JPH0970142A - Filter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter circuit capable of absorbing kickback voltage caused by surge noises entering from the exterior without increasing terminal noise. SOLUTION: A varistor 8 and bead inductors 9a, 9b are placed and connected in series in a line 15 connected in parallel before and behind a common mode coil 1. At this time the bead inductors 9a, 9b are positioned on both sides of the varistor 8. As a result, kickback voltage generated in the common mode coil 1 by noises entering from the exterior is clamped by the varistor 8; meanwhile, high-frequency noises generated from a DC-DC converter 6 is absorbed into the bead inductors 9a, 9b, the common mode coil 1 and capacitors 3a, 3b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter circuit used in a power supply circuit for electric equipment and the like, and more particularly to a filter circuit that absorbs surge noise that enters from a commercial power supply.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing an example of a conventional filter circuit and a power supply circuit to which the circuit is applied.

In the figure, 1 is a common mode coil.
The capacitor 2 is provided between the line 13 and the line 14 connected to the commercial power supply 11. Further, capacitors 3a and 3b are provided between the lines 13 and 14 and the ground, respectively.

The common code coil 1 raises the high frequency impedance of the line, and the capacitors 3a and 3b lower the high frequency impedance between the lines 13 and 14 and the ground, so that these functions as a line filter to reduce noise. Absorb.

The rectifying diodes 4a, 4b, 4c, 4d are arranged so as to form a known full-wave rectifying circuit, and rectify the current supplied from the commercial power supply 11.

A capacitor 5 provided on the output side of a full-wave rectifying circuit composed of rectifying diodes 4a, 4b, 4c and 4d.
Smoothes the output of the current rectified by the rectifying diodes 4a, 4b, 4c, 4d. The DC-DC converter 6 generates an arbitrary DC voltage from the smoothed output.

A protective earth 12 is provided on the commercial power supply 11.

By the way, according to the standards concerning the regulation of radio interference in each country, there are regulations concerning the radiated electric field generated from electric equipment and the high frequency noise such as terminal noise.
In terms of product sales, it is necessary to satisfy this regulatory standard.

Conventionally, in order to satisfy the above-mentioned regulation standard,
Noise is reduced by using the filter circuit described in FIG. That is, in order to prevent switching noise generated from the DC-DC converter 6 from being generated in the line as terminal noise, for example, the common mode coil 1 increases the high frequency impedance of the line, and the capacitors 3a and 3b decrease the high frequency impedance between the grounds. , To absorb noise.

[0010]

However, in the above-mentioned conventional filter circuit, when high frequency surge noise generated by opening / closing of a switch of another device connected to the commercial power source or lightning strikes from the line of the commercial power source, A so-called kickback voltage is generated before and after the common mode coil 1, and due to the impedance difference between the lines, a phase difference occurs in noise that has entered each line, and as a result, DC
There is a drawback that an overvoltage is applied to the DC converter 6 and the circuit may malfunction or be destroyed.

To solve this drawback, a method using a spark gap can be considered.

FIG. 4 is a diagram showing an example of a power supply circuit in which the spark gap 7 is connected in parallel with the common mode coil 1 in the circuit of FIG.

By inserting the spark gap 7, it is possible to discharge the kickback voltage generated before and after the common mode coil 1 at a low voltage. However, the spark gap 7 may be discharged depending on the variation of the components and the operating environment. Since the discharge voltage is affected, it is difficult to define the intrusion noise and it is insufficient to eliminate the above-mentioned drawbacks.

As another method for solving the above-mentioned drawbacks, a method using a varistor can be considered.

FIG. 5 is a diagram showing an example of a power supply circuit in which a varistor 8 is connected in parallel with the common mode coil 1 in the circuit of FIG.

Since the varistor 8 is inserted,
The kickback voltage generated before and after the common mode coil 1 can be clamped by the varistor voltage.

However, in this method, since the varistor 8 is connected in parallel, the effect of raising the high frequency impedance of the line by the common mode coil 1 is impaired, and the capacitance component of the varistor 8 causes the DC-DC converter 6 to generate. There is a problem that the high frequency component of the switching noise passing through the varistor 8 increases the terminal noise.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is a filter circuit capable of absorbing a kickback voltage caused by surge noise intruding from the outside without increasing terminal noise. To provide.

[0019]

In order to achieve the above object, the present invention provides a filter circuit for preventing leakage of high frequency noise to a commercial power source and absorbing surge noise entering from the commercial power source. First inductor means provided in the middle of the line connected to the commercial power source, the impedance increasing as the high frequency component of the applied voltage increases, and the second inductor means and the varistor increasing the impedance as the high frequency component of the applied voltage increases. 3. A filter circuit according to claim 1, further comprising a circuit block connected in series, the circuit block being connected in parallel with the first inductor means.

