Power supply device, image forming apparatus, and image forming

Abstract

To reduce the size and cost of a circuit by reducing noise transmitted from a full-bridge switching power supply to a power source.SOLUTION: In the full-bridge switching power supply 100 including the switching elements Q101 to Q104, when the combined capacitance of the capacitance between the drain terminals and the source terminals of the switching elements Q101 to Q104 and the capacitance of the capacitors C101 to C104 is defined as the capacitance CQ101 to CQ104, at least one of the capacitances CQ101 to is different from the other capacitances. CQ104.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power supply device, an image forming apparatus, and an apparatus, and more particularly to reducing noise in a full-bridge switching power supply, for example. [Background technology]

[0002] A switching power supply that supplies power to a load by switching a rectified and smoothed AC or DC power supply may use a full-bridge switching power supply that uses multiple switching elements to achieve highly efficient power conversion. In a full-bridge switching power supply, a capacitor is provided in parallel with each switching element to reduce power loss when each switching element is turned off, thereby achieving highly efficient operation. Furthermore, a method has been proposed in which the inter-terminal capacitance of the switching elements that make up the active leg is made larger than the inter-terminal capacitance of the switching elements that make up the passive leg in order to achieve highly efficient operation over a wide load range (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6293242 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when each switching element in a full-bridge switching power supply turns off, the capacitance and inductance of the load, electronic components, and patterns resonate with the terminal capacitance of each switching element, causing voltage ringing. This voltage ringing propagates to the power source and becomes noise, which can affect other electronic devices connected to the same power source. Therefore, it is necessary to install a filter element between the full-bridge switching power supply and the AC power supply to reduce noise, which leads to issues such as larger circuit size and higher cost.

[0005] The present invention has been made under these circumstances, and is capable of reducing noise transmitted from a full-bridge switching power supply to a power source, thereby realizing a smaller circuit and lower costs. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) A full-bridge power supply device including: a rectifier circuit that rectifies an AC voltage of an AC power supply; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series to the first switching element; a third switching element; a fourth switching element connected in series to the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; and a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element, wherein the first switching element and the second switching element connected in series are connected in parallel to the smoothing capacitor, and the third switching element and the fourth switching element connected in series are connected in parallel to the smoothing capacitor, a first capacitor connected in parallel to a switching element, a second capacitor connected in parallel to the second switching element, a third capacitor connected in parallel to the third switching element, and a fourth capacitor connected in parallel to the fourth switching element, wherein a first capacitance is a combined capacitance of a capacitance between a drain terminal and a source terminal of the first switching element and a capacitance of the first capacitor, a second capacitance is a combined capacitance of a capacitance between a drain terminal and a source terminal of the second switching element and a capacitance of the second capacitor, a third capacitance is a combined capacitance of a capacitance between a drain terminal and a source terminal of the third switching element and a capacitance of the third capacitor, and a fourth capacitance is a combined capacitance of a capacitance between a drain terminal and a source terminal of the fourth switching element and a capacitance of the fourth capacitor,

[0008] (2) A power supply comprising: a rectifier circuit that rectifies an AC voltage of an AC power source; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series to the first switching element; a third switching element; a fourth switching element connected in series to the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; and a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element, a first capacitance between the drain terminal and the source terminal of the second switching element, a third capacitance between the drain terminal and the source terminal of the third switching element, a third capacitance between the drain terminal and the source terminal of the third switching element, and a fourth capacitance between the drain terminal and the source terminal of the fourth switching element, wherein at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance has a different value from the other capacitances.

[0009] (3) An image forming apparatus for forming an image on a recording material, characterized in that it comprises the power supply device according to (1) or (2).

[0010] (4) A device that consumes power, characterized by comprising the power supply device described in (1) or (2). [Effects of the Invention]

[0011] According to the present invention, it is possible to reduce noise transmitted from a full-bridge switching power supply to a power source, thereby realizing a smaller circuit and lower costs. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagram of switching power supplies according to Examples 1 to 3 [Figure 2] Schematic diagram of the operating waveforms of the switching power supply of Example 1 [Figure 3] Schematic diagram of an image forming apparatus according to a third embodiment DETAILED DESCRIPTION OF THE INVENTION [Example]

[0013] [Switching power supply] FIG. 1 is a diagram showing a switching power supply as a power supply device according to a first embodiment. The switching power supply 100 of the first embodiment is a full-bridge switching power supply that supplies AC power of any frequency to an insulated object to be heated S1. The switching power supply 100 is characterized in that the capacitance between the terminals of each switching element is a different value for each switching element. The circuit configuration of the switching power supply 100 will be explained below, followed by an explanation of voltage ringing that occurs when a switching element is turned off. Note that a primary inductor P1 is located on the primary side of the insulated object to be heated S1, and the primary inductor P1 and the object to be heated S1 together form a load 120.

[0014] The switching power supply 100 has a rectifier unit DA1, a smoothing capacitor C100, switching elements Q101, Q102, Q103, and Q104, capacitors C101, C102, C103, and C104, and a control unit 110. More specifically, the switching power supply 100 has a first switching element Q101, a second switching element Q102, a third switching element Q103, and a fourth switching element Q104. The first to fourth switching elements Q101 to Q104 are, for example, field effect transistors (hereinafter referred to as FETs).

[0015] A first capacitor C101 is connected in parallel to the first switching element Q101; that is, the first capacitor C101 is connected between the drain and source terminals of the first switching element Q101. A second capacitor C102 is connected in parallel to the second switching element Q102; that is, the second capacitor C102 is connected between the drain and source terminals of the second switching element Q102. A third capacitor C103 is connected in parallel to the third switching element Q103; that is, the third capacitor C103 is connected between the drain and source terminals of the third switching element Q103. A fourth capacitor C104 is connected in parallel to the fourth switching element Q104; that is, the fourth capacitor C104 is connected between the drain and source terminals of the fourth switching element Q104. Note that in the following explanation, the terms "first" to "fourth" may be omitted.

