Image forming apparatus

Abstract

To protect a power supply device in a power off mode and a sleep mode without causing an increase in cost and space, even if the device comprises an AC-DC converter in one system.SOLUTION: A CPU 223 has an external trigger port 250 that can detect a signal output from a return circuit 127 in a sleep mode and a power off mode. A cooling fan 125 is operable at 24 V. When detecting that the signal is input from the return circuit 127 to the external trigger port 250 in the sleep mode and the power off mode, the CPU 223 makes a transition from the sleep mode or the power off mode to a standby mode, and controls the cooling fan 125 to operate and cool a power supply unit 120.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, for example a copier, facsimile, printer or other image forming apparatus equipped with a power supply device, and to a configuration for protecting the power supply device from an overload / overcurrent state. [Background technology]

[0002] Image forming apparatuses such as copying machines, facsimiles, and printers that form images on recording materials using electrophotographic processes or the like are equipped with power supplies that generate DC voltages from AC voltages and supply power required for conveying recording materials and forming images. Power supplies often output at least two types of DC voltage, one of which outputs a low voltage (e.g., 3.3V to 5.0V) required for control elements and control circuits such as CPUs and ASICs. The other outputs a high voltage (e.g., about 24V) to be supplied to actuators such as motors and solenoids. Some power supplies are configured with multiple AC-DC converters, while others have only one AC-DC converter that outputs a high voltage (e.g., about 24V). Some power supplies generate a low voltage (e.g., 3.3V to 5.0V) required for control circuits from a high voltage (e.g., about 24V) using a DC-DC converter.

[0003] These power supplies have been provided with a protection circuit, which stops the operation of the power supply when the output becomes an overcurrent state, to protect the power supply from failure. When a large amount of power is consumed in a device to which the power supply supplies power, or when a short circuit or the like occurs on the power supply path, the power supply becomes in an overcurrent state. In this case, the power supply detects the overcurrent state and stops the output in order to avoid the occurrence of a failure or the like. For example, Patent Document 1 proposes a power supply equipped with a protection function that stops the switching control of the primary side control circuit when an abnormality occurs, such as an excessive current flowing in the output due to a load short circuit or the like. In addition, for example, Patent Document 2 proposes a power supply provided with an overcurrent detection means only on the primary side, without providing an overcurrent detection means on the secondary side, in order to achieve further space saving and low cost.

[0004] Furthermore, in today's power supplies, where there is a high demand for lower costs, configurations that limit the number of costly AC-DC converters to just one system are widely adopted. In such power supplies, in power-off mode and sleep mode, the voltage of the AC-DC converter is changed from high voltage (about 24V) to medium voltage (about 6V to 12V), and the DC-DC converter generates the low voltage (3.3V to 5.0V) required for the control circuit. This allows such power supplies to achieve energy savings. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-058166 A [Patent Document 2] JP 2020-156213 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a configuration with only one AC-DC converter, the following problem occurs when the output of the AC-DC converter is dropped to a medium voltage (6V to 12V) in power-off mode and sleep mode: If the load current becomes excessive while a medium voltage is being generated, the primary-side overcurrent protection circuit cannot provide protection, so an overcurrent protection circuit must also be provided on the secondary side, which may increase costs and space.

[0007] The present invention has been made under these circumstances, and aims to protect the device in power-off mode and sleep mode, even in a power supply device equipped with a single AC-DC converter, without incurring any increase in cost or space. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) A power supply device that converts an AC voltage on a primary side into a DC voltage and supplies the DC voltage to a load on a secondary side, a cooling means that cools the power supply device, a temperature detection means that is arranged on the secondary side of the power supply device to detect a temperature of the power supply device, and a control means that controls the cooling means based on a detection result of the temperature detection means, wherein the control means is capable of switching between a first output mode in which the power supply device outputs a first voltage as the DC voltage and a second output mode in which the power supply device outputs a second voltage lower than the first voltage as the DC voltage, and the first mode in which the control means operates in the first output mode and the second mode in which the control means operates in the second output mode. and a signal output circuit that outputs a signal to the control means when the temperature detected by the temperature detection means becomes equal to or higher than a predetermined temperature, the control means has a port that can detect the signal output from the signal output circuit in the second mode, the cooling means is capable of operating at the first voltage, and when the control means detects that the signal has been input from the signal output circuit to the port in the second mode, the image forming apparatus transitions from the second mode to the first mode and controls the cooling means to operate to cool the power supply device. Effect of the Invention

[0010] According to the present invention, even in a power supply device equipped with a single AC-DC converter, it is possible to protect the device in the power-off mode and sleep mode without increasing costs or space. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a configuration of an image forming apparatus according to a first embodiment of the present invention; [Diagram 2] FIG. 1 is a diagram showing the configuration of a power supply unit and an engine controller according to a first embodiment; [Diagram 3] FIG. 1 is a diagram showing the relationship between the secondary current and the primary current in the first embodiment; [Figure 4] FIG. 1 shows the state of a power supply unit and a CPU according to the first embodiment. [Diagram 5] FIG. 1 is a diagram showing a recovery circuit using a thermistor according to the first embodiment. [Figure 6] Flowchart showing return control from power off mode to standby mode in the first embodiment [Figure 7] FIG. 11 is a diagram showing a recovery circuit using a thermistor according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0012] [Image forming device] Hereinafter, an embodiment of the present invention implemented in an image forming apparatus will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus using an electrophotographic process. In the first embodiment, a laser beam printer will be described as an example of the image forming apparatus, but the image forming apparatus may be a copier, a facsimile, or a combination machine of these.

[0013] The laser beam printer main body 101 (hereinafter referred to as the main body 101) shown in Fig. 1 has a paper feed cassette 104, a paper feed roller 141, a pair of transport rollers 142, a top sensor 143, and a pair of registration rollers 144. The paper feed cassette 104 stores recording material S, which is a recording medium. The paper feed roller 141 pays out the recording material S from the paper feed cassette 104. The top sensor 143 is disposed downstream of the pair of transport rollers 142, and detects the leading edge of the recording material S. The pair of registration rollers 144 synchronously transports the recording material S based on the detection result of the top sensor 143.

