JP6188371B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a power supply apparatus that transforms a rectification / smoothing voltage of a commercial AC power supply to a desired voltage and supplies current to a load, and an image forming apparatus including the power supply apparatus, and more particularly, a switching power supply that uses an electrolytic capacitor for smoothing means. About.

  Conventionally, a switching power supply that rectifies and smoothes a commercial AC power supply, transforms the smoothed voltage to a desired voltage, and supplies current to a load is known. In such a switching power supply, an electrolytic capacitor that easily obtains a large capacity at a low cost is often used as the smoothing means, except for special cases such as when the power consumption of the device is very small or when used in a high temperature environment. For example, there is a switching power supply as shown in FIG. The switching power supply shown in FIG. 7 includes a rectifier bridge diode 2, a smoothing electrolytic capacitor 3, and a transformer 6 as a power supply that supplies current to a load 38. Further, the switching power supply includes a rectifier bridge diode 30, a smoothing electrolytic capacitor 26, and a transformer unit 27 as another power supply unit that supplies current to the load 28. The other power supply unit branches off from the connection with the commercial AC power supply 1, transforms the DC voltage to a desired voltage after rectification and smoothing, and supplies current to the load 28 that consumes more current than the load 38. The transformer 6 supplies a voltage such as 3.3V to the control system, for example, and the transformer 27 supplies a voltage such as 24V to the power system. This switching power supply includes a switch element 29 upstream of the rectifying bridge diode 30. And in the function stop state of a device, a standby state, or the state using small electric power, the switch element 29 is made into a non-conduction state by the calculating parts 7, such as CPU. In FIG. 7, the capacity of the electrolytic capacitor 3 is reduced by adding the rectifying bridge diode 30, the smoothing electrolytic capacitor 26, and the transformer 27, and the leakage current of the electrolytic capacitor 26 is cut off. Thereby, power consumption is reduced.

  For example, in Patent Document 1, two rectifying electrolytic capacitors are connected in series after rectification of a commercial AC power supply, and switching means such as a triac is provided between a connection point of the two electrolytic capacitors and a rectifying bridge diode. A switching power supply having a configuration is disclosed. In this switching power supply, when the commercial AC power supply is in a 100V region, voltage rectification is performed by making the switching means conductive, and in the 200V region, full-wave rectification operation is performed by making the switching means non-conductive. . In such a switching power supply, the voltage after rectification and smoothing can be made comparable, and the same operation is performed in both the 100V and 200V regions. For example, Patent Document 2 discloses a DC converter including a first series circuit in which a primary winding of a transformer and first switching means are connected in series after rectification and smoothing of a commercial AC power supply. The DC converter further includes a second series circuit connected to both ends of the first switching means or both ends of the primary winding of the transformer, and having the second switching means and a capacitor connected in series. Then, in a state where the load on the secondary side is small, the second switching means is brought into a conducting state for a short time immediately before the first switching means is brought into a conducting state.

Japanese Patent Application No. 2007-316811 JP 2005-059461 A

  In recent years, a switching power supply unit in a device is required to improve power supply efficiency when a unit having a function other than power supply operates and a large load current is supplied. Further, there is a demand for reduction in power consumption in a standby state in which at least one unit in the apparatus does not operate and waits for an operation start trigger or when the power is turned off. Power off may refer to the following two states. One is a case where the power supply is completely cut off by hardware-cutting the power supply line with a mechanical switch. The other is that the function is not completely cut off from the commercial AC power supply, the function of waiting for the trigger to return from the power-off state is not stopped, and the functions other than waiting for the trigger are stopped, which will be described later. This is a case where the state stands by with power below the standard. Examples of the trigger for return include not only access to the power switch from the user but also a return signal from a timer in the apparatus and a power-on instruction from the remote controller. The power consumption is 0 W (watts) when the power is off. It is not. For example, the German standard Blue Angel stipulates that the power off is 1 W or less in the 100 V range (2 W in the 200 V range) and 0.1 W or less in Korea.

  As described above, an electrolytic capacitor is generally used for the smoothing means. However, the electrolytic capacitor generates a leakage current due to its structure, and the larger the capacitance, the larger the leakage current tends to be. The individual variation is large and the temperature is dependent. Since the loss due to the leakage current is a product of the voltage after smoothing the commercial AC power supply, it is a large value that cannot be ignored with respect to the above-mentioned standard. For example, if the leakage current is 100 μA and the commercial AC power supply is in the 220 V region, it is approximately 220 × √2 × 100 μA = 0.031 W, which occupies 31% of the standard 0.1 W, for example.