[0016] Furthermore, switching element Q101 and switching element Q102 are connected in series, and switching element Q103 and switching element Q104 are connected in series. The junction of switching element Q101 and switching element Q102 is connected to one end of a primary inductor P1 (inductor element), and the junction of switching element Q103 and switching element Q104 is connected to the other end of the primary inductor P1. The series-connected switching element Q101 and switching element Q102 are connected in parallel to a smoothing capacitor C100 that serves as a DC voltage source. The series-connected switching element Q103 and switching element Q104 are also connected in parallel to the smoothing capacitor C100.

[0017] Switching power supply 100 supplies power to primary inductor P1 of load 120 by switching operation of switching elements Q101 to Q104. This allows switching power supply 100 to heat insulated object to be heated S1 using AC power from AC power supply 10. Switching power supply 100 adjusts the power supplied to load 120 so that the temperature of object to be heated S1 (object to be controlled) remains constant. Note that the temperature of object to be heated S1 is detected by temperature detection means such as a thermistor, and the detection result is input to control unit 110 as a signal such as a voltage, and control unit 110 controls the power supplied to load 120 based on the input detection result.

[0018] Although the switching power supply 100 is used as an AC-AC inverter in the first embodiment, it may be used as a switching power supply other than an AC-AC inverter. For example, it may be used as an AC-DC converter by replacing the heated object S1 with a diode and a capacitor and changing the controlled object to an output voltage. Furthermore, it may be used as a DC-AC inverter or a DC-DC converter by removing the rectifier unit DA1 and using a DC power supply instead of the AC power supply 10 as a power source.

[0019] Rectifier unit DA1, which serves as a rectifier circuit, is a diode bridge composed of four diodes, and outputs a voltage obtained by full-wave rectifying the AC voltage of AC power supply 10 to smoothing capacitor C100. Although rectifier unit DA1 is a diode bridge in the first embodiment, a circuit that performs a similar function, such as a power factor compensation (PFC) circuit using switching elements such as FETs, may also be used. Smoothing capacitor C100 is provided to smooth the output of rectifier unit DA1 or to prevent current generated by the switching operations of switching elements Q101 to Q104 from flowing into AC power supply 10 and rectifier unit DA1.

[0020] Switching elements Q101, Q102, Q103, and Q104 are FETs and form a full-bridge circuit. Control signals transmitted from control unit 110 are input to the gate terminals of switching elements Q101, Q102, Q103, and Q104. As a result, switching elements Q101 to Q104 are turned on or off by control unit 110, and power of a desired frequency is supplied to load 120 through phase shift control. Switching elements Q101 and Q102 are controlled to turn on or off complementarily with a dead time between them, and the on and off times of both switching elements Q101 and Q102 are controlled so that they are identical. Similarly, switching elements Q103 and Q104 are controlled to turn on or off complementarily with a dead time between them, and the on and off times of both switching elements Q103 and Q104 are controlled so that they are identical.

[0021] Furthermore, the on-time and off-time of switching elements Q101 to Q104 are the same, and the length of dead time is the same. While FETs are used for switching elements Q101 to Q104 in the first embodiment, insulated gate bipolar transistors (hereinafter referred to as IGBTs) may be used instead, with reverse diodes connected in parallel. Unlike FETs, IGBTs do not have parasitic diodes, so an external reverse diode must be connected. In this case, the anode terminal of the reverse diode is connected to the emitter terminal of the IGBT, and the cathode terminal of the reverse diode is connected to the collector terminal of the IGBT.

[0022] In the first embodiment, switching elements Q101 to Q104 are all of the same type, and all have the same drain-to-source capacitance. However, switching elements Q101 to Q104 may each be of a different type, with different drain-to-source capacitances. The effect of using different types of switching elements with different drain-to-source capacitances will be explained later.

[0023] Capacitors C101, C102, C103, and C104 are ceramic capacitors, film capacitors, or other capacitors with small capacitance changes due to frequency changes. Capacitors C101, C102, C103, and C104 are connected between the drain and source terminals of switching elements Q101, Q102, Q103, and Q104, respectively. Connecting capacitors C101 through C104 increases the capacitance between the drain and source terminals of each switching element. This reduces the increase in drain-source voltage when each switching element is turned off, thereby reducing power loss during turn-off. Furthermore, connecting capacitors C101 through C104 changes the frequency of voltage ringing that occurs when each switching element is turned off. In Example 1, capacitors C101 through C104 each have a different capacitance, and the frequency of voltage ringing during turn-off also varies for each switching element. The relationship between the voltage ringing when switching elements Q101 to Q104 are turned off and the capacitances of capacitors C101 to C104 will be described in detail with reference to FIG.

[0024] (About capacitance) The capacitance between the drain and source terminals of switching element Q101 is defined as follows. Switching element Q101 itself has a capacitance between its drain and source terminals. Here, as shown in FIG. 1, there are two cases: one where capacitor C101 is connected in parallel to switching element Q101, and one where no capacitor is connected to switching element Q101. If capacitor C101 is connected, the capacitance between the drain and source terminals is the combined capacitance of the capacitance of switching element Q101 itself and the capacitance of capacitor C101 (hereinafter referred to as combined capacitance). On the other hand, if capacitor C101 is not connected, the capacitance between the drain and source terminals is only the capacitance of switching element Q101 itself. The same applies to switching elements Q102 to Q104 and capacitors C102 to C104.

[0025] The capacitance between the drain terminal and source terminal of switching element Q101 is defined as CQ101, which is a first capacitance. If capacitor C101 is connected, capacitance CQ101 is a value obtained by combining the capacitance of switching element Q101 itself and the capacitance of capacitor C101. If capacitor C101 is not connected, capacitance CQ101 is the capacitance of switching element Q101 itself. Hereinafter, the capacitance between the drain terminal and source terminal of switching elements Q102 to Q104 will be similarly defined as CQ102, CQ103, and CQ104, which are a second capacitance, a third capacitance, and a fourth capacitance, respectively.

