DC application circuit with suppressed DC magnetization

Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver

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Details

327108, 327190, 327312, 327328, 327482, 327538, 327308, H03K 335

Patent

active

057962790

DESCRIPTION:

BRIEF SUMMARY
This application is filed under 35 U.S.C. .sctn. 371 as a national stage application of PCT/JP94/01746, filed Oct.18, 1994.


TECHNICAL FIELD

The present invention relates to a DC application circuit for applying a direct current to a transformer or a choke coil for use in various transmission circuits.


BACKGROUND ART

In order to extract AC components from signals containing DC components and AC components, use has been hitherto made of a transformer, for example, as shown in FIG. 14. In this diagram, a choke coil L.sub.1 is connected in parallel to the input side of a transformer T.sub.1 via a direct current isolation capacitor C.sub.1. Therefore, when this circuit receives DC/AC superimposed signals, only the AC components are applied to the transformer T.sub.1. However, this configuration entails problems that the choke coil L.sub.1 tends to be large-sized resulting in increased size of the entire circuit or that the use of the choke coil L.sub.1 may lead to raised component costs.
To solve such problems, use as a transformer may be made of a DC applicable transformer T.sub.2, for example, as shown in FIG. 15. The DC applicable-type transformer T.sub.2 includes a large gap in its magnetic path to eliminate the influence of a DC magnetization, thereby allowing application of the DC components.
Disadvantageously, the configuration as shown in FIG. 15 needs to have enlarged external dimensions due to the provision of the gap to eliminate the influence of the DC magnetization. For instance, the number of turns of the transformer T.sub.2 is 1600 turns on both the primary side and the secondary side, with a core size of 35 mm (so-called EI-35). The use of such a large-sized transformer T.sub.2 would result in an attenuation value as low as 3 dB at 100 Hz as seen in FIG. 16.


DISCLOSURE OF THE INVENTION

The present invention was conceived to overcome the above problems. It is therefore an object of the present invention to enable a direct current to be applied to a winding of a transformer or a choke coil without increasing the size of a circuit configuration, as well as to improve the characteristics.
In order to achieve the object, a circuit for applying a direct current to a winding according to the present invention comprises the winding for receiving a DC/AC superimposed signal consisting of DC components and AC components superimposed on each other, and a DC magnetization prevention circuit for preventing a DC magnetization caused in a magnetic member of the winding due to the DC components flowing therethrough.
In the present invention, the DC magnetization, which may be caused by the DC components in the DC/AC superimposed signals supplied to the winding, is reduced or eliminated by the DC magnetization prevention circuit. Thus, there is no need to provide a gap to compensate for influence of the DC magnetization, which will result in no increase in the external dimensions and no degradation in the characteristics. Additionally, upon the evaluation of the characteristics, the characteristics do not vary largely depending on whether inputs are DC/AC superimposed signals or have only AC components, thus facilitating the evaluation and testing. The present invention may be widely applied to general transmission circuits.
The first configuration of the DC magnetization prevention circuit of the present invention is characterized in that it restrains the direction of current of the DC components through the winding so that the DC components flow in the opposite direction with a boundary defined by a center tap placed on the winding in order to input the DC/AC superimposed signal. In the case of employing the first configuration as the DC magnetization prevention circuit, the DC components flow in opposite directions through the winding from the boundary defined by the center tap, whereby the influences of the magnetization due to the DC components can be offset by each other, accomplishing a preferable prevention of the DC magnetization in the magnetic member.
This configuration may be implemented by

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