Power supply device, image forming apparatus, and apparatus

Abstract

The invention discloses a power supply device, an image forming apparatus and an apparatus. A power supply device of a full bridge system includes a rectifying circuit, a smoothing capacitor, and a bridge circuit including first to fourth switching elements. The first to fourth switching elements are respectively provided with first to fourth capacitors connected in parallel therewith. When combined capacitances of capacitances between drain terminals and source terminals of the first to fourth switching elements and capacitances of the first to fourth capacitors are defined as first to fourth capacitances, respectively, at least one value of capacitance among the first to fourth capacitance is a value different from the other capacitance.

Description

TECHNICAL FIELD

[0001] The present application relates to power supply apparatuses, image forming apparatuses, and devices, and for example, relates to noise reduction for a switching power supply for a full-bridge system. BACKGROUND

[0002] In a switching power supply that supplies power to a load by rectifying and smoothing an AC power source or a DC power source through a switch, in order to achieve efficient power conversion, a switching power supply that employs a full-bridge system using a plurality of switching elements is used in some cases. In the switching power supply of the full-bridge system, by providing a capacitor in parallel with each switching element, power loss at the time when each switching element is turned off is reduced, and efficient operation is achieved. Further, in order to achieve efficient operation over a wide load range, a method has been proposed in which the electrostatic capacitance between the terminals of the switching element that constitutes an active leg is set to be greater than the electrostatic capacitance between the terminals of the switching element that constitutes a passive leg. (For example, see Japanese Patent No. 6293242). SUMMARY

[0003] In the switching power supply of the full-bridge system, at the time when each switching element is turned off, voltage ringing occurs due to resonance of the capacitive and inductive components of the load, electronic components, and patterns. This voltage ringing can become noise by propagating to an electrical power source and affect other electronic equipment connected to the same electrical power source. Therefore, there is a problem in that a filter element needs to be provided between the switching power supply of the full-bridge system and the AC power source in order to reduce noise, resulting in an increase in the size and price of the circuit.

[0004] The present application was conceived in such a background, and can achieve reduction of noise that propagates from the switching power supply of the full-bridge system to an electrical power source, and reduction in the size and price of the circuit.

[0005] In order to solve the above-mentioned problems, the present application includes the following configurations.

[0006] (1) A power supply device of a full-bridge system, including: a rectification circuit configured to rectify an AC voltage of an AC power source; a smoothing capacitor connected in parallel to the rectification circuit and configured to smooth the voltage rectified by the rectification 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 of the first switching element and the second switching element and the other end connected to a connection point of the third switching element and the fourth switching element; and a control portion configured to control switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element, wherein the series-connected first switching element and second switching element are connected in parallel to the smoothing capacitor, and the series-connected third switching element and fourth switching element are connected in parallel to the smoothing capacitor, and the power supply device further includes: 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; and a fourth capacitor connected in parallel to the fourth switching element, wherein when a combined capacitance of an electrostatic capacitance between a drain terminal and a source terminal of the first switching element and an electrostatic capacitance of the first capacitor is defined as a first electrostatic capacitance, a combined capacitance of an electrostatic capacitance between a drain terminal and a source terminal of the second switching element and an electrostatic capacitance of the second capacitor is defined as a second electrostatic capacitance, a combined capacitance of an electrostatic capacitance between a drain terminal and a source terminal of the third switching element and an electrostatic capacitance of the third capacitor is defined as a third electrostatic capacitance, and a combined capacitance of an electrostatic capacitance between a drain terminal and a source terminal of the fourth switching element and an electrostatic capacitance of the fourth capacitor is defined as a fourth electrostatic capacitance, at least one value of the electrostatic capacitances among the first electrostatic capacitance, the second electrostatic capacitance, the third electrostatic capacitance, and the fourth electrostatic capacitance is a value different from the other electrostatic capacitances.

[0007] (2) A power supply device of a full-bridge system, comprising: a rectification circuit configured to rectify an AC voltage of an AC power source; a smoothing capacitor connected in parallel to the rectification circuit and configured to smooth the voltage rectified by the rectification 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 of the first switching element and the second switching element and the other end connected to a connection point of the third switching element and the fourth switching element; and a control portion configured to control switching operations of the first switching element, the second switching element, the third switching element, and the fourth switching element, wherein the series-connected first switching element and second switching element are connected in parallel to the smoothing capacitor, and the series-connected third switching element and fourth switching element are connected in parallel to the smoothing capacitor, and wherein when an electrostatic capacitance between a drain terminal and a source terminal of the first switching element is defined as a first electrostatic capacitance, an electrostatic capacitance between a drain terminal and a source terminal of the second switching element is defined as a second electrostatic capacitance, an electrostatic capacitance between a drain terminal and a source terminal of the third switching element is defined as a third electrostatic capacitance, and an electrostatic capacitance between a drain terminal and a source terminal of the fourth switching element is defined as a fourth electrostatic capacitance, at least one value of the electrostatic capacitances among the first electrostatic capacitance, the second electrostatic capacitance, the third electrostatic capacitance, and the fourth electrostatic capacitance is a value different from values of the other electrostatic capacitances.

[0008] (3) An image forming apparatus for performing image formation on a recording material, the image forming apparatus comprising: the power supply device according to (1) or (2).

[0009] (4) An apparatus for consuming electric power, the apparatus comprising: the power supply device according to (1) or (2).

[0010] Further features of the present application will become apparent from the following description of example embodiments with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic view of a switching power supply in Examples 1 to 3.

[0012] Figure 2 is a schematic view of an operation waveform of the switching power supply in Example 1.

[0013] Figure 3 is a schematic configuration view of an image forming apparatus in Example 3. Detailed Implementation

[0014] [Example 1]

[0015] [Switching Power Supply]

[0016] Figure 1 This is a view of a switching power supply as a power supply device in Embodiment 1. The switching power supply 100 in Embodiment 1 is a full-bridge system switching power supply that supplies AC power of any frequency to an insulated heated component S1. The switching power supply 100 is characterized in that the electrostatic capacitance between the terminals of each switching element has a different value for each switching element. The circuit configuration of the switching power supply 100 will be described below, followed by a description of voltage ringing that occurs when the switching elements are turned off. Incidentally, a primary inductor P1 is provided on the primary side of the insulated heated component S1, and the primary inductor P1 and the heated component S1 constitute a load 120.