[0026] In the first embodiment shown in Fig. 1, as described above, the capacitances between the drain terminals and source terminals of switching elements Q101-Q104 themselves are approximately the same. Therefore, the magnitude relationship between capacitances CQ101-CQ104 depends on the magnitude relationship between capacitances C101-C104. Here, "approximately the same" includes cases where they are completely the same and cases where they differ within an allowable range that includes errors caused by variations in the manufacturing process of switching elements of the same production type.

[0027] If the capacitances CQ101 to CQ104 are all set to the same value, the frequency of the voltage ringing that occurs when each switching element is turned off will be approximately the same for all switching elements. In this case, in a spectrum with frequency on the horizontal axis and noise intensity on the vertical axis, the intensity will be maximized at one frequency.

[0028] In contrast, in Example 1, the capacitance value of at least one of the capacitances CQ101, CQ102, CQ103, and CQ104 is set to be different from the other capacitances. For example, in Example 1, the capacitances of the four capacitors C101 to C104 are all set to different values, thereby dispersing the frequency of the generated voltage ringing and creating four maximum values ​​in the spectrum. This allows the peak value of each maximum value to be lower than when there is only one maximum value.

[0029] In this way, the capacitances of the capacitors C101 to C104 may all be set to different values. There are no particular restrictions on the order of magnitude of these four capacitance values. For example, in the first embodiment, the capacitances of the capacitors C101 to C104 are set to satisfy the relationship of the following formula (1). C103>C101>C102>C104 (1)

[0030] This relationship was established with a focus on the amplitude of the voltage ringing that occurs when each switching element is turned off in a circuit that generates voltage ringing, as shown in Figure 2 below. The amplitude of the voltage ringing depends on various factors and differs depending on the circuit configuration, but the larger the amplitude, the more effective it is at dispersing the frequency by setting a larger value for the capacitance between the drain and source terminals of the switching element.

[0031] Alternatively, instead of connecting capacitors in parallel with the switching elements, the capacitances between the drain and source terminals of the four switching elements themselves may all be different values, thereby varying the frequencies of the generated voltage ringing. Alternatively, the capacitances between the drain and source terminals of the four switching elements themselves may all be different values, and capacitors may be connected in parallel with each switching element to make the capacitances CQ101 to CQ104 all different. In this case, there are no particular restrictions on the order of magnitude of the capacitances CQ101 to CQ104. For example, the order of magnitude may be set to the same as in equation (1) above (CQ103 > CQ101 > CQ102 > CQ104).

[0032] Control unit 110 is a circuit that controls the switching state of switching elements Q101 to Q104. Control unit 110 controls the frequency (switching frequency) and phase shift of switching elements Q101 to Q104 based on the temperature of heated body S1. Control unit 110 controls the output power by phase shift control, which shifts the on / off phase of switching elements Q101 and Q102 and the on / off phase of switching elements Q103 and Q104. Note that switching element Q102 is off while switching element Q101 is on, and switching element Q104 is off while switching element Q103 is on.

[0033] When the phase shift amount is 0 rad (radians), switching element Q101 and switching element Q103 are turned on and off simultaneously, and switching element Q102 and switching element Q104 are turned on and off simultaneously. When the phase shift amount is 0 rad, switching element Q101 and switching element Q104, and switching element Q102 and switching element Q103 are not turned on simultaneously, so no current flows to load 120 and the output power of switching power supply 100 is 0W.

[0034] As the phase shift amount increases from 0 rad, the period during which switching element Q101 and switching element Q104 are simultaneously on, and the period during which switching element Q102 and switching element Q103 are simultaneously on, both increase (lengthen). As a result, the output power of switching power supply 100 also increases. The output power of switching power supply 100 is maximum when the phase shift amount is π rad. As an example, the maximum output power of switching power supply 100 in Example 1 is 1000 W or more.

[0035] Load 120 is composed of primary inductor P1 and a heated object S1 on the secondary side. Primary inductor P1 and heated object S1 on the secondary side are magnetically coupled, and power is supplied to heated object S1 from switching element Q101 via primary inductor P1 by the switching operation of switching element Q104. When power is supplied from primary inductor P1, current flows to heated object S1, and object S1 is heated by Joule heat due to the electrical resistance of the heated object S1 itself. Note that although Example 1 uses load 120 separated into a primary side and a secondary side, a configuration equivalent to reinforced insulation or double insulation required by safety standards may not be required between primary inductor P1 and heated object S1 depending on the safety design of the device in which switching power supply 100 is used.

[0036] [Voltage and current during switching operation] Next, we will explain the voltage and current when switching elements Q101 to Q104 are switching, using Figure 2. In Figure 2, the horizontal axis represents time, and the gate-to-source voltage of each of switching elements Q101, Q102, Q103, and Q104 is shown by a dashed line, and the drain-to-source voltage is shown by a solid line.

[0037] 2, control unit 110 controls the switching operation of switching elements Q101 to Q104 at a frequency of 50 kHz, a phase shift of 0.75πrad, and a dead time of 600 ns. Each switching element turns on when the voltage between its gate terminal and source terminal reaches an H (high) level (20 V) and turns off when it reaches an L (low) level (0 V). One cycle of operation of switching power supply 100 can be divided into periods 1 to 8, with the times at which each switching element turns on or off as boundaries. Below, the drain-source voltage of each switching element and the current flowing through each element of switching power supply 100 will be described in chronological order, starting with period 1.

[0038] (Period 1) Period 1 is the period when switching element Q101 and switching element Q104 are simultaneously on. During period 1, the drain-to-source voltages of switching element Q101 and switching element Q104 are approximately 0 V. As a result, current flows through the path of smoothing capacitor C100, switching element Q104, primary inductor P1, and switching element Q101.

