JP2015233383A - Discharge circuit, power supply device with discharge circuit, and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge circuit which enables the materialization of the function of discharging a surge voltage resulting from a lightning strike or the like while retaining the function as a noise filtering circuit.SOLUTION: A discharge circuit comprises: a Y capacitor 6 connected with a live line of a commercial power supply 1; and a Y capacitor 10 having a capacitance different from that of the Y capacitor 6, and connected in series between the Y capacitor 6 and a protection earth 2. A pattern gap B between void portions 13b and 14b made identical in potential to electrodes of the one Y capacitor 10 of the Y capacitor 6 and the Y capacitor 10, which is smaller in capacitance, is smaller than a pattern gap A between void portions 12a and 14a made identical in potential to electrodes of the other Y capacitor 6 of the Y capacitor 6 and the Y capacitor 10, which is larger in capacitance.

Description

  The present invention relates to a discharge circuit, a power supply device including the discharge circuit, and an image forming apparatus, and more particularly, to a discharge circuit provided in a commercial power supply line of an electric device or the like.

  As shown in FIG. 7, in a conventional power supply device such as an electric device, a filter circuit is provided in the power input section, and the common mode noise and normal mode noise entering from the commercial power source 1 side are absorbed by the filter circuit. Yes. Here, the filter circuit is composed of an across-the-line capacitor (hereinafter referred to as X capacitor) 4, a capacitor called line bypass capacitor (hereinafter referred to as Y capacitor) 5 and 6, a common mode coil 3 and the like. Yes. In addition, according to standards regarding radio wave interference regulations in each country, regulations on high-frequency noise such as a radiation electric field generated from an electric device and a noise electric field intensity conducted to the commercial power source 1 are made. In order to satisfy the radio wave interference regulations in each country, power supply devices such as electric devices use the filter circuit described above to reduce high-frequency noise. For this reason, filter circuits such as the X capacitor 4 and the Y capacitors 5 and 6 are indispensable parts for power supply devices such as electric devices. In FIG. 7, the same components as those in the embodiments described later are denoted by the same reference numerals, and the description thereof is omitted here.

  On the other hand, in order to prevent malfunction of the switching regulator 9 due to a surge voltage generated by a lightning strike or the like, a power supply device such as an electric device to which the commercial power supply 1 is connected has a surge voltage applied to the input portion of the power supply. Some have a discharge circuit (see, for example, Patent Document 1). In a conventional discharge circuit, a floating pattern is arranged from a commercial power supply line through a first discharge gap, and a secondary pattern is arranged from the floating pattern through a second discharge gap. Furthermore, the conventional discharge circuit is characterized in that a capacitor is connected between the floating pattern and the secondary pattern. As this capacitor, a Y capacitor satisfying an insulation function in accordance with safety standards is used, and a two-stage discharge gap structure is formed by a first discharge gap and a second discharge gap. Since the total distance between the first discharge gap and the second discharge gap only needs to satisfy the safety standard insulation distance, the distance between the first discharge gap and the second discharge gap is the safety standard. Further, the discharge start voltage can be lowered by making the distance smaller than the necessary distance. With such a structure, when a large surge voltage having a high frequency component is induced in an electrical device due to a lightning strike or the like, the impedance of the capacitor is reduced and a short-circuit state is established. Therefore, a surge voltage is induced only between the commercial power supply line and the floating pattern, and discharge occurs in the first discharge gap. Since the commercial power supply line and the floating pattern are short-circuited by this discharge, all surge voltages induced in the commercial power supply line are induced in the floating pattern. As a result, a surge voltage is induced between the floating pattern and the secondary pattern, and a discharge is generated in the second discharge gap.

Japanese Patent No. 3626414

  However, in the conventional example, the capacitor connected to the floating pattern and the secondary pattern is not connected to the commercial power line. For this reason, this capacitor has a problem that it does not have a filter function for high-frequency noise such as a radiated electric field generated from an electric device and a noise electric field intensity conducted to a commercial power source.

  The present invention has been made under such circumstances, and an object of the present invention is to realize a function as a discharge circuit that discharges a surge voltage due to a lightning strike while maintaining a function as a noise filter circuit.

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

  (1) A first capacitor connected to one supply line of the AC power source and a second capacitor having a different capacity from the first capacitor and connected in series between the first capacitor and the ground A first distance between a portion of the first capacitor and the second capacitor having the same potential as each electrode of the capacitor having a small capacitance is the first capacitor and the second capacitor. A discharge circuit characterized by being smaller than a second distance between portions of the two capacitors having the same potential as each electrode of a capacitor having a large capacity.

  (2) A power supply apparatus that generates a DC voltage from an AC voltage input from an AC power supply, comprising: rectifying means that rectifies the AC voltage; and the discharge circuit according to (1). Power supply.