[0017] The switching power supply 100 includes a rectifier section DA1, a smoothing capacitor C100, switching elements Q101, Q102, Q103, and Q104, capacitors C101, C102, C103, and C104, and a control section 110. More specifically, the switching power supply 100 includes a first switching element Q101, a second switching element Q102, a third switching element Q103, and a fourth switching element Q104. The first switching element Q101 to the fourth switching element Q104 are, for example, field-effect transistors (hereinafter referred to as FETs).

[0018] A first capacitor C101 is connected in parallel to a 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 a 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 a 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 a fourth switching element Q104, that is, the fourth capacitor C104 is connected between the drain and source terminals of the fourth switching element Q104. Incidentally, in the following description, "first" to "fourth" may be omitted.

[0019] Furthermore, switching elements Q101 and Q102 are connected in series, and switching elements Q103 and Q104 are also connected in series. The connection point between switching elements Q101 and Q102 is connected to one end of the primary inductor P1 (inductor element), and the connection point between switching elements Q103 and Q104 is connected to the other end of the primary inductor P1. The series-connected switching elements Q101 and Q102 are connected in parallel to the smoothing capacitor C100, which serves as a DC voltage source. Additionally, the series-connected switching elements Q103 and Q104 are also connected in parallel to the smoothing capacitor C100.

[0020] The switching power supply 100 supplies power to the primary inductor P1 of the load 120 via switching operations of switching elements Q101 to Q104. Thus, the switching power supply 100 can use AC power from the AC power supply 10 to heat the insulated heating component S1. The switching power supply 100 adjusts the power supplied to the load 120 to keep the temperature (control target) of the heated component S1 constant. Incidentally, the temperature of the heated component S1 is detected, for example, by a temperature sensing component such as a thermistor, and the detection result is input to the control section 110 as a signal such as voltage. The control section 110 can control the power supplied to the load 120 based on the input detection result.

[0021] Incidentally, in Embodiment 1, the switching power supply 100 is used as an AC / AC inverter; however, the switching power supply 100 can also be used as a switching power supply other than an AC / AC inverter. As an example, by replacing the heated component S1 with diodes and capacitors and changing the control target to the output voltage, the switching power supply 100 can be used as an AC / DC converter. Furthermore, by removing the rectifier section DA1 and replacing the AC power supply 10 with a DC power supply, the switching power supply 100 can be used as a DC / AC inverter or a DC / DC converter.

[0022] The rectifier section DA1, as a rectifier circuit, is a diode bridge consisting of four diodes, and outputs the voltage obtained by full-wave rectification of the AC voltage of AC power supply 10 to the smoothing capacitor C100. Incidentally, in Embodiment 1, the rectifier section DA1 is a diode bridge; however, circuits operating in a similar manner, such as power factor correction (PFC) circuits using switching elements such as FETs, can also be used. The smoothing capacitor C100 is provided to smooth the output of the rectifier section DA1 or to prevent current generated by the switching operations of switching elements Q101 to Q104 from flowing through AC power supply 10 and the rectifier section DA1.

[0023] Switching elements Q101, Q102, Q103, and Q104 are FETs and form a full-bridge circuit. Control signals transmitted from control section 110 are input to the gate terminals of switching elements Q101, Q102, Q103, and Q104. Thus, switching elements Q101 through Q104 are turned on or off by control section 110, and power of arbitrary frequency is supplied to load 120 via phase shift control. Switching elements Q101 and Q102 are turned on or off complementaryly with a dead time interval, and are controlled to have the same on and off times. Similarly, switching elements Q103 and Q104 are turned on or off complementaryly with a dead time interval, and are controlled to have the same on and off times.

[0024] Furthermore, the turn-on and turn-off times of switching elements Q101 to Q104 are the same, and the dead time lengths are also common. Incidentally, in Embodiment 1, a FET is used for switching elements Q101 to Q104; however, instead, an insulated-gate bipolar transistor (hereinafter referred to as an IGBT) can be used, and a reverse-biased diode can be connected in parallel with it. Since an IGBT does not have a parasitic diode, unlike a FET, a reverse-biased diode needs to be connected externally to it. In this case, the anode terminal of the reverse-biased diode is connected to the emitter terminal of the IGBT, and the cathode terminal of the reverse-biased diode is connected to the collector terminal of the IGBT.

[0025] Furthermore, in Example 1, all switching elements Q101 to Q104 are of the same type, and the capacitance between their drain and source terminals is the same value. Incidentally, for switching elements Q101 to Q104, different types of switching elements with different capacitances between their drain and source terminals can be used respectively. The effects of using different types of switching elements with different capacitances between their drain and source terminals will be described below.

[0026] Capacitors C101, C102, C103, and C104 are capacitors whose capacitance changes little with frequency, such as ceramic capacitors and film capacitors. Capacitors C101, C102, C103, and C104 are connected between the drain and source terminals of switching elements Q101, Q102, Q103, and Q104, respectively. By connecting capacitors C101 to C104, the capacitance between the drain and source terminals of each switching element increases. Consequently, the increase in voltage between the drain and source terminals when each switching element is turned off becomes more gradual, and the power loss during turn-off is reduced. Furthermore, by connecting capacitors C101 to C104, the frequency of voltage ringing that occurs when each switching element is turned off changes. In Example 1, capacitors C101 to C104 have different capacitances, and for each switching element, the frequency of voltage ringing during turn-off also has different values. The following will use… Figure 2 Describe in detail the relationship between the voltage ringing when switching elements Q101 to Q104 are turned off and the electrostatic capacitance of capacitors C101 to C104.

[0027] (Regarding electrostatic capacitors)

[0028] The electrostatic capacitance between the drain and source terminals of switching element Q101 is defined as follows. Switching element Q101 itself has electrostatic capacitance between its drain and source terminals. Here, as... Figure 1 As shown, there are cases where capacitor C101 is connected in parallel to switching element Q101, and cases where the capacitor is not connected to switching element Q101. When capacitor C101 is connected, the electrostatic capacitance between the drain and source terminals becomes the combined capacitance of the electrostatic capacitance of switching element Q101 itself and the electrostatic capacitance of capacitor C101 (hereinafter referred to as the combined capacitance). On the other hand, when capacitor C101 is not connected, the electrostatic capacitance between the drain and source terminals is only the electrostatic capacitance of switching element Q101 itself. The same applies to switching elements Q102 to Q104 and capacitors C102 to C104.