[0039] (Period 2) In period 2, switching element Q104 is turned off, and only switching element Q101 is on. During period 2, the voltage between the drain and source terminals of switching element Q101 remains at approximately 0V. Meanwhile, due to the energy stored in primary inductor P1 during period 1, current flows through the path of primary inductor P1, switching element Q101, smoothing capacitor C100, and capacitor C104. This charges capacitor C104, and the voltage between the drain and source terminals of switching element Q104 gradually increases.

[0040] Furthermore, when switching element Q104 turns off, current also flows through capacitor C103, primary inductor P1, and switching element Q101. This causes capacitor C103 to discharge, gradually reducing the drain-source voltage of switching element Q103. When the drain-source voltage reduces to the voltage at which the body diode of switching element Q103 becomes conductive, current flows through primary inductor P1, switching element Q101, and the body diode of switching element Q103.

[0041] Resonance occurs when the drain-source voltage of switching element Q104 becomes approximately equal to the voltage (approximately 140 V) of smoothing capacitor C100. Specifically, resonance occurs due to the capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C102, switching element Q102, capacitor C104, switching element Q104, primary inductor P1, and patterns. This resonance causes the drain-source voltages of switching element Q102 and switching element Q104 to oscillate at a frequency dependent on capacitor C102 and capacitor C104, centered on the voltage of smoothing capacitor C100. In other words, when switching element Q104 is turned off, voltage ringing occurs between the drain and source terminals of switching element Q102 and switching element Q104.

[0042] (Period 3) During period 3, switching element Q103 is turned on, and switching element Q101 and switching element Q103 are on simultaneously. During period 3, the drain-to-source voltages of switching element Q101 and switching element Q103 are approximately 0 V. Also, due to the energy stored in primary inductor P1 during period 1, a current flows through the path of primary inductor P1, switching element Q101, and switching element Q103. Note that the drain-to-source voltages of switching element Q102 and switching element Q104 continue to oscillate during period 3, but the amplitude gradually decreases due to the resistance component of the resonance.

[0043] (Period 4) Period 4 is the period when switching element Q101 is turned off and only switching element Q103 is on. During period 4, the voltage between the drain and source terminals of switching element Q103 remains at approximately 0V. Meanwhile, due to the energy stored in primary inductor P1 during period 1, current flows through the path of primary inductor P1, capacitor C101, and switching element Q103. This charges capacitor C101, and the voltage between the drain and source terminals of switching element Q101 gradually increases.

[0044] As the drain-source voltage of switching element Q101 increases, the drain-source voltage of switching element Q102 decreases until it reaches a voltage at which the body diode of switching element Q102 becomes conductive. Capacitor C102 then discharges. Current then flows through the primary inductor P1, the body diode of switching element Q102, smoothing capacitor C100, and switching element Q103. When the drain-source voltage of switching element Q101 becomes roughly equal to the voltage of smoothing capacitor C100, resonance occurs. Specifically, resonance occurs due to the capacitance, inductance, and resistance of smoothing capacitor C100, capacitor C101, switching element Q101, capacitor C104, switching element Q104, primary inductor P1, and patterns. This resonance causes the drain-to-source voltages of switching element Q101 and switching element Q104 to oscillate around the voltage of smoothing capacitor C100 at a frequency that depends on capacitors C101 and C104. In other words, when switching element Q101 is turned off, voltage ringing occurs between the drain and source terminals of switching element Q101 and switching element Q104.

[0045] (Period 5) During period 5, switching element Q102 is turned on, and switching elements Q102 and Q103 are on simultaneously. During period 5, the drain-to-source voltages of switching elements Q102 and Q103 are approximately 0 V, and current flows through the path of primary inductor P1, switching element Q102, smoothing capacitor C100, and switching element Q103. During period 5, resonance between primary inductor P1 and smoothing capacitor C100 reverses the direction of the current, and current now flows through smoothing capacitor C100, switching element Q102, primary inductor P1, and switching element Q103. Note that the drain-to-source voltages of switching elements Q101 and Q104 continue to oscillate during period 5, but the amplitude gradually decreases due to the resistance component of the resonance.

[0046] (Period 6) Period 6 is the period when switching element Q103 is turned off and only switching element Q102 is on. During period 6, the voltage between the drain and source terminals of switching element Q102 remains at approximately 0V. Meanwhile, due to the energy stored in primary inductor P1 during period 5, current flows through the path of primary inductor P1, capacitor C103, smoothing capacitor C100, and switching element Q102. This charges capacitor C103, and the voltage between the drain and source terminals of switching element Q103 gradually increases.

[0047] As the drain-source voltage of switching element Q103 increases, the drain-source voltage of switching element Q104 decreases. Note that capacitor C104 is discharged. When the drain-source voltage decreases to a level at which the body diode of switching element Q104 conducts, current flows through primary inductor P1, the body diode of switching element Q104, and switching element Q102. When the drain-source voltage of switching element Q103 becomes roughly equal to the voltage of smoothing capacitor C100, resonance occurs. Specifically, resonance occurs due to the capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C101, switching element Q101, capacitor C103, switching element Q103, primary inductor P1, and patterns. This resonance causes the drain-to-source voltages of switching element Q101 and switching element Q103 to oscillate around the voltage of smoothing capacitor C100 at a frequency that depends on capacitors C101 and C103. In other words, when switching element Q103 is turned off, voltage ringing occurs between the drain and source terminals of switching element Q101 and switching element Q103.

[0048] (period 7) During period 7, switching element Q104 is turned on, and switching element Q102 and switching element Q104 are on simultaneously. During period 7, the drain-to-source voltages of switching element Q102 and switching element Q104 are approximately 0 V. Also, due to the energy stored in primary inductor P1 during period 5, a current flows through the path of primary inductor P1, switching element Q104, and switching element Q102. Note that the drain-to-source voltages of switching element Q101 and switching element Q103 continue to oscillate during period 7, but the amplitude gradually decreases due to the resistance component of the resonance.

