary circuit 310, into a DC voltage. The FET 321 and the transformer 322 are switched by a power supply control IC (not shown), so that the AC voltage flowing through the primary winding of the transformer 322 is transformed through the secondary winding of the transformer 322 and transmitted to the rectifier diode 323 and the smoothing capacitor 324. After the AC voltage is transformed, it is rectified by the rectifier diode 323 (for example, full-wave rectification by a bridge diode) and smoothed by the smoothing capacitor 324, thereby generating a DC voltage with little ripple from the AC voltage. In order to suppress the electrical influence of the AC and DC voltages on the primary circuit 310 and secondary circuit 320, the respective printed wiring patterns, electronic components, and electrical components are arranged at a distance of at least a predetermined distance (for example, at least 5 mm).

[0026] The power supply unit 300 also has a fan drive circuit 325 and a cooling fan 331, and the generated DC voltage is supplied to the fan drive circuit 325 and a DC / DC converter 342 in the control unit 100. As described above, the AC voltage from which noise has been removed in the primary circuit 310 is supplied to the fixing unit 220 via the triac 311. Since a large voltage must be applied to the heater to heat the fixing unit 220, the triac 311, which turns the application of the AC voltage ON and OFF, is a heat-generating circuit element whose heat value is greater than that of other circuit elements. Therefore, a heat sink 312 for dissipating heat from the triac 311 is mounted on the primary circuit side of the substrate 301. The heat from the triac 311 is conducted to the heat sink 312, which serves as a heat dissipation member.

[0027] The power supply unit 300 is also provided with a cooling fan 331 as a cooling unit that blows air onto the heat sink 312 to lower the temperature of the heat sink 312, thereby indirectly cooling the triac 311. A fan drive circuit 325 controls the start / stop and rotation speed of the cooling fan 331 in accordance with a fan drive signal output from a CPU 341 of the control unit 100. The CPU 341 operates using a DC voltage output from a DC / DC converter 342. The DC / DC converter 342 converts the DC voltage supplied from the secondary circuit 320 into a DC voltage required for the CPU 341 to operate.

[0028] Incidentally, it is desirable to appropriately control the start / stop of the cooling fan 331 in accordance with the temperature of the heat sink 312, to which heat from the triac 311 is conducted. This is because constantly driving the cooling fan 331 increases power consumption. Therefore, a temperature detection circuit 326 is disposed on the substrate 301 to detect the temperature of the heat sink 312. The temperature detection circuit 326, which serves as a temperature detection circuit unit, includes a thermistor 328 as a temperature detection element capable of detecting temperature upon application of a DC voltage, and a DC circuit 327 as a DC circuit unit that applies the DC voltage to the thermistor 328. For example, the thermistor 328 is a component whose resistance changes in response to heat when a DC voltage is applied, and the DC circuit 327 applies the DC voltage generated by the secondary circuit 320 to the thermistor 328. In this embodiment, a surface-mount type thermistor 328 is used. The control unit 100 controls the fan drive circuit 325 to start driving the cooling fan 331 when the temperature of the heat sink 312 reaches a temperature equal to or higher than a threshold value, and to stop driving the cooling fan 331 when the temperature of the heat sink 312 reaches a temperature lower than the threshold value.

[0029] In order for the temperature detection circuit 326 to properly detect the temperature of the heat sink 312, it is preferable to arrange the temperature detection circuit 326 on the substrate 301 so that the thermistor 328 is as close as possible to the heat sink 312. However, the heat sink 312 is mounted on the primary circuit side of the substrate 301. Therefore, like the secondary circuit 320, the temperature detection circuit 326, including the thermistor 328, needs to be arranged at a distance of at least a predetermined distance from the primary circuit 310. However, if this is done, the thermistor 328 will be mounted at a position at least a predetermined distance (for example, 5 mm) away from the heat sink 312, making it difficult for the temperature detection circuit 326 to properly detect the temperature of the heat sink 312.