  On the other hand, the minimum capacity required for the electrolytic capacitor for smoothing depends on the maximum amount of current that flows when all the units in the device are operating, and the ripple of the smoothed voltage (referred to as ripple voltage) falls within the desired range. Therefore, it is necessary to increase the maximum load current as the maximum load current increases. When the ripple voltage becomes larger than a specified voltage, the following problems may occur. For example, the power supply IC that controls the switching means for switching the primary winding of the transformer malfunctions, the voltage supplied to the secondary side after transformation is higher than the specified ripple voltage, or the unit malfunctions. Challenges arise. Therefore, the switching power supply of the device having a large maximum load current when all the units in the device are operated increases the capacity of the electrolytic capacitor for smoothing, and the power consumption increases due to the leakage current caused by the electrolytic capacitor.

  On the other hand, a film capacitor or a ceramic capacitor has a smaller leakage current than an electrolytic capacitor because of its structure. However, when trying to obtain the same capacity as an electrolytic capacitor using a film capacitor or a ceramic capacitor, a larger space and cost are required. In the switching power supply of FIG. 7, it is possible to reduce power consumption. However, it is necessary to add a rectifier bridge diode 30, a smoothing electrolytic capacitor 26, and a switch element 29 for controlling power supply to the rectifier bridge diode 30, and adding a transformer 27 further increases the space and cost. Need. Further, Patent Document 1 provides a power supply that can cope with a wide commercial AC power supply range by providing means for switching the withstand voltage and capacity of a smoothing electrolytic capacitor. However, power consumption due to a leakage current of the smoothing electrolytic capacitor is provided. There is no effect on reduction. Furthermore, in Patent Document 2, the loss when switching the current flowing through the primary winding of the transformer by the switching means is reduced, but the power consumption due to the leakage current of the smoothing electrolytic capacitor upstream from the switching means is It does not change.

  The present invention has been made under such circumstances, and an object of the present invention is to reduce power consumption of a smoothing means that smoothes a voltage obtained by rectifying an AC voltage when the apparatus is in a low power consumption state. .

  In order to solve the above-described problems, the present invention has the following configuration.

(1) Rectifying means for rectifying an alternating voltage, first smoothing means for smoothing the voltage rectified by the rectifying means, and transforming means for transforming the voltage smoothed by the first smoothing means. A power supply device for supplying a voltage transformed by the transformer means to a load, wherein the switch means is connected in series to the first smoothing means, and the first smoothing means and the switch are connected in series. A second smoothing means connected in parallel to the means and having a smaller capacity than the first smoothing means, and when the load is in a first state that consumes a predetermined power, the switch means is in a conducting state, Control means for turning off the switch means when the load is in a second state consuming less power than the first state, the control means from the second state to the First When transitioning the state, the power supply apparatus characterized by starting the operation of the load switch to a conductive state the switching means from the non-conductive state after a lapse of the first time.

  (2) An image forming apparatus comprising: an image forming unit that forms an image on a recording material; and the power supply device according to (1).

  According to the present invention, when the apparatus is in a low power consumption state, the power consumption of the smoothing means that smoothes the voltage obtained by rectifying the AC voltage can be reduced.

1 is a circuit diagram illustrating a switching power supply according to a first embodiment. Time chart for explaining the operation of the switching power supply according to the first embodiment Circuit diagram for explaining a switching power supply according to Embodiment 2 Time chart for explaining the operation of the switching power supply according to the second embodiment Circuit diagram for explaining a switching power supply according to Embodiment 3 FIG. 6 is a diagram illustrating an image forming apparatus according to a fourth embodiment. Circuit diagram illustrating a conventional switching power supply

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In addition, the component described in the following embodiment is an illustration to the last, and is not a thing of the meaning which limits the range of this invention only to them.

[Switching power supply]
FIG. 1 shows a circuit diagram of a switching power supply as a power supply device mounted on the apparatus of the first embodiment. Here, the apparatus refers to, for example, a television or a printer, and the load 8 in FIG. 1 refers to a unit that outputs, for example, video on a television, and a unit that conveys a recording material for performing a printing operation on a printer. Point to. Further, the operation state that is the first state refers to a state in which a unit in the apparatus is consuming a certain amount of electric power, such as during video output or printing operation. Furthermore, the low power consumption state, which is the second state, refers to a state where the power is turned off by a remote control switch in a television, for example. The low power consumption state refers to a state in which the printer has been operated by a user's operation panel or has transitioned to a sleep mode or the like in order to reduce power consumption after a predetermined time after printing.