[0029] The electrostatic capacitance between the drain and source terminals of switching element Q101 is defined as CQ101 as the first electrostatic capacitance. If capacitor C101 is connected, then the electrostatic capacitance CQ101 becomes the combined value of the electrostatic capacitance of switching element Q101 itself and the electrostatic capacitance of capacitor C101. If capacitor C101 is not connected, then the electrostatic capacitance CQ101 is the electrostatic capacitance of switching element Q101 itself. In the following text, for the electrostatic capacitance between the drain and source terminals of switching elements Q102 to Q104, CQ102 is defined as the second electrostatic capacitance, CQ103 as the third electrostatic capacitance, and CQ104 as the fourth electrostatic capacitance, in the same manner.

[0030] exist Figure 1 In Embodiment 1 shown, as described above, the electrostatic capacitance between the drain and source terminals of the switching elements Q101 to Q104 is substantially the same. Therefore, the magnitude relationship between the electrostatic capacitances CQ101 to CQ104 depends on the magnitude relationship of the electrostatic capacitances of capacitors C101 to C104. Here, the term "substantially the same" includes cases where they are completely identical and cases where they differ within an allowable range of errors caused by variations in the manufacture of switching elements of the same product type.

[0031] Here, with all capacitors CQ101 to CQ104 set to the same value, the frequency of voltage ringing that occurs when the switching element is turned off will have essentially the same value for all switching elements. In this case, in the spectrum where the horizontal axis represents frequency and the vertical axis represents noise intensity, the intensity has a local maximum at a certain frequency.

[0032] In contrast, in Embodiment 1, the capacitance values ​​of capacitors CQ101, CQ102, CQ103, and CQ104 are configured such that at least one value is different from the other capacitors. For example, in Embodiment 1, by configuring the capacitance values ​​of the four capacitors C101 to C104 to all have different values, the frequency of the generated voltage ringing is dispersed so that it has four local maxima in the spectrum. Thus, compared to the case with a single local maximum, it becomes possible to make the peak value of each local maximum lower.

[0033] Therefore, the electrostatic capacitances of capacitors C101 to C104 can be set to all different values. There is no particular restriction on the order of these values ​​of the four electrostatic capacitances. For example, in embodiment 1, the electrostatic capacitances of each capacitor C101 to C104 are set to be in the relationship of the following inequality (1).

[0034] C103 > C101 > C102 > C104 (1)

[0035] As will be described below Figure 2 The circuit shown for generating voltage ringing is configured by focusing on the amplitude of the voltage ringing generated by the turn-off of each switching element. The amplitude of the voltage ringing depends on several factors and varies depending on the circuit configuration; however, as the amplitude increases, dispersing the frequency of the voltage ringing becomes more effective by setting a larger electrostatic capacitance between the drain and source terminals of the switching elements.

[0036] Incidentally, it can be configured such that, instead of connecting the capacitors in parallel to the switching elements, the frequency of voltage ringing is different by making the electrostatic capacitance between the drain and source terminals of the four switching elements all have different values. Furthermore, it can be configured such that the electrostatic capacitances CQ101 to CQ104 are all different by making the electrostatic capacitance between the drain and source terminals of the four switching elements all have different values, and further by connecting the capacitors in parallel to each switching element. In this case, there is no particular restriction on the order of the magnitudes of the electrostatic capacitances CQ101 to CQ104; however, as an example, the magnitudes can be set in the same order as in inequality (1) above (CQ103>CQ101>CQ102>CQ104).

[0037] Control section 110 is a circuit that controls the switching states of switching elements Q101 to Q104. Control section 110 controls the frequency (switching frequency) and phase shift of switching elements Q101 to Q104 based on the temperature of the heated component S1. Control section 110 controls the output power through phase shift control, which shifts the on / off phases of switching elements Q101 and Q102, as well as the on / off phases of switching elements Q103 and Q104. Incidentally, during the "on" period of switching element Q101, switching element Q102 is off, and during the "on" period of switching element Q103, switching element Q104 is off.

[0038] When the phase shift is 0 rad, switching elements Q101 and Q103 are simultaneously turned on or off, and switching elements Q102 and Q104 are simultaneously turned on or off. When the phase shift is 0 rad, switching elements Q101 and Q104, and switching elements Q102 and Q103 are not simultaneously turned on, so that no current flows to the load 120 and the output power of the switching power supply 100 becomes 0W.

[0039] As the phase shift increases from 0 rad, the time periods during which switching elements Q101 and Q104 are simultaneously on, and the time periods during which switching elements Q102 and Q103 are simultaneously on, respectively increase (become longer). Therefore, the output power of the switching power supply 100 also increases. When the phase shift is π rad, the output power of the switching power supply 100 becomes maximum. Incidentally, as an example, the maximum output power of the switching power supply 100 in Embodiment 1 is 1000 W or greater.

[0040] The load 120 consists of a primary inductor P1 and a heated component S1 on the secondary side. The primary inductor P1 is magnetically connected to the heated component S1 on the secondary side, and power is supplied to the heated component S1 via the primary inductor P1 through the switching operations of switching elements Q101 to Q104. When power is supplied from the primary inductor P1, current flows through the heated component S1, and the heated component S1 is heated by Joule heating due to its own resistance. Incidentally, in Embodiment 1, a load 120 divided into a primary side and a secondary side is used; however, depending on the safety design of the device using the switching power supply 100, there is no need for a configuration between the primary inductor P1 and the heated component S1 that corresponds to reinforced insulation or double insulation under safety standards.

[0041] [Voltage and current during switching operation]

[0042] Next, we will use Figure 2 Describe the voltage and current when switching elements Q101 to Q104 perform switching operations. Figure 2 The view is as follows: the horizontal axis represents time, and the voltage between the gate terminal and the source terminal of each switching element Q101, Q102, Q103 and Q104 is shown as dashed lines and the voltage between its drain terminal and the source terminal is shown as solid lines.

[0043] exist Figure 2 In this circuit, control section 110 controls the switching operations of switching elements Q101 to Q104 at a frequency of 50 kHz, a phase shift of 0.75 π rad, and a dead time of 600 ns. Each switching element is turned on when the voltage between the gate terminal and the source terminal reaches level H (high) (20V), and each switching element is turned off when the voltage reaches level L (low) (0V). The operation of the switching power supply 100 in one cycle can be divided into time periods 1 to 8, with the time of each switching element's on or off as the boundary. In the following, starting from time period 1, the voltage between the drain terminal and the source terminal of each switching element and the current flowing through each element of the switching power supply 100 will be described chronologically.

[0044] (Time slot 1)

[0045] Time period 1 is the period when switching elements Q101 and Q104 are simultaneously turned on. During time period 1, the voltage between the drain and source terminals of switching elements Q101 and Q104 is approximately 0V. Therefore, current flows through the smoothing capacitor C100, switching element Q104, primary inductor P1, and the path of switching element Q101.