[0014] The main body 101 has a cartridge unit 105 downstream of the registration roller pair 144, which forms a toner image on the recording material S based on a laser beam from a laser scanner 106. The cartridge unit 105 has a photosensitive drum 148, which is an image carrier, a charging roller 147, a developing roller 146, etc., which are necessary for a known electrophotographic process, and forms a toner image on the recording material S together with a transfer roller 145. The main body 101 has a fuser 103 downstream of the cartridge unit 105 for thermally fixing an unfixed toner image formed on the recording material S. The fuser 103 has a fixing film 149, a pressure roller 150, a heater 102 arranged inside the fixing film 149, and a thermistor 109 arranged near the heater 102 to detect the temperature of the heater 102 in the fixing film 149. The main body 101 has a discharge roller pair 151 downstream of the fuser 103, which discharges the recording material S after the toner image is formed and thermally fixed.

[0015] The main body 101 includes a power supply unit 120, which is a power supply device described later. The power supply unit 120 converts an AC voltage on the primary side into a DC voltage and supplies it to a load on the secondary side. The power supply unit 120 can switch between a first voltage of 24 V and a second voltage of 10 V that is lower than the first voltage, and generates a voltage of 24 V when the main body 101 is in a print mode or standby mode. The print mode is a mode in which the main body 101 is printing (image forming operation) and is ready to print immediately, and the standby mode is a mode in which the main body 101 can switch to the print mode when a print command is received.

[0016] The power supply unit 120 supplies a voltage of 24V via an engine controller 123 (described later) as a drive system voltage to a drive unit (not shown), a high-voltage power supply (not shown), a drive section (not shown) of the rotating polygon mirror, etc. Here, the drive unit includes a motor, a clutch, etc. (not shown). The high-voltage power supply supplies a high voltage to the cartridge unit 105. The laser scanner 106 has a rotating polygon mirror (not shown), and the drive section drives the rotating polygon mirror.

[0017] The main body 101 has a cooling fan 125. The cooling fan 125, which is a cooling means, is a fan for cooling the power supply unit 120, and cools the power supply unit 120 by blowing air (wind) onto the power supply unit 120. Note that the direction of the air is indicated by an arrow in Fig. 1. The cooling fan 125 can blow wind only when a voltage of 24V is being output from the power supply unit 120.

[0018] The main body 101 has an engine controller 123. The engine controller 123 controls the main body 101. The engine controller 123 controls the above-mentioned drive unit to operate each roller and control the conveyance of the recording material S. The engine controller 123 also controls the laser scanner 106, the cartridge unit 105, the fixing device 103, etc. to perform an image forming (hereinafter, also referred to as printing) operation. The engine controller 123 also includes a DC-DC converter 121 described later, which generates a voltage of 3.3V mainly used in the control system based on a voltage supplied from a power supply unit 120. The voltage of 3.3V is supplied to a control circuit (not shown) inside the engine controller 123, a video controller 131 described later, a laser light emitting unit (not shown) of the laser scanner 106, a top sensor 143, etc.

[0019] The main body 101 has a video controller 131. The video controller 131 is connected to the engine controller 123 via an interface 133. The video controller 131 is also connected to an external device 132 such as a personal computer via a general-purpose external interface 134 (for example, a USB (Universal Serial Bus) or the like).

[0020] The power supply unit 120 detects the zero-cross timing of an AC power supply 200 (see FIG. 2), which will be described later, and transmits a zero-cross detection signal (not shown) to the engine controller 123. Here, the zero-cross timing is the timing at which the waveform of the AC voltage changes from positive to negative or from negative to positive. The engine controller 123 appropriately controls a switching means (not shown) of the heater 102 so that the power from the AC power supply 200 is synchronized with the zero-cross timing and has a duty ratio of a predetermined phase angle or a predetermined wave number. In this way, the engine controller 123 controls the heater 102 to be at a predetermined temperature.

[0021] The video controller 131 receives print information (including, for example, the number of copies and various settings) and print data from the external interface 134. The video controller 131 has an internal image control unit (not shown) and converts the print data into image data that can actually be printed. Thereafter, the engine controller 123 receives the converted image data from the video controller 131 via the interface 133 at a predetermined timing and sends it to the laser scanner 106. Note that the image forming apparatus to which the power supply device of the present invention can be applied is not limited to the configuration described in FIG. 1, and can also be applied to, for example, a color image forming apparatus.

[0022] [Power supply unit and engine controller] Fig. 2 is a diagram showing the configuration of the power supply unit 120 and the engine controller 123 of the first embodiment. In Fig. 2, the left side of the dashed line is the primary side, and the right side of the dashed line is the secondary side. An AC power supply 200 is connected to the power supply unit 120, which generates a DC voltage Vo2 (also an output voltage) from an input AC voltage and outputs it to the secondary side. Here, the power supply unit 120 is capable of outputting two DC voltages, 24V and 10V, as the DC voltage Vo2.

[0023] Specifically, when the main body 101 is in a print mode or a standby mode (a standby state in which instant printing is possible), the power supply unit 120 outputs 24V as the DC voltage Vo2. On the other hand, when the main body 101 is in a sleep mode (power saving mode) or a power off mode in which the power consumption is reduced, the power supply unit 120 outputs 10V as the DC voltage Vo2. Note that even in the power off mode, an AC voltage is input to the power supply unit 120. A state in which the power supply unit 120 outputs a DC voltage Vo2 of 24V is called a first output mode, and a state in which the power supply unit 120 outputs 10V is called a second output mode. The first output mode and the second output mode are collectively called power supply modes. The switching of the DC voltage Vo2 is performed by the CPU 223, which is a control means mounted on the engine controller 123. The main body 101 can operate by switching between a first mode (print mode and standby mode) in which it operates in the first output mode, and a second mode (sleep mode and power off mode) in which it operates in the second output mode.