[0049] (period 8) Period 8 is the period when switching element Q102 is turned off and only switching element Q104 is on. During period 8, the drain-to-source voltage of switching element Q104 remains at approximately 0V. Meanwhile, due to the energy stored in primary inductor P1 during period 5, current flows through the path of primary inductor P1, switching element Q104, and capacitor C102. This charges capacitor C102, and the drain-to-source voltage of switching element Q102 gradually increases. Furthermore, when switching element Q102 is turned off, current also flows through the path of capacitor C101, primary inductor P1, switching element Q104, and smoothing capacitor C100. This gradually reduces the drain-to-source voltage of switching element Q101. Capacitor C101 is discharged.

[0050] When the drain-source voltage of switching element Q101 drops to a voltage at which the body diode of switching element Q101 becomes conductive, current flows through the following path: primary inductor P1, switching element Q104, smoothing capacitor C100, and the body diode of switching element Q101. When the drain-source voltage of switching element Q102 becomes approximately equal to the voltage of smoothing capacitor C100, resonance occurs. Specifically, resonance occurs due to the capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C102, switching element Q102, capacitor C103, switching element Q103, primary inductor P1, and patterns. This resonance causes the drain-source voltages of switching element Q102 and switching element Q103 to oscillate around the voltage of smoothing capacitor C100 at a frequency dependent on capacitor C102 and capacitor C103. That is, when switching element Q102 is turned off, voltage ringing occurs between the drain terminal and source terminal of switching element Q102 and switching element Q103. After the end of period 8, switching element Q101 turns on, returning to period 1.

[0051] As described above, the frequency of the voltage ringing that occurs when each switching element is turned off is determined by the capacitance of the corresponding capacitor. Table 1 shows the voltage ringing and its corresponding capacitor. For example, if the switching element that is turned off is switching element Q101, the capacitances that affect the frequency of the voltage ringing that occurs are the capacitances of capacitors C101 and C104.

[0052] [Table 1]

[0053] In FIG. 2, the voltage ringings generated by the turn-off of each switching element are labeled α1 through α8. The α1 oscillation is caused by the turn-off of switching element Q104, and according to Table 1, its frequency depends on the capacitances of capacitors C102 and C104 (period 2). The α2 oscillation is also caused by the turn-off of switching element Q104, and therefore its frequency is the same as the α1 oscillation (period 2). The α3 oscillation is caused by the turn-off of switching element Q101, and according to Table 1, its frequency depends on the capacitances of capacitors C101 and C104 (period 4). The α4 oscillation is also caused by the turn-off of switching element Q101, and therefore its frequency is the same as the α3 oscillation (period 4). The α5 oscillation is caused by the turn-off of switching element Q103, and according to Table 1, its frequency depends on the capacitances of capacitors C101 and C103 (period 6). The oscillation of α6 is also caused by the turning off of switching element Q103, so its frequency is the same as that of α5 (period 6). The oscillation of α7 is caused by the turning off of switching element Q102, and according to Table 1, its frequency depends on the capacitance of capacitors C102 and C103 (period 8). The oscillation of α8 is also caused by the turning off of switching element Q102, so its frequency is the same as that of α7 (period 8).

[0054] [Reason for different capacitance] Next, the reason why capacitors C101 to C104 have different capacitances will be explained. The reason why capacitors C101 to C104, which are connected in parallel to switching elements Q101 to Q104 in switching power supply 100, have different capacitances is to reduce noise propagating to AC power supply 10 and to achieve smaller and less expensive circuits.

[0055] 2, in the full-bridge switching power supply 100, when a switching element is turned off, voltage ringing occurs between the terminals of the switching element. If this voltage ringing propagates to the AC power supply 10 through parasitic components in the rectifier section or stray capacitance between patterns, it may cause noise and affect devices connected to the same AC power supply 10. For this reason, the voltage ringing that occurs when the switching element is turned off needs to be reduced as much as possible before it propagates to the AC power supply 10.

[0056] A common method for reducing noise propagating from the switching power supply 100 to the AC power supply 10 is to provide a filter element, such as a choke coil or an across-the-line capacitor, between the AC power supply 100 and the switching power supply 100. However, when using a filter element to reduce noise propagating from the switching power supply 100 to the AC power supply 10, in order to enhance the noise reduction effect, it is necessary to use a larger and more expensive filter element or to increase the number of filter elements. In addition, generally, the higher the output power of a switching power supply, the greater the noise generated by the switching power supply. Therefore, attempting to suppress noise using only a filter element in a switching power supply with high output power, such as the switching power supply 100, leads to an increase in the size and cost of the switching power supply itself.

[0057] Therefore, in the first embodiment, the capacitance of the capacitors connected in parallel with the switching elements is set to different values ​​for each switching element, thereby changing the frequency of the voltage ringing generated when the switching elements are turned off and reducing the noise propagating to the AC power supply 10. The frequency of the voltage ringing generated when each switching element is turned off strictly depends on the combined capacitance of the capacitor's capacitance and the capacitance between the terminals of the switching element itself. Furthermore, because there are tolerances in the capacitance between the terminals of the switching elements themselves and the capacitance of the capacitors, even when elements of the same type are used, the capacitance between the terminals of the switching elements themselves varies depending on the individual components. Therefore, even if all switching elements and capacitors of the same type are used, the capacitance between the terminals of each switching element is likely to be different. However, if the capacitance between the terminals of the switching elements themselves is set to different values ​​due to component tolerances, the difference will be small, thereby reducing the noise reduction effect.

[0058] Therefore, if the capacitance between the terminals of the switching elements themselves is to be different for each switching element, it is desirable to place capacitors with different nominal capacitance values ​​in parallel with the switching elements. However, it is also possible to change the frequency of the voltage ringing when the switching elements turn off by means other than changing the capacitance of the parallel capacitor, such as by using a different type of switching element with a significantly different capacitance between its terminals.