  (3) a first capacitor having one end connected to one supply line of the AC power supply, a second capacitor having one end connected to the other supply line of the AC power supply, and the first and second capacitors A third capacitor having a capacitance value different from that of the first and second capacitors, the first capacitor and the third capacitor are connected in series between a connection point connecting the other ends of the two and the ground. The first distance between the first capacitor and the third capacitor or the second capacitor and a portion of the third capacitor having the same potential as each electrode of the capacitor having a small capacity is A discharge circuit characterized by being smaller than a second distance between portions of the second capacitor and the third capacitor that have the same potential as each electrode of a capacitor having a large capacity.

  (4) A power supply device for generating a DC voltage from an AC voltage input from an AC power supply, comprising: rectifying means for rectifying the AC voltage; and the discharge circuit according to (3). Power supply.

  (5) The image forming means for forming an image on a recording material, the control means for controlling the image forming means, and supplying power to the image forming means and the control means (2) or (4) An image forming apparatus comprising: a power supply device.

  According to the present invention, it is possible to realize a function as a discharge circuit that discharges a surge voltage due to a lightning strike while maintaining the function as a noise filter circuit.

The figure which shows the discharge circuit of Example 1. The figure which shows the pattern of the discharge circuit of Example 1. The figure which shows the operation | movement waveform of the discharge circuit of Example 1. The figure which shows the discharge circuit of Example 2, The figure which shows the pattern of a discharge circuit The figure which shows the discharge circuit of Example 3, The figure which shows the pattern of a discharge circuit FIG. 10 is a diagram illustrating a configuration of an image forming apparatus according to a fourth embodiment. The figure which shows the filter circuit of the conventional example

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail by way of examples with reference to the drawings.

[Power supply unit]
FIG. 1 is a diagram illustrating an example of a power supply device to which the filter circuit of the first embodiment and the filter circuit of the present embodiment are applied. A commercial power source 1 that is an AC power source is provided with a protect earth 2 that is a ground. A common mode coil 3 and an across-the-line capacitor (hereinafter referred to as “the common mode coil 3”) are provided between a live (LIVE) line that is one supply line of the commercial power supply 1 and a neutral (NEUTRAL) line that is the other supply line of the commercial power supply 1. , X capacitor) 4 is connected. Further, a line bypass capacitor (hereinafter referred to as a Y capacitor) 5 is connected between the neutral line of the commercial power source 1 and the protect earth 2. Rectifier diodes 7a, 7b, 7c, and 7d (hereinafter referred to as rectifier diodes 7) that are rectifiers are arranged to constitute a full-wave rectifier circuit, and rectify the AC voltage input from the commercial power source 1. Further, a smoothing capacitor 8 is connected to the output side of the full-wave rectifier circuit constituted by the rectifier diode 7 to smooth the rectified AC voltage. A switching regulator 9 is connected to the subsequent stage of the rectifier diode 7 and the smoothing capacitor 8, and a predetermined output voltage is generated by switching the smoothed voltage at a high frequency.

  In this embodiment, a Y capacitor 6 as a first capacitor and a Y capacitor 10 as a second capacitor are connected in series between the live line of the commercial power source 1 and the protect earth 2. Further, the Y capacitor 6 and the Y capacitor 10 of this embodiment have different capacitance values, and the pattern distance between lands on the printed circuit board 100 described later has a predetermined distance. Specifically, in this embodiment, the capacitance value C6 of the Y capacitor 6 is 820 pF, and the capacitance value C10 of the Y capacitor 10 is 560 pF. The combined capacitance value of the capacitance value C6 of the Y capacitor 6 and the capacitance value C10 of the Y capacitor 10 is about 330 pF, which is the same capacitance value as that of the Y capacitor 5. Thus, by setting the combined capacitance value of the Y capacitor 6 and the Y capacitor 10 to a capacitance value substantially equal to the capacitance value of the Y capacitor 5, the impedance between each line of the commercial power supply 1 and the protect earth 2 becomes the same. Therefore, in the configuration of the present embodiment, it is possible to suppress noise entering from the commercial power source 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power source 1 side. That is, the Y capacitors 5, 6, and 10 of this embodiment function as a part of the filter circuit. In this embodiment, the capacitance values of the Y capacitor 6 and the Y capacitor 10 are the values described above. However, since the amount of noise generated varies depending on the configuration of the switching power supply and the configuration of the electrical equipment, these capacitance values are the values described above. It is not limited to. In the example described above, the combined capacitance value of the Y capacitors 6 and 10 and the capacitance value of the Y capacitor 5 are equal. However, these capacitance values do not necessarily have to be equal, and may function as a filter circuit.

[Pattern on printed circuit board]
FIG. 2 shows only the patterns around the Y capacitors 6 and 10 on the printed circuit board 100 according to the present embodiment. The solder on the side opposite to the component surface on which the components such as the Y capacitor 6 are mounted is shown. It is a figure which shows a surface. The pattern 11 is a pattern on the neutral line side of the commercial power source 1, the pattern 12 is a pattern on the live line side, and the pattern 13 is a pattern of the protect earth 2. The pattern 14 is a pattern for connecting the Y capacitor 6 and the Y capacitor 10 in series. White portions 12 a, 13 b, 14 a, and 14 b provided in contact with lands indicated by double white circles on the patterns 12, 13, and 14 are portions where the resist is not applied on the printed circuit board 100, This is the part where the conductor is exposed. The white portion 12a has the same potential as the pattern 12, the white portion 13b has the same potential as the pattern 13, and the white portions 14a and 14b have the same potential.