[0024] The AC voltage input to the power supply unit 120 is rectified by the bridge diode 204 and then smoothed by the capacitor 210 to become a DC voltage with the DCL line as the negative polarity and the DCH line as the positive polarity. The DCH line is connected to one of the two terminals of the primary winding 205a of the transformer 205, and is also connected to the VH terminal of the power supply IC 222 via a resistor 230, and a voltage is supplied to the DCH line. The power supply IC 222 starts operating when a voltage is applied to the VH terminal. In addition to the VH terminal, the power supply IC 222 also has a Vcc terminal, a Gnd terminal, an FB terminal, an OUT terminal, and an IS terminal.

[0025] A field effect transistor (hereinafter, referred to as FET) 243 has a drain terminal connected to the other terminal of the primary winding 205a and a source terminal connected to the DCL line via a current detection resistor 241. A gate terminal of the FET 243 is connected to an OUT terminal of the power supply IC 222 via a gate resistor 242. The power supply IC 222 controls the ON / OFF of the FET 243, so that a current flows through the primary winding 205a. The current flowing through the primary winding 205a is converted to a voltage by the current detection resistor 241 and input to the IS terminal of the power supply IC 222. The power supply IC 222 monitors the voltage of the IS terminal. When the current flowing through the primary winding 205a and the FET 243 exceeds a predetermined value, the power supply IC 222 turns off the FET 243 via the OUT terminal to prevent an overcurrent when a short circuit occurs on the primary side or a short circuit occurs in a voltage output section on the secondary side. The overcurrent detection circuit configured by the current detection resistor 241 and the power supply IC 222 can provide protection against overcurrent in a small space and at low cost. In this manner, the power supply unit 120 of the first embodiment has an overcurrent detection circuit on the primary side.

[0026] When a current flows through the primary winding 205a, a flyback voltage with reverse polarity is induced in the auxiliary winding 205b and the secondary winding 205c. The voltage induced in the auxiliary winding 205b is rectified and smoothed through a resistor 233, a diode 234, and a capacitor 235, and is output as a voltage Vcc. The voltage Vcc generated by the auxiliary winding 205b is supplied to a Vcc terminal as a power supply for the power supply IC 222. The voltage induced in the secondary winding 205c is rectified by a rectifier diode 251 on the secondary side, and then smoothed by a smoothing capacitor 252 on the secondary side, and is output as a DC voltage Vo2.

[0027] (Feedback circuit) Next, the feedback circuit 224 will be described. The feedback circuit 224 includes resistors 253, 254, 255, 256, and 257, a shunt regulator 258, a FET 259, a photocoupler 206, and a capacitor 207. The feedback circuit 224 monitors the DC voltage Vo2, and feeds back the DC voltage Vo2 as an FB signal from the secondary circuit to the FB terminal of the power supply IC 222 on the primary side via the photocoupler 206 so that the DC voltage Vo2 is 10 V or 24 V. The power supply IC 222 controls the ON / OFF of the FET 243 based on the voltage input to the FB terminal so that the DC voltage Vo2 becomes a predetermined voltage.

[0028] Furthermore, a 10V / 24V signal is input to the feedback circuit 224 from the engine controller 123. Specifically, the CPU 223 of the engine controller 123 outputs the 10V / 24V signal from the Port 203 to the gate terminal of the FET 259 of the feedback circuit 224 via a resistor 264. The feedback circuit 224 switches the circuit according to the 10V / 24V signal so that the DC voltage Vo2 becomes 10V or 24V.

[0029] For example, when the 10V / 24V signal is at a high level, the feedback circuit 224 feeds back to the power supply IC 222 so that the DC voltage Vo2 becomes 10 V. On the other hand, when the 10V / 24V signal is at a low level, the feedback circuit 224 feeds back to the power supply IC 222 so that the DC voltage Vo2 becomes 24 V. In this manner, the CPU 223 can switch between a first output mode in which the power supply unit 120 is controlled so that the DC voltage Vo2 becomes 24 V, and a second output mode in which the power supply unit 120 is controlled so that the DC voltage Vo2 becomes 10 V.

[0030] Resistors 253, 254, and 256 are connected in series between the DC voltage Vo2 and ground (hereinafter referred to as Gnd), and a FET 259 is connected in parallel to the resistor 256. That is, the drain terminal of the FET 259 is connected to the connection point between the resistors 254 and 256, and the source terminal is connected to Gnd on the secondary side. Furthermore, the 10V / 24V signal output from the engine controller 123 as described above is input to the gate terminal of the FET 259.

[0031] The photodiode 206a on the secondary side of the photocoupler 206 has an anode terminal connected to a DC voltage Vo2 via a resistor 255, and a cathode terminal connected to the cathode terminal of a shunt regulator 258. A resistor 257 connected in parallel to the photodiode 206a of the photocoupler 206 is a resistor for bypassing a leakage current of the shunt regulator 258.

[0032] The shunt regulator 258 has an anode terminal connected to the Gnd of the DC voltage Vo2 and a reference terminal connected to the connection point of the resistors 253 and 254. The phototransistor 206b on the primary side of the photocoupler 206 has a collector terminal connected to the FB terminal of the power supply IC 222 as the FB signal and an emitter terminal connected to the DCL line. The capacitor 207 is a noise absorbing capacitor provided for the FB signal and is connected between the FB terminal of the power supply IC 222 and the DCL line.

[0033] (Switching DC voltage Vo2) Next, a method in which the feedback circuit 224 switches the DC voltage Vo2 to 24V or 10V will be described. When the 10V / 24V signal output from the engine controller 123 is at a high level, the FET 259 is turned on. At this time, a voltage obtained by dividing the DC voltage Vo2 by resistors 253 and 254 is input to a reference terminal of the shunt regulator 258. Then, the voltage is fed back to the FB terminal of the power supply IC 222 via the photocoupler 206 so that the reference terminal of the shunt regulator 258 has the same voltage as the internal reference voltage, and as a result, the DC voltage Vo2 is controlled to 10V.

[0034] Furthermore, when the 10V / 24V signal is at a low level, the FET 259 is turned off (OFF). At this time, a voltage obtained by dividing the DC voltage Vo2 by the resistor 253 and the combined resistance of the resistors 254 and 256 is input to the shunt regulator 258. Then, the voltage is fed back to the FB terminal of the power supply IC 222 via the photocoupler 206 so that the reference terminal of the shunt regulator 258 becomes the same voltage as the internal reference voltage, and as a result, the DC voltage Vo2 is controlled to 24V.