  In the switching power supply in the apparatus, the positive side of the voltage rectified from the commercial AC power supply (hereinafter simply referred to as the commercial power supply) 1 by the rectifying bridge diode 2 that is the rectifying means is connected to one of the switch elements 5 such as bidirectional thyristors. Has been. The bidirectional thyristor is hereinafter referred to as a triac. On the other hand, the other of the switch elements 5 is connected to the plus side of a first electrolytic capacitor 3 (hereinafter simply referred to as an electrolytic capacitor 3) which is a first smoothing means. Further, the negative side of the voltage rectified by the rectifying bridge diode 2 is connected to the negative side of the electrolytic capacitor 3. Further, a second capacitor 4 (hereinafter simply referred to as a capacitor 4), which is a second smoothing means, is connected in parallel to the switch element 5 and the electrolytic capacitor 3 connected in series.

  The transformer 6 includes a switching element such as a FET (field effect transistor) that switches the current of the transformer and the primary winding of the transformer, a power supply IC, and a rectifying / smoothing circuit that rectifies and smoothes the secondary voltage on the secondary side. Yes. The details of the transformer 6 will be described in Example 3 to be described later. Then, the transformer 6 transforms the voltage smoothed on the primary side into a desired voltage and supplies it to the secondary side. In this way, the transformer 6 supplies power to the arithmetic unit 7 such as the CPU on the secondary side and the load 8. The computing unit 7 is connected to the control terminal of the switch element 5 and outputs a control signal to the control terminal of the switch element 5 to control the switch element 5 to be in a conductive or non-conductive state.

  Since the load 8 uses a large current in the operating state of the apparatus, a ripple occurs in the smoothing voltage of the electrolytic capacitor 3. The ripple voltage is reduced as the smoothing capacitor capacity is increased. However, if the capacitor capacity is large, the ripple voltage becomes expensive or requires a larger space. For this reason, the capacity of the smoothing capacitor is determined within a range that makes it possible to stabilize the operation of the power supply IC of the transformer 6 and stabilize the voltage after transformation within a specified range as described above. In addition, since a capacitor with a large capacity is required, the switching power supply of this embodiment includes an electrolytic capacitor 3 that easily obtains a large capacity at low cost.

  On the other hand, in the low power consumption state, a part of the load 8 consumes a small current or is cut off and does not consume at all, so that a large capacity like the electrolytic capacitor 3 is not required. The power consumption due to the leakage current of the electrolytic capacitor 3 is very small and negligible compared to the total power consumed by the load 8 in the operating state of the apparatus. However, compared with the total power in the low power consumption state, the size is not negligible, and the power due to the leakage current continues to be consumed as long as the device is connected to the commercial power source 1 even though the device is not operating. Therefore, in the present embodiment, when the apparatus transitions to the low power consumption state, the calculation unit 7 outputs a control signal to the control terminal of the switch element 5 so that the switch element 5 is in a non-conductive state. Thereby, power consumption due to the leakage current of the electrolytic capacitor 3 is eliminated.

[Operation of switching power supply]
FIG. 2 is a time chart for explaining the operation of the circuit shown in FIG. FIG. 2A shows a voltage waveform after the voltage of the commercial power source 1 is rectified by the rectifying bridge diode 2. FIG. 2B shows the waveform of the voltage (smoothing voltage) of the capacitor 4, and the waveform after rectification of the commercial power supply 1 is indicated by a broken line. FIG. 2C shows the waveform of the voltage (smooth voltage) of the electrolytic capacitor 3, and shows the waveform after rectification of the commercial power supply 1 by a broken line. FIG. 2D shows the conductive or non-conductive state of the switch element 5, where the conductive state is on (ON) and the non-conductive state is off (OFF). FIG. 2E shows the waveform of the current flowing through the load 8 (current consumption by the load 8). In either case, the horizontal axis represents time.