[0059] [Voltage ringing frequency and noise] Next, we will explain why changing the frequency of the voltage ringing that occurs when a switching element turns off reduces the noise propagating to the AC power supply. As explained in Figure 2 and Table 1, the frequency of the voltage ringing that occurs when each switching element turns off is determined by the capacitance between the drain and source terminals of each switching element when the capacitor is connected. Therefore, as in a typical full-bridge switching power supply, if all the switching elements used are the same type and the capacitance of the capacitors connected in parallel with the switching elements is also the same, the voltage ringing at turn-off will also have approximately the same frequency. Therefore, when a typical full-bridge switching power supply is connected to an AC power supply, the noise generated when each switching element turns off reinforces each other, resulting in the noise spectrum propagating to the AC power supply having high intensity at certain frequencies.

[0060] On the other hand, in the switching power supply 100 of the first embodiment, the capacitance between the drain terminal and the source terminal of each switching element is a different value, as shown in, for example, equation (1). Therefore, the frequencies of the voltage ringing that occurs when each switching element is turned off are all different values. Therefore, although the spectrum of the noise propagating to the AC power supply 10 in the switching power supply 100 has maximal values ​​at four frequencies, the maximum intensity can be kept lower than when a typical full-bridge switching power supply is used. Therefore, the switching power supply 100 can use filter elements that are smaller and less expensive than those in a typical full-bridge switching power supply.

[0061] As an example, in the switching power supply 100, the capacitance of capacitor C101 is 5600 pF, the capacitance of capacitor C102 is 3900 pF, the capacitance of capacitor C103 is 6800 pF, and the capacitance of capacitor C104 is 2200 pF. In this specific example, the capacitances of the capacitors satisfy the relationship of equation (1). As a result, the frequency of voltage ringing when each switching element is turned off is as shown in Table 2. From Table 2, it can be seen that in the switching power supply 100, the frequency of voltage ringing when each switching element is turned off is different. This means that the maximum value of the spectrum of noise propagating to the AC power supply 10 is distributed over four points.

[0062] [Table 2]

[0063] For example, if Tables 1 and 2 are applied to Figure 2, when switching element Q101 is turned off, the frequency of oscillation of α3 and α4 is 9.64 MHz. When switching element Q102 is turned off, the frequency of oscillation of α7 and α8 is 8.20 MHz. When switching element Q103 is turned off, the frequency of oscillation of α5 and α6 is 7.66 MHz. Furthermore, when switching element Q104 is turned off, the frequency of oscillation of α1 and α2 is 10.63 MHz.

[0064] As described above, according to the first embodiment, it is possible to reduce noise transmitted from the full-bridge switching power supply to the power source, and to realize a smaller circuit and lower cost. [Example]

[0065] A switching power supply 200 (not shown) of the second embodiment differs from the switching power supply 100 of the first embodiment in the capacitances CQ101 to CQ104 between the terminals of the switching elements. The capacitances CQ101 to CQ104 and the frequency of voltage ringing when each switching element is turned off are described below. The circuit configuration of the switching power supply 200 is the same as that of the switching power supply 100 of the first embodiment, and only the capacitances CQ101 to CQ104, which are the combined capacitances of the capacitors C101 to C104 and the capacitances of the switching elements themselves, are different. For this reason, FIG. 1 will be used, and a description of the circuit configuration will be omitted.

[0066] In the second embodiment, at least one of the capacitances CQ101, CQ102, CQ103, and CQ104 is set to a first value, and the remaining capacitances are set to a second value different from the first value, i.e., two types of capacitance values ​​are set. In this case, the capacitance of one switching element may be the first value and the capacitances of the remaining three switching elements may be the second value, or the capacitances of two switching elements may be the first value and the capacitances of the remaining two switching elements may be the second value.

[0067] Also in the second embodiment, the capacitances between the drain terminals and source terminals of the switching elements Q101 to Q104 themselves are set to approximately the same value. Therefore, the magnitude relationship between the capacitances CQ101 to CQ104 depends on the magnitude relationship between the capacitances of the capacitors C101 to C104. In the second embodiment, the capacitances of two of the four capacitors are set to a first value, and the capacitances of the remaining two capacitors are set to a second value. There are no particular restrictions on which two capacitors have the same capacitance. In the second embodiment, for example, in the switching power supply 200, the capacitances of the capacitors C101 to C104 are set to have the relationship of the following equation (2). C102=C103>C101=C104 (2)

[0068] The frequency of the voltage ringing that occurs when each switching element is turned off is determined by the capacitance of each capacitor, as shown in Table 1. Therefore, in switching power supply 200 in which the capacitance of each capacitor satisfies the relationship shown in equation (2), for example, the frequency of the voltage ringing that occurs when switching element Q103 is turned off will be equal to the frequency of the voltage ringing that occurs when switching element Q104 is turned off.

[0069] On the other hand, the frequencies of the voltage ringing when switching element Q101 is turned off and the frequencies of the voltage ringing when switching element Q102 is turned off are different from the frequencies of the voltage ringing when switching element Q103 or Q104 is turned off. Furthermore, the frequencies of the voltage ringing when switching element Q101 is turned off are also different from the frequencies of the voltage ringing when switching element Q102 is turned off. Therefore, in the second embodiment, the spectrum of the noise propagating to AC power supply 10 has maximal values ​​at three frequencies. As an example, Table 3 shows the frequencies of the voltage ringing when the capacitance of capacitors C101 and C104 is 2200 pF and the capacitance of capacitors C102 and C103 is 4700 pF.