[0035] (Engine Controller) The engine controller 123 has a CPU 223 and a DC-DC converter 121. The DC voltage Vo2 output from the power supply unit 120 is connected from the engine controller 123 to the drive unit and high voltage power supply (neither of which are shown), together with a control signal (not shown) output from the CPU 223. Note that in order to prevent the DC voltage Vo2 from being needlessly supplied to the drive unit and the like in the sleep mode and power-off mode, a switch or the like may be provided to cut off the supply of the DC voltage Vo2 in the sleep mode.

[0036] A 10V / 24V signal is output from the engine controller 123 to the power supply unit 120. The 10V / 24V signal is output from the Port 203 terminal of the CPU 223 via a resistor 264, and a high level / low level is input to the power supply unit 120. The CPU 223 switches the Port 203 terminal to a high level / low level, thereby switching the DC voltage Vo2 to 10V or 24V.

[0037] The CPU 223 has an A / D converter that receives the detection result of the thermistor 208 and performs analog-to-digital conversion. The A / D converter operates in the print mode and standby mode and stops operating in the sleep mode and power-off mode. The A / D converter converts a voltage input from the A / D terminal 201. The CPU 223 has an external trigger port 250 that is a port capable of detecting a signal output from the recovery circuit 127 in the sleep mode and power-off mode. The CPU 223 also has Port 202 and Port 203.

[0038] (DC-DC converter) The DC voltage Vo2 output from the power supply unit 120 is input to the engine controller 123. The DC-DC converter 121 also receives the DC voltage Vo2 and converts it to output the DC voltage Vo. The DC-DC converter 121 operates to output 3.3 V as the DC voltage Vo regardless of whether the input DC voltage Vo2 is 24 V or 10 V. As described above, the DC voltage Vo is supplied to the internal control circuit (not shown) of the engine controller 123, the video controller 131, the laser emission unit (not shown) of the laser scanner 106, the top sensor 143, and other control system circuits.

[0039] (Thermistor) The thermistor 208 (temperature detection means) which is a temperature detection element is located in the power supply unit 120 and is disposed near the transformer 205 (here, the secondary winding 205c of the transformer 205) and the rectifier diode 251 which are elements which generate heat due to an increase in the load current. That is, the thermistor 208 is disposed on the secondary side of the power supply unit 120 to detect the temperature of the power supply unit 120. The thermistor 208 has one terminal connected to the Gnd on the secondary side and the other terminal inputted to the A / D terminal 201 which is the A / D port of the CPU 223 on the engine controller 123 via a resistor 211 as a thermistor signal (hereinafter referred to as a TH signal). The TH signal is pulled up by a pull-up resistor 209 on the engine controller 123. The TH signal is connected to the recovery circuit 127, and the output of the recovery circuit 127 by the thermistor 208 is inputted to the external trigger port 250 of the CPU 223. The recovery circuit 127 using the thermistor 208 will be described in detail later with reference to FIG.

[0040] The CPU 223 also has a number of other ports. Of the multiple ports that the CPU 223 has, a port that needs to periodically monitor a signal input to that port even when the main body 101 is in sleep mode (for example, a signal from a sensor) is hereinafter referred to as IO port A. Also, of the multiple ports that the CPU 223 has, a port that does not operate even if a signal is input to that port when the main body 101 is in sleep mode or power off mode is hereinafter referred to as IO port B. Here, the A / D terminal 201 and the external trigger port 250 will be described below as ports independent of the IO port A and IO port B.

[0041] (Cooling fan drive circuit) The drive circuit 126 is a circuit that drives the cooling fan 125 for cooling the power supply unit 120. The drive circuit 126 supplies a voltage to the cooling fan 125 according to a signal output from a port 202 of the CPU 223. The port 202 connected to the drive circuit 126 for driving the cooling fan 125 is included in the above-mentioned IO port B. When the signal output from the port 202 is a high-level signal (hereinafter, referred to as a Hi signal), the drive circuit 126 outputs 24V, and the cooling fan 125 rotates at full speed. When the signal output from the port 202 is a PWM signal, the drive circuit 126 outputs a voltage according to the PWM signal, and the cooling fan 125 rotates at a low speed according to the voltage.

[0042] The CPU 223 controls the cooling fan 125 based on the detection result of the thermistor 208. Specifically, when the main body 101 is in standby mode or print mode (when the 10V / 24V signal is at a low level), the CPU 223 monitors the TH signal and judges whether the temperature detected by the thermistor 208 is within the normal range. When the detected temperature is equal to or lower than a predetermined temperature, the CPU 223 judges that the transformer 205 and the rectifier diode 251 on the secondary side are operating normally and that the load current of the power supply unit 120 is within the normal range. On the other hand, when the detected temperature is higher than the predetermined temperature, the CPU 223 judges that the load current of the power supply unit 120 is abnormally high and that the transformer 205 and the rectifier diode 251 have risen to an abnormal temperature. Then, the CPU 223 controls the cooling fan 125 to rotate at full speed even when the cooling fan 125 is stopped or rotating at a low speed. This allows the power supply unit 120 to be cooled, and failure of the transformer 205 and the rectifier diode 251 can be prevented, and safety can be ensured.

[0043] [Overcurrent detection] Next, the overcurrent detection on the primary side when the DC voltage Vo2 is 24V and 10V will be described with reference to FIG. 3. FIG. 3 is a graph in which the horizontal axis represents the secondary current when the value of the secondary current (hereinafter referred to as the secondary current) is increased, and the vertical axis represents the primary current (hereinafter referred to as the primary current) flowing through the current detection resistor 241 at that time. In FIG. 3, the solid line indicates the case when the DC voltage Vo2 is 24V, and the dashed line indicates the case when the DC voltage Vo2 is 10V. In addition, the dotted line indicates the overcurrent detection threshold Ath when determining that there is an overcurrent on the primary side. In the first embodiment, for example, the threshold Ath is set to 2A, but is not limited to this value. The threshold Ath is set in consideration of the variation in the AC voltage of the AC power supply 200, which is the input voltage, with respect to the secondary current during normal use.