  The operation will be described with reference to the time chart of FIG. Even in a period (OFF period) in which the operating current of the load 8 is very small and the switch element 5 is in a non-conductive state, ripples are generated in the voltage smoothed by the capacitor 4. As shown in FIG. 2 (b), the ripple voltage generated in the smoothing voltage of the capacitor 4 is within the specified range described above at a frequency twice that of the commercial power supply 1, and the ripple is not reduced more than necessary. . The reason for this is that the capacitance of the capacitor 4 is the same as that of the electrolytic capacitor 3, and the generation of ripple can be reduced by increasing the capacitance, but by reducing the capacitance within the allowable range of the ripple voltage, This is because space and cost can be reduced. Since the capacity of the capacitor 4 can be made smaller than that of the electrolytic capacitor 3, even if an electrolytic capacitor is used, the leakage current generated when the capacitor 4 is used as an electrolytic capacitor is the leakage current generated in the electrolytic capacitor 3. Can be reduced. For this reason, in the present embodiment, smoothing is performed by the capacitor 4 during the non-conducting period. Furthermore, even when a film capacitor or a ceramic capacitor is used as the capacitor 4, the leakage current can be further reduced without generating a large space and cost.

  As long as the low power consumption state is maintained for a long time, the voltage of the electrolytic capacitor 3 is discharged by a leak current and becomes a voltage close to 0V. When the arithmetic unit 7 such as a CPU receives an operation command (not shown) of the load 8, the arithmetic unit 7 brings the switch element 5 into a conductive state (ON state). At this time, the electric charge rapidly moves from the capacitor 4 to the electrolytic capacitor 3 which was a voltage close to 0 V, and the voltage of the capacitor 4 decreases only for a short time as shown in FIG. This is because when the commercial power source 1 is about 0 V, the voltage after rectification is low, so that neither the electrolytic capacitor 3 nor the capacitor 4 can be charged. Further, even when the switch element 5 becomes conductive at the timing of the maximum voltage of the commercial power supply 1, the capacitor 4 is rapidly charged to the electrolytic capacitor 3. This is because a noise filter (not shown) or an impedance due to a long pattern exists between the commercial power source 1 and the electrolytic capacitor 3. However, this time is short. Therefore, normal operation can be maintained even when the switching power supply is not IC controlled, for example, a ringing choke converter (RCC) type or the power supply is controlled by the IC. In this case, in order to maintain normal operation, the capacity of the electrolytic capacitors 3 and 4, the power supply system, the magnitude of the current of the load 8, the size of the secondary smoothing capacitor, the specifications of the IC, etc. Adjust the conditions.

  Once the capacitor 4 is rapidly charged to the electrolytic capacitor 3, the electrolytic capacitor 3 and the capacitor 4 are charged by the current supplied from the commercial power source 1. During this time, the total capacity of the two smoothing capacitors is a capacity capable of maintaining the specified ripple in the operating state, and the current of the load 8 is still small. For this reason, as shown in FIGS. 2B and 2C, the ripple voltage of the electrolytic capacitor 3 and the capacitor 4 becomes very small. After the switch element 5 is turned on, the operation of the load 8 is started after a certain time t1, which is the first time, which is sufficiently longer than the time required for completing the charging of the electrolytic capacitor 3. When current begins to flow through the load 8 as shown in FIG. 2 (e), the voltage smoothed by the electrolytic capacitor 3 and the capacitor 4 has an allowable range as shown in FIG. 2 (b) and FIG. 2 (c). The ripple in the inside occurs. Thus, the time t1 is set to a time sufficiently longer than the time necessary for charging the electrolytic capacitor 3. Thereby, it is possible to avoid the problem that the smoothing voltage of the capacitor 4 exceeds the allowable ripple voltage and decreases for a long time, and the operation of the switching power supply becomes unstable.

  When receiving the operation stop command (not shown) of the load 8, the arithmetic unit 7 stops the unit that was operating. Thereby, as shown in FIG.2 (e), the electric current which flows into the load 8 reduces. Then, after the fixed time t2, which is the second time, necessary for the operation of the apparatus to stop reliably and the load current to become equal to or less than a predetermined value and stabilize in the low power consumption state, the switch element 5 is brought into a non-conductive state. To. During the time t2, for the same reason as during the time t1, as shown in FIGS. 2B and 2C, the voltage ripple of the electrolytic capacitor 3 and the capacitor 4 becomes very small. When the switch element 5 is turned off, the electrolytic capacitor 3 is not charged, and as shown in FIG. 2 (c), it is discharged by a leak current and the voltage gradually decreases. The time t2 is set to a time sufficiently longer than the time necessary for the load 8 to be completely stopped and stabilized in a state where the load current is reduced. As a result, even though the load current has not decreased, the electrolytic capacitor 3 becomes non-conductive, the smoothing voltage of the capacitor 4 exceeds the allowable ripple voltage, and decreases for a long time, and the operation of the switching power supply is impaired. Problems such as stabilization can be avoided. Thus, by setting the time t1 and the time t2, it is possible to stabilize the operation of the switching power supply when switching the state of the apparatus.