[0046] (Time slot 2)

[0047] Period 2 is the period when switching element Q104 is 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. On the other hand, 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. As a result, capacitor C104 is charged, and the voltage between the drain and source terminals of switching element Q104 gradually increases.

[0048] Furthermore, when switching element Q104 is turned off, current also flows through the path of capacitor C103, primary inductor P1, and switching element Q101. Therefore, capacitor C103 is discharged, and the voltage between the drain and source terminals of switching element Q103 gradually decreases. When the voltage between the drain and source terminals decreases to the voltage at which the body diode of switching element Q103 becomes conductive, current flows through the path of primary inductor P1, switching element Q101, and the body diode of switching element Q103.

[0049] Resonance occurs when the voltage between the drain and source terminals of switching element Q104 becomes approximately equal to the voltage of smoothing capacitor C100 (approximately 140V). Specifically, this resonance occurs due to the electrostatic capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C102, switching element Q102, capacitor C104, primary inductor P1, and the pattern. Because of this resonance, the voltage between the drain and source terminals of switching elements Q102 and Q104 oscillates around the voltage of smoothing capacitor C100 at a frequency dependent on capacitors C102 and C104. In other words, voltage ringing occurs between the drain and source terminals of switching elements Q102 and Q104 because switching element Q104 is turned off.

[0050] (Time slot 3)

[0051] Time period 3 is the period when switching element Q103 is turned on and switching elements Q101 and Q103 are turned on simultaneously. During time period 3, the voltage between the drain and source terminals of switching elements Q101 and Q103 is approximately 0V. Furthermore, due to the energy stored in the primary inductor P1 during time period 1, current flows through the path of primary inductor P1, switching elements Q101, and switching elements Q103. Incidentally, during time period 3, the voltage between the drain and source terminals of switching elements Q102 and Q104 also oscillates continuously; however, due to the resonant resistive component, its amplitude gradually decreases.

[0052] (Time slot 4)

[0053] Period 4 is the period when switching element Q101 is turned off and only switching element Q103 is turned on. During period 4, the voltage between the drain and source terminals of switching element Q103 remains at approximately 0V. On the other hand, 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. As a result, capacitor C101 is charged, and the voltage between the drain and source terminals of switching element Q101 gradually increases.

[0054] As the voltage between the drain and source terminals of switching element Q101 increases, the voltage between the drain and source terminals of switching element Q102 decreases, continuing to decrease until the body diode of switching element Q102 becomes conductive. Incidentally, capacitor C102 is discharged. Current then flows through the path of primary inductor P1, the body diode of switching element Q102, smoothing capacitor C100, and switching element Q103. Resonance occurs when the voltage between the drain and source terminals of switching element Q101 becomes approximately equal to the voltage of smoothing capacitor C100. Specifically, resonance occurs due to the electrostatic capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C101, switching element Q101, capacitor C104, switching element Q104, primary inductor P1, and the circuitry. Due to this resonance, the voltage between the drain and source terminals of switching elements Q101 and Q104 oscillates at a frequency dependent on the voltage of smoothing capacitor C100. In other words, voltage ringing occurs between the drain and source terminals of switching elements Q101 and Q104 because switching element Q101 is turned off.

[0055] (Time slot 5)

[0056] Time period 5 is the period when switching element Q102 is turned on and both switching elements Q102 and Q103 are turned on simultaneously. During time period 5, the voltage between the drain and source terminals of switching elements Q102 and Q103 becomes approximately 0V, and current flows through the path of primary inductor P1, switching element Q102, smoothing capacitor C100, and switching element Q103. During time period 5, due to the resonance between primary inductor P1 and smoothing capacitor C100, the current direction reverses, and the current flows in the direction of smoothing capacitor C100, switching element Q102, primary inductor P1, and switching element Q103. Incidentally, during time period 5, the voltage between the drain and source terminals of switching elements Q101 and Q104 also oscillates continuously, but its amplitude gradually decreases due to the resonant resistive component.

[0057] (Time slot 6)

[0058] Period 6 is the period when switching element Q103 is turned off and only switching element Q102 is turned on. During period 6, the voltage between the drain and source terminals of switching element Q102 remains at approximately 0V. On the other hand, 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. As a result, capacitor C103 is charged, and the voltage between the drain and source terminals of switching element Q103 gradually increases.

[0059] As the voltage between the drain and source terminals of switching element Q103 increases, the voltage between the drain and source terminals of switching element Q104 decreases. Incidentally, capacitor C014 is discharged. When the voltage between the drain and source terminals decreases to the voltage at which the body diode of switching element Q104 becomes conductive, current flows through the path of primary inductor P1, switching element Q104, the body diode of switching element Q104, and switching element Q102. Resonance occurs when the voltage between the drain and source terminals of switching element Q103 becomes approximately equal to the voltage of smoothing capacitor C100. In detail, resonance occurs due to the electrostatic capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C101, switching element Q101, capacitor C103, switching element Q103, primary inductor P1, and the pattern. Due to this resonance, the voltage between the drain and source terminals of switching elements Q101 and Q103 oscillates at a frequency dependent on the voltage of smoothing capacitor C100. In other words, voltage ringing occurs between the drain and source terminals of switching elements Q101 and Q103 because switching element Q103 is turned off.

[0060] (Time slot 7)

[0061] Period 7 is the period when switch element Q104 is turned on and switch elements Q102 and Q104 are turned on simultaneously. During period 7, the voltage between the drain and source terminals of switch elements Q102 and Q104 becomes approximately 0V. Furthermore, due to the energy stored in primary inductor P1 during period 5, current flows through the path of primary inductor P1, switch element Q104, and switch element Q102. Incidentally, during period 7, the voltage between the drain and source terminals of switch elements Q101 and Q103 also oscillates continuously; however, due to the resonant resistive component, its amplitude gradually decreases.

[0062] (Segment 8)

[0063] Period 8 is the period when switching element Q102 is turned off and only switching element Q104 is turned on. During period 8, the voltage between the drain and source terminals of switching element Q104 remains at approximately 0V. On the other hand, 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. As a result, capacitor C102 is charged, and the voltage between the drain and source terminals 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. Therefore, the voltage between the drain and source terminals of switching element Q101 gradually decreases. Incidentally, capacitor C101 is discharged.

