JP2014155370A - Power supply device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an accurate operation, without erroneously detecting an input voltage, even when the supply of a voltage from an AC power supply is stopped, in a universal power supply.SOLUTION: A power supply device comprises: voltage detection means for detecting an inputted AC voltage; input detection means for detecting the presence or absence of the input of the AC voltage; and a converter for switching between double-voltage rectification and full-wave rectification, according to the detection result of the voltage detection means. With determination means for determining the value of the inputted AC voltage from the detection result of the input detection means and the detection result of the voltage detection means, the converter switches between the full-wave rectification and the double-voltage rectification, according to the determination result of the determination means, when such a state that the AC voltage is not inputted is obtained.

Description

  The present invention relates to a power supply device that generates a DC voltage from an AC voltage input from a commercial AC power supply.

  2. Description of the Related Art Image forming apparatuses such as laser beam printers, facsimiles, and copiers as electronic devices include a power supply device that converts an AC voltage from a commercial AC power supply (hereinafter referred to as an AC power supply) into a DC voltage. The rated voltage of the AC power supply differs in each country and each region, and is classified into two types, 100V system (100V and 120V) such as Japan and North America and 200V system (220V and 240V) such as Europe.

  Usually, a power supply apparatus adapted to input voltages of 100V system and 200V system is used. However, in order to cope with each country and each region, two types of power supply devices of 100V system and 200V system are required, and products having both 100V system and 200V system power supply devices are manufactured. Accordingly, a facility for manufacturing a product having different power supply devices is required, and the manufacturing cost increases. In order to reduce such an increase in manufacturing cost, a power supply device (hereinafter referred to as a universal power supply) that can handle both 100V and 200V input voltages has been proposed.

  The universal power supply does not require equipment for separately manufacturing 100 V system and 100 V system power supply devices, and the manufacturing cost can be reduced. There is also a method of outputting a voltage by switching the configuration of a rectifier circuit according to an input voltage as in Patent Document 1. This is a circuit configuration that performs voltage doubler rectification in the case of 100V system and outputs a voltage twice the power supply voltage, and outputs the same voltage as the AC power supply voltage by full wave rectification in the case of 200V system. With this configuration, the AC-DC converter (hereinafter referred to as the converter) in the subsequent stage of the rectifier circuit may have a circuit configuration corresponding to the 200V system. In the case of such a switching-type universal power supply, an AC power supply voltage detection circuit that detects the voltage of the AC power supply is provided, and the rectifier circuit is switched between a voltage doubler rectifier circuit and a full-wave rectifier circuit according to the detection result.

JP 2000-316280 A

  Here, in the universal power supply that switches the rectification method as in Patent Document 1, a voltage detection circuit that detects the input voltage from the AC power supply is required. The voltage detection circuit detects whether the voltage from the AC power supply is 100V or 200V, and outputs a binarized signal (High or Low signal) as a detection result. Here, for example, when a power failure occurs, the supply of voltage from the AC power supply may be temporarily stopped. If the power supply is interrupted for a long time, the universal power supply stops operating because power is not supplied. On the other hand, if the voltage supply is interrupted for a short time, the voltage is immediately supplied and the universal power supply can continue to operate. In such a short-time power failure, the voltage detection circuit operates. For example, when a power failure occurs with an input voltage of 200V system, the output of the voltage detection circuit changes due to a voltage drop, and it is erroneously detected as being 100V system. In some cases, the rectification method is switched (switched to voltage doubler rectification). After that, when the power is restored from the power failure and the voltage is supplied from the AC power supply, voltage doubler rectification may occur regardless of the 200 V system, and the circuit element may be destroyed.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a universal power supply that switches a rectification method according to an input voltage, and a power supply device or power supply that operates correctly without erroneously detecting the input voltage even when the supply of voltage from the AC power supply is stopped. An object is to provide an image forming apparatus equipped with the apparatus.

  A power supply apparatus of the present invention for solving the above-described problems includes a voltage detection unit that detects an AC voltage input from a commercial AC power source, and an input presence / absence detection unit that detects whether a voltage is input from the commercial AC power source. A converter that switches between double voltage rectification and full wave rectification according to the detection result of the voltage detection means and changes the AC voltage to a DC voltage, and the detection result of the input presence / absence detection means and the voltage detection Determining means for determining the value of the AC voltage input from the commercial AC power supply from the detection result of the means, and when the AC voltage from the commercial AC power supply is not input, the converter is configured to determine the determining means. The full-wave rectification and the voltage doubler rectification are switched according to the determination result.

