JP2002094348A - Dc line filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC line filter that has backup function with which output voltage to the next stage will not drop momentarily, even when an output voltage of an AC/DC converter is decreased. SOLUTION: X and Y capacitors are provided to one end of a common mode choke coil and a static capacitance of an X capacitor provided to the other end to satisfy a prescribed time constant, with respect to the input resistance of a load unit is selected in a range of 100 μF-470 mF. Furthermore, an electrolytic capacitor with a diode, connected in parallel therewith and a fuse connected in series therewith, is employed for the X capacitor and configures the DC line filter further provided with a discharge resistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line filter for smoothing an input voltage of a DC (direct current) power supply, and more particularly to a line filter having a backup function for a fixed time against an instantaneous power failure.

[0002]

2. Description of the Related Art Switching power supplies are used as power supplies for various electronic devices. Normally,
An AC / DC (AC / DC) converter with a switching frequency of several KHz is used, and the switching frequency and its higher harmonic components are superimposed on the DC output voltage. 2, a line filter as shown in the circuit diagram of FIG.

In the configuration of the line filter circuit diagram shown in FIG. 2, since a direct current flows through the core of the choke coil, a ring-shaped closed magnetic circuit core or a ferrite wound around an amorphous ultrafine crystal alloy thin plate which is hardly magnetically saturated. Use a core. Further, a slit is formed in a part of the closed magnetic path core to form an open magnetic path to avoid magnetic saturation. The X capacitor C1 connected between the lines at the previous stage of the common mode choke coil, the X capacitor C2 connected between the lines at the subsequent stage, and the Y capacitors C3 and C4 connected between the lines and the ground are both plastic films and metal. It is composed of a film capacitor formed by winding foil, has a capacitance value of several μF or less, and attenuates high frequency component noise.

A common mode choke coil and a Y capacitor are used to reduce common mode noise, and an X capacitor is used to reduce normal mode noise. For this reason, a smoother DC voltage with a small potential change with respect to the zero potential and with a reduced switching frequency and its harmonic components is supplied to the subsequent load device. Further, even when a DC / DC (DC / DC) converter having a switching frequency of several hundred kHz is connected to the subsequent stage of the line filter, bidirectional noise propagation can be performed without propagating noise generated therefrom to the preceding stage. Has been reduced.

Usually, the AC / DC converter is used as a common power supply, and a plurality of DC / DC
In many cases, DC converters are connected in parallel to constitute a system for supplying a predetermined DC voltage. With such a configuration, the load circuits of other DC / DC converters are ON.
At the time of ON when the / OFF operation is performed, an inrush current flows instantaneously and the AC / DC converter is overloaded, causing a voltage drop. Therefore, the input voltage of another DC / DC converter decreases, and the output to the next stage is output. The voltage dropped momentarily and the next stage circuit did not operate, resulting in the same result as a so-called momentary power failure.

[0006]

As described above, as described above, AC
The DC / DC converter is used as a common power supply, a plurality of DC / DC converters are connected in parallel to the load circuit at the subsequent stage, and the load circuits of other DC / DC converters are turned ON / OF.
An object of the present invention is to provide a DC line filter having a backup function in which the output voltage to the next stage does not instantaneously decrease even in a system configuration that operates in F-mode.

[0007]

A first aspect of the present invention is a line filter connected to a DC power supply, wherein an X capacitor and a Y capacitor are provided at one end of a common mode choke coil, and an X capacitor provided at the other end is a load. A DC line filter having a capacitance value that satisfies a certain time constant corresponding to an input resistance value of a device and having a backup function against an instantaneous power failure.

When the capacitance value of the capacitor C1 constituting the line filter shown in the circuit diagram of FIG. 2 is C and the input resistance value of the load device is R, the time constant represented by the product of CR is
A time constant indicating a discharge characteristic capable of maintaining a power supply voltage at which the load device can operate, that is, a capacitance value of the capacitor C1, is set until the output voltage of the AC / DC converter instantaneously decreases and recovers. .

If the case where the output voltage of the AC / DC converter is reduced is regarded as an instantaneous power failure, it can be regarded as a transient phenomenon in which the capacitance value C1 of the X capacitor is discharged to the input resistance R of the load device. Assuming that the voltage V1 is the output voltage V2 in the transient state, the rate of voltage drop (V2 / V1)
Is expressed as (V2 / V1) = Exp {-t / (CR)}, so that C = (-t) / {ln (V2 / V1) *
R｝, and the minimum value of the capacitance value C1 of the X capacitor is determined from the input resistance R of the load device, the allowable voltage drop ratio (V2 / V1), and the time (t).

[0010] In a second aspect of the present invention, the X capacitor has a capacitance value that satisfies a constant time constant corresponding to an input resistance value of a load device, and has a backup function against an instantaneous power failure. In the DC line filter, the sum of the capacitance values of the X capacitors is from 100 μF to 470.
A DC line filter characterized by being in the range of mF.