Furthermore, the present invention provides a filter circuit according to claim 2, wherein the second inductor means and the varistor of claim 1 are integrated.

Further, the present invention provides the filter circuit according to claim 3, wherein in the structure of claim 1 or 2, the second inductor means is a bead inductor.

Here, the first inductor means described in claim 1 means, for example, a common mode coil or the like.

The integration according to the second aspect means that the element is physically fixed with, for example, resin so that it can be handled as a single element.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of a filter circuit according to an embodiment of the present invention and a power supply circuit to which the circuit is applied.

In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. Only parts different from those of FIG. 3 will be explained. In this circuit, the varistor 8 and the bead inductor 9
The circuit block in which a and 9b are connected in series is connected to the line 15
It is connected in parallel with the common mode coil 1 via. At that time, the bead inductors 9a and 9b are connected to the varistor 8
Placed on both sides of.

According to this filter circuit, the kickback voltage generated in the common mode coil 1 due to the noise that has entered from the outside is clamped by the varistor 8. Further, bead inductors 9 provided at both ends of the varistor 8
Since the line 15 high-frequency impedance is high due to a and 9b, DC-DC (high-frequency noise generated from the converter 6 does not pass through the varistor 8;
It is absorbed by the common code coil 1 and the capacitors 3a and 3b.

As described above, the kickback voltage can be clamped and the high frequency noise can be absorbed at the same time, so that surge noise from the outside can be absorbed without increasing the terminal noise.

In this embodiment, the bead inductors 9a and 9b are inserted into both ends of the varistor 8, but the present invention is not limited to this, and may be inserted into either one of the front and rear ends. . Further, the number of varistor and bead actuators to be inserted is not limited to one or two.

Further, in the present embodiment, the varistor 8 and the bead inductors 9a and 9b are inserted into the circuit as separate elements, but these elements are integrated into one element in advance. , May be applied to this filter circuit.

The integrated element will be described below.

FIG. 2 is a diagram showing an example of the structure of an element composed of a varistor and a bead inductor.

In the figure, 16 is a varistor, and bead inductors 17a and 17b are connected in series to both ends of the varistor 16. These elements connected in series are integrated and encapsulated by resin 10 such as epoxy.

The material used for the integration is not limited to the resin and may be another material or another method.

As described above, the varistor 16 and the bead inductors 17a and 17b are integrally enclosed, and are mounted in place of the varistor 8 and the bead inductors 9a and 9b in the present embodiment. Similar effects can be obtained with respect to points, mounting area, and mounting cost.

In this embodiment, a so-called bead inductor without an iron core is adopted because it is easy to mount, but an inductor with an iron core may be used.

[0037]

As described above, according to the first aspect of the present invention.
According to the filter circuit of the present invention, the varistor clamps the kickback voltage due to the surge noise, and the second inductor means blocks the passage of the high frequency noise. Therefore, the surge noise that enters from the outside without increasing the terminal noise is caused. The kickback voltage can be absorbed.

According to the filter circuit of the second aspect of the present invention, since the second inductor means and the varistor are integrally connected, the number of components can be reduced, and the mounting area of components and the mounting cost can be reduced. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a filter circuit according to an embodiment of the present invention and a power supply circuit to which the circuit is applied.

FIG. 2 is a diagram showing an example of a configuration of an element including a varistor and a bead inductor according to the same embodiment.

FIG. 3 is a diagram showing an example of a conventional filter circuit and a power supply circuit to which the circuit is applied.

FIG. 4 is a diagram showing an example of a conventional filter circuit using a spark gap and a power supply circuit to which the circuit is applied.

FIG. 5 is a diagram showing an example of a conventional filter circuit using a varistor and a power supply circuit to which the circuit is applied.

[Explanation of symbols]

 1 Common Mode Coil 2 Capacitor 3a Capacitor 3b Capacitor 6 DC-DC Converter 8 Varistor 9a Bead Inductor 9b Bead Inductor 10 Epoxy Resin 11 Commercial Power 13 Line 14 Line 15 Line 16 Varistor 17a Bead Inductor 17b Bead Inductor

Claims (3)

[Claims] 1. A filter circuit for preventing leakage of high frequency noise to a commercial power source and absorbing surge noise intruding from the commercial power source, wherein the filter circuit is provided in the middle of a line connected to the commercial power source. Of the first inductor means whose impedance increases as the high-frequency component of the voltage increases, and a circuit block in which the second inductor means and the varistor whose impedance increases as the high-frequency component of the applied voltage increases are connected in series. A filter circuit, wherein the filter circuit is connected in parallel with the first inductor means. 2. The filter circuit according to claim 1, wherein the second inductor means and the varistor are integrated. 3. The filter circuit according to claim 1, wherein the second inductor means is a bead inductor.