JPS6214926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wideband transformer circuit used in various communication devices, and more particularly to a transformer circuit that can greatly reduce the influence of longitudinal current.

Conventionally, in order to prevent a noise current induced in a transmission line by external induction, that is, a vertical current, from flowing into communication equipment, as shown in FIG. A broadband transformer circuit 5 in which an isolated transformer 3 and a longitudinal current blocking wire 4 are connected in cascade is connected. However, the degree to which longitudinal current is blocked in such a transformer circuit, that is, the amount of longitudinal current attenuation, has a steep drop at frequency fo, as shown by curve A in FIG. This drop is caused by the series resonance (fo=
This is caused by 1/2π√・). As a result,
The longitudinal current Iu flows into the communication device 2 connected to the unbalanced winding 8, causing problems such as deterioration of communication quality and damage to the communication device 2.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a wideband transformer circuit with good longitudinal current attenuation characteristics over a wideband.

In the broadband transformer circuit according to the present invention, balanced and unbalanced windings are tightly coupled at an arbitrary winding ratio,
an insulated transformer having a tap at its midpoint; a line-type longitudinal current blocking coil connected to the balanced system winding side of the insulated transformer and tightly wound with a turns ratio of 1:1;
It consists of a capacitor connected to the center tap of the isolation transformer, and the value of this capacitor is set at the frequency
By selecting fo so that the potential of the balanced winding of the isolated transformer has an impedance value that can be considered to be approximately the ground potential with respect to the longitudinal current, the longitudinal current flows to the ground and is connected to the unbalanced winding. It is characterized by greatly reducing the influence of longitudinal current on communication equipment, and by insulating the windings in terms of direct current.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a circuit diagram showing one embodiment of the present invention. The transformer circuit of the present invention includes a balanced winding 6 and an unbalanced winding 8 wound in close coupling at an arbitrary winding ratio, and an isolated transformer 3 having a tap 12 at the midpoint of the balanced winding. , a line type longitudinal current blocking wire 4 connected to the balanced system winding 6 side of this transformer 3 and having two windings 10 and 11 wound at a turns ratio of 1:1, and an isolation transformer balanced system It consists of a capacitor 13 connected between the center tap 12 of the winding 6 and ground.

The impedance of this capacitor 13 is set to a value that can be almost ignored at the frequency fo shown in FIG. Therefore, the longitudinal current Iu flowing from one side 14 of the longitudinal current blocking coil 4 flows to the ground via the winding 16 and capacitor B, and the longitudinal current flowing from one side 15 of the coil 4 flows through the winding 17 and capacitor 13. flows to the earth through it. Therefore, the magnetic fluxes generated in the windings 16 and 17 cancel each other out, so that no magnetic flux is generated in the magnetic core 18. Therefore, both ends 19 and 20 of the balanced winding 6 of the isolated transformer 3 are approximately equal to the ground potential with respect to the longitudinal current Iu, and the longitudinal current
Iu no longer affects the winding 8 side.

Furthermore, by appropriately selecting the capacitance value of the capacitor 13, it is possible to prevent commercial frequency noise, which is the main component of earth current, and its second and third-order high frequency noises from flowing into the transmission line, thereby preventing a ground fault at one end of the transmission line. Damage to the transmission line and the isolation transformer 3 due to such causes can be prevented.

Curve B in Figure 2 shows the improvement effect of this example, and shows that compared to curve A, there is no steep drop and the longitudinal current attenuation is greatly improved over the entire band. There is.

FIG. 4 is a circuit diagram showing another embodiment of the present invention. In this embodiment, in order to improve the vertical current drop, a coil 15 is connected in addition to the capacitor shown in FIG. 3. The capacitance value _C2 of this capacitor 13 and the impedance value L2 of the coil 14 are fo≒1/2π√2・
It has been selected to be C2.

Therefore, since the impedance of the series circuit 15 becomes extremely small at the resonant frequency fo, the midpoint tap of the balanced system winding 6 becomes almost the ground potential at that frequency fo, and as in the embodiment of FIG. 3, the unbalanced system due to the longitudinal current Iu The influence on the winding 8 side can be prevented.

Curve B in FIG. 5 shows the improvement effect of this embodiment. Compared to the longitudinal current attenuation characteristic curve A of the conventional broadband transformer circuit 5, the longitudinal current is reduced over the entire band without a steep drop. It can be seen that the amount of attenuation can be greatly improved.

As described above, according to the present invention, since the longitudinal current attenuation characteristic is good and the balanced winding is DC-insulated from the ground, it is possible to realize a communication line with good communication quality and no inductive interference.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional wideband transformer circuit, FIGS. 2 and 5 are diagrams showing the improvement effect of the present invention,
FIGS. 3 and 4 are diagrams showing embodiments of the present invention. In Figures 3 and 4, 3...insulated transformer, 4...vertical current blocking coil, 6...balanced winding, 8...unbalanced winding, 10, 11...1 pair wire ring, 12... middle point tap, 13... capacitor, 14... wire ring, 15... series circuit.

Claims (1)

[Claims] 1. One-to-one on the balanced winding side of an insulation transformer in which balanced windings and unbalanced windings are wound at an arbitrary turns ratio.
Line-type longitudinal current blocking coils wound with a turns ratio of 1. A wideband transformer circuit, characterized in that it is grounded with a capacitor having an impedance sufficiently lower than the impedance of the equivalent stray capacitance of the isolated transformer at a frequency at which the equivalent stray capacitance resonates in series. 2 One-to-one on the balanced winding side of an isolation transformer where balanced and unbalanced windings are wound at an arbitrary turns ratio.
Line-type longitudinal current blocking coils wound with a turns ratio of A broadband transformer circuit characterized in that it is grounded by a series circuit composed of a capacitor and a wire ring having a resonant frequency equal to the series resonant frequency determined by the equivalent stray capacitance of the transformer.