[0044] (When DC voltage Vo2 is 24V) The primary side current when the secondary side current is increased when the DC voltage Vo2 is 24 V will be described. As the secondary side current increases, the primary side current reaches the threshold value Ath when the secondary side current reaches 10 A. In this way, when the DC voltage Vo2 is 24 V, the primary side current becomes equal to or exceeds the threshold value Ath when the secondary side current becomes 10 A, so that an overcurrent can be detected by the overcurrent detection circuit.

[0045] (When DC voltage Vo2 is 10V) Next, the primary side current when the secondary side current is increased when the DC voltage Vo2 is 10V will be described. When the DC voltage Vo2 is 10V, the increase in the primary side current when the secondary side current is increased is smaller than when the DC voltage Vo2 is 24V. For this reason, even if the secondary side current is increased to 20A, the primary side current value does not reach the threshold value Ath. This is because the value of the primary side current is determined by the power used on the secondary side, and when the DC voltage Vo2 is low, the power used on the secondary side is also low, resulting in a low value of the primary side current. Thus, when the DC voltage Vo2 is 10V, the primary side overcurrent detection circuit cannot detect an overcurrent even if the secondary side current exceeds 10A.

[0046] [Printer mode, power mode, and status of each CPU port] (When the printer is in print mode or standby mode) Next, each mode of the main body 101 and the power supply mode, the state of the CPU 223, and the state of each port at that time will be explained using Fig. 4. First, when the main body 101 is in the print mode or the standby mode, the power supply mode is the first output mode, and 24V is output as the DC voltage Vo2. The mode of the CPU 223 (hereinafter referred to as the CPU mode) is a state in which all modules are operable and detectable, and the IO port A, IO port B, A / D terminal 201, and external trigger port 250 are all valid. This is indicated as "FULL" in Fig. 4.

[0047] (When the printer is in sleep mode or power off mode) When the main body 101 is in the sleep mode or the power off mode, the power supply mode is the second output mode, and 10 V is output from the DC voltage Vo2. The mode of the CPU 223 is the low power mode, and low power is achieved by turning off the power supply of the modules inside the CPU 223 and slowing down the operation of the CPU 223.

[0048] In the power off mode, the main body 101 is often set to an even lower power state than in the sleep mode. In this case, the CPU 223 stops (disables) the operation of the IO port A, the IO port B, and the A / D terminal 201. The CPU 223 operates (enables) only the external trigger port 250 so as to detect only the recovery circuit 127 by the thermistor 208 and the pressing of the power switch (not shown). This achieves even lower power consumption in the power off mode of the main body 101.

[0049] In the sleep mode of the main body 101, the IO port A is operated intermittently compared to the power off mode. As a result, even when the main body 101 is in the sleep mode, the CPU 223 periodically detects a sensor to be detected (for example, a door sensor, etc.), and when a door, etc. is opened by a user, the main body 101 can return from the sleep mode to the standby mode.

[0050] In the sleep mode and power off mode, the CPU 223 is in a low power mode, and each port is in a functionally limited state, so that the cooling fan 125 for cooling the power supply cannot be operated. In addition, the A / D converter is also in a stopped state, so that the temperature of the thermistor 208 cannot be detected by the A / D terminal 201, which is an A / D port. In the sleep mode and power off mode, the power supply mode is the second output mode that outputs 10 V. For this reason, it may be difficult to protect the secondary winding 205c of the transformer 205 and the rectifier diode 251 from damage caused by an overcurrent and to ensure safety using an overcurrent detection circuit on the primary side.

[0051] FIG. 4 is a diagram summarizing the modes and power modes of the main body 101, and the state of each port of the CPU 223. The power modes (24V, 10V) corresponding to the print, standby, sleep, and power off states of the main body 101 are shown. Also, the CPU modes are shown for the print, standby, sleep, and power off states of the main body 101. Here, the CPU modes include FULL, low power, and a state lower than sleep. Also, the states of IO port A, IO port B, A / D converter (in other words, A / D terminal 201), and external trigger port 250 are shown corresponding to the CPU modes. Regarding the state of each port, "○" indicates that it is operating, "×" indicates that it is not operating, and "△" indicates that it is operating intermittently.

[0052] Looking at the modes of the main body 101, that is, looking vertically at FIG. 4, it can be seen that, for example, in the print mode, the power supply mode is the first output mode, the DC voltage Vo2 is 24V, and the CPU mode is FULL. At this time, all the ports of the CPU 223 are marked with "◯" and all ports are operating. Also, for example, when the power supply is off, it can be seen that the power supply mode is the second output mode, the DC voltage Vo2 is 10V, and the CPU mode is lower power than the sleep mode. At this time, of the ports of the CPU 223, only the external trigger port 250 operates, and the other ports are disabled. Also, looking at a certain port of the CPU 223, that is, looking horizontally at FIG. 4, it can be seen that, for example, the IO port A operates in the print mode and standby mode, does not operate in the power supply off mode, and operates intermittently in the sleep mode. Also, for example, it can be seen that the external trigger port 250 operates so as to be always detectable in all modes of the main body 101.

[0053] Thus, in the sleep mode and the power off mode, the cooling fan 125 cannot be operated, the temperature cannot be detected via the A / D terminal 201 due to the operation restrictions, and the protection by the primary side overcurrent detection circuit does not work when the DC voltage Vo2 is low at 10 V. Even in such a case, in the first embodiment, a configuration and a method capable of preventing damage due to an overcurrent in the secondary winding 205c of the transformer 205 and the rectifier diode 251 and ensuring safety will be described.

[0054] [Recovery circuit] 5, the detailed circuitry of recovery circuit 127 using thermistor 208 will be described. Recovery circuit 127, which is a signal output circuit, outputs a signal to CPU 223 when the temperature detected by thermistor 208 reaches or exceeds a predetermined temperature. Recovery circuit 127 has resistor 212, resistor 213, pull-up resistor 215, and FET 214, which is a switch element.