  When switch unit 5 becomes non-conductive and the voltage of electrolytic capacitor 3 is decreasing, operation unit 7 makes switch element 5 conductive when it receives an operation command (not shown) for load 8 again. . Also in this case, as described above, the operation of the load 8 is started after time t1 after the switch element 5 is turned on. When the switch element 5 is in a conductive state, the voltage of the electrolytic capacitor 3 has not yet decreased to near 0V, but has reached a predetermined voltage. For this reason, the amount of charge transfer from the capacitor 4 to the electrolytic capacitor 3 is small. Therefore, the amount of voltage drop of the capacitor 4 is smaller as shown in FIG. 2B than when the electrolytic capacitor 3 is switched from 0V to the switch element 5 being conductive.

  Control is performed with the circuit configuration and timing as described above, and the capacitor to be smoothed is switched according to the operating state and low power consumption state of the apparatus. Specifically, smoothing is performed by the electrolytic capacitor 3 and the capacitor 4 in the operating state of the apparatus, and smoothing is performed only by the capacitor 4 in the low power consumption state. Thereby, the power consumption in the low power consumption state can be reduced while maintaining the stability of the operation of the switching power supply.

  As described above, according to the present embodiment, the power consumption of the smoothing means that smoothes the voltage obtained by rectifying the AC voltage can be reduced when the apparatus is in the low power consumption state.

[Switching power supply]
FIG. 3 shows an example of a circuit diagram of the switching power supply according to the second embodiment. The same reference numerals are given to the same components as those in the first embodiment, and the description thereof will be omitted. The switching power supply in the apparatus of the present embodiment includes a diode 9 in which the charging direction of the electrolytic capacitor 3 is a forward direction in parallel with the switch element 5 and a resistor 10 connected in series to the diode 9. That is, the cathode side of the diode 9 is connected to the plus side of the electrolytic capacitor 3, and the anode side of the diode 9 is connected to one end of the resistor 10. The other end of the resistor 10 is connected to the positive side of the voltage rectified by the rectifying bridge diode 2. The diode 9 has a sufficient withstand voltage against the smoothing voltage of the electrolytic capacitor 3, and the resistor 10 has a resistance value sufficiently larger than the internal impedance calculated from the leakage current of the electrolytic capacitor 3. Thereby, in a present Example, the leakage current of the electrolytic capacitor 3 can be restrict | limited.

[Operation of switching power supply]
4 is a time chart for explaining the operation of the circuit shown in FIG. 3. The waveforms shown in FIGS. 4 (a) to 4 (e) are the same as those shown in FIGS. 2 (a) to 2 (e) of the first embodiment. The waveform is the same as that shown in FIG.

  The operation will be described with reference to the time chart of FIG. When the switch element 5 is in a non-conductive state, the diode 9 passes a current limited by the resistor 10 only in the charging direction of the electrolytic capacitor 3 and does not supply power from the electrolytic capacitor 3 to the transformer 6. For this reason, the electric charge charged in the electrolytic capacitor 3 is not discharged, and as shown in FIG. 4C, the voltage of the electrolytic capacitor 3 is maintained even when the switch element 5 is in the non-conductive state. That is, in the graph of FIG. 2C, the switching element 5 is 0 V in the first off period, whereas in the graph of FIG. 4C, the switching element 5 is in the on period in the off period. The voltage is about the same as the voltage of. Therefore, as described in the first embodiment, the capacitor 4 is not charged to the electrolytic capacitor 3 immediately after the switch element 5 is turned on, and the voltage drop of the capacitor 4 does not occur or the voltage drop is very small. Can be suppressed. Therefore, the switching power supply can be stably operated regardless of the power supply method, the magnitude of the current of the load 8, the capacity of each capacitor, the specifications of the power supply IC, and the like.

[Setting of time t1 and time t2]
Here, depending on the device, there may be two or more states in each of the low power consumption state and the operating state, and the load current may be different among them. In such a case, the load current is Time to stabilize may vary. The time required for charging the electrolytic capacitor 3 becomes longer when the current flowing through the load 8 in the low power consumption state (hereinafter referred to as load current) is large. At this time, the calculation unit 7 sets the time t1 longer than when the load current is small, thereby shortening the waiting time until the operation of the load 8 is started after the switch element 5 is turned on. Can do. For example, as shown in FIG. 4E, when the load current is large, the time from when the switch element 5 is switched from the non-conductive state to the conductive state until the operation of the load 8 is started is time t1. On the other hand, as shown in FIG. 4E, when the load current is small, the time from when the switch element 5 is switched from the non-conductive state to the conductive state until the operation of the load 8 is started is time t3. Here, time t1> time t3 holds. That is, the time from when the switch element 5 is switched from the non-conductive state to the conductive state until the operation of the load 8 is started is set longer as the load current is larger.