An image forming apparatus according to the present invention includes an image forming unit for forming an image on a recording material,
A driving unit that drives the image forming unit; and a power source for supplying power to the driving unit. The power source detects a AC voltage input from a commercial AC power source. An input presence / absence detecting means for detecting the presence / absence of input of a voltage from an AC power supply; and a converter for switching the AC voltage to a DC voltage by switching between double voltage rectification and full wave rectification according to a detection result of the voltage detection means And determining means for determining the value of the AC voltage input from the commercial AC power supply from the detection result of the input presence / absence detection means and the detection result of the voltage detection means, and the AC voltage from the commercial AC power supply. The converter switches between the full-wave rectification and the voltage doubler rectification according to the determination result of the determination means.

  According to the present invention, even if the supply of voltage from the AC power supply is stopped, it can operate correctly without erroneously detecting the input voltage.

1 is a configuration diagram of an image forming apparatus according to the present invention. It is a block diagram of the power supply device in this invention. It is a block diagram of the AC power supply voltage detection circuit and the zero cross detection circuit in the present invention. It is a block diagram of the protection circuit in this invention. It is a flowchart of the control at the time of power ON in this invention. It is a control flowchart of AC power supply voltage detection in Example 1 of this invention. It is a time chart at the time of the power failure generation in Example 1 of this invention. It is a control flowchart of AC power supply voltage detection in Example 2 of this invention. It is a time chart at the time of the power failure generation in Example 2 of this invention. It is a control flowchart of the conventional AC power supply voltage detection. It is a time chart at the time of the conventional power failure occurrence.

  Next, specific configurations of the present invention for solving the above-described problems will be described based on examples. In addition, the Example shown below is an example, Comprising: It is not the meaning which limits the technical scope of this invention only to them.

Example 1
FIG. 1 shows the configuration of an electrophotographic image forming apparatus as an example of an apparatus equipped with a power supply apparatus according to the present invention. In FIG. 1, the recording materials stacked on the paper feed cassette 101 are sent one by one from the paper feed cassette 101 by the pickup roller 102 and conveyed toward the registration roller 104 by the paper feed roller 103. Thereafter, the recording material is conveyed by the registration roller 104 to the process cartridge 105 as an image forming unit at a predetermined timing. In the process cartridge 105, a charging roller 106 as a charging unit, a developing roller 107 as a developing unit, a cleaner 108 as a cleaning unit, and a photosensitive drum 109 as an electrophotographic photosensitive member are integrally configured. An image (a toner image described later) is formed on the recording material by the process cartridge 105.

  After the surface of the photosensitive drum 109 is uniformly charged by the charging roller 106, the exposure is performed based on the image signal by the scanner unit 111 which is an image exposure unit. Laser light emitted from the laser diode 112 in the scanner unit 111 is scanned in the main scanning direction orthogonal to the rotational direction of the photosensitive drum through the rotating polygon mirror 113 and the reflecting mirror 114. Then, as the photosensitive drum 109 rotates, laser light is also scanned in the rotational direction of the photosensitive drum 109, and an electrostatic latent image is formed on the surface of the photosensitive drum. The electrostatic latent image on the photosensitive drum 109 is visualized as a toner image by supplying toner by the developing roller 107, and the toner image is transferred to the recording material conveyed from the registration roller 104 by the transfer roller 110.

  When the recording material to which the toner image has been transferred is conveyed to the fixing device 115, the recording material is heated and pressurized, and the toner image transferred to the recording material is fixed to the recording material. The recording material is further discharged out of the image forming apparatus main body by the intermediate discharge roller 116 and the discharge roller 117, and a series of printing operations is completed. The above is the flow of the image forming operation.

  The image forming apparatus is provided with a plurality of power supplies for supplying voltages necessary for operating the respective internal units. For example, it is necessary to generate 3.3V as a power source for a CPU and a sensor, and 24V is used as a power source for a motor and a fan. Therefore, a power source that generates two voltages of 3.3V and 24V is provided. In the present invention, the power source generating 3.3V is a full-range universal power source corresponding to all AC power supply voltages in one circuit, and the power source generating 24V is from a commercial AC power source (hereinafter referred to as AC power source). A universal power supply that switches the rectification method according to the input voltage.

