Power supply device and image forming apparatus

Abstract

To reduce a noise level radiated from a product device by suppressing noise propagated to a secondary side.SOLUTION: The switching power supply 200 includes a bridge diode 203, a transformer 206 having a primary winding 206a and a secondary winding 206c, a smoothing capacitor 207, a FET208, a diode 209, and a smoothing capacitor 210, and further includes a capacitor 220 having one end of the secondary winding 206c connected to the ground on the secondary side and the other end of the secondary winding 206c connected to the primary side, and a capacitor 221 having one end connected to the other end of the secondary winding 206c and the other end connected to the primary side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power supply device and an image forming apparatus equipped with the power supply device. [Background technology]

[0002] It is known that switching power supplies that use switching elements generate noise when the switching elements are turned on and off. Most of this noise is emitted from the primary-side switching element, and some of it is propagated into the secondary-side circuit via a transformer. To address this issue, switching power supplies have been proposed that return noise propagated to the secondary side via a capacitor to the primary side and suppress the noise via a primary-side filter. For example, Patent Document 1 discloses a technology for suppressing noise by connecting the secondary-side ground and primary-side ground with a capacitor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3473853 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while conventional technology has taken measures to reduce noise generated in the ground connected to the secondary winding of the isolation transformer, it has not taken into consideration noise generated on the secondary output side. As a result, in the case of switching power supplies that use a hard switching method and have high output power, there is an issue that noise from the secondary output side is likely to leak into each unit.

[0005] The present invention has been made under these circumstances, and has an object to suppress noise propagated to the secondary side and reduce the noise level radiated from a product device. [Means for solving the problem]

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

[0007] (1) A power supply device comprising: first rectifying means for rectifying an AC voltage; first smoothing means for smoothing the AC voltage rectified by the first rectifying means; an isolation transformer having a primary winding to which the voltage smoothed by the first smoothing means is supplied; and a secondary winding insulated from the primary winding; a switching element for conducting or non-conducting a current flowing through the primary winding; second rectifying means for rectifying the current flowing through the secondary winding; and second smoothing means for smoothing the voltage rectified by the second rectifying means, and outputting an output voltage smoothed by the second smoothing means, wherein one end of the secondary winding is connected to a ground on the secondary side and the other end of the secondary winding is connected to a side from which the output voltage is output; a first capacitor having one end connected to a ground on the secondary side and the other end connected to the primary side; and a second capacitor having one end connected to the other end of the secondary winding and the other end connected to the primary side.

[0008] (2) An image forming apparatus comprising: an image forming unit that forms an image on a sheet; and the power supply device according to (1) above that supplies power to the image forming unit. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress noise propagated to the secondary side and reduce the noise level radiated from the product device. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing the configuration of an image forming apparatus according to first and second embodiments; [Figure 2] Circuit diagram showing the circuit configuration of a switching power supply according to a first embodiment [Figure 3] FIG. 1 is a diagram illustrating a current route in the first embodiment. [Figure 4] FIG. 1 is a diagram illustrating noise in the first embodiment. [Figure 5] Circuit diagram showing the circuit configuration of a switching power supply according to a second embodiment DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0012] [Configuration of image forming device] FIG. 1 is a cross-sectional view showing the configuration of a laser beam printer as an example of an image forming apparatus. The laser beam printer 100 (hereinafter referred to as printer 100) includes a photosensitive drum 101 on which an electrostatic latent image is formed, a charging unit 102 that uniformly charges the photosensitive drum 101, and a developing unit 103 that develops the electrostatic latent image formed on the photosensitive drum 101 to form a toner image. The printer 100 also includes an exposure device 110 that irradiates the photosensitive drum 101 with laser light to form an electrostatic latent image on the surface of the photosensitive drum 101. In the printer 100, the toner image formed on the photosensitive drum 101 is transferred by a transfer unit 105 to a sheet S as a recording material fed from a cassette 104. The sheet S with the transferred toner image is transported to a fixing unit 106, where the toner image is fixed to the sheet S. The sheet S with the fixed toner image is then ejected onto a tray 107. The photosensitive drum 101, charging unit 102, developing unit 103, and transfer unit 105 constitute an image forming unit (image forming means). The printer 100 also includes a low-voltage power supply device 108, which supplies power to a control unit that controls driving units such as motors, image forming operations by the image forming unit, and conveyance operations of the sheet S. The printer 100 also includes a control unit 109, which controls the entire printer 100.