  Further, when the load 8 that has been operating is surely stopped and a long time is required for the load current to decrease or when the load current is large, the time until the load 8 is stabilized in the low power consumption state becomes longer. At this time, the calculation unit 7 can shorten the waiting time to the minimum necessary by setting the time t2 longer than when the time for reducing the load current is short or when the load current is small. For example, as shown in FIG. 4E, when the load current is large, the time from the start of the operation of the load 8 until the switch element 5 is switched from the conductive state to the non-conductive state is time t2. On the other hand, as shown in FIG. 4E, when the load current is small, the time from the start of the operation of the load 8 until the switch element 5 is switched from the conductive state to the non-conductive state is time t4. Here, time t2> time t4 holds. That is, the time from the start of the operation of the load 8 until the switch element 5 is switched from the conductive state to the non-conductive state is set longer as the load current is larger. The configuration in which the time t1 or the time t2 is set longer as the load current is larger is also applicable to the configuration of the first embodiment.

  By controlling with the circuit configuration as described above, a more stable smoothing voltage can be obtained. Therefore, the switching power supply can be stably operated regardless of the power supply method and the load current. Further, the time t1 and the time t2 are determined based not only on the length of time required for charging the electrolytic capacitor 3 but also on the magnitude of the load current, thereby minimizing the waiting time during the state transition of the device. It can be shortened. In this embodiment, the diode 9 has been described as an example. However, it may be a rectifying element and is not limited to the diode.

  As described above, according to the present embodiment, the power consumption of the smoothing means that smoothes the voltage obtained by rectifying the AC voltage can be reduced when the apparatus is in the low power consumption state.

[Switching power supply]
FIG. 5 shows the switching power supply of Example 3 as an example of a quasi-resonant flyback power supply. In the present embodiment, a specific example of the transformer 6 described in the first embodiment and the second embodiment is shown. In addition, the same code | symbol is attached | subjected to the structure demonstrated in Example 1, 2, and description is abbreviate | omitted. In the switching power supply in the apparatus of the present embodiment, the commercial power supply 1 is connected to the rectifier bridge diode 2 via the noise filter 11. Here, the noise filter 11 is, for example, a line filter, an X capacitor, a Y capacitor, or the like. Further, in the present embodiment, as in the first embodiment, the electrolytic capacitor 3 and the switch element 5 are connected in series, and the capacitor 4 is provided in parallel with the switch element 5 and the electrolytic capacitor 3 connected in series. It is connected. As in the second embodiment, the diode 9 and the resistor 10 connected in series are connected in parallel to the switch element 5. In addition, you may apply a present Example to the structure of Example 1 without the diode 9 and the resistance 10. FIG.

  On the positive side of the voltage rectified by the rectifier bridge diode 2, a power supply IC 15, which is a power supply control means, is connected via the starting resistor 12. The power supply IC 15 activated by the current from the activation resistor 12 controls the field effect transistor (hereinafter referred to as FET) 16 to be in a conductive state or a non-conductive state, thereby turning on or off the current flowing through the primary winding 18 of the transformer. Control the switching operation. The energy stored in the transformer core by the switching operation of the primary winding 18 is transmitted to the secondary winding 20 of the transformer as a flyback voltage, and then rectified and smoothed by the secondary rectifier diode 24 and the secondary smoothing capacitor 25. Is done. The voltage rectified and smoothed on the secondary side is monitored by the error amplifier 23 and fed back to the power supply IC 15 via the photocoupler 22. In addition, the arithmetic unit 7 controls the switch element 5 to be in a conductive state or a non-conductive state via the photocoupler 21.

  The power supply IC 15 stabilizes the output voltage on the secondary side in accordance with the feedback voltage input through the photocoupler 22 and the switching timing of the primary winding 18 of the transformer obtained by the auxiliary winding 19 of the transformer. The switching operation of the FET 16 is controlled. During the switching operation, high-frequency noise is generated in the primary winding 18 or the FET 16 of the transformer and flows out to the commercial power supply 1 through the rectifier bridge diode 2 and the noise filter 11, which may increase terminal noise and radiation noise. . In particular, since the switching current is large when the current of the load 8 is large, the level of generated noise tends to increase because the ringing of the switching voltage increases.