[0055] (In print mode and standby mode) In the print mode and the standby mode, the power supply mode is the first output mode, and 24V is output as the DC voltage Vo2. At that time, the A / D terminal 201 of the CPU 223 is in an operable state as described in FIG. 4. Therefore, a voltage obtained by dividing the DC voltage Vo by the combined resistance of the thermistor 208, the resistors 212 and 213, and the pull-up resistor 209 is input to the A / D terminal 201 as a TH signal. As the temperature of thermistor 208 rises, the resistance value of thermistor 208 decreases, and the voltage input to the A / D terminal 201 decreases. As the resistance value of thermistor 208 changes, the CPU 223 can detect the temperature of thermistor 208 via the A / D terminal 201.

[0056] (In sleep mode and power off mode) Next, the sleep mode and the power off mode will be described. In the sleep mode and the power off mode, the power supply mode is the second output mode and 10V is output as the DC voltage Vo2. Also, since the CPU 223 is in the low power mode, the A / D converter is stopped and the temperature of the thermistor 208 cannot be detected via the A / D terminal 201.

[0057] Here, in the recovery circuit 127, the voltage obtained by dividing the DC voltage Vo by the combined resistance of the thermistor 208, the resistor 212, and the resistor 213 and the pull-up resistor 209 becomes the voltage at point A shown in FIG. 5. Furthermore, the voltage obtained by dividing the voltage at point A by the resistors 212 and 213 becomes the voltage at point B, and the voltage at point B is input to the gate terminal of the FET 214. When the voltage at point B is lower than the threshold voltage Vth at which the FET 214 transitions from non-conductive to conductive, the FET 214 is turned off, and the voltage input to the external trigger port 250 of the CPU 223 becomes a high level by the pull-up resistor 215. On the other hand, when the voltage at point B is higher than the threshold voltage Vth of the FET 214, the FET 214 is turned on, and the voltage input to the external trigger port 250 of the CPU 223 becomes a low level.

[0058] When the temperature of the transformer 205 or the rectifier diode 251 rises to an abnormal level, the temperature of the thermistor 208 rises and the resistance value of the thermistor 208 falls. The voltage at point B gradually falls, and when it falls below the threshold voltage Vth of the FET 214, the voltage input to the external trigger port 250 of the CPU 223 switches from low level to high level. When the voltage input to the external trigger port 250 of the CPU 223 switches from low level to high level, the CPU 223 determines that the transformer 205 or the rectifier diode 251 is in an abnormal state. Then, the CPU 223 returns the main body 101 to the standby mode from the power off mode or the sleep mode. When the CPU 223 returns the main body 101 to the standby mode and detects through the A / D terminal 201 that the temperature of the thermistor 208 is equal to or higher than a predetermined temperature, the cooling fan 125 is rotated at full speed. This allows the power supply unit 120 to be cooled, and makes it possible to prevent breakdowns in the transformer 205 and the rectifier diode 251 and ensure safety.

[0059] It is necessary to determine the constants of the resistance values ​​of resistors 212, 213 and pull-up resistor 209 of recovery circuit 127 taking into consideration both of the following: That is, it is necessary to determine the constants taking into consideration both the resolution when detecting temperature at A / D terminal 201 and the threshold temperature when returning to standby mode from power off mode or sleep mode by thermistor 208. In the first embodiment, the temperature detection circuit and recovery circuit 127 by thermistor 208 are constituted by an NTC thermistor whose resistance value decreases with increasing temperature. However, the present invention is not limited to the first embodiment, and the temperature detection circuit and recovery circuit by thermistor 208 may be constituted by a PTC thermistor whose resistance value increases with increasing temperature.

[0060] [Overcurrent detection using a recovery circuit] A process of returning to the standby mode by the return circuit 127 in the first embodiment will be described with reference to the flowchart of Fig. 6. In the first embodiment, the overheat protection in the power off mode will be described, but the operation in the sleep mode is the same as that in the power off mode, so the description will be omitted in the flowchart. When the CPU 223 detects that a signal is output from the return circuit 127 in the power off mode (or the sleep mode), it transitions from the sleep mode to the standby mode and controls the cooling fan 125 to operate and cool the power supply unit 120. When the overheat protection sequence in the power off mode starts, the CPU 223 executes the process from step (hereinafter, S) 101 onwards.

[0061] In S101, the CPU 223 determines whether or not a power-off command has been issued by detecting the operation of a power switch (not shown). If the CPU 223 determines in S101 that a power-off command has not been issued, the process returns to S101, and if the CPU 223 determines that a power-off command has been issued, the process proceeds to S102. In S102, the CPU 223 sets the 10V / 24V signal to a high level (Hi) to transition the power supply mode from the first output mode to the second output mode.

[0062] In S103, the CPU 223 enters the internal function restricted state described in Fig. 4 in order to reduce energy consumption. Specifically, low power consumption is achieved by turning off the power of some of the IO ports and the A / D converter and slowing down the operation of the CPU 223. In S104, the CPU 223 determines whether or not it has detected that the temperature of the thermistor 208 has risen due to some abnormality such as an overcurrent and that the input voltage of the external trigger port 250 has changed from a low level (Lo) to a high level (Hi). If the CPU 223 determines in S104 that the change has not been detected, it returns the process to S104, and if it determines that the change has been detected, it advances the process to S105.

[0063] In S105, the CPU 223 judges whether the level (logic) of the input voltage (signal) of the external trigger port 250 is high level or not. If the CPU 223 judges that the input voltage is low level in S105, it judges that the change in S104 was a false detection and returns the process to S104, whereas if the CPU 223 judges that the input voltage is high level, it advances the process to S106. In S106, the CPU 223 returns the mode of the main body 101 to the standby mode. Specifically, the 10V / 24V signal is set to low level, the power supply mode is transitioned from the second output mode to the first output mode, and the functional restrictions of the CPU 223 are released.