[0013] [Configuration of switching power supply] FIG. 2 is a circuit diagram showing the circuit configuration of a switching power supply 200 serving as a power supply device according to the first embodiment, which is provided as the low-voltage power supply 108 in the printer 100 shown in FIG. 1. The basic configuration is a flyback power supply. Thanks to advances in semiconductors and circuit innovations, the output limits of flyback power supplies have been improving year by year, with switching power supplies capable of outputting more than 500 W now available. Furthermore, flyback power supplies are hard-switching power supplies that are relatively prone to generating noise. Flyback power supplies with increased output require greater noise suppression than ever before.

[0014] 2, when AC plug 201 is connected to an outlet, AC voltage is input from an AC power supply (not shown) to switching power supply 200. The input AC voltage is input to diode bridge 203, which serves as first rectifying means, via filter circuit 202. Diode bridge 203 has input-side terminals 203a and 203b and output-side terminals 203c (first output terminal) and 203d (second output terminal). Diode bridge 203 full-wave rectifies the AC voltage input from input-side terminals 203a and 203b, and outputs the full-wave rectified AC voltage to output-side terminals 203c and 203d. Output-side terminal 203c of diode bridge 203 is connected to one end (high potential terminal) of smoothing capacitor 207, and terminal 203d is connected to the other end (low potential terminal) of smoothing capacitor 207. The AC voltage that has been full-wave rectified by the diode bridge 203 is smoothed by a smoothing capacitor 207 as a first smoothing means, and becomes a substantially constant DC voltage.

[0015] Transformer 206 is an insulating transformer for converting energy on the primary side (primary energy) to energy on the secondary side. Transformer 206 has primary winding 206a to which voltage from smoothing capacitor 207 is supplied, secondary winding 206c insulated from primary winding 206a, and auxiliary winding 206d. Note that, since FIG. 2 shows an example in which a flyback circuit is applied, secondary winding 206c is wound in the opposite direction to primary winding 206a. Similarly to secondary winding 206c, auxiliary winding 206d is also wound in the opposite direction to primary winding 206a.

[0016] One end of the smoothing capacitor 207 is connected to one end of a primary winding 206a of the transformer 206, and the other end of the primary winding 206a is connected to a drain terminal of a field effect transistor (hereinafter referred to as FET) 208 serving as a switching element. A source terminal of the FET 208 is connected to the other end of the smoothing capacitor 207 and a terminal 203d on the output side of the diode bridge 203. A gate terminal of the FET 208 is connected to a control IC (not shown) that controls the switching operation of the FET 208.

[0017] One end of secondary winding 206c of transformer 206 is connected to the cathode terminal of diode 209 serving as second rectifying means, and the anode terminal of diode 209 is connected to the other end of smoothing capacitor 210 serving as second smoothing means and to ground. One end of smoothing capacitor 210 is connected to the other end of secondary winding 206c of transformer 206. The charging voltage of smoothing capacitor 210 is output as output voltage Vo of switching power supply 200 to an external load connected to switching power supply 200.

[0018] 2, a low-level signal is input from a control IC (not shown) to the gate terminal of FET 208, and at the timing when FET 208 turns off, a large surge voltage occurs at the drain terminal of FET 208. The circuit that suppresses the surge voltage is snubber circuit 214, surrounded by a dashed line. The effect of snubber circuit 214 enables switching power supply 200 to produce a large output. Snubber circuit 214 is composed of auxiliary winding 206d of transformer 206, two rectifying elements, diodes 212 and 213, and clamp capacitor 211.