  On the other hand, since the electrolytic capacitor 3 has low response sensitivity to high frequencies, the ability to reduce high frequency noise is low. Therefore, the noise level can be reduced by using a ceramic capacitor or a film capacitor for the capacitor 4 having high response sensitivity to high frequencies. Furthermore, the wiring length from the primary winding 18 of the transformer to the capacitor 4 is shorter than the wiring length to the switch element 5, and the wiring length from the current detection resistor 17 connected in series to the FET 16 to the capacitor 4 is The wiring length to the electrolytic capacitor 3 can be made shorter. That is, the electrolytic capacitor 3 has a larger capacity than the capacitor 4 and must be provided far from the transformer, whereas the capacitor 4 has a smaller capacity than the electrolytic capacitor 3 and is provided at a position close to the transformer. Is possible. This prevents noise from being amplified due to high-frequency noise flowing through a smaller closed path, that is, a loop formed by the capacitor 4, the transformer primary winding 18, the FET 16 and the current detection resistor 17, and is commercially available. Noise flowing out to the power source 1 can be reduced.

  Further, an inductor such as a winding coil or a ferrite bead is connected in series to at least one of the positive voltage side wiring 13 and the negative voltage side wiring 14 between the electrolytic capacitor 3 and the capacitor 4. As a result, noise outflow to the commercial power supply 1 is limited, and more noise flows and is absorbed in the closed path (the loop described above) formed by the capacitor 4, thereby enabling reduction of the noise level.

  As described above, this embodiment includes the capacitor 4 that is a ceramic capacitor or a film capacitor in order to smooth the commercial power source 1 in a low power consumption state. Further, the capacitor 4 is provided in the vicinity of the primary winding 18 and the FET 16 where switching noise is generated. Further, the closed path formed by the capacitor 4, the primary winding 18, and the FET 16 is reduced. In this embodiment, by providing at least one of these configurations, the generated high frequency noise is prevented from being amplified. Furthermore, in the present embodiment, by adding an inductor upstream of the capacitor 4, it is possible to reduce the noise level of the power supply apparatus by further suppressing noise from flowing out to the commercial power source 1. Thus, in this embodiment, the capacitor 4 that smoothes the rectified voltage when the apparatus is in a low power consumption state also functions as a measure against noise.

  As described above, according to the present embodiment, the power consumption of the smoothing means that smoothes the voltage obtained by rectifying the AC voltage can be reduced when the apparatus is in the low power consumption state.

  As described above, the power supply apparatus described in the first to third embodiments can be applied as, for example, a low-voltage power supply for an image forming apparatus, that is, a power supply that supplies power to a drive unit such as a controller (control unit) or a motor. The calculation part 7 of Examples 1-3 corresponds to a controller, and the load 8 corresponds to a drive part such as a motor. In the case where the power supply device includes a calculation unit 7 such as a CPU, the controller of the image forming apparatus is included in the load 8. Further, in the case of a configuration further including a converter or the like after the transformer unit 6 of the first to third embodiments, the converter is also included in the load 8, and when the image forming apparatus includes various sensors or the like, Sensors and the like are also included in the load 8. The normal state in the first to third embodiments corresponds to, for example, a printing mode of the image forming apparatus, and the low power consumption state corresponds to, for example, a power saving mode of the image forming apparatus. Hereinafter, the configuration of the image forming apparatus to which the power supply devices of Embodiments 1 to 3 are applied will be described.

[Configuration of Image Forming Apparatus]
A laser beam printer will be described as an example of the image forming apparatus. FIG. 6 shows a schematic configuration of a laser beam printer which is an example of an electrophotographic printer. The laser beam printer 300 includes a photosensitive drum 311 as an image carrier on which an electrostatic latent image is formed, a charging unit 317 (charging unit) that uniformly charges the photosensitive drum 311, and an electrostatic latent image formed on the photosensitive drum 311. A developing unit 312 (developing unit) that develops an image with toner is provided. The toner image developed on the photosensitive drum 311 is transferred to a sheet (not shown) as a recording material supplied from the cassette 316 by a transfer unit 318 (transfer means), and the toner image transferred to the sheet is fixed to the fixing device 314. Then, the toner is fixed and discharged onto the tray 315. The photosensitive drum 311, the charging unit 317, the developing unit 312, and the transfer unit 318 are image forming units. The laser beam printer 300 includes the power supply device 400 described in the first to third embodiments. Note that the image forming apparatus to which the power supply device 400 according to the first to third embodiments can be applied is not limited to that illustrated in FIG. 6, and may be an image forming apparatus including a plurality of image forming units, for example. Further, the image forming apparatus may include a primary transfer unit that transfers the toner image on the photosensitive drum 311 to the intermediate transfer belt and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to the sheet.