[0030] In view of the above, in this embodiment, the temperature detection circuit 326 is configured to be able to properly detect the temperature of the heat sink 312 even if the thermistor 328 is located at a position that is a predetermined distance or more away from the heat sink 312. A power supply unit 300 according to this embodiment that achieves this will be described below with reference to FIGS. 3(a) and 3(b). FIG. 3(a) is a cross-sectional view showing a portion of the power supply unit 300 according to the first embodiment, and FIG. 3(b) is a schematic view showing a portion of the back surface of the power supply unit 300 according to the first embodiment. Note that in FIGS. 3(a) and 3(b), components of the secondary circuit 320 other than the temperature detection circuit 326 are omitted from the illustration in order to facilitate understanding of the description.

[0031] As shown in FIG. 3( a), a printed wiring pattern 310a of a primary circuit 310 is formed on the front surface (first surface) of the substrate 301 using, for example, copper foil or copper plating, and circuit elements such as a triac 311 are soldered to the printed wiring pattern 310a in a conductive manner. A heat sink 312 is also mounted on the front surface of the substrate 301. The heat sink 312 is provided to dissipate heat generated by the triac 311. Screw fastening holes 330 and 340 are formed in the substrate 301, penetrating from the front surface to the back surface. The heat sink 312 is fixed to the substrate 301 with screws 401 and 402 inserted into the screw fastening holes 330 and 340 from the back surface of the substrate 301. In this embodiment, the screws 401 and 402 are made of a metal, such as an aluminum alloy, that readily conducts heat from the mounted heat sink 312. The screw 401 connects the heat sink 312 and the thermally conductive member 410 in a thermally conductive manner.

[0032] Furthermore, a printed wiring pattern 326a of a temperature detection circuit 326 is formed on the surface of the substrate 301 using, for example, copper foil or copper plating. A circuit element such as a resistor 600 is electrically soldered to the printed wiring pattern 326a to form a DC circuit 327 (see FIG. 2). In this embodiment, as shown in FIGS. 3(a) and 3(b), a thermistor 328 of the temperature detection circuit 326 is mounted on the back surface (second surface) of the substrate 301, opposite the front surface. As shown in FIG. 3(c), one end terminal of the thermistor 328 is attached to a first attachment portion 350 formed on the substrate 301, and the other end terminal is attached to a second attachment portion 360 formed on the substrate 301. As a result, the thermistor 328 is electrically connected in series with the resistor 600 to the printed wiring pattern 326a formed on the surface of the substrate 301.

[0033] <Thermal conductive material> In this embodiment, a thermally conductive member 410 is disposed on the rear surface of the substrate 301. The thermally conductive member 410 is formed on the rear surface of the substrate 301 as a pattern of an electrical conductor using, for example, copper foil or copper plating, which has high thermal conductivity, similar to the printed wiring patterns 310a, 326a, etc. As shown in FIGS. 3(b) and 3(c), one end of the thermally conductive member 410 is formed in a screw fastening hole 330 so that heat is conducted from a screw 401 serving as a connecting member fastening the heat sink 312. That is, the thermally conductive member 410 (pattern) formed on the rear surface of the substrate 301 is in indirect contact with the heat sink 312 via the screw 401 fastening the heat sink 312. The thermally conductive member 410 is formed from the heat sink 312 to a position where a portion of the thermally conductive member 410 is closer to the temperature detection circuit 326 than to the primary circuit 310. In this embodiment, the distance between the other end of the heat conductive member 410 and the temperature detection circuit 326 (specifically, thermistor 328) is less than a predetermined distance (e.g., less than 5 mm). In other words, a first distance (H1) from the heat conductive member 410 to the temperature detection circuit 326 (specifically, thermistor 328) is shorter than a second distance (H2, a predetermined distance) from the primary circuit 310 to the temperature detection circuit 326. Furthermore, the first distance (H1) is shorter than a third distance (H3) from the heat sink 312 to the temperature detection circuit 326 (specifically, thermistor 328).

