JP2557773B2 - Noise removal circuit for polarity reversal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for removing noise when reversing polarity.

[0002]

2. Description of the Related Art When a telephone line is used for communication, noise may occur during a polarity reversal transition, and the semiconductor may be damaged by this noise. Conventionally, however, circuits that prevent noise during polarity reversal have been used. It doesn't exist.

By the way, the conventional general receiving circuit shown in FIG. 4 has a primary side of the audio transformer T1 and a line side terminal A.
A capacitor C1 is connected between the line terminals A and B
The coil L is connected between and. The capacitance of the capacitor C1 is 2.2 μF, the inductance of the coil L is 1H, the symbol Z is a load, and the capacitor C1 is
The DC current to the transformer T1 is cut off.

In the case where the general receiving circuit is constructed as shown in FIG. 4, if the polarity is inverted at time t1 in FIG. 5, the current changes as shown by the bold line in FIG. That is,
When the polarity is reversed at time t1 while a positive steady current is flowing, the current suddenly changes to negative, and due to the sudden reaction of the counter electromotive voltage, the current approaches 0 at time t2, and then, It gradually approaches the negative steady current, and settles to the negative steady current at time t3. In this case, the change in current around time t2 becomes noise.

[0005]

By the way, the hatched area in FIG. 5 shows an example of the European standard. In this standard, t1 to t2 are 2 ms,
t2-t3 is 10 ms, the current allowable value at the time point t2 is -18 mA, and the steady-state current is +1 mA-
-1 mA is the allowable range of the steady current, and in the conventional example, the current allowable value of -18 mA is exceeded at the time t2.

As described above, in the above-mentioned conventional example, since the European standard cannot be satisfied, it is the actual situation that the electrical standard such as insertion loss is intentionally deteriorated to comply with the European standard. That is, in the conventional example, there is a problem that electrical performance is deteriorated when the predetermined amount of the noise is removed when the polarity is reversed.

An object of the present invention is to prevent electrical performance from deteriorating even if a predetermined amount of noise at the time of polarity reversal is removed.

[0008]

According to the present invention, a first series circuit in which a first coil and a first diode are connected in series is connected to a line terminal side, and a second coil and a second coil are connected. A second series circuit in which a diode is connected in series is connected in parallel with the first series circuit, a first coil and a second coil are connected in opposite polarities, and a first coil and a second coil are connected. Is closely wound, and the first diode and the second diode are connected with opposite polarities.

[0009]

According to the present invention, the first series circuit in which the first coil and the first diode are connected in series is connected to the line terminal side, and the second coil and the second diode are connected in series. The second series circuit is connected in parallel with the first series circuit, the first coil and the second coil are connected in opposite polarities, and the first coil and the second coil are in close contact with each other. Since the first diode and the second diode are connected with opposite polarities, the noises at the time of polarity inversion cancel each other and the noises are effectively removed. Performance does not deteriorate.

[0010]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The noise elimination circuit 10 of this embodiment is composed of a first series circuit 11 and a second series circuit 12, and the first series circuit 11 and the second series circuit 12 are connected in parallel with each other. . The first series circuit 11 is a circuit in which the first coil L1 and the first diode D1 are connected in series, and is connected to the line terminals A and B. The second series circuit 12 is a circuit in which the second coil L2 and the second diode D2 are connected in series.

Further, the first coil L1 and the second coil L
2 are connected to each other with opposite polarities, the first coil L1 and the second coil L2 are closely wound, and the first diode D1 and the second diode D2 are connected with opposite polarities. . That is, the polarity of the first coil L1 and the polarity of the second coil L2 may be opposite to the state of FIG.
Both the polarities of the first diode D1 and the second diode D2 may be opposite to those in the state of FIG. Also, the first
The coil L1 and the second coil L2 are wound by bifilar winding. The inductance of the coils L1 and L2 is 1H, and the capacitance of the capacitor C1 is 2.2 μ.
F is the load and Z is the load.