  The laser beam printer 300 includes a controller (not shown) that controls an image forming operation by the image forming unit and a sheet conveying operation. The power supply device 400 according to the first to third embodiments supplies power to the controller, for example. To do. The power supply device 400 described in the first to third embodiments supplies power to a driving unit such as a motor for rotating the photosensitive drum 311 or driving various rollers for conveying the sheet. That is, the calculation part 7 of Examples 1-3 corresponds to a controller, and the load 8 corresponds to a drive part. When the image forming apparatus according to the present exemplary embodiment is in a standby state (for example, a power saving mode or a standby mode) that realizes power saving, the switch element 5 can be turned off to reduce power consumption. In addition, the image forming apparatus according to the present exemplary embodiment can stabilize the operation of the switching power supply when switching between the printing mode and the power saving mode by providing the time t1 and the time t2. Further, in the image forming apparatus including the power supply device according to the third embodiment, noise can be reduced by the capacitor 4.

  As described above, according to this embodiment, when the image forming apparatus is in a low power consumption state, it is possible to reduce the power consumption of the smoothing unit that smoothes the voltage obtained by rectifying the AC voltage.

2 Rectifier diode bridge 3 Electrolytic capacitor 4 Capacitor 5 Switching element 6 Transformer 7 Computing unit

Claims (12)

Rectifying means for rectifying the AC voltage;
First smoothing means for smoothing the voltage rectified by the rectifying means;
Transforming means for transforming the voltage smoothed by the first smoothing means;
A power supply device for supplying a voltage transformed by the transformer means to a load,
Switch means connected in series to the first smoothing means;
A second smoothing means connected in parallel to the first smoothing means and the switch means connected in series and having a smaller capacity than the first smoothing means;
The switch means is turned on when the load is in a first state consuming predetermined power, and the switch means is turned on when the load is in a second state consuming lower power than the first state. Control means for non-conducting state;
Equipped with a,
When the control means transitions from the second state to the first state, the control means starts the operation of the load after a first time has elapsed since the switch means was switched from the non-conductive state to the conductive state. A power supply device characterized by that . A resistor having one end connected to the positive side of the voltage rectified by the rectifier;
A rectifying element having an anode connected to the other end of the resistor and a cathode connected to the first smoothing means;
With
The power supply apparatus according to claim 1, wherein the resistor and the rectifying element connected in series are connected in parallel to the switch unit. Before SL is the first time, the power supply device according to claim 1 or 2, wherein the first smoothing means and said Rukoto be determined based on the time to be charged.   The power supply apparatus according to claim 3, wherein the control unit increases the first time as the current flowing through the load increases. When the control means transitions from the first state to the second state, the switch means is switched from the conductive state to the non-conductive state after a second time has elapsed since the operation of the load was stopped. the power supply device according to any one of claims 1 to 4, characterized and Turkey. The power supply device according to claim 5, wherein the second time is determined based on a time when a current flowing through the load becomes a predetermined value or less. The power supply device according to claim 6 , wherein the control unit lengthens the second time as the current flowing through the load increases. The power supply device according to any one of claims 1 to 7 , wherein the first smoothing means is an electrolytic capacitor. Said second smoothing means, the power supply device according to any one of claims 1 to 8, characterized in that a ceramic capacitor or a film capacitor. The transformer means is
A transformer having a primary winding, a secondary winding and an auxiliary winding;
A switching element connected in series to the primary winding of the transformer;
A current detection resistor for detecting a current flowing in the primary winding of the transformer;
Power control means for controlling the switching element to a conductive state or a non-conductive state;
Have
The length of the path formed by the second smoothing means, the primary winding of the transformer, the switching element and the current detection resistor is the first smoothing means, the switch means, the primary winding of the transformer, the power supply device according to any one of claims 1 to 9, wherein the shorter than the length of the switching element and the current detecting resistor by paths formed. The positive side of the voltage rectified by the rectifying means, between the switch means and the second smoothing means, and the negative side of the voltage rectified by the rectifying means, the first side The power supply device according to claim 10 , wherein an inductor is connected to at least one of the smoothing unit and the second smoothing unit. Image forming means for forming an image on a recording material;
The power supply device according to any one of claims 1 to 11 ,
An image forming apparatus comprising:

Images