[0070] [Table 3]

[0071] When switching element Q103 is turned off and when switching element Q104 is turned off, the frequency of the generated voltage ringing is the same, 10.1 MHz. On the other hand, when switching element Q101 is turned off, the frequency of the generated voltage ringing is 12.5 MHz, and when switching element Q102 is turned off, the frequency of the generated voltage ringing is 8.84 MHz. Thus, when the capacitances of capacitors C101 to C104 are set to satisfy the relationship of equation (2), the frequency of the generated voltage ringing will have three different values. Because the frequency of the voltage ringing when the switching elements are turned off is not the same for all switching elements, switching power supply 200 has a lower peak intensity of noise propagating to the AC power supply compared to a typical full-bridge switching power supply.

[0072] The reason why the switching power supply 200 uses two types of capacitance capacitors connected in parallel to the switching elements rather than four types is to reduce costs. Generally, in a full-bridge switching power supply, the current flowing through the capacitors connected in parallel to each switching element increases as the output power of the switching power supply increases. For example, when the maximum output power is 1000 W or more, the current flowing through the capacitors connected in parallel to each switching element is large, with an effective value of 0.5 Arms or more and an instantaneous value of up to 5 A or more. Capacitors with excellent frequency characteristics and the ability to handle large currents are limited, and capacitors with capacitances that are not commonly used can be expensive. Therefore, using capacitors with many different capacitances can increase the cost of the circuit. On the other hand, because the switching power supply 200 requires only two types of capacitors (excluding smoothing capacitor C100), the intensity of noise propagating to the AC power supply can be reduced more inexpensively than when using capacitors with many different capacitances.

[0073] The capacitances of capacitors C101 to C104 can be combined in four ways: four different values ​​(in the first embodiment), three different values, two different values ​​(in the second embodiment), or one different value. All three of these combinations, except for the one-value combination, can reduce noise propagating to the AC power supply 10. Therefore, the inter-terminal capacitances of the switching elements do not necessarily have to have the relationship shown in the first or second embodiment. When the capacitances have three different values, the relationship is as follows: Among the capacitances CQ101, CQ102, CQ103, and CQ104, any two of them may be set to a first value, one of the remaining two may be set to a second value different from the first value, and the other of the remaining two may be set to a third value different from the first and second values. That is, it is sufficient that at least one of the capacitances between the drain terminal and the source terminal of each of the four switching elements is set to a different capacitance.

[0074] As described above, according to the second embodiment, it is possible to reduce noise transmitted from the full-bridge switching power supply to the power source, and to realize a smaller circuit and lower cost. [Example]

[0075] [Explanation of laser beam printer] FIG. 3 shows a schematic configuration of a laser beam printer as an example of an image forming apparatus. The laser beam printer 1000 (hereinafter referred to as printer 1000) includes a photosensitive drum 1010, a charging unit 1020, and a developing unit 1030. The photosensitive drum 1010 is an image carrier on which an electrostatic latent image is formed. The charging unit 1020 uniformly charges the photosensitive drum 1010. An optical scanning device 1025, which serves as an exposure means, forms an electrostatic latent image by scanning a laser beam corresponding to image data onto the photosensitive drum 1010. The developing unit 1030 develops the electrostatic latent image formed on the photosensitive drum 1010 with toner to form a toner image. The toner image formed on the photosensitive drum 1010 (image carrier) is transferred by a transfer unit 1050 to a sheet S, which serves as a recording material and is supplied from a cassette 1040. The unfixed toner image transferred to the sheet S is then fixed by a fixer 1060 and discharged onto a tray 1070. The fixing unit 1060 has a heated body S1. The heated body S1 is, for example, a heater that heats an unfixed toner image transferred onto the sheet S to fix the toner image.

[0076] The image forming unit includes the photosensitive drum 1010, charging unit 1020, developing unit 1030, and transfer unit 1050. The printer 1000 also includes a power supply unit 1080, which has the above-mentioned switching power supplies 100 and 200, and the switching power supplies 100 and 200 supply power to the heated body S1.

[0077] The control unit 5000 includes a CPU (not shown) and controls the image forming operation by the image forming unit, the temperature control of the heated member S1 in the fixing unit 1060, the conveyance operation of the sheet S, and the like. In other words, the control unit 5000 corresponds to the control unit 110 in FIG. 1 . The control unit 5000 may be provided separately from the control unit 110. When the printer 1000 completes a print operation, a predetermined time elapses before it transitions to a standby state in which it can immediately perform a print operation. After a further predetermined time elapses, the printer 1000 transitions from the standby state to a sleep state, which is a low-power consumption mode, to reduce power consumption during standby. The printer 1000 has three states: a sleep state and a standby state, which are second modes, and a print state, which is a first mode, and the control unit 5000 transitions it to each state. The image forming apparatus to which the power supply device of the present invention can be applied is not limited to the configuration illustrated in FIG. 3 .

[0078] The switching power supply 100 of the first embodiment and the switching power supply 200 of the second embodiment can be applied as a power source for various components that consume power in a printer. Furthermore, the switching power supply 100 of the first embodiment and the switching power supply 200 of the second embodiment can also be applied to various devices other than a printer that require a power source and consume power.

[0079] As described above, in the third embodiment as well, it is possible to reduce noise transmitted from the full-bridge switching power supply to the power source, and to realize a smaller circuit and lower cost.