  FIG. 2 shows a configuration diagram of the power supply device according to the present embodiment, which includes two universal power supplies for generating 3.3V and 24V. The 3.3V power source 202 includes a rectifier circuit 205 including a diode bridge 206 and a smoothing capacitor 207, and a first converter 208, and corresponds to both 100V and 200V AC power supply voltages with one circuit configuration. It is a full range universal power supply. The AC power supply 201 is full-wave rectified by the diode bridge 206, and the DC voltage smoothed by the smoothing capacitor 207 is converted to a DC voltage of 3.3 V by the first converter 208 and output. Since 3.3V is used as a power source for the CPU 204, sensor (not shown), etc., the output power is small. With such a configuration, both 100V and 200V systems can be handled.

  Next, the power supply 203 for 24V will be described. 24V is used as a power source for supplying power to the drive unit such as a motor or a fan, so the output power is large, and it supports both 100V system and 200V system with one circuit configuration like the power source 202 for 3.3V. Difficult to do. Therefore, a universal power supply having a circuit configuration in which the rectifier circuit 210 is switched between voltage doubler rectification and full-wave rectification according to the voltage of the AC power supply 201 is used. The live (ACH) of the AC power supply 201 is provided with a bidirectional thyristor (also referred to as a gate-controlled semiconductor switch) 209. When 3.3V is output, the bidirectional thyristor 209 is turned on, and the 24V power supply 203 is An AC power supply 201 is connected. When 3.3V is not output, the bidirectional thyristor 209 is turned off, and the 24V power source 203 and the AC power source 201 are disconnected. The bidirectional thyristor 212 in the rectifier circuit 210 is connected to the middle point of the smoothing capacitors 213 and 214 connected in series and the neutral (ACN) of the AC power supply. Switching between rectification and rectification methods. The bidirectional thyristor 212 is controlled by a TRON signal from the CPU 204. A second converter 216 that outputs a DC voltage of 24 V is connected to the subsequent stage of the rectifier circuit 210 and is activated by a 24 VON signal from the CPU 204. The protection circuit 215 detects a mismatch between the input voltage from the AC power supply and the rectification method. When the mismatch is detected, the CNVOFF signal is output, the first converter 208 is stopped, and the output of 3.3 V is turned off. The bidirectional thyristor 209 is turned off and the 24V power supply 203 is disconnected from the AC power supply to shut down the power supply apparatus.

  When the AC power supply voltage is 200V, the TRON signal is turned off, the bidirectional thyristor 212 is turned off to make the rectifier circuit 210 a full-wave rectifier circuit, and both ends of the smoothing capacitors 213 and 214 connected in series (between DCH2 and DCL2). ) Is applied with an input voltage from a 200V AC power source and full-wave rectified. On the other hand, when the input voltage from the AC power supply is 100V, the TRON signal is turned on to turn on the bidirectional thyristor 212 to form a voltage doubler rectifier circuit. In voltage doubler rectification, the positive half-wave of the AC power supply voltage is charged to the smoothing capacitor 213, and the negative half-wave is charged to the smoothing capacitor 214, so that both ends of the smoothing capacitors 213 and 214 (between DCH2 and DCL2). Generates a voltage twice the peak voltage of the AC power supply voltage. In this way, by switching the rectification method according to the voltage from the AC power supply, a voltage corresponding to the 200V system is always generated at the output of the rectifier circuit 210 (input of the second converter 216) regardless of the voltage from the AC power supply. Therefore, the second converter 216 may be configured to convert the voltage from the 200V AC power source into a DC voltage of 24V and output it. In order to start the second converter 216 after switching the rectification method by the TRON signal, the CPU 204 outputs the start signal 24VON signal to the second converter 216. When the 24VON signal is turned ON, the second converter 216 is started and 24V is supplied. I am trying to output.

