JP2004236413A - Noise filter circuit for switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise filter circuit for a switching power supply capable of preventing fluctuations in the output voltage of the switching power supply by preventing a surge current of a common mode from flowing into the ground. <P>SOLUTION: This noise filter for the switching power supply includes a series circuit of a gas tube arrester and an oxidized metal varistor, which is connected between an AC supply line and a ground line; and a line bypass capacitor connected between the AC supply line and the ground line. In this noise filter, a surge current inhibiting resistor is connected in series to the line bypass capacitor. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a noise filter circuit for a switching power supply.
[0002]
[Prior art]
The switching power supply circuit is provided with a noise filter circuit for protecting the switching power supply circuit from external noise invading from the input side or for suppressing conduction noise from the switching power supply circuit appearing at the AC input terminal.
[0003]
FIG. 1 shows the configuration of the switching power supply circuit.
[0004]
The switching power supply circuit includes an input unit 1, a noise filter unit (noise filter circuit) 2, a rectifying and smoothing unit 3, and a converter unit 4. The input AC voltage is rectified and smoothed by the rectifying and smoothing unit 3 and then converted by the converter unit 4 to output a predetermined DC voltage.
[0005]
Commercial AC power from a commercial AC power supply is sent by an AC supply line composed of a line (line line) L and a neutral (neutral line) N. In the input unit 1, an overcurrent protection fuse F1 is connected to the line L.
[0006]
In the noise filter unit 2, an across-the-line capacitor C1 for reducing high-frequency noise between L and N is connected between the line L after the fuse F1 and the neutral N. In the subsequent stage, a series circuit of a gas tube arrester A1 and a metal oxide varistor B1 is connected between the line L and the frame ground FG, and a gas tube arrester is connected between the neutral N and the frame ground FG. A series circuit of A2 and a metal oxide varistor B2 is connected.
[0007]
In the subsequent stage, a line bypass capacitor C3 for reducing high-frequency noise between the line L and the FG is connected between the line L and the frame ground (ground line) FG, and the neutral N and the frame ground FG are connected. Is connected to a line bypass capacitor C4 for reducing high-frequency noise between N and FG.
[0008]
In the subsequent stage, a choke coil L1 for removing noise of the in-phase component is connected between the line L and the neutral N.
[0009]
In the subsequent stage of the choke coil L1, an across-the-line capacitor C2 is connected between the line L after the fuse F1 and the neutral N. In the subsequent stage, a line bypass capacitor C5 is connected between the line L and the frame ground FG, and a line bypass capacitor C6 is connected between the neutral N and the frame ground FG.
[0010]
The line bypass capacitors C3, C4, C5, and C6 in the noise filter unit 2 are common mode generated by a current flowing through a parasitic capacitor between a collector or a source of a switching element (not shown) in the DC-DC converter and the frame ground FG. This is to remove noise.
[0011]
The series circuit of the gas tube arrester A1 and the metal oxide varistor B1 in the noise filter unit 2 is used to absorb the surge energy of a common mode surge current between the line L and the frame ground FG. Things. Similarly, the series circuit of the gas tube arrester A2 and the metal oxide varistor B2 is for absorbing the surge energy when a common mode surge current enters between the neutral N and the frame ground FG. .
[0012]
The AC input that has passed through the noise filter unit 2 is rectified by a diode bridge D in the rectifying / smoothing unit 3 and then smoothed by a diode C7 in the rectifying / smoothing unit 3 to become an unstable DC voltage. This unstable DC voltage is stabilized by a DC-DC converter in the converter section and is output as a predetermined DC voltage.
[0013]
[Patent Document 1] JP-A-8-191570 [Patent Document 2] JP-A-7-39136 [Patent Document 3] JP-A-1994-153382 [Patent Document 4] JP-A-2000-98797 ]
[Problems to be solved by the invention]
In a conventional noise filter, as shown in FIG. 1, when a surge current enters between an AC supply line (L, N) and a frame ground FG, a gas tube arrester (A1, A2) and a metal oxide A series circuit with the varistors (B1, B2) generally absorbs the surge energy.
[0015]