[0080] The disclosure of this embodiment includes the following configuration. (Configuration 1) a rectifier circuit that rectifies the AC voltage of the AC power supply; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series to the first switching element; a third switching element; a fourth switching element connected in series to the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element; a full-bridge power supply device comprising: the first switching element and the second switching element connected in series connected in parallel to the smoothing capacitor; and the third switching element and the fourth switching element connected in series connected in parallel to the smoothing capacitor; a first capacitor connected in parallel to the first switching element; a second capacitor connected in parallel to the second switching element; a third capacitor connected in parallel to the third switching element; a fourth capacitor connected in parallel to the fourth switching element; Equipped with When a combined capacitance of the capacitance between the drain terminal and the source terminal of the first switching element and the capacitance of the first capacitor is defined as a first capacitance, a combined capacitance of the capacitance between the drain terminal and the source terminal of the second switching element and the capacitance of the second capacitor is defined as a second capacitance, a combined capacitance of the capacitance between the drain terminal and the source terminal of the third switching element and the capacitance of the third capacitor is defined as a third capacitance, and a combined capacitance of the capacitance between the drain terminal and the source terminal of the fourth switching element and the capacitance of the fourth capacitor is defined as a fourth capacitance, A power supply device characterized in that a value of at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance is different from the other capacitances. (Configuration 2) The power supply device according to configuration 1, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element have substantially the same capacitance between their drain terminals and their source terminals. (Configuration 3) a rectifier circuit that rectifies the AC voltage of the AC power supply; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series to the first switching element; a third switching element; a fourth switching element connected in series to the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element; a full-bridge power supply device comprising: the first switching element and the second switching element connected in series connected in parallel to the smoothing capacitor; and the third switching element and the fourth switching element connected in series connected in parallel to the smoothing capacitor; When the capacitance between the drain terminal and the source terminal of the first switching element is a first capacitance, the capacitance between the drain terminal and the source terminal of the second switching element is a second capacitance, the capacitance between the drain terminal and the source terminal of the third switching element is a third capacitance, and the capacitance between the drain terminal and the source terminal of the fourth switching element is a fourth capacitance, A power supply device characterized in that a value of at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance is different from the other capacitances. (Configuration 4) The power supply device according to any one of configurations 1 to 3, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element are field effect transistors. (Configuration 5) The power supply device according to any one of configurations 1, 2, and 4, which does not cite configuration 3, is characterized in that the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are ceramic capacitors or film capacitors. (Configuration 6) The power supply device according to any one of configurations 1 to 5, wherein the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance are all different values. (Configuration 7) The power supply device according to any one of configurations 1 to 5, wherein at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance has a first value, and the remaining capacitances have second values ​​different from the first value. (Configuration 8) The power supply device according to any one of configurations 1 to 5, wherein any two of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance have a first value, one of the remaining two capacitances has a second value different from the first value, and the other of the remaining two capacitances has a third value different from the first value and the second value. (Configuration 9) An image forming apparatus for forming an image on a recording material, 9. An image forming apparatus comprising the power supply device according to any one of configurations 1 to 8. (Configuration 10) A power consuming device, 9. An apparatus comprising the power supply apparatus of any one of configurations 1 to 8. [Explanation of symbols]

[0081] 100 Switching Power Supply 110 control section C100 smoothing capacitor C101~C104 capacitors P1 Primary inductor Q101~Q104 switching elements

Claims

1. a rectifier circuit that rectifies the AC voltage of the AC power supply; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series with the first switching element; a third switching element; a fourth switching element connected in series with the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element; a full-bridge power supply device comprising: the first switching element and the second switching element connected in series connected in parallel to the smoothing capacitor; and the third switching element and the fourth switching element connected in series connected in parallel to the smoothing capacitor; a first capacitor connected in parallel to the first switching element; a second capacitor connected in parallel to the second switching element; a third capacitor connected in parallel to the third switching element; a fourth capacitor connected in parallel to the fourth switching element; Equipped with When a combined capacitance of the capacitance between the drain terminal and the source terminal of the first switching element and the capacitance of the first capacitor is defined as a first capacitance, a combined capacitance of the capacitance between the drain terminal and the source terminal of the second switching element and the capacitance of the second capacitor is defined as a second capacitance, a combined capacitance of the capacitance between the drain terminal and the source terminal of the third switching element and the capacitance of the third capacitor is defined as a third capacitance, and a combined capacitance of the capacitance between the drain terminal and the source terminal of the fourth switching element and the capacitance of the fourth capacitor is defined as a fourth capacitance, A power supply device characterized in that the value of at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance is different from the other capacitances.

2. 2. The power supply device according to claim 1, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element have substantially the same capacitance between their drain terminals and their source terminals.

3. a rectifier circuit that rectifies the AC voltage of the AC power supply; a smoothing capacitor connected in parallel to the rectifier circuit and smoothing the voltage rectified by the rectifier circuit; a first switching element; a second switching element connected in series with the first switching element; a third switching element; a fourth switching element connected in series with the third switching element; an inductor element having one end connected to a connection point between the first switching element and the second switching element and the other end connected to a connection point between the third switching element and the fourth switching element; a control unit that controls switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element; a full-bridge power supply device comprising: the first switching element and the second switching element connected in series connected in parallel to the smoothing capacitor; and the third switching element and the fourth switching element connected in series connected in parallel to the smoothing capacitor; When the capacitance between the drain terminal and the source terminal of the first switching element is a first capacitance, the capacitance between the drain terminal and the source terminal of the second switching element is a second capacitance, the capacitance between the drain terminal and the source terminal of the third switching element is a third capacitance, and the capacitance between the drain terminal and the source terminal of the fourth switching element is a fourth capacitance, A power supply device characterized in that the value of at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance is different from the other capacitances.

4. 4. The power supply device according to claim 1, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element are field effect transistors.

5. 2. The power supply device according to claim 1, wherein the first capacitor, the second capacitor, the third capacitor, and the fourth capacitor are ceramic capacitors or film capacitors.

6. 4. The power supply device according to claim 1, wherein the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance all have different values.

7. 4. The power supply device according to claim 1, wherein at least one of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance has a first value, and the remaining capacitances have second values ​​different from the first value.

8. 4. The power supply device according to claim 1, wherein any two of the first capacitance, the second capacitance, the third capacitance, and the fourth capacitance have a first value, one of the remaining two capacitances has a second value different from the first value, and the other of the remaining two capacitances has a third value different from the first value and the second value.

9. An image forming apparatus for forming an image on a recording material, An image forming apparatus comprising the power supply device according to claim 1 or 3.

10. A power consuming device, A device comprising the power supply device according to claim 1 or 3.

Images