[0034] As described above, the screws 401 are inserted from the rear surface of the substrate 301 through the screw fastening holes 330 to fasten the heat sink 312 to the front surface of the substrate 301. Therefore, in this embodiment, the heat of the triac 311 is conducted to the heat sink 312, the screws 401, and the thermally conductive member 410. Because the heat sink 312, the screws 401, and the thermally conductive member 410 are all made of a metal or the like with high thermal conductivity (for example, 60 W / (m·K) or more), the heat of the heat sink 312 is conducted to the thermally conductive member 410 without significant loss. Therefore, even if the thermistor 328 is disposed at a distance greater than a predetermined distance from the heat sink 312, the temperature detection circuit 326 can appropriately detect the temperature of the heat sink 312 by having the thermistor 328 detect the heat of the thermally conductive member 410.

[0035] The method of connecting heat sinks 312 arranged on the front and back surfaces of substrate 301 with thermally conductive member 410 does not have to be by screws 401. For example, solder containing tin as its main component may also be used.

[0036] As described above, in this embodiment, the thermally conductive member 410 that conducts heat from the heat sink 312 is disposed on the substrate 301. The thermally conductive member 410 is formed from the heat sink 312 toward the thermistor 328 to a position close to the thermistor 328, at a distance shorter than the distance between the primary circuit 310 and the secondary circuit 320, which are disposed on the substrate 301 at a distance to suppress electrical influences due to AC and DC voltages. Because the thermally conductive member 410 conducts heat from the heat sink 312 without significant loss, the temperature detection circuit 326 can appropriately detect the temperature of the heat sink 312 by detecting the heat of the thermally conductive member 410 using the thermistor 328. As described above, in this embodiment, the temperature detection circuit 326 including the thermistor 328 that is disposed at a distance equal to or greater than a predetermined distance from the primary circuit 310 to which AC voltage is input can appropriately detect the temperature of the heat sink 312 mounted on the primary circuit 310. Therefore, the control unit 100 can control the start / stop and rotation speed of the cooling fan 331 in accordance with the temperature of the heat sink 312 detected by the temperature detection circuit 326, at a timing that matches the temperature change of the triac 311.

[0037] The thermistor 328 may also be of a lead wire type. Therefore, it is conceivable to arrange the DC circuit 327 in the temperature detection circuit 326 at a predetermined distance or more from the primary circuit 310, and then place the lead wire type thermistor closer to the heat sink 312. However, lead wire type thermistors are more expensive than surface-mount type thermistors, and are difficult to work with because they must be routed while maintaining a safe distance. Furthermore, compared to surface-mount type thermistors, they are more susceptible to electrical influences from the AC and DC voltages in the primary circuit 310 and temperature detection circuit 326. Therefore, lead wire type thermistors are not used.

[0038] [Second embodiment] As described above, the thermal conduction member 410 is formed from the heat sink 312 to a position where a portion of the thermal conduction member 410 is closer to the temperature detection circuit 326 than to the primary circuit 310. To achieve this, the thermal conduction member 410 is formed so that the distance between the thermal conduction member 410 and the temperature detection circuit 326 (specifically, the thermistor 328) is less than a predetermined distance. The thermal conduction member 410 is not limited to this, and it is more preferable to enable the temperature detection circuit 326 to more appropriately detect the temperature of the heat sink 312 via the thermal conduction member 410 using the thermistor 328. A thermal conduction member 410A according to a second embodiment that achieves this is shown in FIGS. 4(a) to 4(c). Note that in the second embodiment shown in FIGS. 4(a) to 4(c), components similar to those in the first embodiment (see FIGS. 3(a) to 3(c)) are designated by the same reference numerals, and descriptions thereof will be simplified or omitted.