[0019] In the snubber circuit 214, one end of the clamp capacitor 211 is connected to the other end of the primary winding 206a of the transformer 206 and the drain terminal of the FET 208, and the other end of the clamp capacitor 211 is connected to the anode terminal of the diode 212. The cathode terminal of the diode 212 is connected to one end of the smoothing capacitor 207 and one end of the primary winding 206a of the transformer 206. The anode terminal of the diode 213 is connected to the source terminal of the FET 208, the other end of the smoothing capacitor 207, and the output terminal 203d of the diode bridge 203. On the other hand, the cathode terminal of the diode 213 is connected to one end of the auxiliary winding 206d of the transformer 206. The other end of the auxiliary winding 206d of the transformer 206 is connected to the connection point where the clamp capacitor 211 and the anode terminal of the diode 212 are connected.

[0020] When a high-level signal is input from a control IC (not shown) to the gate terminal of FET 208, conduction occurs between the drain terminal and the source terminal of FET 208, and FET 208 enters a conductive state (ON state). As a result, current from smoothing capacitor 207 flows to primary winding 206a, and energy corresponding to the conductive period of FET 208 is stored in transformer 206. While FET 208 is in a conductive state, a voltage is generated in secondary winding 206c of transformer 206, with the start of the winding being positive and the end of the winding being negative. However, because the voltage at the anode terminal of diode 209 on the secondary side of transformer 206 is lower than the voltage at the cathode terminal, diode 209 remains non-conductive, and no current flows from secondary winding 206c through diode 209.

[0021] On the other hand, when a low-level signal is input from a control IC (not shown) to the gate terminal of the FET 208, the drain terminal and source terminal of the FET 208 are opened, and the FET 208 is in a non-conductive state (off state). This generates a voltage in the secondary winding 206c of the transformer 206, with the starting side of the winding being negative and the ending side being positive. Because the voltage at the anode terminal of the diode 209 on the secondary side of the transformer 206 is higher than the voltage at the cathode terminal, the diode 209 is in a conductive state, and a current flows from the secondary winding 206c of the transformer 206 through the diode 209 on the secondary side. In this way, a pulse-like voltage is generated in the secondary winding 206c in conjunction with the switching operation of the FET 208. The voltage generated in the secondary winding 206c of the transformer 206 is rectified by the diode 209 and smoothed by the smoothing capacitor 210, generating an output voltage Vo. The output voltage Vo is controlled to a constant voltage by the switching operation of the FET 208.

[0022] [Snubber circuit operation] Next, the operation of the snubber circuit 214 will be described with reference to the state diagram shown in FIG. 3. FIG. 3 is a circuit diagram illustrating the peripheral circuit of the snubber circuit 214 of FIG. 2, in order to explain the operation of the snubber circuit 214. FIG. 3(a) is a diagram illustrating the circuit operation immediately after the FET 208 is turned off (immediately after switching from the on state to the off state), and FIG. 3(b) is a diagram illustrating the circuit operation immediately after the FET 208 is turned on (immediately after switching from the off state to the on state). Note that the snubber circuit 214 of the present invention is characterized in terms of circuit operation immediately after the FET 208 is turned off and immediately after the FET 208 is turned on. Circuit operation during periods other than immediately after the FET 208 is turned off and immediately after the FET 208 is turned on is the same as that of a general switching power supply device not including the above-described snubber circuit 214, and therefore will not be described here.