  As described above, the power source 203 for 24V needs to switch the rectification method by turning on / off the bidirectional thyristor 212 in accordance with the voltage from the AC power source, so that the AC power source voltage detection circuit that detects the voltage from the AC power source. 217 is required. FIG. 3 is a configuration diagram of the AC power supply voltage detection circuit 217. The neutral voltage (ACN) potential of the AC power supply 201 with respect to the reference potential DCL after the rectification of the diode bridge 206 of the 3.3V power supply 202 is detected to detect whether it is a 100V system or a 200V system. When the potential of ACN gradually becomes higher than DCL, the voltage divided by resistors 301 and 302 provided between ACN and DCL exceeds the Zener voltage of Zener diode 303, and Zener diode 303 is turned on. When the Zener diode 303 is turned on, the transistor 306 is turned on and the light emitting element 308a of the photocoupler 308 is turned off.

  The power source of the light emitting element 308a of the photocoupler 308 uses a voltage Vpc generated by an auxiliary winding provided on the primary side of a transformer (not shown) in the first converter 208. When the light emitting element 308a in the photocoupler 308 is turned off, the light receiving element 308b is turned off, and the capacitor 311 is charged from the power supply for 3.3V through the resistor 309 and the diode 310. During the period until the potential of ACN becomes equal to or higher than the voltage at which the Zener diode 303 is turned on, the capacitor 311 is charged and the voltage of the capacitor 311 increases. On the other hand, when the potential of ACN is lower than the potential at which the Zener diode 303 is turned on, the transistor 306 is turned off, the light emitting element 308a of the photocoupler 308 emits light, and the light receiving element 308b is turned on. Therefore, the capacitor 311 is not charged, and the resistor 312 gradually discharges the charge. When this operation is repeated for each frequency of the voltage of the AC power supply, when the voltage of the AC power supply is high, the capacitor 311 is charged and the voltage rises every cycle of the commercial frequency, so that the voltage of the capacitor 311 becomes the resistance 313 and the resistance 314. The threshold voltage set in step S1 is exceeded, and the output signal ACVOLT of the comparator 315 becomes low. Further, when the voltage from the AC power source is low, the capacitor 311 is not charged, so that the ACVOLT signal of the comparator 315 becomes High. That is, when the voltage from the AC power source is 200V system, the capacitor 311 is charged, and when the voltage is 100V system, the threshold value determined by the resistor 301, the resistor 302, and the Zener diode 303 so as not to charge the capacitor 311 (in this example, as an example (AC160V as a threshold value) may be set. If the threshold value is set in this way, the output signal ACVOLT becomes Low in the case of the 200V system, and becomes High in the case of the 100V system. As a result, the voltage from the AC power source can be determined.

  Further, the image forming apparatus includes a zero-cross detection circuit 218 that detects the frequency of the AC voltage from the AC power source and the timing of zero-cross. This zero cross detection circuit also functions as an AC voltage input presence / absence detection circuit. The zero-cross detection circuit 218 is used to control the fixing device 115 of the image forming apparatus, and is used to determine the ON / OFF timing of a heater that is a heating unit in the fixing device 115. In the zero cross detection circuit 218, when the potential of ACN is higher than DCL, the transistor 323 is turned on, the light emitting element 325a in the photocoupler 325 is turned off, the light receiving element 325b is turned off, and the ZEROX signal becomes High. On the other hand, when the potential of ACN is lower than DCL, the transistor 323 is turned off, the light emitting element 325a of the photocoupler 325 is turned on, and the light receiving element 325b is turned on, so that the ZEROX signal becomes Low. If this is repeated for each AC voltage frequency, the zero cross detection circuit 218 outputs a clock-like signal at the same frequency as the commercial frequency, so the CPU 204 can detect the commercial frequency and the zero cross timing.

  As described above, the power supply 203 for 24V is configured to switch the rectification method by the TRON signal based on the output of the voltage detection circuit 217 of the AC power supply and the ACVOLT signal. However, as described above, the voltage from the power supply may be erroneously detected due to the occurrence of a short power failure or the like. Further, for example, when the bidirectional thyristor 212 is short-circuited, there is a possibility that voltage rectification is always performed regardless of the logic of the TRON signal. In such a case, if the voltage from the AC power source is a 200V system, a 200V system voltage is applied to each of the two smoothing capacitors 213 and 214, so that a voltage double that of the 200V system is output from the rectifier circuit 210. An overvoltage may be applied to the capacitors 213 and 214 and the second converter, causing a circuit failure.