  Here, a pattern gap A which is a second distance between the white portion 12a and the white portion 14a, which is a portion having the same potential as each electrode (also referred to as a terminal or a terminal electrode) of the Y capacitor 6 having a capacitance value of 820 pF. Is 1.6 mm. The pattern gap B, which is the first distance between the white portion 13b and the white portion 14b, which is a portion having the same potential as each electrode of the Y capacitor 10 having a capacitance value of 560 pF, is 1.1 mm. Therefore, the total distance between the pattern gap A and the pattern gap B is 2.7 mm (= 1.6 mm + 1.1 mm). The total distance between the pattern gap A and the pattern gap B is larger than a value satisfying the creeping distance and the spatial distance of the safety standard of each country that is different for each electric device, that is, a necessary insulation distance (predetermined distance) in the safety standard. It is configured. In addition, each distance between the pattern gap A and the pattern gap B is configured to be shorter than a necessary insulation distance in accordance with safety standards. Further, a slit Sa is provided between the pattern gaps A, and a slit Sb is provided between the pattern gaps B. In the present embodiment, the values of the pattern gap A and the pattern gap B are the values described above. However, since the necessary insulation distance varies depending on the voltage value of the commercial power source 1, the safety standards of each country, and the type of electrical equipment, the value of each pattern gap is not limited to the above-described values.

[Comparison with conventional example]
The effect obtained by connecting the Y capacitor 6 and the Y capacitor 10 having different capacitance values in series between the commercial power source 1 and the protect earth 2 and providing the pattern gap A and the pattern gap B will be described in comparison with the conventional example. FIG. 3A is a graph showing the surge voltage of the power supply device of the conventional example described in FIG. 7, and enters the live line of the commercial power supply 1 due to lightning or the like when the configuration of this embodiment is not applied. An excessive surge voltage waveform is shown. In FIG. 3A, the horizontal axis indicates time, the vertical axis indicates voltage, and the right diagram shows a waveform obtained by enlarging the broken-line frame in the left diagram. FIG. 3B is a graph showing the voltage of the power supply device of this embodiment shown in FIG. 1, and shows the waveform of the surge voltage entering the live line. FIG. 3B is also a graph similar to that of FIG. 3A, and the right diagram shows a waveform obtained by enlarging the broken-line frame portion of the left diagram.

  As shown in FIG. 3A, in the conventional power supply device, when a surge voltage is induced from the commercial power source 1, the live line of the commercial power source 1 in FIG. An induced voltage as shown by the solid line is generated. At this time, in the power supply apparatus having the conventional filter circuit shown in FIG. 7, only the Y capacitors 5 and 6 are connected between each line of the commercial power supply 1 and the protect earth 2. For this reason, in the conventional power supply device shown in FIG. 7, each pattern gap is set to 2.7 mm in order to ensure an insulation distance according to safety standards. However, since the pattern gap (2.7 mm) of the conventional power supply device is too large, no discharge occurs even if a surge voltage is induced. Or, even if a discharge occurs, the induced voltage reaches an excessive voltage before the discharge. For this reason, as shown in FIG. 3A, the surge voltage induced in the commercial power supply line remains at a high value. Therefore, in the conventional power supply device, the induced voltage induced by the surge voltage is supplied to the subsequent switching regulator 9 as it is, and there is a possibility that the subsequent switching regulator 9 or the like malfunctions.

[Discharge start voltage during lightning strike]
On the other hand, as shown in FIG. 3B, in the circuit of the present embodiment, the Y capacitor 6 and the Y capacitor 10 having different capacitance values are connected in series between the live line and the protect earth 2, and the pattern gap A and the pattern A gap B is provided. For this reason, the discharge start voltage of the induced voltage at the time of a lightning strike becomes low. The reason for this will be described in detail below.

If the surge voltage induced in the live line of the commercial power source 1 is V, the both-ends voltage V6 of the Y capacitor 6 and the both-ends voltage V10 of the Y capacitor 10 are divided by the ratio of the capacitance values as shown in the following equations.
V6 = V × C10 / (C6 + C10)
V10 = V × C6 / (C6 + C10)
Therefore, the induced voltage is larger at the both-end voltage V10 of the Y capacitor 10 having a smaller capacitance value than the both-end voltage V6 of the Y capacitor 6 having a larger capacitance (V10> V6). This is shown by the dotted waveform in the enlarged view of FIG. The pattern gap B of the Y capacitor 10 is 1.1 mm. Therefore, at the timing T1 when the voltage between the pattern gaps B is induced to a voltage that cannot withstand the discharge, the first discharge (short circuit) between the pattern gaps B, that is, between the white portions 14b and 13b. ) Occurs. Thus, the timing T1 is a timing at which discharge is started between the pattern gaps B. As a result of the first discharge being performed between the pattern gaps B, the protective earth 2 and the pattern 14 are short-circuited, so that the induced voltage V of the commercial power supply 1 is induced only at both ends of the Y capacitor 6.