[0064] When the voltage between the drain and source terminals of switching element Q101 decreases to the voltage at which the body diode of switching element Q101 becomes conductive, current flows through the following path: the path of primary inductor P1, switching element Q104, smoothing capacitor C100, and the body diode of switching element Q101. Resonance occurs when the voltage between the drain and source terminals of switching element Q102 becomes approximately equal to the voltage of smoothing capacitor C100. Specifically, resonance occurs due to the electrostatic capacitance, inductance, and resistance components of smoothing capacitor C100, capacitor C102, switching element Q102, capacitor C103, switching element Q103, primary inductor P1, and the circuitry. Due to this resonance, the voltages between the drain and source terminals of switching elements Q102 and Q103 oscillate around the voltage of smoothing capacitor C100 at a frequency dependent on capacitors C102 and C103. In other words, voltage ringing occurs between the drain and source terminals of switching elements Q102 and Q103 because switching element Q102 is turned off. After the end of period 8, the cycle returns to period 1 because switching element Q101 is turned off.

[0065] As mentioned above, the frequency of voltage ringing that occurs when each switching element is turned off depends on the frequency corresponding to the electrostatic capacitance of each capacitor. Table 1 summarizes the voltage ringing and the corresponding capacitors. For example, when the switching element being turned off is switching element Q101, the electrostatic capacitance that affects the frequency of voltage ringing is the electrostatic capacitance of capacitors C101 and C104.

[0066] [Table 1]

[0067]

[0068] exist Figure 2In the diagram, voltage ringing caused by the turn-off of each switching element is indicated by reference numerals from α1 to α8. The oscillation of α1 is caused by the turn-off of switching element Q104, and according to Table 1, its frequency depends on the electrostatic capacitance of capacitors C102 and C104 (segment 2). Since the oscillation of α2 is also caused by the turn-off of switching element Q104, its frequency has the same value as the oscillation of α1 (segment 2). The oscillation of α3 is caused by the turn-off of switching element Q101, and according to Table 1, its frequency depends on the electrostatic capacitance of capacitors C101 and C104 (segment 4). Since the oscillation of α4 is also caused by the turn-off of switching element Q101, its frequency has the same value as the oscillation of α3 (segment 4). The oscillation of α5 is caused by the turn-off of switching element Q103, and according to Table 1, its frequency depends on the electrostatic capacitance of capacitors C101 and C103 (segment 6). Since the oscillation of α6 is also caused by the turn-off of switching element Q103, its frequency has the same value as the oscillation of α5 (segment 6). The oscillation of α7 is caused by the turn-off of switching element Q102, and according to Table 1, its frequency depends on the electrostatic capacitance of capacitors C102 and C103 (segment 8). Since the oscillation of α8 is also caused by the turn-off of switching element Q102, its frequency has the same value as the oscillation of α7 (segment 8).

[0069] [Reasons for different electrostatic capacitances]

[0070] Next, the reason for the different electrostatic capacitances of capacitors C101 to C104 will be described. The reason for the different electrostatic capacitances of capacitors C101 to C104, which are provided in parallel with the switching elements Q101 to Q104 in the switching power supply 100, is to reduce the noise propagating to the AC power supply 10 and to reduce the size and cost of the circuit.

[0071] like Figure 2 As described above, in the full-bridge switching power supply 100, voltage ringing occurs between the terminals of the switching elements when the switching elements are turned off. If this voltage ringing propagates to the AC power supply 10 through parasitic components and / or stray capacitance between patterns in the rectifier section, it may generate noise and cause damage to devices connected to the same AC power supply 10. Therefore, it is necessary to minimize the voltage ringing that occurs when the switching elements are turned off before it propagates to the AC power supply 10.

[0072] One common method for reducing noise propagating from the switching power supply 100 to the AC power supply 10 is to provide filter elements (such as chokes and cross-line capacitors) between the AC power supply 100 and the switching power supply 100. However, when attempting to reduce noise propagation from the switching power supply 100 to the AC power supply 10 using filter elements, larger and more expensive filter elements or an increased number of filter elements are required to enhance the noise reduction effect. Furthermore, generally speaking, the larger the output power of the switching power supply, the greater the noise generated from it. Therefore, in switching power supplies with large output power, such as the switching power supply 100, attempting to provide noise countermeasures solely using filter elements may lead to an increase in the size and cost of the switching power supply itself.

[0073] Therefore, in Embodiment 1, by making the capacitance of the capacitor provided in parallel with the switching elements have different values ​​for each switching element, the frequency of voltage ringing that occurs during turn-off is changed and the noise propagating to the AC power supply 10 is reduced. Incidentally, strictly speaking, the frequency of voltage ringing that occurs when each switching element is turned off depends on the combined capacitance of the capacitor and the capacitance between the terminals of the switching element itself. Furthermore, since there are tolerances between the capacitance between the terminals of the switching element and the capacitance of the capacitor, the capacitance between the terminals of the switching element varies between the individual components, even when using the same type of components. Therefore, even when the same type of components are used for all each switching element and for all each capacitor, the capacitance value between the terminals of each switching element is likely to be completely different. However, in cases where the capacitance between the terminals of the switching elements differs due to component tolerances, the difference in capacitance is small, thus reducing the noise reduction effect.

[0074] Therefore, when the electrostatic capacitance between the terminals of the switching element itself has a different value for each switching element, it is desirable to provide capacitors with different rated values ​​of electrostatic capacitance in parallel with the switching elements. However, the frequency of voltage ringing when the switching element is turned off can be changed by means other than changing the electrostatic capacitance of the capacitors provided in parallel, such as by using different types of switching elements with significantly different electrostatic capacitances between their terminals.

[0075] [Regarding the frequency and noise of voltage ringing]

[0076] Next, the reason for reducing noise propagating to the AC power supply by changing the frequency of voltage ringing that occurs when the switching element is turned off will be described. Figure 2As described in Table 1, the frequency of voltage ringing that occurs when each switching element is turned off is determined by the electrostatic capacitance between the drain and source terminals of each switching element when the capacitor is connected to it. Therefore, as in a typical full-bridge switching power supply, where all the switching elements used are of the same type and the electrostatic capacitance of the capacitors provided in parallel with the switching elements is also the same, the voltage ringing at turn-off has approximately the same frequency. Therefore, when a typical full-bridge switching power supply is connected to and used with an AC power supply, the noise spectrum propagating to the AC power supply has a high intensity at a specific frequency because the noise occurring when each switching element is turned off amplifies each other.