[0039] As described above, the substrate 301 is formed with a first mounting portion 350 for mounting one end of the thermistor 328 disposed on the back surface to the temperature detection circuit 326 (more specifically, the DC circuit 327) disposed on the front surface, and a second mounting portion 360 formed at a distance from the first mounting portion 350 for mounting the other end of the thermistor 328. As shown in FIGS. 4(a) to 4(c), the heat conduction member 410A is formed on the back surface of the substrate 301 so that a portion of the heat conduction member 410A is located between the first mounting portion 350 and the second mounting portion 360, which are formed at a distance from each other. That is, the heat conduction member 410A of the second embodiment is formed from the heat sink 312 to a position where a portion of the heat conduction member 410A is closer to the temperature detection circuit 326 than the primary circuit 310, compared to the heat conduction member 410 of the first embodiment described above. In this case, the first distance (see H1 in FIG. 3A) from the heat conductive member 410A to the temperature detection circuit 326 (specifically, thermistor 328) can be said to be "0" and is shorter than the second distance (H2) from the primary circuit 310 to the temperature detection circuit 326 (specifically, thermistor 328). Thus, the thermistor 328 is disposed across the heat conductive member 410A and is in contact with the heat conductive member 410A. This improves the accuracy of the operation of the thermistor 328 with respect to heat conducted from the triac 311 to the heat sink 312, the screw 401, and the heat conductive member 410A. Therefore, the temperature detection circuit 326 can detect the heat of the heat conductive member 410A more accurately than in the first embodiment. [Explanation of symbols]

[0040] 100...control unit, 201...image forming apparatus, 301...board, 310...first circuit unit (primary circuit), 311...circuit element (triac), 312...heat dissipation member (heat sink), 320...second circuit unit (secondary circuit), 326...temperature detection circuit unit (temperature detection circuit), 327...DC circuit unit (DC circuit), 328...temperature detection member (thermistor), 331...cooling unit (cooling fan), 350...first mounting portion, 360...second mounting portion, 401...connecting member (screw), 410 (410A)...heat conduction member, 710...AC power supply

Claims

1. a first circuit unit having a circuit element and outputting an AC voltage; a heat dissipation member that dissipates heat generated from the circuit element; a temperature detection circuit unit that detects temperature; a heat conduction member connected to the heat dissipation member and conducting heat from the heat dissipation member, a first distance from the heat conducting member to the temperature detection circuit unit is shorter than a second distance from the first circuit unit to the temperature detection circuit unit; An image forming apparatus characterized by:

2. the first distance is shorter than a third distance from the heat dissipation member to the temperature detection circuit unit; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. the temperature detection circuit detects the temperature of the heat conduction member; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. a second circuit unit disposed at a distance from the first circuit unit and configured to generate a DC voltage from the AC voltage output from the first circuit unit; the temperature detection circuit is driven by application of the DC voltage generated by the second circuit; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. further comprising a substrate on which the first circuit unit, the second circuit unit, and the temperature detection circuit unit are arranged; 5. The image forming apparatus according to claim 4.

6. the thermally conductive member is a pattern of an electrical conductor formed on the substrate; 6. The image forming apparatus according to claim 5,

7. the temperature detection circuit unit includes a temperature detection element that can perform temperature detection by application of a DC voltage, and a DC circuit unit that applies a DC voltage to the temperature detection element; the first circuit unit, the second circuit unit, the DC circuit unit, and the heat dissipation member are disposed on a first surface of the substrate, the temperature sensing member is disposed on a second surface of the substrate opposite to the first surface, the thermal conduction member is a pattern formed on the second surface of the substrate, a connecting member that thermally connects the heat dissipation member disposed on the first surface and the heat conduction member that is a pattern formed on the second surface, so as to be capable of thermal conduction; 7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. the connecting member is a screw that penetrates from the second surface to the first surface and fixes the heat dissipation member to the substrate.

8. The image forming apparatus according to claim 7,

9. the substrate has a first mounting portion for mounting one end of the temperature detection member disposed on the second surface to the DC circuit portion disposed on the first surface, and a second mounting portion formed at an interval from the first mounting portion and for mounting the other end of the temperature detection member; the heat conduction member is formed so that a portion thereof is located between the first mounting portion and the second mounting portion; 8. The image forming apparatus according to claim 7,

10. The temperature detection component is a surface-mount type thermistor.

8. The image forming apparatus according to claim 7,

11. a cooling unit that cools the heat dissipation member; a control unit that controls the cooling unit in accordance with the temperature detected by the temperature detection circuit unit, 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

12. The heat dissipation member is a heat sink.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

13. The circuit element is a triac.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

14. The cooling unit is a cooling fan.

12. The image forming apparatus according to claim 11.

Images