  Next, the pattern gap A is 1.6 mm. Therefore, at the timing T2 when the voltage between the pattern gaps A is induced to a voltage that cannot withstand the discharge, a second discharge (short) occurs between the pattern gaps A, that is, between the white portions 12a and 14a. Occur. Thus, the timing T2 is a timing at which discharge is started between the pattern gaps A. At this time, since the discharge start voltage becomes lower as the pattern gap is shorter, when the configuration of the present embodiment is applied (pattern gap A 1.6 mm), the configuration of the present embodiment is not applied (for example, the conventional pattern). The discharge start voltage is lower than that of the gap (2.7 mm).

  In this embodiment, the discharge when a surge voltage occurs in the live line has been described. However, when a surge voltage occurs in the neutral line, the surge voltage is induced in the live line via the X capacitor 4. . Here, since the combined capacity of the Y capacitors 6 and 10 connected in series is considerably smaller than the capacity of the X capacitor 4, a surge voltage is induced in the Y capacitors 6 and 10 connected in series. Therefore, even when a surge voltage is generated in the neutral line, discharge occurs in the Y capacitors 6 and 10 due to the same effect as described above. Thus, in this embodiment, the Y capacitors 6 and 10 also function as a discharge circuit.

  As shown in FIG. 2, a slit Sa and a slit Sb are provided in the pattern gap A and the pattern gap B, which are discharge locations, respectively. By providing the slit Sa and the slit Sb, even if a discharge occurs between the pattern gaps, the printed circuit board 100 is not carbonized and the withstand voltage is not reduced. Further, in the present embodiment, since the discharge portion (white portion 12a and the like) is provided on the pattern of the printed circuit board 100, additional components are not required and the cost can be reduced. However, the discharge part is not limited to the pattern of the printed circuit board 100, and the same potential part as that of the Y capacitor is formed using a terminal such as a metal at a place other than the pattern of the printed circuit board 100, and a gap is provided for discharging. Also good. For example, the discharge portion may be formed of a wire-like metal on the component surface side of the printed circuit board 100 and discharged between the wire-like metals, and the same applies to the following embodiments.

  Thus, in this embodiment, the discharge start voltage of the surge voltage can be lowered while ensuring an insulation distance necessary for safety standards between the line of the commercial power source 1 and the protect earth 2. For this reason, the switching regulator 9 connected in the subsequent stage does not cause a malfunction. Unlike the conventional discharge circuit, Y capacitors 6 and 10 are connected between each line of the commercial power source 1 and the protect earth 2. For this reason, it also has a function as a filter circuit that suppresses noise entering from the commercial power source 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power source 1 side.

  In this embodiment, the Y capacitor 6 and the Y capacitor 10 are connected in series. However, the Y capacitor 5 and the Y capacitor 10 may be connected in series. A capacitor may be connected in series. In this embodiment, the Y capacitors 5, 6, and 10 are connected to the commercial power source 1 that is upstream of the common mode coil 3, but the downstream side of the common mode coil 3 and the rectifier diode 7 are connected to each other. Y capacitors 5, 6, and 10 may be connected between them. Furthermore, in the present embodiment, the case of the filter circuit constituted by only one common mode coil 3 has been described. However, in the case of a two-stage filter circuit in which two common mode coils are connected, Y capacitors 5, 6, 10 may be connected between the rectifier diode 7 and the downstream side of the second common mode coil. The same applies to the first embodiment.

  In the above-described embodiment, the capacity of the Y capacitor 6 and the capacity of the Y capacitor 10 have been described as C6> C10, but C6 <C10 may be used. However, in this case, the pattern gap A of the Y capacitor 6 and the pattern gap B of the Y capacitor 10 are configured to satisfy A <B. That is, of two Y capacitors connected in series, the pattern gap distance of the Y capacitor having a small capacity is configured to be smaller than the distance of the pattern gap of the Y capacitor having a large capacity.

  As described above, according to the present embodiment, a function as a discharge circuit that discharges a surge voltage due to a lightning strike or the like can be realized while maintaining a function as a noise filter circuit.

[Power supply unit]
In the second embodiment, when the X capacitor is not connected between the lines of the commercial power supply 1 with respect to the first embodiment, two Y capacitors are connected in series to both lines of the commercial power supply 1 respectively. Different. FIG. 4A is a diagram illustrating an example of a filter circuit of the present embodiment and a circuit of a power supply device to which the filter circuit is applied. In addition, the same code | symbol is attached | subjected to the same structure as Example 1, and description is abbreviate | omitted. In FIG. 4A, a Y capacitor 5 as a third capacitor and a Y capacitor 15 as a fourth capacitor are connected in series between the neutral line of the commercial power source 1 and the protect earth 2. The Y capacitors 5 and 15 are connected to the input side of the rectifier diode 7. Further, the Y capacitor 5 and the Y capacitor 15 have different capacitance values, and the pattern distance between lands of the printed circuit board 100 has a predetermined distance.