[0077] On the other hand, using the switching power supply 100 in Embodiment 1, for example, as shown in inequality (1), the electrostatic capacitance between the drain and source terminals of each switching element is all different. Therefore, the frequency of voltage ringing that occurs when each switching element is turned off is all different. Thus, in the switching power supply 100, the spectrum of noise propagating to the AC power supply 10 has local maxima at four frequencies; however, compared to the case of a switching power supply using a typical full-bridge system, the maximum intensity can be suppressed much lower. Therefore, for the switching power supply 100, smaller and cheaper filter elements than those of a typical full-bridge system switching power supply can be used.

[0078] As an example, suppose that in the switching power supply 100, the capacitance of capacitor C101 is 5600pF, the capacitance of capacitor C102 is 3900pF, the capacitance of capacitor C103 is 6800pF, and the capacitance of capacitor C104 is 2200pF. In this specific example, the capacitance of each capacitor satisfies the relationship in inequality (1). Thus, the frequency of voltage ringing when each switching element is turned off becomes as shown in Table 2. According to Table 2, it is found that in the switching power supply 100, the frequency of voltage ringing when turned off is different for all switching elements. This means that the local maxima in the spectrum of noise propagating to the AC power supply 10 are dispersed into four.

[0079] [Table 2]

[0080]

[0081] For example, applying Table 1 and Table 2 Figure 2When switch Q101 is turned off, the oscillation frequencies of α3 and α4 become 9.64 MHz. Furthermore, when switch Q102 is turned off, the oscillation frequencies of α7 and α8 become 8.20 MHz. Furthermore, when switch Q103 is turned off, the oscillation frequencies of α5 and α6 become 7.66 MHz. Furthermore, when switch Q104 is turned off, the oscillation frequencies of α1 and α2 become 10.63 MHz.

[0082] As described above, according to Embodiment 1, it becomes possible to reduce noise propagating from the switching power supply of the full-bridge system to the electrical power supply, and to reduce the size and cost of the circuit.

[0083] [Example 2]

[0084] The switching power supply 200 (not shown) in Embodiment 2 differs from the switching power supply 100 in Embodiment 1 in that the electrostatic capacitances CQ101 to CQ104 between the terminals of the switching elements are [not specified]. The frequency of voltage ringing when each switching element in Embodiment 2 is turned off, and the electrostatic capacitances CQ101 to CQ104, will be described below. Incidentally, the circuit configuration of the switching power supply 200 is the same as that of the switching power supply 100 in Embodiment 1, and the only difference is that the electrostatic capacitances of capacitors C101 to C104 are combined with the electrostatic capacitances of the switching elements themselves to form electrostatic capacitances CQ101 to CQ104. Therefore, Figure 1 This is used as a reference, and the description of the circuit configuration will be omitted.

[0085] In Embodiment 2, the electrostatic capacitors CQ101, CQ102, CQ103, and CQ104 are configured such that at least one of them has a first value, while the other value of the electrostatic capacitor is a second value different from the first value; that is, the electrostatic capacitor values ​​have two types. In this case, the electrostatic capacitor value of one switching element can be the first value and the electrostatic capacitor values ​​of the remaining three switching elements can be the second value, or the electrostatic capacitor values ​​of two switching elements can be the first value and the electrostatic capacitor values ​​of the remaining two switching elements can be the second value.

[0086] Furthermore, in Embodiment 2, the electrostatic capacitance between the drain and source terminals of the switching elements Q101 to Q104 is also substantially the same. Therefore, the magnitude relationship between the electrostatic capacitances CQ101 to CQ104 depends on the magnitude relationship of the electrostatic capacitances of capacitors C101 to C104. In Embodiment 2, the electrostatic capacitance values ​​of two of the four capacitors are configured as a first value, and the electrostatic capacitance values ​​of the remaining two capacitors are configured as a second value. There is no restriction on which two capacitors have the same electrostatic capacitance. In Embodiment 2, for example, in the switching power supply 200, the electrostatic capacitances of capacitors C101 to C104 are set to have the following relationship of equality and inequality (2).

[0087] C102 = C103 > C101 = C104 (2)

[0088] As shown in Table 1, the frequency of voltage ringing that occurs when each switching element is turned off is determined by the electrostatic capacitance of each capacitor. Therefore, in the switching power supply 200 where the electrostatic capacitance of each capacitor has, for example, the relationship between the equation and the inequality (2), the frequency of voltage ringing when switching element Q103 is turned off becomes the same as the frequency of voltage ringing when switching element Q104 is turned off.

[0089] On the other hand, the voltage ringing frequencies when switching element Q101 is turned off and when switching element Q102 is turned off are different from the voltage ringing frequencies when switching element Q103 or switching element Q104 is turned off. Furthermore, the voltage ringing frequency when switching element Q101 is turned off is also different from the voltage ringing frequency when switching element Q102 is turned off. Therefore, in Embodiment 2, the spectrum of noise propagating to the AC power supply 10 has local maxima at three frequencies. As an example, Table 3 shows the voltage ringing frequencies when the capacitance of capacitors C101 and C104 is 2200 pF and the capacitance of capacitors C102 and C103 is 4700 pF.

[0090] [Table 3]

[0091]

[0092] When switching element Q103 is turned off and when switching element Q104 is turned off, the frequency of voltage ringing becomes the same, 10.1 MHz. On the other hand, the frequency of voltage ringing when switching element Q101 is turned off is 12.5 MHz, and the frequency of voltage ringing when switching element Q102 is turned off is 8.84 MHz. Therefore, when the electrostatic capacitances of capacitors C101 to C104 are set to satisfy the relationship of equality and inequality (2), the frequency of voltage ringing takes three different values. Since the frequency of voltage ringing when the switching elements are turned off is not the same for all switching elements, the peak intensity of the noise propagating to the AC power supply in the switching power supply 200 is lower than that in a typical full-bridge switching power supply system.

[0093] Incidentally, the reason why the capacitors provided in parallel with the switching elements in the switching power supply 200 have only two types of electrostatic capacitance instead of four is due to cost reduction. Generally speaking, in a full-bridge switching power supply system, as the output power of the switching power supply increases, the current flowing through the capacitors provided in parallel with each switching element also increases. As an example, when the maximum output power is 1000W or greater, the current flowing through the capacitors provided in parallel with each switching element has a large value of 0.5 Arms or greater as an effective value and a maximum of 5A or greater as an instantaneous value. The types of capacitors with excellent frequency response and capable of carrying large currents can be limited, and capacitors with electrostatic capacitance values ​​that are not widely used can also be expensive. Therefore, the circuit can become expensive when using capacitors with many types of electrostatic capacitance. On the other hand, since the capacitors required in the switching power supply 200 are only of two types besides the smoothing capacitor C100, it becomes cheaper to reduce the intensity of noise propagating to the AC power supply compared to the case of using capacitors with many types of electrostatic capacitance.

