JP2004236059A - Noise filter circuit for switching power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise filter circuit for a switching power source in which the width of a conductor pattern can be made small and the conductor pattern can be prevented from being burnt when a line bypass capacitor short-circuits. <P>SOLUTION: In this noise filter circuit for a switching power source provided with the line bypass capacitor connected between an ac feeding line and a ground line, a fuse for capacitor short circuit is connected serially to the line bypass capacitor between the ac feeding line with the line bypass capacitor connected thereto and the ground line. <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 section 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 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.
[0007]
In the subsequent stage, a choke coil L1 for removing in-phase component noise is connected between the line L and the neutral N.
[0008]
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.
[0009]
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.
[0010]
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.
[0011]
[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]
According to safety standards, a short circuit test of the elements is performed in consideration of abnormal times of each capacitor in the noise filter section 2 so that a dangerous state is not caused by burning of a conductor pattern on a circuit board.
[0013]
Abnormality tests are also performed on the line bypass capacitors C3, C4, C5, and C6. Even when these elements are short-circuited, the conductor pattern from the line L or the neutral N to the capacitor and the conductor pattern from each capacitor to the frame ground FG can be obtained. The width of these conductor patterns is increased so that the conductor patterns do not burn out.
[0014]
That is, when the line bypass capacitor is short-circuited, the width of the conductor pattern is increased so that the conductor pattern does not burn out before the overcurrent protection fuse F1 is blown. For example, in a domestic specification having an AC power supply voltage of 100 V, a fuse of 15 A is often used as the overcurrent protection fuse F1, and therefore, the width of the conductor pattern is often required to be 20 mm or more. .
[0015]
However, as the miniaturization of equipment is progressing, the switching power supply circuit is also required to be miniaturized.However, in the conventional circuit, it is necessary to increase the width of the conductor pattern as described above. Has become difficult.
[0016]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a noise filter circuit for a switching power supply that can reduce the width of a conductor pattern and can prevent the conductor pattern from being burned out when a line bypass capacitor is short-circuited.
[0017]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a noise filter circuit for a switching power supply including a line bypass capacitor connected between an AC supply line and a ground line, wherein the AC supply line to which the line bypass capacitor is connected is provided. A fuse for short-circuiting the capacitor is connected in series with the line bypass capacitor between the ground line and the ground line. The AC supply line includes the line (line line) L and the neutral (neutral line) N in FIGS.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
[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 this noise filter section 2A, a fuse F2 for short-circuiting a capacitor 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 capacitor short-circuit fuse F3 is connected.
[0021]
In this example, assuming that the AC power supply voltage is 100 V and a 15-A fuse is used as the overcurrent protection fuse F1, for example, a 1-A fuse is used as the capacitor short-circuit fuses F2 and F3.
[0022]
In the noise filter section 2A of FIG. 2, when the line bypass capacitor C3 is short-circuited, the capacitor short-circuit fuse F2 is blown immediately. Therefore, it is possible to prevent a large current from flowing through the conductor pattern from the line L to the capacitor C3 and the conductor pattern from the capacitor C3 to the frame ground FG. When the line bypass capacitor C4 is short-circuited, the capacitor short-circuit fuse F2 is blown immediately. Therefore, a large current is prevented from flowing through the conductor pattern from the neutral N to the capacitor C4 and the conductor pattern from the capacitor C4 to the frame ground FG.
[0023]
When the line bypass capacitor C5 is short-circuited, the capacitor short-circuit fuse F3 is blown immediately. Therefore, it is possible to prevent a large current from flowing through the conductor pattern from the line L to the capacitor C5 and the conductor pattern from the capacitor C5 to the frame ground FG. When the line bypass capacitor C6 is short-circuited, the capacitor short-circuit fuse F3 is blown immediately. For this reason, a large current is prevented from flowing through the conductor pattern from the neutral N to the capacitor C6 and the conductor pattern from the capacitor C6 to the frame ground FG.
[0024]
That is, even when the line bypass capacitors C3, C4, C5, and C6 are short-circuited, a large current does not flow through the conductor pattern from the line L or the neutral N to the capacitor and the conductor pattern from each capacitor to the frame ground FG. Can be made smaller than the width of the noise filter section 2 of FIG. As a result, the size of the switching power supply circuit can be reduced.
[0025]
Note that instead of providing the capacitor short-circuit fuses F2 and F3 as shown in FIG. 2, a capacitor short-circuit fuse F4 is provided between the capacitor C3 and the line L as in a noise filter unit 2B shown in FIG. A fuse F5 for short-circuiting between the capacitor C4 and the neutral N, a fuse F6 for short-circuiting between the capacitor C5 and the line L, and a fuse F6 for short-circuiting between the capacitor C6 and the neutral N. , May be provided.
[0026]
【The invention's effect】
According to the present invention, the width of the conductor pattern can be reduced, and furthermore, the conductor pattern can be prevented from burning when the line bypass capacitor is short-circuited.
[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 wire)
FG frame ground (ground line)
C3, C4, C5, C6 Line bypass capacitors F2, F3, F4, F5, F6, F7 Fuse for capacitor short circuit

Claims (1)

In a noise filter circuit for a switching power supply having a line bypass capacitor connected between an AC supply line and a ground line,
A noise filter circuit for a switching power supply, wherein a capacitor short-circuit fuse 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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