  Specifically, in this embodiment, the capacitance value C5 of the Y capacitor 5 is 820 pF, and the capacitance value C15 of the Y capacitor 15 is 560 pF. Therefore, the combined capacitance value of the Y capacitor 5 and the Y capacitor 15 is about 330 pF. Become. On the other hand, since the capacitance value C6 of the Y capacitor 6 is 820 pF and the capacitance value C10 of the Y capacitor 10 is 560 pF as in the first embodiment, the combined capacitance value of the Y capacitor 6 and the Y capacitor 10 is about 330 pF. . Thus, in this embodiment, the combined capacitance value of the Y capacitor 6 and the Y capacitor 10 is configured to be the same as the combined capacitance value of the Y capacitor 5 and the Y capacitor 15. In this embodiment, by setting the capacitance values of the Y capacitors 5, 6, 10, and 15 to the above-described capacitance values, the impedance between each line of the commercial power source 1 and the protect earth 2 becomes the same. Therefore, it functions as a filter circuit that suppresses noise entering from the commercial power supply 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power supply 1 side.

  The capacitance values of the Y capacitors 5, 6, 10, and 15 are the above-described capacitance values. However, since the amount of noise generated varies depending on the configuration of the switching power supply and the configuration of the electrical equipment, the capacitance value is set to the above-described value. It is not limited. In the above-described example, the combined capacitance value of the Y capacitors 5 and 15 and the combined capacitance value of the Y capacitors 6 and 10 are equal. However, these combined capacitance values do not necessarily have to be equal, and can function as a filter circuit. Good. Further, the capacitance value C5 of the Y capacitor 5 may be smaller than the capacitance value C15 of the Y capacitor 15. In this case, a pattern gap C that is a third distance of a Y capacitor 5 described later may be configured to be smaller than a pattern gap D that is a fourth distance of a Y capacitor 15 described later.

[Pattern on printed circuit board]
FIG. 4B shows only the patterns around the Y capacitors 5, 6, 10, and 15 on the printed circuit board 100 in this embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The pattern 16 is a pattern for connecting the Y capacitor 5 and the Y capacitor 15 in series. Also, the white portions 11c, 13d, 16c, and 16d on the patterns 11, 13, and 16 are portions where the resist of the printed circuit board 100 is not applied and the conductors are exposed. The white portion 11c has the same potential as the pattern 11, the white portion 13d has the same pattern 13, and the white portions 16c and 16d have the same potential.

  In the first embodiment, as shown in FIG. 2, the white portions 12a, 14a and the like where the discharge is generated are configured in contact with the land. On the other hand, in this embodiment, the white portions 12a, 14a and the like where discharge occurs are configured at positions shifted from the land, unlike the first embodiment. That is, in the present embodiment, discharge occurs at a position different from the land to which the Y capacitor 6 and the like are soldered. Further, for example, the white portion 12a and the white portion 14a facing the white portion 12a have convex shapes on the sides facing each other, so that discharge is more likely to occur.

  Here, the pattern gap C between the white portion 11c and the white portion 16c at the same potential as the land to which the electrode of the Y capacitor 5 having a capacitance value of 820 pF is soldered is 1.6 mm. The pattern gap D between the white portion 13d and the white portion 16d at the same potential as the land to which the terminal of the Y capacitor 15 having a capacitance value of 560 pF is soldered is 1.1 mm. Therefore, the total distance between the pattern gap C and the pattern gap D is 2.7 mm. This total distance is a value that satisfies the creepage distance and the spatial distance of the safety standards of different countries for each electrical device, and the distances of the pattern gap C and the pattern gap D are shorter than the necessary insulation distances in accordance with the safety standards. It is configured. Similarly to Example 1, the pattern gap A is 1.6 mm, and the pattern gap B is 1.1 mm. In the present embodiment, each pattern gap is the distance described above. However, since the required insulation distance varies depending on the voltage value of the commercial power source 1, the safety standard of each country, and the type of electrical equipment, the pattern gap distance is the distance described above. It is not limited to.

[Discharge without X capacitor]
Hereinafter, the reason why the pattern capacitors A, B, C, and D are provided by connecting the Y capacitors 5 and 15 and the Y capacitors 6 and 10 having different capacitance values in series between each line of the commercial power source 1 and the protect earth 2 respectively. Will be explained. In the configuration of the first embodiment, the X capacitor 4 is connected between the lines of the commercial power source 1. For this reason, as described in the first embodiment, even if an excessive surge voltage is generated only in the neutral line during a lightning strike, a surge voltage is induced on the live line side via the X capacitor 4. However, when the X capacitor 4 is not connected between the lines of the commercial power supply 1 as in the configuration of the present embodiment, if an excessive surge voltage is generated only in the neutral line, there is no X capacitor 4 and the live line No surge voltage is induced on the side. For this reason, no discharge occurs in the Y capacitors 6 and 10. Therefore, as in the configuration of the present embodiment, when the X capacitor 4 is not between lines, the problem is solved by connecting two Y capacitors in series to each line of the commercial power source 1.