However, since the line bypass capacitors (C3, C4, C5, C6) are connected between the AC supply lines (L, N) and the frame ground FG, the AC supply lines (L, N) and the frame ground FG are connected to each other. When a surge current intrudes during the period, the surge current flows into the frame ground FG through the line bypass capacitors (C3, C4, C5, C6). When the surge current flows into the frame ground FG, the potential of the frame ground FG fluctuates, and as a result, the output voltage of the switching power supply fluctuates.
[0016]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply noise filter circuit that can prevent a common mode surge current from flowing into the ground and prevent fluctuations in the output voltage of the switching power supply.
[0017]
[Means for Solving the Problems]
According to the first aspect of the present invention, a series circuit of a gas tube arrester and a metal oxide varistor is connected between an AC supply line and a ground line, and a line is connected between the AC supply line and the ground line. In a noise filter circuit for a switching power supply to which a bypass capacitor is connected, a surge current blocking resistor is connected in series with the line bypass capacitor between an AC supply line to which the line bypass capacitor is connected and a ground line. It is characterized by having.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0019]
FIG. 2 shows the configuration of the switching power supply circuit. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
[0020]
In this switching power supply circuit, the configuration of the noise filter unit 2A is different from the configuration of the noise filter unit 2 in FIG. In the noise filter section 2A, a surge current blocking resistor R1 is connected between the line bypass capacitors C3 and C4 and the frame ground FG, and between the line bypass capacitors C5 and C6 and the frame ground FG. The surge current blocking resistor R2 is connected.
[0021]
In the noise filter section 2A of FIG. 2, when a surge current enters from the line L and flows into the frame ground FG from the line bypass capacitors C3 and C5, the surge current is suppressed by the impedance of the surge current blocking resistors R1 and R2. Is prevented from flowing. Similarly, when a surge current flows from the neutral N and a surge current flows from the line bypass capacitors C4 and C6 to the frame ground FG, the flow of the surge current is prevented by the impedance of the surge current blocking resistors R1 and R2.
[0022]
In the noise filter section 2A, the surge current that has intruded into the AC supply lines (L, N) is prevented from flowing into the frame ground FG through the line bypass capacitors (C3, C4, C5, C6). Fluctuations in the output voltage of the power supply are prevented.
[0023]
Instead of providing the surge current blocking resistors R1 and R2 as shown in FIG. 2, a surge current blocking resistor R3 is provided between the capacitor C3 and the line L, as in a noise filter section 2B shown in FIG. A surge current blocking resistor R4 is provided between the capacitor C4 and the neutral N, a surge current blocking resistor R5 is provided between the capacitor C5 and the line L, and a surge current blocking resistor R6 is provided between the capacitor C6 and the neutral N. , May be provided.
[0024]
【The invention's effect】
According to the present invention, it is possible to prevent the common mode surge current from flowing into the ground, and to prevent the output voltage of the switching power supply from fluctuating.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing a configuration of a conventional switching power supply circuit.
FIG. 2 is an electric circuit diagram showing a configuration of a switching power supply circuit according to the embodiment.
FIG. 3 is an electric circuit diagram showing a modification.
[Explanation of symbols]
2A, 2B Noise filter section L line (line line)
N Neutral (neutral line)
FG frame ground (ground line)
A1, A2 Gas tube arresters B1, B2 Metal oxide varistors C3, C4, C5, C6 Line bypass capacitors R1, R2, R3, R4, R5, R6 Surge current blocking resistors

Claims (1)

A switching power supply in which a series circuit of a gas tube arrester and a metal oxide varistor is connected between the AC supply line and the ground line, and a line bypass capacitor is connected between the AC supply line and the ground line. In the noise filter circuit for
A noise filter circuit for a switching power supply, wherein a surge current blocking resistor is connected in series with a line bypass capacitor between an AC supply line to which a line bypass capacitor is connected and a ground line.

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