[0064] In S107, CPU 223 obtains the temperature detection result of thermistor 208 from A / D converter via A / D terminal 201. In S108, CPU 223 determines whether the temperature of thermistor 208 is equal to or higher than a first threshold (overheating threshold) used to determine whether the temperature is overheating. If CPU 223 determines in S107 that the temperature of thermistor 208 is less than the first threshold, the process returns to S102, and if CPU 223 determines that the temperature is equal to or higher than the first threshold, the process proceeds to S109. In S109, CPU 223 rotates cooling fan 125 at full speed. In S110, CPU 223 determines whether the temperature of thermistor 208 is equal to or lower than a second threshold (normal temperature threshold) used to determine whether the temperature is normal due to cooling by cooling fan 125. If CPU 223 determines in S110 that the temperature of thermistor 208 is higher than the second threshold, it returns the process to S110, and if it determines that the temperature is equal to or lower than the second threshold, it ends this sequence.

[0065] As described above, even when cooling fan 125 cannot be operated, temperature detection by the A / D converter of CPU 223 cannot be performed due to functional limitations, and protection by primary side overcurrent detection does not work when DC voltage Vo2 is low at 10 V, the following can be done. That is, main body 101 is returned to standby mode by recovery circuit 127 using thermistor 208, and power supply unit 120 is cooled by cooling fan 125. This makes it possible to prevent failure of transformer 205 and rectifier diode 251 and maintain safety.

[0066] In this way, in the first embodiment, the power supply unit 120 is configured to have only one AC-DC converter system. Also, the power supply unit 120 is configured to be able to prevent damage to components due to overcurrent and ensure safety without providing a secondary overcurrent protection circuit against short circuits during medium voltage (6V to 12V) output in the power off mode and sleep mode.

[0067] As described above, according to the first embodiment, even if the power supply device has a single AC-DC converter, it is possible to protect the device in the power off mode and the sleep mode without increasing the cost or space. EXAMPLES

[0068] In the first embodiment, the resistors 212, 213, 215, and the FET 214 constitute the recovery circuit 127 using the thermistor 208. In the first embodiment, an example in which the recovery circuit 127 operates based on the TH signal of the thermistor 208 to return to the standby mode when the temperature rises excessively during the power-off mode and the sleep mode has been described, but in the second embodiment, a recovery circuit using a comparator will be described.

[0069] The recovery circuit 127 described in the first embodiment can be configured only with a resistor and a FET, so that a recovery circuit using the thermistor 208 can be constructed in a small space. The recovery circuit 127 is configured to connect the resistors 212 and 213 in parallel to the thermistor 208, so that the CPU 223 detects the temperature of the thermistor 208 through the A / D terminal 201 by dividing the voltage value with the pull-up resistor 209. For this reason, it was necessary to set the constants of the resistors 212 and 213 in consideration of the voltage resolution of the CPU 223. In addition, it was necessary to set the constants of the resistors 212 and 213 so that the voltage at point B when the temperature of the thermistor 208 becomes the temperature at which the external trigger port 250 causes the thermistor 208 to recover is equal to or lower than the threshold voltage Vth of the FET 214. In addition, it was necessary to set the constants of the resistors 212 and 213 so that the voltage at point B when the temperature of the thermistor 208 is within the normal range is equal to or higher than the threshold voltage Vth of the FET 214.

[0070] [Recovery circuit] In the second embodiment, a configuration with a higher degree of freedom in design compared to the recovery circuit 127 using the thermistor 208 in the first embodiment will be described. In the second embodiment, a recovery circuit 127' using the thermistor 208 that uses a comparator will be described with reference to FIG. 7. The same components as in FIG. 5 are denoted by the same reference numerals. The recovery circuit 127' using the thermistor 208 shown in FIG. 7 has a resistor 312, a resistor 313, a pull-up resistor 215, and a comparator 314.

[0071] The voltage (voltage at point B) input to the - terminal (inverting input terminal) of the comparator 314 is a value (hereinafter referred to as a divided voltage value) obtained by dividing the DC voltage Vo by resistors 312 and 313. The voltage at point B is set to a voltage equivalent to the temperature of thermistor 208 for recovery by a signal (hereinafter referred to as an external trigger signal) input to an external trigger port 250 of the CPU 223. The voltage at point A is the divided voltage value of the DC voltage Vo and thermistor 208, and is input to the + terminal (non-inverting input terminal) of the comparator 314. The voltage at point A is also input to the A / D terminal 201 of the CPU 223 via resistor 211.

[0072] When the temperature of thermistor 208 rises and the voltage at point A drops below the voltage at point B, the voltage output from the output terminal of comparator 314 and input to external trigger port 250 of CPU 223 switches from high level to low level. When the voltage input to external trigger port 250 of CPU 223 switches from high level to low level, CPU 223 determines that transformer 205 or rectifier diode 251 is in an abnormal state. Then, CPU 223 returns main body 101 from power off mode or sleep mode to standby mode.

[0073] When the CPU 223 returns the main body 101 to the standby mode and detects through the A / D terminal 201 that the temperature of the thermistor 208 is equal to or higher than a predetermined temperature, it rotates the cooling fan 125 at full speed to cool the power supply unit 120. This makes it possible to prevent failure of the transformer 205 and the rectifier diode 251 and ensure safety. Note that the process in the second embodiment is similar to that in the flowchart of FIG. 6. However, in the determination process in S104, it is determined whether or not there has been a change from Hi to Lo. Also, in the determination process in S105, it is determined whether or not it is Lo.

[0074] In the configuration of the second embodiment, the temperature of thermistor 208 for returning to standby mode can be determined independently by external trigger port 250 depending on the voltage input to the negative terminal of the comparator, regardless of the voltage input to A / D terminal 201. As described above, recovery circuit 127 can be designed without considering the resolution of temperature detection of thermistor 208 at A / D terminal 201, making it possible to further prevent failures of transformer 205 and rectifier diode 251 and ensure safety.

[0075] As described above, even a power supply device including a single AC-DC converter can protect the device in the power-off mode and sleep mode without increasing costs or space.