  In the present embodiment, the capacitance ratio of the Y capacitors connected in series and the distance between the pattern gaps are the same in each line. For this reason, even if an excessive surge voltage is generated only in one of the lines, discharge is performed between the pattern gaps of the Y capacitors 6 and 10 or the Y capacitors 5 and 15 according to the principle described in the first embodiment. That is, for example, among the two Y capacitors connected in series, a first discharge is generated by the Y capacitor 15 having a small capacitance value, and then the capacitance value of the two Y capacitors connected in series is large. A second discharge is generated in the Y capacitor 5. In the Y capacitors 5 and 15 of the present embodiment, the total distance of the pattern gaps C and D maintains the necessary insulation distance according to safety standards, and the distance between the pattern gaps C and D is shorter than that of the conventional circuit. Then, discharge is started at a lower voltage than in the prior art. In addition, the slit Sc is provided in the pattern gap C as a discharge location, and the slit Sd is provided in the pattern gap D in the same manner as in the first embodiment. For this reason, even if it discharges between each pattern gap, the printed circuit board 100 does not carbonize, and a withstand voltage does not fall.

  As described above, even if the circuit configuration is such that no X capacitor is connected between the lines of the commercial power supply 1, it is possible to discharge the surge voltage induced in only one line of the commercial power supply 1 to the protective earth 2. Become. The switching regulator 9 connected to the subsequent stage of the discharge circuit will not malfunction. Unlike the conventional discharge circuit, a Y capacitor is connected between each line of the commercial power source 1 and the protect earth 2. For this reason, it also functions as a filter circuit that suppresses noise entering from the commercial power source 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power source 1 side.

  In this embodiment, Y capacitors 5, 6, 10, and 15 are connected to the commercial power supply 1 side that is upstream from the common mode coil 3, but between the downstream side from the common mode coil 3 and the rectifier diode 7. Y capacitors 5, 6, 10, and 15 may be connected. The configuration of the present embodiment in which the two Y capacitors 5 and 15 are connected to the neutral line can also be applied to the configuration of the first embodiment having the X capacitor 4.

  As described above, according to the present embodiment, a function as a discharge circuit that discharges a surge voltage due to a lightning strike or the like can be realized while maintaining a function as a noise filter circuit.

[Power supply unit]
In the third embodiment, one end of two Y capacitors is connected to both lines of the commercial power supply 1 in the second embodiment, and the other end of the two Y capacitors and the protective earth are connected in series with one Y capacitor. Are different. FIG. 5A is a diagram illustrating an example of a filter circuit of the present embodiment and a circuit of a power supply device to which the filter circuit is applied. The same components as those in the second embodiment are denoted by the same reference numerals and description thereof is omitted. In FIG. 5A, one end of each of Y capacitors 5 and 6 as first and second capacitors is connected to each line of the commercial power source 1. Further, one end of the Y capacitor 10 as a third capacitor is connected to the protect earth 2. A connection point where the other ends of the Y capacitors 5 and 6 are connected is connected to the other end of the Y capacitor 10. That is, the Y capacitor 10 is connected in series between the connection point where the other ends of the Y capacitors 5 and 6 are connected to the ground.

  In this embodiment, the capacitance value C5 of the Y capacitor 5 and the capacitance value C6 of the Y capacitor 6 are 820 pF, and the capacitance value C10 of the Y capacitor 10 is 560 pF. For this reason, the combined capacitance value between the live line of the commercial power supply 1 and the protect earth 2 is equal to the combined capacitance value of the Y capacitor 6 and the Y capacitor 10 and is about 330 pF. On the other hand, the combined capacitance value between the neutral line of the commercial power source 1 and the protect earth 2 is the combined capacitance of the Y capacitor 5 and the Y capacitor 10, which is about 330 pF. In the present embodiment, by setting the capacitance values of the Y capacitors 5, 6, and 10 to the above-described capacitance values, the impedance between each line of the commercial power source 1 and the protect earth 2 becomes the same. Therefore, it functions as a filter circuit that suppresses noise entering from the commercial power supply 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power supply 1 side. In this embodiment, the capacitance values of the Y capacitors 5, 6, and 10 are set to the above-described values. However, since the amount of noise generated varies depending on the configuration of the switching power supply and the configuration of the electrical equipment, the capacitance value is set to the above-described value. It is not limited. The combined capacitance value of the Y capacitors 5 and 10 and the combined capacitance value of the Y capacitors 6 and 10 are not necessarily equal.

[Pattern on printed circuit board]
FIG. 5B shows only the patterns around the Y capacitors 5, 6, and 10 on the printed circuit board 100 of this embodiment. The same components as those in the second embodiment are denoted by the same reference numerals and description thereof is omitted. The white portion 11c on the pattern 11, the white portion 12a on the pattern 12, the white portion 13b on the pattern 13, and the white portions 14a, 14b and 14c on the pattern 14 are coated with the resist of the printed circuit board 100. The conductor is bare at the part that is not. The white portion 11c has the same potential as the pattern 11, the white portion 12a has the same pattern 12, the white portion 13b has the same pattern 13, and the white portions 14a, 14b and 14c have the same potential.