[0023] (Circuit operation immediately after FET 208 is turned off) First, with reference to FIG. 3(a), the circuit operation immediately after the FET 208 is turned off will be described. When a low-level signal is input from a control IC (not shown) to the gate terminal of the FET 208, the drain terminal and source terminal of the FET 208 are opened. Then, the current that had been flowing from the primary winding 206a to the drain terminal of the FET 208 starts to flow to the clamp capacitor 211, and the clamp capacitor 211 is charged by the current from the primary winding 206a. The current route of the charging current to the clamp capacitor 211 is indicated by the thick arrow in FIG. 3(a), and flows from the primary winding 206a to the clamp capacitor 211 and then to the diode 212. At this time, the drain voltage of the FET 208 has an arc-shaped voltage waveform due to the resonance between the capacitance of the clamp capacitor 211 and the inductance of the primary winding 206a, causing the voltage to rise gradually and limiting a sudden rise in voltage.

[0024] (Circuit operation immediately after FET208 is turned on) On the other hand, when a high-level signal is input from a control IC (not shown) to the gate terminal of the FET 208, conduction occurs between the drain terminal and the source terminal of the FET 208. This state is shown in FIG. 3(b). The thick arrow in FIG. 3(b) indicates the current route of the discharge current from the clamp capacitor 211. The primary winding 206a and the auxiliary winding 206d are coupled within the transformer 206. Therefore, due to the turns ratio between the primary winding 206a and the auxiliary winding 206d, the discharge current flowing from the clamp capacitor 211 is divided into a current flowing through the FET 208 and a current flowing backward through the primary winding 206a. The current flowing backward through the primary winding 206a becomes a regenerative current to the smoothing capacitor 207, and part of the energy (the charging voltage of the clamp capacitor 211) generated by the surge voltage when the FET 208 is turned off is regenerated in the smoothing capacitor 207 and reused. Then, as the discharge current flows, the voltage charged by the surge voltage is discharged from the clamp capacitor 211, which returns to the state it was in just before the charging current flowed, as shown in Figure 3(a), and is reset to a state where it can again store energy due to the surge voltage.

[0025] Meanwhile, the current flowing from the clamp capacitor 211 to the FET 208 flows to the auxiliary winding 206d via the diode 213, and the current energy of the discharge current is stored in the auxiliary winding 206d. The energy stored in the auxiliary winding 206d is converted into a secondary current the next time the FET 208 is turned off, and the energy stored in the primary winding 206a is added to the converted secondary current. The diode 213 has the function of blocking the discharge of the charge of the clamp capacitor 211 through the auxiliary winding 206d. The diode 213 and the auxiliary winding 206d are connected in this order in the direction in which the discharge current from the clamp capacitor 211 flows; however, the same circuit operation would be achieved if the diode 213 was connected first to the auxiliary winding 206d, then to the diode 213.

[0026] To suppress noise in the switching power supply 200 configured as described above and having a high output, as shown in Fig. 2, the switching power supply 200 is provided with a first capacitor 220 and a second capacitor 221. Capacitor 220 is connected between the secondary-side ground and the primary-side ground, and its main role is to return noise that has propagated to the secondary-side ground to the primary side. On the other hand, capacitor 221 is connected between the secondary-side output and the primary-side power supply, and its main role is to return noise that has propagated to the secondary-side output to the primary side.

[0027] The specific connection relationship is as follows: One end of primary winding 206a of transformer 206 is connected to the high-potential side of smoothing capacitor 207, and the other end is connected to FET 208. One end of secondary winding 206c of transformer 206 is connected to diode 209, and outputs output voltage Vo from the other end. Diode 209 has a cathode terminal connected to one end of secondary winding 206c and an anode terminal connected to ground. Capacitor 220 has one end connected to the ground on the secondary side and the other end connected to the low-potential side of smoothing capacitor 207. Capacitor 221 has one end connected to the output voltage side, specifically the other end of secondary winding 206c, and the other end connected to the high-potential side of smoothing capacitor 207.