[0076] The disclosure of this embodiment includes the following configuration. (Configuration 1) A power supply device that converts a primary side AC voltage into a DC voltage and supplies the DC voltage to a secondary side load; a cooling means for cooling the power supply device; temperature detection means disposed on the secondary side of the power supply device for detecting a temperature of the power supply device; a control means for controlling the cooling means based on a detection result of the temperature detection means; Equipped with the control means is capable of switching between a first output mode in which the power supply device outputs a first voltage as the DC voltage and a second output mode in which the power supply device outputs a second voltage lower than the first voltage as the DC voltage, An image forming apparatus capable of switching between a first mode in which the image forming apparatus operates in the first output mode and a second mode in which the image forming apparatus operates in the second output mode, a signal output circuit for outputting a signal to the control circuit when the temperature detected by the temperature detection circuit becomes equal to or higher than a predetermined temperature; the control means has a port capable of detecting the signal output from the signal output circuit in the second mode, the cooling means is operable at the first voltage; The image forming apparatus is characterized in that, when the control means detects that the signal has been input from the signal output circuit to the port in the second mode, the control means transitions from the second mode to the first mode and controls the cooling means to operate and cool the power supply device. (Configuration 2) the control means includes an A / D converter that receives the detection result of the temperature detection means and performs analog-to-digital conversion, the A / D converter operating in the first mode and stopping its operation in the second mode; The image forming apparatus according to claim 1, wherein the control means controls the cooling means based on the detection result of the temperature detection means converted by the A / D converter in the first mode. (Configuration 3) the temperature detection means is a thermistor, The image forming apparatus according to the above, wherein the signal output circuit has at least two resistors connected in parallel to the thermistor, and a switch element. (Configuration 4) the temperature detection means is a thermistor, The image forming apparatus according to the above, wherein the signal output circuit includes a comparator and at least two resistors. (Configuration 5) The above-mentioned image forming apparatus, characterized in that the first mode includes a print mode in which an image forming operation can be performed on a recording material, and a standby mode in which it is possible to transition to the print mode upon receiving a print command. (Configuration 6) The image forming apparatus according to any one of the above, wherein the second mode includes a sleep mode and a power-off mode in which the AC voltage is input and power consumption is reduced compared to the sleep mode. (Configuration 7) The image forming apparatus according to any one of the above, wherein the power supply device has an overcurrent detection circuit provided on the primary side for detecting an overcurrent flowing through the load. (Configuration 8) the power supply device includes a transformer having a primary winding and a secondary winding, and a rectifier diode that rectifies a voltage induced in the secondary winding, The image forming apparatus according to the above, wherein the temperature detection means detects the temperatures of the secondary winding of the transformer and the rectifier diode. [Explanation of symbols]

[0077] 101 Main body (image forming device) 120 Power supply unit 125 Cooling Fan 127 Recovery Circuit 208 Thermistor 223 CPU

Claims

1. An image forming apparatus capable of operating in a first mode and a second mode, A power supply device that converts the AC voltage on the primary side to a DC voltage and supplies it to the load on the secondary side, the power supply device being capable of operating in a first output mode in which the image forming apparatus operates in the first mode and a second output mode in which the image forming apparatus operates in the second mode, the power supply device outputting a first DC voltage in the first output mode and outputting a second DC voltage lower than the first DC voltage in the second output mode, A cooling means for cooling the power supply unit, A temperature detection means is provided on the secondary side of the power supply in order to detect the temperature of the power supply, A control means capable of controlling the cooling means based on the detection result of the temperature detection means and switching between the first output mode and the second output mode of the power supply device, A signal output circuit that outputs a signal to the control means when the temperature detected by the temperature detection means exceeds a predetermined temperature, Equipped with, The control means has a port capable of detecting the signal output from the signal output circuit in the second mode. The cooling means is capable of operating at the first DC voltage, The image forming apparatus is characterized in that, when the signal is input from the signal output circuit to the port in the second mode, the control means switches from the second mode to the first mode and controls the cooling means to operate and cool the power supply unit.

2. The control means includes an A / D converter that receives the detection result of the temperature detection means as input, performs analog-to-digital conversion, operates in the first mode, and stops operating in the second mode. The image forming apparatus according to claim 1, characterized in that the control means controls the cooling means based on the detection result of the temperature detection means converted by the A / D converter in the first mode.

3. The temperature detection means is a thermistor, The image forming apparatus according to claim 1, characterized in that the signal output circuit comprises at least two resistors connected in parallel with the thermistor and a switch element.

4. The temperature detection means is a thermistor, The image forming apparatus according to claim 1, characterized in that the signal output circuit comprises a comparator and at least two resistors.

5. The image forming apparatus according to claim 1, characterized in that the first mode includes a print mode in which an image forming operation can be performed on a recording material, and a standby mode in which the apparatus can transition to the print mode upon receiving a print command.

6. The image forming apparatus according to claim 1, characterized in that the second mode includes a sleep mode and a power-off mode in which the AC voltage is input and the power consumption is reduced compared to the sleep mode.

7. The image forming apparatus according to claim 1, characterized in that the power supply device is provided on the primary side and has an overcurrent detection circuit that detects when an overcurrent flows through the load.

8. The power supply device comprises a transformer having a primary winding and a secondary winding, and a rectifier diode that rectifies the voltage induced in the secondary winding. The image forming apparatus according to claim 1, characterized in that the temperature detection means detects the temperature of the secondary winding of the transformer and the rectifier diode.

9. The image forming apparatus according to claim 1, characterized in that the operation of the cooling means is restricted when the power supply is in the second output mode.

10. When the port is defined as a first port, the control means further has at least one second port, When the power supply is in the first output mode, the control means is in a mode in which the first port and at least one second port are active. When the power supply is in the second output mode, the control means is in a power-saving mode in which the first port is enabled and at least one of the second ports is disabled. The image forming apparatus according to feature 1.

11. The port is an external trigger port, The signal output circuit is configured such that when the temperature detected by the temperature sensing means reaches or exceeds a predetermined temperature, the input voltage input to the external trigger port switches from one of a low level and a high level to the other of the low level and the high level. When the power supply is in the second output mode and the input voltage switches from one of the low level and the high level to the other of the low level and the high level, the control means switches the power supply from the second output mode to the first output mode. The image forming apparatus according to feature 1.

Images