  Here, the distance of the pattern gap C which is the second distance between the white portion 11c and the white portion 14c of the same potential portion as the land to which the terminal of the Y capacitor 5 having a capacitance value of 820 pF is soldered is 1.6 mm. It is. The distance of the pattern gap A, which is the second distance between the white portion 12a and the white portion 14a of the same potential portion as the land to which the terminal of the Y capacitor 6 having a capacitance value of 820 pF is soldered, is 1.6 mm. is there. Thus, the distance between the pattern gap A and the pattern gap C is equal. Further, the distance of the pattern gap B, which is the first distance between the white portion 13b and the white portion 14b of the same potential portion as the land to which the terminal of the Y capacitor 10 having a capacitance value of 560 pF is soldered, is 1.1 mm. is there. Therefore, the total distance between the pattern gap A and the pattern gap B is 2.7 mm, and the total distance between the pattern gap C and the pattern gap B is also 2.7 mm. This total distance is a value that satisfies the creepage distance and clearance distance of the safety standards of different countries for each electrical device, and each gap is configured to be shorter than the necessary insulation distance in accordance with the safety standards.

  In the present embodiment, the distance between the pattern gaps is the distance described above. However, since the necessary insulation distance varies depending on the voltage value of the commercial power source 1, the safety standard of each country, and the type of electrical equipment, the distance between the pattern gaps is as described above. It is not limited to the distance. The distance of the pattern gap may be configured to satisfy the following relationship. That is, of the two Y capacitors (Y capacitor 5, 10 or Y capacitor 6, 10) connected in series, the pattern gap distance of the Y capacitor having the smaller capacity is larger than the pattern gap distance of the Y capacitor having the larger capacity. May be configured to be smaller.

  In the present embodiment, similarly to the second embodiment, the capacitance ratios and pattern gaps of the Y capacitors 5, 6, and 10 are configured to have the same capacitance ratio for each line. For this reason, even if an excessive surge voltage is generated only in one of the lines, discharge is performed between the line of the commercial power source 1 and the protective earth 2 according to the principle described in the first embodiment. As in the second embodiment, a slit Sa is provided in the pattern gap A serving as a discharge location, a slit Sb is provided in the pattern gap B, and a slit Sc is provided in the pattern gap C. For this reason, even if a discharge occurs between the pattern gaps, the printed circuit board 100 is not carbonized, and the withstand voltage is not reduced.

  As described above, even if the circuit configuration is such that no X capacitor is connected between the lines of the commercial power source 1, the surge voltage can be discharged to the protective earth 2. Then, the switching regulator 9 connected to the subsequent stage of the discharge circuit does not malfunction. Unlike the conventional discharge circuit, a Y capacitor is connected between each line of the commercial power source 1 and the protect earth 2. For this reason, it also functions as a filter circuit that suppresses noise entering in the common mode and noise flowing out from the switching regulator 9 to the commercial power supply 1 side. Furthermore, since one Y capacitor can be reduced with respect to the second embodiment, the cost can be reduced and the space of the printed circuit board 100 can be saved.

  In this embodiment, Y capacitors 5, 6, and 10 are connected to the commercial power supply 1 side that is upstream from the common mode coil 3, but the Y capacitor is connected between the rectifier diode 7 and the downstream side from the common mode coil 3. 5, 6, and 10 may be connected. The configuration of the present embodiment in which the Y capacitor 10 is connected to the connection point between the Y capacitor 6 and the Y capacitor 5 can also be applied to the configuration of the first embodiment having the X capacitor 4.

  As described above, according to the present embodiment, a function as a discharge circuit that discharges a surge voltage due to a lightning strike or the like can be realized while maintaining a function as a noise filter circuit.

  The power supply apparatus described in the first to third embodiments can be applied as, for example, a low-voltage power supply for an image forming apparatus, that is, a power supply that supplies power to a drive unit such as a controller (control unit) or a motor. Hereinafter, the configuration of the image forming apparatus to which the power supply devices of Embodiments 1 to 3 are applied will be described.

[Configuration of Image Forming Apparatus]
A laser beam printer will be described as an example of the image forming apparatus. FIG. 6 shows a schematic configuration of a laser beam printer which is an example of an electrophotographic printer. The laser beam printer 300 includes a photosensitive drum 311 as an image carrier on which an electrostatic latent image is formed, a charging unit 317 (charging unit) that uniformly charges the photosensitive drum 311, and an electrostatic latent image formed on the photosensitive drum 311. A developing unit 312 (developing unit) that develops an image with toner is provided. The toner image developed on the photosensitive drum 311 is transferred to a sheet (not shown) as a recording material supplied from the cassette 316 by a transfer unit 318 (transfer means), and the toner image transferred to the sheet is fixed to the fixing device 314. Then, the toner is fixed and discharged onto the tray 315. The photosensitive drum 311, the charging unit 317, the developing unit 312, and the transfer unit 318 are image forming units. The laser beam printer 300 includes the power supply device 400 described in the first to third embodiments, and the switching regulator 9 of the power supply device 400 generates a DC voltage of 24V or 3V, for example. Note that the image forming apparatus to which the power supply device 400 according to the first to third embodiments can be applied is not limited to that illustrated in FIG. 6, and may be an image forming apparatus including a plurality of image forming units, for example. Further, the image forming apparatus may include a primary transfer unit that transfers the toner image on the photosensitive drum 311 to the intermediate transfer belt and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to the sheet.

