JPS5826204B2 - Choke for high frequency filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of the L element of an L and C power supply filter, and particularly to an L element that can use a small capacitor or achieve sufficient noise prevention even in a C circuit. It is.

Conventionally, high frequency noise was blocked, and the L of the C power supply filter was
The element uses a ferrite rod core, a dust core with high saturation magnetic flux density, etc. to prevent magnetic saturation due to power supply current.

However, in the VHF band (30 to 300 MH2), effective magnetic permeability is low, so sufficient noise prevention cannot be achieved, and therefore L and C have to be increased.

This has the disadvantage that the filter becomes large and expensive.

On the other hand, a common mode choke, in which multiple windings are applied to a closed magnetic circuit core so as to cancel out the magnetic flux caused by the normal mode power supply current and signal current, has a great effect on common mode noise, but the signal current For normal mode noise that is in phase with , it does not act as a nonductor and has no effect at all.

Noise protection must be achieved for both normal mode and common mode.

In view of the above drawbacks, it is an object of the present invention to provide an L element that can sufficiently prevent both common mode and normal mode high frequency noise in an LC circuit using a small capacitor.

Although the choke coil according to the present invention has a basic configuration and is a common mode choke, by considering the magnetic permeability-frequency characteristics, shape, and winding of the magnetic core, it effectively blocks noise in both common mode and normal mode. It has been made possible.

That is, the present invention provides a common mode choke in which a plurality of windings are wound around a closed magnetic circuit core so that magnetic fluxes caused by normal mode signals flowing between drawing lines cancel each other out.
The closed magnetic circuit core is made of a material that exhibits high magnetic permeability at low frequencies and low magnetic permeability at high frequencies, and the plurality of windings are wound sufficiently apart from each other. be.

According to the present invention, since the core acts as a high permeability core for low frequency current, magnetic saturation does not occur for normal mode signals.

However, for high frequency signals, the magnetic permeability of the core is low, and both windings are spaced sufficiently apart from each other and are tightly wound, so leakage magnetic flux will occur around the windings.

Therefore, this choke also has inductance against high frequency normal mode noise.

Of course, common mode noise has inductance at both low and high frequencies.

Therefore, this choke is effective in removing both common mode and normal mode noise.

The present invention will be explained below with reference to the drawings.

FIG. 1A shows the basic configuration of a conventional common mode choke, in which windings 2 and 3 are wound around a ring core 1 so that the magnetic fluxes caused by the normal mode signal 4 are mutually canceled.

In FIG. 1, the windings 2 and 3 are wound with a pie filer for better balance.

Generally, such conventional choke coils are used for the purpose of blocking common mode noise, as described above, and are not effective against normal mode noise.

FIG. 2 shows an embodiment of the present invention, in which windings 5 and 6 are wound in common mode choke windings at positions optically separated from each other on a core 7 which is sufficiently large for the number of windings.

The core 7 is made of a material that has a high magnetic permeability for signals of a sufficiently low frequency such as the power supply frequency, but has a characteristic that the magnetic permeability decreases when the frequency reaches the VHF band.

Therefore, in the case of a high frequency signal, a leakage magnetic flux of 10°11 is generated near the windings 5 and 6.

Therefore, this choke also acts as an inductor against high frequency normal mode noise.

That is, it has almost no effect on normal mode noise at low frequencies, but gradually begins to operate as an inductor at high frequencies.

On the other hand, with respect to common mode noise, a sufficiently high impedance is maintained from low frequencies to high frequencies according to the basic principle of common mode chokes.

In the configuration shown in FIG. 2, the windings 5 and 6 are each tightly wound in order to increase the effect of leakage inductance.

3 and 4 show other embodiments of the present invention, and FIG.
This structure has a structure that further enhances the effect of leakage inductance.

In other words, a large gap is provided in the central columnar part of the EE type core, and at low frequencies, almost no magnetic flux passes through the central columnar part, but high frequency leakage magnetic flux passes through it more easily, so it effectively produces high normal mode noise. It is possible to obtain the inductance for

FIG. 5 shows the characteristics of filters using the choke coil according to the present invention and the conventional choke coil, and the noise level was measured using a spectrum analyzer.

13 is the noise level without a filter, 14 is a conventional filter using a bar core choke and a capacitor, and 15 is a filter using the choke coil of the present invention and a capacitor with a capacity 1/10 of the capacitor used in 14. It was there.

As is clear from the figure, although the capacitor using the choke coil of the present invention has a capacity that is 1/10 of the capacitor used when using a conventional choke coil, the noise level is improved compared to the conventional choke coil. The present invention is industrially very useful because it is small and inexpensive as a filter.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional common mode choke, Figures 2, 3, and 4 are schematic diagrams of embodiments of the present invention, and Figure 5 is a filter using the present invention and a conventional choke coil, respectively. The implementation characteristics diagram is shown. The symbols used in the figure are as follows. 1.7 is the ring core, 2, 3, 5, 6 are the windings, 4 is the normal mode signal, 8, 9 are the magnetic flux, 10° 11 is the leakage magnetic flux, 12 is the capacitor

Claims (1)

[Claims] 1. In a common mode choke in which a plurality of windings are wound around a closed magnetic circuit core so that the magnetic flux caused by the normal mode signal flowing between the lines cancels each other, the closed magnetic circuit core has high magnetic permeability at low frequencies. 1. A choke for a high frequency filter, characterized in that the plurality of windings are wound sufficiently apart from each other.