  In this embodiment, in order to prevent the occurrence of a failure when such a mismatch between the voltage from the AC power source and the rectification method occurs, the voltage applied to each of the smoothing capacitors 213 and 214 is monitored, and the voltage A protection circuit 215 that outputs a shutdown signal CNVOFF when a certain value exceeds a certain value is provided. Hereinafter, the configuration of the protection circuit 215 of this embodiment will be described with reference to FIG.

  The protection circuit 215 of this embodiment is a circuit that monitors the voltage applied to each of the two smoothing capacitors 213 and 214 and operates when the voltage applied to one of the smoothing capacitors exceeds a predetermined value. Normally, only a 100V system voltage is applied to the smoothing capacitors 213 and 214 regardless of the rectification method. That is, when a voltage of 100V or higher is applied, it is in an abnormal state, so that the protection circuit 215 is set to operate when a voltage of 200V (for example, voltage from an AC power supply: 200V) is applied. When the applied voltages of the smoothing capacitors 213 and 214 are 100V system and are normal, the resistors 401, 402, 403, 404, and 405 are set so that the potential of the reference terminal (REF terminal) of the shunt regulator 411 does not exceed the threshold value. , 406, 407, 408, and 409 are set, and the shunt regulator 411 is OFF. The light emitting element 412a of the photocoupler 412 is connected to a primary auxiliary winding of a transformer (not shown) in the second converter 216 via a current limiting resistor 413, and supplied with a voltage Vpc2 generated by the auxiliary winding. The When the shunt regulator 411 is OFF, no current flows through the light emitting element 412a of the photocoupler 412, so no light is emitted, the light receiving element 412b is turned OFF, and the CNVOFF signal becomes LOW. However, when an overvoltage is applied to the smoothing capacitor 213, the voltage divided by the resistors 405 and 406 exceeds the threshold value of the REF terminal of the shunt regulator 411, and the shunt regulator 411 is turned on. When the shunt regulator 411 is turned on, a current flows through the light emitting element 412a in the photocoupler 412 to emit light, the light receiving element 412b is turned on, and the CNVOFF signal becomes High. The CNVOFF signal is connected to the first converter 208 that outputs 3.3V. When the CNVOFF signal becomes High, the first converter 208 is forcibly stopped and the power supply apparatus is shut down. When an overvoltage is applied to the smoothing capacitor 214, the voltage divided by the combined resistance of the resistor 401 and the resistor 402 and the resistor 403 is increased, and the FET 404 is turned on. When the FET 404 is turned on, the drain voltage of the FET 404 becomes Low. On the other hand, the voltage divided by the combined resistance of the resistor 402 and the resistor 403 and the resistor 401 also increases, exceeds the threshold value of the REF terminal of the shunt regulator 411 via the diode 407, and the shunt regulator 411 is turned on. Then, as described above, the light receiving element 412b of the photocoupler 412 is turned ON and the CNVOFF signal becomes High. As described above, when an overvoltage of 200 V system or more is applied to either of the smoothing capacitors 213 and 214, the protection circuit operates, the CNVOFF signal becomes High, and 3.3 V is not output. Therefore, the bidirectional thyristor 209 is turned off. The connection between the second converter 216 and the smoothing capacitors 213 and 214 and the AC power supply is cut off so that no overvoltage is applied.

  Next, control using the configuration of the power supply device described above will be described. FIG. 5 shows a startup sequence after the image forming apparatus is powered on. When the power is turned on, the 3.3V power source 202 is activated (step S101), and the CPU 204 starts operating. The CPU 204 detects an AC power supply voltage, which will be described later, and switches the rectification method of the 24V power supply 203 by a TRON signal according to the result (step S102). When the 24VON signal is turned ON to activate the second converter 216 (step S103), the startup sequence ends.

  Next, a method for detecting a voltage from an AC power source will be described. FIG. 10 is a flowchart of voltage detection of a conventional AC power source. The logic of the output ACVOLT signal of the AC power supply voltage detection circuit 217 is confirmed (step S401). As a result of the confirmation, if it is Low, it waits until the state is continuously determined for a predetermined time (step S402). The rectifier circuit 210 is turned off and full-wave rectification is performed (step S403). If the ACVOLT signal is High, the process waits until the state continues for a predetermined time (step S404). When the predetermined time elapses, it is determined that the voltage from the AC power supply is 100V system, the TRON signal is turned on, the bidirectional thyristor 212 is turned on, and the rectifier circuit 210 is double voltage rectified (step S405).