Next, the operation of the above embodiment will be described. It is assumed that the DC current applied between the line terminals A and B flows through the diode D1 and the coil L1, and if the polarity of the DC current is reversed at this time, the DC current flows through the diode D2 and the coil L2. . At the time of this polarity reversal, the counter electromotive voltage of the coil L1 is induced in the coil L2, and since the coils L1 and L2 are connected with opposite polarities, the counter electromotive voltage of the coil L1 and the counter electromotive voltage of the coil L2 are mutually different. Noises due to the counter electromotive voltage generated between the line terminals A and B are canceled by canceling each other out.

A DC current applied between the line terminals A and B flows through the diode D2 and the coil L2 before the polarity is reversed, and when the polarity is reversed, the DC current is transferred to the diode D1,
The same applies when the current flows through the coil L1. That is, when the polarity is reversed, the back electromotive voltage of the coil L2 is
1 and the coils L1 and L2 are connected with opposite polarities, the counter electromotive voltage of the coil L1 and the coil L2
Of the counter electromotive force and the counter electromotive force of the line terminals A and B cancel each other, and the noise due to the counter electromotive voltage generated between the line terminals A and B is eliminated.

FIG. 2 is a diagram showing a change in current when the polarity is reversed in the above embodiment. As shown in FIG. 2, in the above embodiment, the European standard can be surely met, and the noise due to the back electromotive force generated between the line terminals A and B can be surely erased. It is possible to reliably prevent damage to parts. Further, in the above embodiment, it is not necessary to intentionally deteriorate the electrical characteristics such as insertion loss. In particular, when the above-described embodiment is used in a facsimile machine, it is possible to effectively eliminate the troubles such as the damage and malfunction due to the noise.

Further, in the above embodiment, when a direct current flows through the coil L1, heat is generated in the coil L1 and the temperature of the coil L1 rises. On the other hand, at this time, since no direct current flows in the coil L2, the coil L2 does not generate heat and absorbs the heat generated in the coil L1. Therefore, the coil L
The temperature rise of 1 and L2 is small. In particular, the coils L1 and L2
When the coil is wound with a bifilar coil, the coils L1 and L2 are arranged closer to each other, so that the heat absorption is improved.
The inductance of the coils L1 and L2 may be a value other than 1H, and the capacitance of the capacitor C1 may be a value other than 2.2 μF.

FIG. 3 is a diagram showing a test circuit for determining the state of current change when the polarity is reversed. The value of the resistor R1 is 250 to 1100Ω and the value of the resistor R2 is 240 to 1100Ω. The value of the resistor R3 is 10Ω. The present invention can also be applied to relay coils and general rectification circuits.

[0017]

According to the present invention, the noises at the time of polarity reversal cancel each other, the noises are effectively removed, and the electric performance is not deteriorated.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a change in current when the polarity is reversed in the embodiment.

FIG. 3 is a diagram showing a test circuit for obtaining a state of current change when the polarity is reversed.

FIG. 4 is a diagram showing a general receiving circuit of a conventional example.

FIG. 5 is a diagram showing a change in current when the polarity is reversed in the conventional example.

[Explanation of symbols]

 10 Noise Removal Circuit 11 First Series Circuit L1 First Coil D1 First Diode 12 Second Series Circuit L2 Second Coil D2 Second Diode C1 Capacitor T1 Transformer Z Load

Claims (2)

(57) [Claims] 1. A first series circuit in which a first coil and a first diode are connected in series is connected to a line terminal side, and a second coil and a second diode are connected in series. A second series circuit is connected in parallel with the first series circuit, the first coil and the second coil are connected in opposite polarities, and the first coil and the second coil are connected. Is closely wound, and the first diode and the second diode are connected in opposite polarities to each other. 2. The noise removing circuit at the time of polarity reversal according to claim 1, wherein the first coil and the second coil are wound by bifilar winding.