The instantaneous power failure time (t) of the AC / DC converter at the preceding stage of the DC line filter is 0.001 second or less, the latter stage circuit operates until the power supply voltage (Vcc) drops by 90%, and the input resistance (R) is 100Ω. In the case of the above formula;
From C = (− t) / {ln (V2 / V1) * R}, the capacitance value of the X capacitor is approximately 95 μF, so a capacitance value of 100 μF is required with a margin. Similarly, D
When the instantaneous power failure time (t) of the AC / DC converter before the C line filter is 0.5 seconds or less, the next stage circuit operates until the power supply voltage (Vcc) drops 95%, and the input resistance (R) is 25Ω. From the above formula, the capacitance value of the X capacitor is about 390 mF.
Is required. Normally, the limit is that the next-stage circuit operates until the power supply voltage (Vcc) drops by 90%. When the input resistance (R) is 25Ω or more and the instantaneous power failure time (t) is 0.
If you expect from 001 seconds to 0.5 seconds, you can roughly respond,
The capacitance value of the X capacitor in this range is 100 μ
F to 470 mF.

According to a third aspect of the present invention, there is provided a DC line filter, wherein the X capacitor comprises a plurality of electrolytic capacitors each having a diode connected in parallel and a fuse connected in series, and having a discharge resistor.

Since a large capacitance value is required for the X capacitor, one or more electrolytic capacitors are used. As shown in FIG. 1, a diode is connected in parallel so that a reverse polarity voltage is not applied, a fuse is connected in series as a countermeasure when the electrolytic capacitor is broken, and a DC line filter having a discharge resistance of the capacitor is configured. I do.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An X capacitor and a Y capacitor using a plastic film capacitor of several μF or less are provided at one end of a common mode choke coil. = (-T)
/ {Ln (V2 / V1) * R}. In a normal circuit, the X capacitor is constituted by an electrolytic capacitor having a capacitance value of 100 μF to 470 mF.

[0015]

Embodiment 1 The instantaneous power failure time (t) of the AC / DC converter before the DC line filter is 0.005 seconds or less, the subsequent circuit operates until the power supply voltage (Vcc) drops by 90%, and the input resistance (R) Is 100Ω, the above formula;
From C = (− t) / {ln (V2 / V1) * R}, the capacitance value of the X capacitor is about 475 μF. Therefore, a 560 μF functional polymer capacitor is used with a margin.

[0016]

[Embodiment 2] As in Embodiment 1, the instantaneous power failure time (t) of the AC / DC converter before the DC line filter is set to 0.
005 seconds or less, and the next stage circuit has a power supply voltage (Vcc) of 9
It operates up to 5% drop and when the input resistance (R) is 25Ω,
From the above formula, the capacitance value of the X capacitor is about 390
Since it is 0 μF, two 2200 μF electrolytic capacitors were prepared in order to increase the margin to 4400 μF. Based on the circuit diagram of FIG. 1, the capacitors C2, C3, and C4 use polyester capacitors wound with a metallized film, each having a capacitance of 0.47 μF,
1.0 μF and 1.0 μF.

A common mode choke coil Lha, outer diameter: φ25 mm, inner diameter: φ15 mm, thickness: 12 mm, a manganese / zinc ferrite core in a case of 12 mm and a polyester-coated copper wire; , And a choke coil of about 150 μH was formed in a common mode winding.

Others: fusing current; 7.5 A fuse and 5.1 MΩ resistor; reverse voltage: 200 V;
A diode Di having a forward current of 20 A was prepared. Next, the input terminal 7, the output terminal 8 and the ground terminal 9
The above components are mounted on the wiring board 10 having the fixing holes 11 to which the components are attached according to the circuit diagram of FIG. 1, and the rated voltage shown in the plan view of FIG. A DC line filter having a backup function was configured.

[0019]

A system in which an AC / DC converter is used as a common power source, a plurality of DC / DC converters are connected in parallel to a subsequent load circuit, and the load circuits of other DC / DC converters are turned on / off. Even with this configuration, a DC line filter having a backup function in which the output voltage to the next stage does not drop for an instant can be configured.

[0020]

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a DC line filter according to a second embodiment.

FIG. 2 shows a conventional DC line filter circuit diagram.

FIG. 3 is a plan view in which a DC line filter according to a second embodiment is mounted.

[Explanation of symbols]

 C1, C2 X capacitor C3, C4 Y capacitor C5 Electrolytic capacitor L Common mode choke coil Di diode R High resistance for discharge 7 Input terminal 8 Output terminal 9 Ground terminal 10 Wiring board 11 Fixing hole

Claims (3)

[Claims] 1. A line filter connected to a DC power supply, wherein an X capacitor and a Y capacitor are provided at one end of a common mode choke coil, and the X capacitor provided at the other end is constant corresponding to an input resistance value of a load device. A DC line filter having a capacitance value satisfying the following time constant, and having a backup function against an instantaneous power failure. 2. The DC line filter according to claim 1, wherein a sum of capacitance values of said X capacitors is 100 μm.
DC within a range of F to 470 mF
Line filter. 3. The DC line filter according to claim 2, wherein the X capacitor comprises a plurality of electrolytic capacitors in which diodes are connected in parallel and fuses are connected in series, and has a discharge resistor. DC line filter.