  On the other hand, FIG. 6 is a flowchart of voltage detection of the AC power supply in the present invention. The feature of the present invention is that the AC power supply voltage is detected in a state where the voltage is surely input from the AC power supply by confirming the output of the ZEROX signal when detecting the voltage of the AC power supply. The same control (step) as in the conventional example is given the same number. First, it is confirmed whether or not the ZEROX signal is output (whether the frequency of the AC power source can be switched between High / Low) (step S201). If the ZEROX signal is output, the logic of the ACVOLT signal is confirmed (step S401), and the rectification method of the 24V power source 203 is switched according to the logic of the ACVOLT signal as in the conventional detection method (steps S402 to S405). . If the output of the ZEROX signal cannot be confirmed (NO in step S201), it is determined that the voltage from the AC power source is not input, and the process returns to step S201 to wait for the output of the ZEROX signal without detecting the voltage of the AC power source. . The voltage detection control of the AC power source is always executed not only during the start-up sequence, but the voltage from the AC power source is constantly monitored. When the voltage from the AC power supply fluctuates, this control detects the fluctuation, and switches the rectifier circuit 210 according to the detection result of the voltage from the AC power supply after the fluctuation. At this time, as described above, when the output of the ZEROX signal cannot be confirmed, the AC power supply voltage is not detected (or the AC power supply voltage detection result is not updated), so the rectifier circuit 210 is switched during a power failure. There is no.

  Here, since the voltage from the AC power supply is not input during a power failure, the voltage detection circuit 217 of the AC power supply operates in the same manner as the 100V system. That is, the ACVOLT signal becomes the same as the 100V system. For example, when a power failure occurs when the voltage from the AC power supply is 200V, the ACVOLT signal output from the voltage detection circuit 217 of the AC power supply changes from Low to High during the power failure. In the case of conventional control, a change in the ACVOLT signal during a power failure is erroneously determined that the voltage from the AC power supply has changed from the 200V system to the 100V system, and the TRON signal is turned on and the bidirectional thyristor 212 is turned on for rectification. Switch circuit 210 to voltage doubler rectification. After that, when the power is restored from the power failure, the voltage from the AC power supply is 200V, whereas the rectifier circuit 210 is double voltage rectification, so mismatching occurs, and the protection circuit 215 operates to shut down the image forming apparatus. . In order to prevent such a situation, the present invention detects not only the 100V / 200V system voltage from the AC power supply but also the state of no input (power failure). Therefore, not only the voltage detection circuit 217 of the AC power supply but also the zero cross detection circuit 218 is used to determine the input state of the voltage from the AC power supply, so that the voltage detection of the AC power supply is not performed during a power failure.

  FIG. 11 shows a time chart in the conventional AC power supply voltage detection method in which shutdown occurs at the end of the power failure described above. FIG. 11 is a time chart when a power failure occurs while the AC power supply is operating in the 200V system. When the voltage from the AC power supply is input, the voltage detection circuit 217 of the AC power supply operates and the ACVOLT signal becomes Low, and the CPU 204 is determined to be in the 200V system (until time t1). When a power failure occurs at time t1, the output of the ZEROX signal is stopped, and then the ACVOLT signal is switched from low to high at time t2. When this state continues for a fixed time for detecting the voltage of the AC power supply, at time t3, the CPU 204 erroneously determines that the voltage from the AC power supply has become the 100V system, turns on the TRON signal, and doubles the rectifier circuit 210. Switch to. After that, when the power is restored from the power failure at time t4 and the 200V system voltage is input again as the voltage from the AC power source, the rectifier circuit 210 is double voltage rectified, and therefore the 200V system voltage is applied to each of the smoothing capacitors 213 and 214. Will be applied. The protection circuit 215 detects this overvoltage application, and shuts down the power supply device by setting the shutdown signal (CONVOFF signal) to High at time t5. When such a situation occurs, it is a case where the power failure time is longer than the confirmation time of voltage detection of the AC power supply. However, if the power failure time is too long, power is not supplied and the power supply device cannot operate, so the power supply device can continue to operate for a length of time that is shorter than the power failure time and longer than the AC power supply voltage detection confirmation time. It becomes.