[0028] [Noise suppression effect] Figure 4 shows noise data indicating the noise suppression effects of capacitor 221 and capacitor 220. The horizontal axis of the graph in Figure 4 is frequency [MHz], and the vertical axis is decibels [dB]. Figure 4(a) shows a state where only capacitor 221 is mounted, and capacitor 220 is not mounted. Figure 4(b) shows a state where only capacitor 220 is mounted, and capacitor 221 is not mounted. In other words, Figure 4(b) is a conventional configuration. Figure 4(c) shows a state where both capacitors 220 and 221 are mounted.

[0029] Comparing the noise waveforms, when either capacitor 220 or capacitor 221 is not installed, large broad noise appears in the 50 to 70 MHz range. Also, in Figures 4(a) and (b), which show the state where only capacitor 220 is installed, it can be seen that the broad noise in the 120 to 130 MHz and 180 to 190 MHz range is worse. In contrast, in the state of Example 1 where both capacitors 220 and 221 are installed, as shown in Figure 4(c), it can be seen that the noise state is good. This result shows that, from the perspective of noise suppression, it is important not only to return to the primary side the noise that has sneaked into the secondary-side ground using capacitor 220, but also to return to the primary side the noise that has sneaked into the secondary-side output using capacitor 221.

[0030] As explained above, by connecting both capacitor 220, which connects the secondary side ground to the primary side ground, and capacitor 221, which connects the secondary side output to the primary side power supply, it is possible to significantly reduce the primary side noise propagating to the secondary side. In the first embodiment, a switching power supply with a large output power based on a flyback power supply has been taken as an example for explanation, but the present invention can be applied to other power supply methods including not only a general flyback power supply but also a forward power supply.

[0031] As described above, according to the first embodiment, it is possible to suppress the noise propagated to the secondary side and reduce the noise level radiated from the product device. [Example]

[0032] In Example 1, a good product condition with noise suppression was achieved by implementing both a capacitor 220 connecting the secondary-side ground and the primary-side ground, and a capacitor 221 connecting the secondary-side output and the primary-side power supply. In Example 2, as a modification of Example 1, a configuration that provides the same effect will be described with reference to Figure 5. Note that the circuit system of the switching power supply is a basic flyback configuration to omit explanation, and the same components as those in the switching power supply in Figure 2 are assigned the same reference numerals.

[0033] [Variation 1] Figure 5(a) shows a configuration in which the connection position of the diode 209 is changed from that of the switching power supply in Figure 2. The anode terminal of the diode 209 is connected to the other end of the secondary winding 206c, and the cathode terminal is connected to one end of the smoothing capacitor 210. The connection position of the diode 209 is the same in Figures 5(b) and 5(c).

[0034] The connection of capacitor 220 between the secondary-side ground and the primary-side ground remains unchanged. On the other hand, capacitor 221 is connected not to the power output line but between the output side of secondary winding 206c of transformer 206 and the primary-side power supply side. Specifically, one end of capacitor 221 is connected to the anode terminal of diode 209, and the other end is connected to the high-potential side of smoothing capacitor 207. In the configuration of FIG. 5(a), noise generated on the primary side propagates to the secondary side via transformer 206, but is returned to the primary side by capacitor 221, thereby significantly suppressing noise propagation to the secondary side.

[0035] [Variation 2] 5(b) is an example in which the primary side of capacitor 221 is connected to the primary-side ground, as opposed to FIG. 5(a). Specifically, one end of capacitor 221 is connected to the anode terminal of diode 209, and the other end is connected to the low-potential side of smoothing capacitor 207. In the configuration of FIG. 5(b), primary-side noise that sneaks into the output side of the secondary side is returned to the primary-side ground, thereby significantly suppressing noise propagation to the secondary side.