  The laser beam printer 300 includes a controller 320 that controls an image forming operation by the image forming unit and a sheet conveying operation. The power supply device 400 according to the first to third embodiments supplies power to the controller 320, for example. . The power supply device 400 described in the first to third embodiments supplies power to a driving unit such as a motor for rotating the photosensitive drum 311 or driving various rollers for conveying the sheet. Since the image forming apparatus of the present embodiment includes the power supply device 400 described in the first to third embodiments, a necessary insulation distance in accordance with safety standards is secured between each line of the commercial power supply 1 and the protect earth 2. The discharge start voltage of the surge voltage can be lowered. For this reason, the switching regulator 9 connected in the subsequent stage does not cause a malfunction. Further, unlike a power supply device having a conventional discharge circuit, a Y capacitor is connected between each line of the commercial power supply 1 and the protect earth 2. For this reason, it also functions as a filter circuit that suppresses noise entering from the commercial power source 1 in the common mode and noise flowing out from the switching regulator 9 to the commercial power source 1 side.

  As described above, according to the present embodiment, in the power supply device of the image forming apparatus, it is possible to realize a function as a discharge circuit that discharges a surge voltage due to a lightning strike while maintaining the function as a noise filter circuit.

1 Commercial power supply 2 Protect earth 5, 6, 10 Line bypass capacitor

Claims (16)

A first capacitor connected to one supply line of the AC power source;
A second capacitor having a different capacity from the first capacitor and connected in series between the first capacitor and ground;
With
Of the first capacitor and the second capacitor, the first distance between the parts having the same potential as each electrode of the capacitor having a small capacity is the capacity of the first capacitor and the second capacitor. A discharge circuit characterized by being smaller than a second distance between portions having the same potential as each electrode of a large capacitor. The sum of the first distance and the second distance is greater than a predetermined distance;
The discharge circuit according to claim 1, wherein each of the first distance and the second distance is smaller than the predetermined distance.   The discharge circuit according to claim 1, wherein the first capacitor and the second capacitor are line bypass capacitors. A third capacitor connected to the other supply line of the AC power supply;
A fourth capacitor having a different capacity from the third capacitor and connected in series between the third capacitor and ground;
With
Of the third capacitor and the fourth capacitor, the third distance between the parts having the same potential as each electrode of the capacitor having a small capacity is the capacity of the third capacitor and the fourth capacitor. The discharge circuit according to any one of claims 1 to 3, wherein the discharge circuit is smaller than a fourth distance between portions having the same potential as each electrode of the large capacitor. The sum of the third distance and the fourth distance is greater than a predetermined distance,
The discharge circuit according to claim 4, wherein each of the third distance and the fourth distance is smaller than the predetermined distance.   6. The discharge circuit according to claim 4, wherein the third and fourth capacitors are connected to an input side of a rectifier that rectifies an input AC voltage.   The discharge circuit according to any one of claims 4 to 6, wherein the third capacitor and the fourth capacitor are line bypass capacitors. A power supply device that generates a DC voltage from an AC voltage input from an AC power supply,
Rectifying means for rectifying the AC voltage;
A discharge circuit according to any one of claims 1 to 7,
A power supply device comprising: A first capacitor having one end connected to one supply line of an AC power source;
A second capacitor having one end connected to the other supply line of the AC power supply;
A third capacitor having a capacitance value different from that of the first and second capacitors, connected in series between a connection point connecting the other ends of the first and second capacitors and the ground,
The first distance between the first capacitor and the third capacitor or the second capacitor and the third capacitor having the same potential as each electrode of the capacitor having a small capacity is the first capacitor. The capacitor and the third capacitor or the second capacitor and the third capacitor are smaller than the second distance between the parts having the same potential as each electrode of the capacitor having a large capacity. Discharge circuit. The sum of the first distance and the second distance is greater than a predetermined distance;
The discharge circuit according to claim 9, wherein each of the first distance and the second distance is smaller than the predetermined distance.   11. The discharge circuit according to claim 9, wherein the first to third capacitors are connected to an input side of a rectifier that rectifies an input AC voltage.   The discharge circuit according to any one of claims 9 to 11, wherein the first to third capacitors are line bypass capacitors.   13. The across-the-line capacitor is not connected between one supply line of the AC power supply and the other supply line of the AC power supply. 13. Discharge circuit.   13. The across-the-line capacitor is connected between one supply line of the AC power supply and the other supply line of the AC power supply. 13. Discharge circuit. A power supply device that generates a DC voltage from an AC voltage input from an AC power supply,
Rectifying means for rectifying the AC voltage;
A discharge circuit according to any one of claims 9 to 14,
A power supply device comprising: Image forming means for forming an image on a recording material;
Control means for controlling the image forming means;
The power supply device according to claim 8 or 15, wherein power is supplied to the image forming unit and the control unit;
An image forming apparatus comprising:

Images