  On the other hand, FIG. 7 is a time chart when a power failure occurs in the voltage detection control of the AC power supply of the present invention. Those corresponding to the same time as in the time chart of FIG. 11 are given the same numbers. Until time t1, since a 200V system voltage is input as the AC power supply voltage, the ZEROX signal is output and the ACVOLT signal is Low, so it is determined that the 200V system is used. When a power failure occurs at time t1, the voltage from the AC power supply is not input, so the ACVOLT signal switches from Low to High at time t2, but since the ZEROX signal is not output, the determination result of the AC power supply voltage detection does not change. When the power failure ends at time t4, the ZEROX signal is output, and the voltage detection of the AC power supply is performed again. Since the voltage from the AC power supply is 200V, the ACVOLT signal switches from High to Low at time t6 after recovery from the power failure. If the state continues for a fixed time, the determination is determined as being 200V system at time t7. Actually, since it was already determined that the system is 200V before the power failure, the TRON signal remains OFF, so that the shutdown does not occur and continues to operate normally.

  As described above, the voltage value of the AC power supply is determined based on the ACVOLT signal that detects the voltage from the AC power supply while detecting whether or not the voltage is input from the AC power supply based on the ZEROX signal that detects the zero crossing of the voltage from the AC power supply. As a result, it is possible to prevent a power outage from being erroneously determined as a fluctuation in the AC power supply voltage, and the universal power supply is not shut down as described above. In this embodiment, the zero cross detection circuit is used as the voltage input presence / absence detection circuit from the AC power supply. However, the present invention is not limited to this, and any circuit that can confirm the input of the AC power supply voltage may be used.

  As described above, according to the present embodiment, even when the supply of voltage from the AC power supply is stopped, the universal power supply can operate correctly without erroneously detecting the input voltage.

(Example 2)
The configurations of the image forming apparatus and the universal power supply in the present embodiment are the same as those in the first embodiment, and a description thereof will be omitted. Normally, the voltage from the AC power source does not seem to change before and after the occurrence of a power failure, but the status of the AC power source varies, and the voltage from the AC power source may change after the power failure. For example, although it is originally a 200V system voltage, if the line impedance of the AC power supply is high and many loads are connected, the actual input voltage drops to the 100V system range. Sometimes. If a power failure occurs in such a situation, it can be assumed that the voltage is in the 100V system voltage range before the power failure and that the voltage has returned to the 200V system upon recovery from the power failure. In such a case, in the first embodiment, it is determined that the system is a 100V system before the power failure, and the switching to the voltage doubler rectification is performed. The protection circuit 215 detects an overvoltage and a shutdown occurs.

  Therefore, in this embodiment, when a power failure is detected by the ZEROX signal, the determination result of the voltage from the AC power supply is forcibly set to 200 V regardless of the logic of the ACVOLT signal, and the rectifier circuit 210 of the power supply 203 for 24 V is full-wave rectified. And the occurrence of shutdown by the protection circuit 215 is avoided.

  FIG. 8 shows a flowchart of the control operation of this embodiment. Since the basic flow is the same as that of the first embodiment, only different points will be described. If the output of the ZEROX signal cannot be confirmed due to a power failure (NO in step S201), the process proceeds to step S403 to forcibly determine that the voltage from the AC power supply is 200V system, and the TRON signal is turned off to turn off the bidirectional thyristor 212. And switch to full-wave rectification. This control loop operates during the period when the ZEROX signal is not output, and full-wave rectification continues. When the power failure ends and a voltage from the AC power supply is input, a ZEROX signal is output. Therefore, the voltage detection of the AC power supply is performed again, and the rectifier circuit 210 is switched according to the result (steps S401 to S405). Accordingly, since full-wave rectification is always performed at the time of recovery from a power failure, there is no concern that an overvoltage is applied to the smoothing capacitors 213 and 214, and shutdown by the protection circuit 215 does not occur.