[0036] [Variation 3] In FIG. 5(c), the primary-side connection destination of capacitor 220 and the primary-side connection destination of capacitor 221 are reversed compared to FIG. 5(a). That is, capacitor 220 is connected between the primary-side power supply and the secondary-side ground, and capacitor 221 is connected between the primary-side ground and the secondary-side output. Specifically, one end of capacitor 220 is connected to the secondary-side ground, and the other end is connected to the high-potential side of smoothing capacitor 207. One end of capacitor 221 is connected to the anode terminal of diode 209, and the other end is connected to the low-potential side of smoothing capacitor 207. Even in the configuration of FIG. 5(c), primary-side noise that has leaked to the secondary-side ground and the secondary-side power supply can be returned to the primary side, thereby significantly suppressing noise propagation to the secondary side.

[0037] As described above, by connecting both ends of the secondary winding 206c of the transformer 206 to the primary circuit via the capacitors 220 and 221, noise that has entered the secondary side can be returned to the primary side. This significantly reduces noise propagating to the secondary side. The circuit example shown in the second embodiment also allows for greater flexibility in the placement of the capacitors 220 and 221, even when the print pattern is constrained by the component sizes used or various other conditions. In the second embodiment, the capacitor 221 is connected to the anode side of the diode 209 (upstream side of the diode 209). However, the same effect can be achieved by connecting the capacitor 221 to the cathode side of the diode 209 (downstream side of the diode 209). Furthermore, in the first and second embodiments, a FET can be used as the second rectifier instead of the diode 209 described in the first embodiment.

[0038] As described above, one end of capacitor 220 or capacitor 221 is connected to the upstream side of diode 209. Alternatively, one end of capacitor 220 or capacitor 221 may be connected to the downstream side of diode 209. Alternatively, the other end of capacitor 220 or capacitor 221 is connected to the high-potential terminal side of smoothing capacitor 207. Alternatively, the other end of capacitor 220 or capacitor 221 may be connected to the low-potential terminal side of smoothing capacitor 207. That is, it is sufficient that one end of capacitor 220 is connected to the ground on the secondary side and the other end is connected to the primary side, so that noise from the ground on the secondary side is returned to the primary side. It is sufficient that one end of capacitor 221 is connected to the output voltage Vo on the secondary side of transformer 206 and the other end is connected to the primary side, so that noise on the output voltage Vo side on the secondary side is returned to the primary side.

[0039] As described above, according to the second embodiment, it is possible to suppress the noise propagated to the secondary side and reduce the noise level radiated from the product device.

[0040] The disclosure of this embodiment includes the following configuration. (Configuration 1) a first rectifying means for rectifying an AC voltage; a first smoothing means for smoothing the AC voltage rectified by the first rectifying means; an isolation transformer having a primary winding to which the voltage smoothed by the first smoothing means is supplied and a secondary winding insulated from the primary winding; a switching element that conducts or discontinuously controls the current flowing through the primary winding; a second rectifying means for rectifying a current flowing through the secondary winding; a second smoothing means for smoothing the voltage rectified by the second rectifying means; a power supply device that outputs an output voltage smoothed by the second smoothing means, One end of the secondary winding is connected to a ground on the secondary side, and the other end of the secondary winding is connected to a side from which the output voltage is output, a first capacitor having one end connected to the ground of the secondary side and the other end connected to the primary side; a second capacitor having one end connected to the other end of the secondary winding and the other end connected to the primary winding; A power supply device comprising: (Configuration 2) 2. The power supply device according to configuration 1, wherein one end of the first capacitor or the second capacitor is connected to the upstream side of the second rectifying means. (Configuration 3) 2. The power supply device according to configuration 1, wherein one end of the first capacitor or the second capacitor is connected to the downstream side of the second rectifying means. (Configuration 4) 2. The power supply device according to configuration 1, wherein the other end of the first capacitor or the second capacitor is connected to the high potential terminal side of the first smoothing means. (Configuration 5) 2. The power supply device according to configuration 1, wherein the other end of the first capacitor or the second capacitor is connected to the low potential terminal side of the first smoothing means. (Configuration 6) one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the second rectifying means and the other end is connected to one end of the second smoothing means; the second rectifying means has a cathode terminal connected to one end of the secondary winding and an anode terminal connected to the other end of the second smoothing means; the other end of the first capacitor is connected to the low potential side of the first smoothing means, 2. The power supply device according to claim 1, wherein the other end of the second capacitor is connected to the high potential side of the first smoothing means. (Configuration 7) one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the low potential side of the first smoothing means, The power supply device according to configuration 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the high potential side of the first smoothing means. (Configuration 8) one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the low potential side of the first smoothing means, The power supply device according to configuration 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the low potential side of the first smoothing means. (Configuration 9) one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the high potential side of the first smoothing means, The power supply device according to configuration 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the low potential side of the first smoothing means. (Configuration 10) an image forming means for forming an image on a sheet; the power supply device according to any one of configurations 1 to 9, which supplies power to the image forming unit; An image forming apparatus comprising: [Explanation of symbols]