[0094] Incidentally, as a combination of the electrostatic capacitances of capacitors C101 to C104, it is conceivable that they could be configured with four types of values ​​(Example 1), three types of values, two types of values ​​(Example 2), and one type of value. In the three cases other than the case with only one type of value, noise propagating to the AC power supply 10 can be reduced. Therefore, the electrostatic capacitances between the terminals of the switching elements do not necessarily need to be in the relationship described in Example 1 or Example 2. Incidentally, in the case of three types of values, the configuration can be as follows: That is, it can be configured such that any two values ​​of the electrostatic capacitances CQ101, CQ102, CQ103, and CQ104 are set to a first value, one of the remaining two values ​​is set to a second value different from the first value, and the other of the remaining two values ​​is set to a third value different from the first and second values. In other words, it is sufficient to configure the electrostatic capacitances between the drain and source terminals of the four switching elements such that at least one electrostatic capacitance is different from the others.

[0095] As described above, according to Embodiment 2, it becomes possible to reduce noise propagating from the switching power supply of the full-bridge system to the electrical power supply, and to reduce the size and cost of the circuit.

[0096] [Example 3]

[0097] [Description of laser beam printer]

[0098] exist Figure 3The following diagram illustrates a general 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 section 1020, and a developing section 1030. The photosensitive drum 1010 is an image-carrying member on which an electrostatic latent image is formed. The charging section 1020 uniformly charges the photosensitive drum 1010. An optical scanning device 1025, serving as an exposure component, forms an electrostatic latent image by scanning a laser corresponding to image data onto the photosensitive drum 1010. The developing section 1030 forms a toner image by developing the electrostatic latent image formed on the photosensitive drum 1010 with toner. The toner image formed on the photosensitive drum 1010 (on the image carrier member) is transferred by the transfer unit 1050 to a recording material sheet S fed from the cartridge 1040. The unfixed toner image transferred to the sheet S is fixed by the fixing unit 1060, and the sheet S is discharged onto the tray 1070. The fixing unit 1060 includes a heated member S1. The heated member S1 is, for example, a heater that fixes the unfixed toner image transferred to the sheet S by heating.

[0099] The photosensitive drum 1010, charging section 1020, developing section 1030, and transfer section 1050 constitute the image forming section. In addition, the printer 1000 is provided with a power supply section 1080, which includes the aforementioned switching power supply 100 or 200, and the switching power supply 100 or 200 supplies power to the heated member S1.

[0100] The control unit 5000 includes a CPU (not shown) and controls the image forming operation of the image forming unit, the temperature control of the heated member S1 included in the fixing unit 1060, and the conveying operation of the sheet S, etc. In other words, the control unit 5000 and... Figure 1 This corresponds to the control section 110. Incidentally, the control section 5000 can be provided separately from the control section 110. When the printer 1000 completes the printing operation, after a predetermined time, the printer 1000 switches to standby mode, where it can immediately perform printing operations.

[0101] After a further predetermined period, in order to reduce power consumption during standby, printer 1000 transitions from standby mode to sleep mode, a low-power consumption mode. Printer 1000 has three states: sleep mode and standby mode (second mode), and printing mode (first mode), and control unit 5000 switches the printer between these states. Incidentally, the image forming apparatus to which the power supply device of the present invention can be applied is not limited to... Figure 3 The configuration illustrated in .

[0102] Incidentally, the switching power supply 100 in Embodiment 1 and the switching power supply 200 in Embodiment 2 can be used as power supplies for various types of power-consuming components in a printer. Furthermore, the switching power supply 100 in Embodiment 1 and the switching power supply 200 in Embodiment 2 can also be used for various types of devices that require power and consume electricity, other than printers.

[0103] As described above, in Embodiment 3, it also becomes possible to reduce noise propagating from the switching power supply of the full-bridge system to the electrical power supply, and to reduce the size and cost of the circuit.

[0104] The disclosure of this embodiment includes the following components.

[0105] (Component 1)

[0106] A power supply device for a full-bridge system, comprising:

[0107] The rectifier circuit is configured to rectify the AC voltage of the AC power supply.

[0108] A smoothing capacitor is connected in parallel to the rectifier circuit and is configured to smooth the voltage rectified by the rectifier circuit.

[0109] First switching element;

[0110] A second switching element connected in series with the first switching element;

[0111] Third switching element;

[0112] A fourth switching element connected in series with the third switching element;

[0113] An inductor element, one end of which is connected to the connection point of a first switching element and a second switching element, and the other end of which is connected to the connection point of a third switching element and a fourth switching element; and

[0114] The control section is configured to control the switching operations of the first, second, third, and fourth switching elements.

[0115] The first and second switching elements, connected in series, are connected in parallel to the smoothing capacitor, and the third and fourth switching elements, also connected in series, are connected in parallel to the smoothing capacitor.

[0116] The power supply device also includes:

[0117] The first capacitor is connected in parallel to the first switching element;

[0118] The second capacitor is connected in parallel to the second switching element;

[0119] A third capacitor connected in parallel to the third switching element; and

[0120] The fourth capacitor is connected in parallel to the fourth switching element.

[0121] Wherein, the combined capacitance of the electrostatic capacitance between the drain and source terminals of the first switching element and the electrostatic capacitance of the first capacitor is defined as the first electrostatic capacitance; the combined capacitance of the electrostatic capacitance between the drain and source terminals of the second switching element and the electrostatic capacitance of the second capacitor is defined as the second electrostatic capacitance; the combined capacitance of the electrostatic capacitance between the drain and source terminals of the third switching element and the electrostatic capacitance of the third capacitor is defined as the third electrostatic capacitance; and the combined capacitance of the electrostatic capacitance between the drain and source terminals of the fourth switching element and the electrostatic capacitance of the fourth capacitor is defined as the fourth electrostatic capacitance,

[0122] At least one of the electrostatic capacitors, namely the first electrostatic capacitor, the second electrostatic capacitor, the third electrostatic capacitor, and the fourth electrostatic capacitor, has a value that is different from the other electrostatic capacitors.

[0123] (Component 2)

[0124] According to the power supply device described in configuration 1, the electrostatic capacitance between the drain terminal and the source terminal of the first switching element, the second switching element, the third switching element and the fourth switching element is substantially the same.

[0125] (Component 3)

[0126] A power supply device for a full-bridge system, comprising:

[0127] The rectifier circuit is configured to rectify the AC voltage of the AC power supply.

[0128] A smoothing capacitor is connected in parallel to the rectifier circuit and is configured to smooth the voltage rectified by the rectifier circuit.