  FIG. 9 is a time chart when a power failure occurs such that the AC power supply voltage before the power failure is 100V and the AC power supply voltage after the power failure is 200V. The same time as the first embodiment is given the same number. Initially, when a voltage from a 100V AC power supply is input, the TRON signal is turned on to double voltage rectification. When it is detected at time t8 that a power failure has occurred at time t1 and the ZEROX signal is no longer output, it is forcibly determined that the AC power supply voltage has become 200V, and the TRON signal is turned off to switch to full-wave rectification. Then, the power failure ends at time t4, but this time, the voltage from the AC power supply is input to the 200V system. However, since it has already switched to full wave rectification, it continues to operate normally. Then, since the ZEROX signal starts to be output, the AC power supply voltage detection is performed again, and the determination of the 200V system is confirmed at time t7. However, since full-wave rectification has already been performed, the operation can be continued normally.

  As described above, according to this embodiment, even if the supply of voltage from the AC power supply is stopped, the universal power supply can operate correctly without erroneously detecting the input voltage. Also, when a power failure is detected, the rectifier circuit of the 24V power supply is forcibly switched to full-wave rectification, so that a shutdown occurs regardless of whether the voltage from the AC power supply is 100V / 200V after recovery from the power failure. It is possible not to let it.

201 Commercial AC Power Supply 202 3.3V Power Supply 203 24V Power Supply 204 CPU
217 AC power supply voltage detection circuit 218 Zero cross detection circuit

Claims (12)

Voltage detection means for detecting an AC voltage input from a commercial AC power supply;
Input presence / absence detection means for detecting presence / absence of voltage input from the commercial AC power supply
A converter that switches between double voltage rectification and full wave rectification according to the detection result of the voltage detection means, and converts the AC voltage into a DC voltage.
Judgment means for judging the value of the AC voltage input from the commercial AC power source from the detection result of the input presence / absence detection means and the detection result of the voltage detection means;
When the AC voltage from the commercial AC power supply is not input, the converter switches between the full-wave rectification and the voltage doubler rectification according to the determination result of the determination means. .   2. The converter according to claim 1, wherein the converter switches between the full-wave rectification and the voltage doubler rectification according to a determination result of the determination unit when a detection result of the input presence / absence detection unit is obtained. The power supply described.   2. The power supply device according to claim 1, wherein the converter switches to the full-wave rectification when there is no input of an AC voltage from the commercial AC power source as a result of detection by the input presence / absence detection unit.   4. The power supply device according to claim 1, wherein the input presence / absence detection unit is a zero-cross detection unit that detects a zero-cross timing of an AC voltage from the commercial AC power source. 5.   5. The power supply device according to claim 4, wherein when the zero-cross timing cannot be detected by the zero-cross detection unit and the AC voltage is not input, the converter switches to the full-wave rectification.   6. The converter according to claim 1, wherein the converter switches to the double voltage rectification when the AC voltage is 100 V, and switches to the full-wave rectification when the AC voltage is 200 V. 6. The image forming apparatus described. An image forming means for forming an image on a recording material;
Driving means for driving the image forming means;
A power source for supplying power to the driving means,
The power supply is
Voltage detection means for detecting an AC voltage input from a commercial AC power supply;
Input presence / absence detection means for detecting presence / absence of voltage input from the commercial AC power source;
A converter that switches between double voltage rectification and full wave rectification according to the detection result of the voltage detection means, and converts the AC voltage into a DC voltage.
Judgment means for judging the value of the AC voltage input from the commercial AC power source from the detection result of the input presence / absence detection means and the detection result of the voltage detection means;
When the AC voltage from the commercial AC power supply is not input, the converter switches between the full-wave rectification and the voltage doubler rectification according to a determination result of the determination unit. apparatus.   8. The converter according to claim 7, wherein the converter switches between the full-wave rectification and the voltage doubler rectification according to a determination result of the determination unit when a detection result of the input presence / absence detection unit is obtained. The image forming apparatus described.   The image forming apparatus according to claim 7, wherein the converter switches to the full-wave rectification when there is no input of an AC voltage from the commercial AC power source as a result of detection by the input presence / absence detection unit.   The image forming apparatus according to claim 7, wherein the input presence / absence detection unit is a zero cross detection unit that detects a zero cross timing of an AC voltage from the commercial AC power supply.   11. The power supply device according to claim 10, wherein when the zero-cross timing cannot be detected by the zero-cross detection unit and the AC voltage is not input, the converter switches to the full-wave rectification.   12. The converter according to claim 7, wherein the converter switches to the double voltage rectification when the AC voltage is 100V, and switches to the full-wave rectification when the AC voltage is 200V. The image forming apparatus described.

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