[0041] 203 Diode Bridge 206 transformer, 206a primary winding, 206c secondary winding 207 Smoothing capacitor 208 FET 220 Capacitor 221 Capacitor

Claims

1. a first rectifying means for rectifying an AC voltage; a first smoothing means for smoothing the AC voltage rectified by the first rectifying means; an isolation transformer having a primary winding to which the voltage smoothed by the first smoothing means is supplied, and a secondary winding insulated from the primary winding; a switching element that conducts or discontinuously conducts current flowing through the primary winding; a second rectifying means for rectifying a current flowing through the secondary winding; a second smoothing means for smoothing the voltage rectified by the second rectifying means; a power supply device that outputs an output voltage smoothed by the second smoothing means, One end of the secondary winding is connected to a ground on the secondary side, and the other end of the secondary winding is connected to a side from which the output voltage is output, a first capacitor having one end connected to a ground on the secondary side and the other end connected to the primary side; a second capacitor having one end connected to the other end of the secondary winding and the other end connected to the primary winding; A power supply device comprising:

2. 2. The power supply device according to claim 1, wherein one end of the first capacitor or the second capacitor is connected to the upstream side of the second rectifier.

3. 2. The power supply device according to claim 1, wherein one end of the first capacitor or the second capacitor is connected to the downstream side of the second rectifier.

4. 2. The power supply device according to claim 1, wherein the other end of the first capacitor or the second capacitor is connected to the high potential terminal side of the first smoothing means.

5. 2. The power supply device according to claim 1, wherein the other end of the first capacitor or the second capacitor is connected to the low potential terminal side of the first smoothing means.

6. one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the second rectifying means and the other end is connected to one end of the second smoothing means; the second rectifying means has a cathode terminal connected to one end of the secondary winding and an anode terminal connected to the other end of the second smoothing means; the other end of the first capacitor is connected to the low potential side of the first smoothing means, 2. The power supply device according to claim 1, wherein the other end of the second capacitor is connected to the high potential side of the first smoothing means.

7. one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the low potential side of the first smoothing means, 2. The power supply device according to claim 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the high potential side of the first smoothing means.

8. one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the low potential side of the first smoothing means, 2. The power supply device according to claim 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the low potential side of the first smoothing means.

9. one end of the primary winding is connected to the high potential side of the first smoothing means and the other end is connected to the switching element; one end of the secondary winding is connected to the other end of the second smoothing means and the other end is connected to the second rectifying means; the second rectifying means has a cathode terminal connected to one end of the second smoothing means and an anode terminal connected to the other end of the secondary winding; the other end of the first capacitor is connected to the high potential side of the first smoothing means, 2. The power supply device according to claim 1, wherein one end of the second capacitor is connected to the anode terminal of the second rectifying means and the other end is connected to the low potential side of the first smoothing means.

10. an image forming means for forming an image on a sheet; a power supply device according to any one of claims 1 to 9, which supplies power to the image forming means; An image forming apparatus comprising:

Images