[0129] First switching element;

[0130] A second switching element connected in series with the first switching element;

[0131] Third switching element;

[0132] A fourth switching element connected in series with the third switching element;

[0133] An inductor element, one end of which is connected to the connection point of a first switching element and a second switching element, and the other end of which is connected to the connection point of a third switching element and a fourth switching element; and

[0134] The control section is configured to control the switching operations of the first, second, third, and fourth switching elements.

[0135] The first and second switching elements, connected in series, are connected in parallel to the smoothing capacitor, and the third and fourth switching elements, also connected in series, are connected in parallel to the smoothing capacitor.

[0136] Wherein, the electrostatic capacitance between the drain and source terminals of the first switching element is defined as the first electrostatic capacitance, the electrostatic capacitance between the drain and source terminals of the second switching element is defined as the second electrostatic capacitance, the electrostatic capacitance between the drain and source terminals of the third switching element is defined as the third electrostatic capacitance, and the electrostatic capacitance between the drain and source terminals of the fourth switching element is defined as the fourth electrostatic capacitance,

[0137] At least one of the electrostatic capacitors, namely the first electrostatic capacitor, the second electrostatic capacitor, the third electrostatic capacitor, and the fourth electrostatic capacitor, has a value that is different from the values ​​of the other electrostatic capacitors.

[0138] (Component 4)

[0139] 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.

[0140] (Component 5)

[0141] The power supply device according to any one of configurations 1 to 4, wherein the first capacitor, the second capacitor, the third capacitor and the fourth capacitor are ceramic capacitors or film capacitors.

[0142] (Composition 6)

[0143] The power supply device according to any one of configurations 1 to 5, wherein the first electrostatic capacitor, the second electrostatic capacitor, the third electrostatic capacitor and the fourth electrostatic capacitor are all different values.

[0144] (Component 7)

[0145] According to any one of configurations 1 to 5, in the power supply device, at least one value of the electrostatic capacitor among the first electrostatic capacitor, the second electrostatic capacitor, the third electrostatic capacitor and the fourth electrostatic capacitor is a first value, and another value of the electrostatic capacitor is a second value different from the first value.

[0146] (Composition 8)

[0147] According to any one of configurations 1 to 5, in the power supply device, any two values ​​of the electrostatic capacitors, the second electrostatic capacitor, the third electrostatic capacitor, and the fourth electrostatic capacitor are first values, one of the remaining two values ​​of the electrostatic capacitor is a second value different from the first value, and the other value of the remaining two values ​​of the electrostatic capacitor is a third value different from the first and second values.

[0148] (Composition 9)

[0149] An image forming apparatus for performing image formation on a recording material, the image forming apparatus comprising:

[0150] The power supply device according to any one of configurations 1 to 8.

[0151] (Composition 10)

[0152] A device for consuming electricity, the device comprising:

[0153] The power supply device according to any one of configurations 1 to 8.

[0154] According to the present invention, it becomes possible to reduce noise propagating from the switching power supply of a full-bridge system to the electrical power supply, and to reduce the size and cost of the circuit.

[0155] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. A power supply device of a full-bridge system, comprising: a rectification circuit configured to rectify an AC voltage of an AC power source; a smoothing capacitor connected in parallel to the rectification circuit and configured to smooth the voltage rectified by the rectification 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 of the first switching element and the second switching element and the other end connected to a connection point of the third switching element and the fourth switching element; and a control portion configured to control 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, and the power supply device further comprises: 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; and a fourth capacitor connected in parallel to the fourth switching element, wherein when a combined capacitance of a static capacitance between a drain terminal and a source terminal of the first switching element and a static capacitance of the first capacitor is defined as a first static capacitance, a combined capacitance of a static capacitance between a drain terminal and a source terminal of the second switching element and a static capacitance of the second capacitor is defined as a second static capacitance, a combined capacitance of a static capacitance between a drain terminal and a source terminal of the third switching element and a static capacitance of the third capacitor is defined as a third static capacitance, and a combined capacitance of a static capacitance between a drain terminal and a source terminal of the fourth switching element and a static capacitance of the fourth capacitor is defined as a fourth static capacitance, at least one value of the static capacitances among the first static capacitance, the second static capacitance, the third static capacitance, and the fourth static capacitance is a value different from the other static capacitances.

2. The power supply device according to claim 1, wherein the static capacitances between the drain terminals and the source terminals of the first switching element, the second switching element, the third switching element, and the fourth switching element are substantially the same.

3. A power supply device of a full-bridge system, comprising: a rectification circuit configured to rectify an AC voltage of an AC power source; a smoothing capacitor connected in parallel to the rectification circuit and configured to smooth the voltage rectified by the rectification 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; a fourth switching element connected in series to the third switching element; an inductor element connected at one end to a connection point of the first switching element and the second switching element and connected at the other end to a connection point of the third switching element and the fourth switching element; and a control portion configured to control 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, and wherein when an electrostatic capacitance between a drain terminal and a source terminal of the first switching element is defined as a first electrostatic capacitance, an electrostatic capacitance between a drain terminal and a source terminal of the second switching element is defined as a second electrostatic capacitance, an electrostatic capacitance between a drain terminal and a source terminal of the third switching element is defined as a third electrostatic capacitance, and an electrostatic capacitance between a drain terminal and a source terminal of the fourth switching element is defined as a fourth electrostatic capacitance, at least one value of the electrostatic capacitances among the first electrostatic capacitance, the second electrostatic capacitance, the third electrostatic capacitance, and the fourth electrostatic capacitance is a value different from values of the other electrostatic capacitances.

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. 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 thin film capacitors.

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

7. The power supply device according to claim 1, wherein at least one value of the electrostatic capacitances among the first electrostatic capacitance, the second electrostatic capacitance, the third electrostatic capacitance, and the fourth electrostatic capacitance is a first value, and another value of the electrostatic capacitances is a second value different from the first value.

8. The power supply device according to claim 1, wherein among the first electrostatic capacitance, the second electrostatic capacitance, the third electrostatic capacitance, and the fourth electrostatic capacitance, any two values of the electrostatic capacitances are a first value, one value of the electrostatic capacitances among the remaining two values is a second value different from the first value, and the other value of the electrostatic capacitances among the remaining two values is a third value different from the first value and the second value.

9. An image forming apparatus for performing image formation on a recording material, the image forming apparatus comprising: the power supply device according to claim 1.

10. An apparatus for consuming electric power, the apparatus comprising: the power supply device according to claim 1. ​

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